Dump'r - 2003/10

ump’r is a relatively simple device that
safely discharges four- to 18-cell
Nickel Cadmium (Ni-Cd) and Nickel
Metal Hydride (NiMH) batteries at a fixed
1⁄2-amp rate. Discharge is initiated with the
push of a button and automatically
terminates when the pack reaches the
equivalent of .9 volt per cell. Dump’r
requires no external power and, other than
setting the “cell count” switch, needs no
adjustment or calibration.
Dump’r was designed for the Electrics
enthusiast, but it is easy for anyone with
batteries to discharge to use. It is fuseprotected
against polarity reversal. Only a
seven-cell pack, a Digital Multi Meter
(DMM), a test resistor, and some test/clip
leads are needed to check out proper
operation. All parts and supplies are readily
available, and anyone with electronic
soldering experience can build Dump’r.
Dump’r was conceived when it became
routine for me to charge more E-power
motor packs than I had the opportunity to fly
out. This happens easily with Electrics that
may have interchangeable packs.
I prefer not to store motor packs in
charged condition longer than a day or so for
a couple of reasons. One is that charged
packs can slowly self-discharge unequally
among the cells. Under
these conditions, it is
not good practice to
“top off” with a fast
refresh charge or use
the pack in subsequent
flight. A fresh, fast
charge from empty
seems to yield better
flight performance
anyway.
Aeromodelers do
have several ways to
run down packs,
including running
motors, using the
“discharge” function
that is built into some
chargers, using
“cyclers” in limited
cases, or using banks
of auto lamps and/or
power resistors that
vary with the cell count. Dump’r, being a
self-powered, one-size-fits-all alternative, is
more convenient than most of the preceding
approaches.
Since Dump’r was designed with banana
jack connectors, all that is needed to
accommodate any battery is a suitable
adapter cable. Short cables with banana
plugs on one end and the appropriate
connector on the other end will do the job.
I use Dump’r with 150-3000 mAh
batteries, but there is no upper capacity limit.
With the fixed 1⁄2-amp rate, the time needed
to discharge packs varies widely. The lowest
capacities take less than an hour and the
largest require hours. Cell count has no
72 MODEL AVIATION
Dump’r ■ Bob Kopski
Dump’r is a safe, one-size-fits-all Ni-Cd/NiMH battery discharger. Short cables adapt to any battery connector style.
Assembled circuit board shown is ready for nine flexible wires to
be added. All components are easy to obtain.
D
effect on discharge time. Whatever the time, it is inconsequential to
me; I just want “empty” packs before the next outing.
The cell-count range and discharge rate keep the power
dissipation and associated heating to safe levels. However, the heatsink
fins on Dump’r can reach 170° with a fully charged 18-cell
pack. That is fine, but you probably don’t want to touch it—just like
you wouldn’t hold onto a 7-watt night-light bulb! Keep this in mind
when you deploy Dump’r (or any other discharger).
Discharging to a nominal .9 volt per cell is generally considered
good practice. For a pack that is in good condition, that is a safe
target value that adequately drains all cells to approximately the same
state. All of the cells are equally empty, which is a great place to
begin a fresh charge the next time.
Discharging a pack without an appropriate cutoff point puts at
least some cells at risk of being “reverse charged,” which is a known
cell-killer condition. Dump’r can be well worth having!
How It Works: If you are one of the many readers who truly enjoys
knowing the operational details of projects such as this, this section is
for you!
Referring to the schematic, the discharge current is held stable by
operational amplifier IC2b, power transistor Q3, and some associated
passive components. This portion of the circuit—an electronic
“current source” configuration—holds the current steady no matter
the cell count.
IC1 is a precision 1.225-volt 1% reference diode. This reference,
in conjunction with some 1% resistors, establishes the current level
October 2003 73
Rotary switch SW2/resistor subassembly and 1⁄8 plywood spacer
plate. Assemble with resistors at solder lug height.
Copy full-size drill pattern, glue to metal box’s outer surface,
center punch, and drill as dimensioned.
Box subassembly ready for circuit board and rotary switch. Everything is wired, and SW2 and spacer is in place.
Dump’r is done! Tuck the fuse inside, install the box cover, hold
with four supplied screws, and have at it!
Photos by the author Graphic Design by Lydia Whitehead
76 MODEL AVIATION
and permits accurate representation by the “cell count” switch. These
precision parts are also the reason why no tune-up or calibration is
needed; put Dump’r together correctly, and it works correctly. Every
Dump’r should have the same discharge current under all conditions
within 5%.
Indicator LED (light-emitting diode) D1 is on when discharge is
in progress and goes off at the end of discharge. LED current is held
steady at roughly 6 mA by transistor Q4. This assures equal
brightness and safe operation throughout the wide cell-count range.
With the cell-count switch properly set, Dump’r operation
commences when a battery is connected and push button SW1 is
activated. Prior to this, circuit voltage V1 is 0, so nothing in the
circuit is operational. SW1 momentarily connects battery voltage to
circuit buss V1 for circuit “start-up.”
This initiative action results in operation of IC2 and all associated
circuitry including discharge operation. Comparator-configured
operational amplifier IC2a immediately goes “high,” thereby biasing
Q1, hence Q2 on. The latter allows continued presence of V1, which
is nearly equal to the battery voltage, after SW1 is released.
Basically, Dump’r is “latched on” after being put there with a
momentary push of SW1.
IC2a comparator operates as follows. The noninverting input is
biased by a fixed percentage of the battery voltage via divider R1/R2.
A precision inverting input is step-selected by rotary switch SW2.
Thus divider R1/R2 applies a voltage that declines with the discharge
of the battery while SW2 applies a stable voltage that is
representative of the cell count.
When the battery voltage drops so that the comparator
noninverting input voltage falls below the SW2 switch-selected level,
IC2a output goes “low” and removes drive from transistor Q1, thus
from switch Q2. This disconnects V1, and all control circuitry shuts
down. Discharge ceases and indicator LED D1 goes out. With no
current drain present, it is safe for Dump’r to
remain connected until it’s convenient for
you to attend to the matter.
The cell-count switch selects cells
individually from four through 12 and
thereafter by twos up to 18. Numerically, the
last three switch steps are electrically
equivalent to 131⁄2, 151⁄2, and 171⁄2 cells
respectively.
This is a satisfactory way to represent
“higher” cell counts because there is
diminished resolution of cell voltage
available as the actual total voltage gets high
enough. So in the worst cell-count position
of 13/14, the greatest “volts per cell” error is
only roughly 0.035 volt—which is
acceptable.
Building Dump’r: The circuit board is cut
from a standard RadioShack General
Purpose Component PC Board. It has a
specific conductor pattern as seen by “Xray”
view in the assembly drawings. It is
important to cut the board exactly to the
conductor pattern shown; count holes to get
it right. Drill the two 1⁄8-inch mounting holes
and the wire relief slot.
Install the nine solid jumper wires as
shown, beginning with the two small
jumpers that will be located under the IC2
socket. Put these two wires in the board,
install the IC socket over them, then solder
eight socket pins and two wire connections.
Make sure you get this right! Install and
solder the seven remaining jumper wires.
Again, count holes!
Now you can install the circuit-board
components in any order you want. Do keep
the parts close to the board; there will be
limited “headroom” in the aluminum box.
Verify the correct orientation of all
semiconductors. Finish with the nine flexible
leadout wires, leaving them a bit long for
now. Strip the wire ends approximately 1⁄4
inch to allow later subassembly testing.
Examine all solder work with a lens,
touch up as needed, clean the solder flux
with a brush and solvent (e.g., acetone), and
reinspect. Make sure everything is correct
and that there are no land-to-land shorts, and
that all component leads are clipped off near
the board. IC2 will be installed later. Set this
circuit subassembly aside.
Assemble the resistor string R14 through
R24 around SW2 as shown, making sure that
the “rotation” is correct. Visually inspect all
joints, then, using an ohmmeter, verify the
accuracy of this switched resistor assembly.
Connect one ohmmeter lead to the switch
wiper terminal and the other to the beginning
of the resistor string at the bottom lead of
R24. With a temporary knob on the shaft,
rotate the switch for a reading of 0 ohms. (A
fractional ohm may be indicated because of
test lead resistance.)
Rotate the switch clockwise (knob view)
one step at a time and verify that the meter
reads the progressive resistance value as
predicted by the schematic. All readings
should fall within 1% of the exact value.
Before removing the knob, preset the switch
position back to 0 ohms as in the preceding.
Set this switch subassembly aside.
The mechanical work is shown herein full
size and includes a drill pattern and labels for
the finished Dump’r. Make a photocopy of
this page, and cut out the drill pattern. Use
glue stick or similar to adhere this paper
pattern around the outside of the metal box.
Make sure you do this accurately, then
center-punch and drill as shown. If you do
this work carefully, everything from here on
will fit nicely.
Remove the paper, deburr all holes, and
clean the box with a suitable solvent. (Soapy
water or alcohol will work well on most
glue-stick material.) Cut and drill the 1⁄8
plywood switch spacer plate as shown. This
piece indexes SW2 and prevents it from
working loose and rotating inside the box.
78 MODEL AVIATION
80 MODEL AVIATION
Trial-fit this piece along with SW2 in the
box, then remove.
The box subassembly proceeds as
follows. Install the 1-inch nylon standoffs
using 4-40 x 1⁄4-inch pan-head machine
screws with inside star washers between the
standoffs and the box.
Install Q3 and the heat sink with 6-32 x
1⁄2-inch screws going through the transistor
mounting holes, the heat sink, 1⁄8-inch-thick
spacers, then the box. The spacers are 6-32
hex nuts drilled out to 5⁄32 inch. (The two
transistor screws are used to mount it and
the heat sink. The latter is spaced up off of
the box roughly 1⁄8 inch by the drilled nut
spacers.)
Inside the box, install one #6 inside star
washer and the specified solder lug over the
protruding screws followed by hex nuts, as
shown.
Next are the banana jacks, SW1, LED
D1/holder, diode D2 (observe polarity),
resistor R25, and any associated wire.
Delay soldering at the negative banana jack
and the solder lug until later.
Make fuse connectors using the clips
specified with leads of 18-gauge lamp cord.
I chose this material for ready availability
and mechanical appropriateness for this
particular task: supporting a dangling fuse.
Sweat-solder the wire to the “flat” of the
fuse clip, then fully cover the clip with
heat-shrink tubing. Make sure that the
wire/clip assemblies are thoroughly
insulated, as shown. Glue the labels to the
box, and protect them with clear tape or
similar. This completes the box
subassembly.
Subassembly Checkout and Final
Assembly: The circuit-board subassembly
is preliminarily tested with an ohmmeter
from lead to lead, as in the following table.
(Remember that IC2 is not in the socket.)
Use the meter on the appropriate scale
(range), and make each measurement twice;
measure, reverse the meter leads, and
measure again.
Although this test does not guarantee
total assembly perfection, an incorrect
result means that you must track down the
reason and fix it before proceeding.
Table of Ohmmeter Tests
Wire Pair Ohms
8-9 “Very High” to Infinite
2-4 3-3.3 K
2-9 9.5-10
4-8 “Very High” to Infinite
6-7 “Very High” to Infinite
6-9 “Very High” to Infinite
1-All “Very High” to Infinite
With the preliminary board checkout
complete, eyeball the final lead dress
needed, and trim and restrip the leads to
installation length. Solder six of the wire
leads to the proper locations in the box and
three to SW2. Insert the fuse. Inspect all.
Mount the switch plus the spacer plate
and knob setting the pointer at “4.” Position
Dump’r Versatile Battery Discharger Parts List
All resistors are 1⁄4 watt except where noted. Some must be 1%, and some need
only be 5%. It may be less costly to use the nearest 1% value for the 5% parts; see
catalog reference. All catalog numbers are Mouser Electronics ([800] 346-6873 or
www.mouser.com) except RadioShack, indicated as “RS ... ” All other items are
common and/or hobby shop/hardware-store supplies.
Item Part/Value Catalog Number
R1 16.9K, 1% 660-MF1/4CL1692F
R2 1.0K, 1% 660-MF1/4CL1001F
R3, 9, 11 10K, 5% (three pieces) 30BJ250-10K
R4 6.8K, 5% 30BJ250-6.8K
R5 681 Ohms, 1% 660-MF1/4CL6810F
R6 2.7K, 5% 30BJ250-2.7K
R8 6.81K, 1% 660-MF1/4CL6812F
R10 1K, 5% 30BJ250-1.0K
R12 1.00 Ohms, 1%, 1W 71-RS1A-1.0
R13 100 Ohms, 5% 30BJ250-100
R14, 15 200 Ohms, 1% (two pieces) 660-MF1/4CL2000F
R16 150 Ohms, 1% 660-MF1/4CL1500F
R17-R24 100 Ohms, 1% (eight pieces) 660-MF1/4CL1000F
R25 392 Ohms, 1% 660-MF1/4CL3920F
Rt 7.5 Ohms, 5%, 5W 280-CR5-7.5
C1 0.1 uF, 50V, Ceramic 80-C315C104M5U
D1 LED 351-5111
D2 1N5401 Rectifier 583-1N5401
Q1, Q4 2N3904 Transistor 512-2N3904
Q2 2N3906 Transistor 512-2N3906
Q3 2N3055 Transistor 511-2N3055
IC1 1.225V Reference 511-TS821AIZ
IC2 LM358 Dual Op. Amp. 511-LM358AN
SW1 SPST Momentary n/o 103-1012
SW2 1P12T Rotary, Shorting 10WW112
F1 ATO, 1 amp 5768-57001
Clips Fuse, two pieces 534-3522
PC holeboard RS 276-168
Chassis box 537-TF-770
Heat sink 532-500403B00
Solder lug 534-904
1⁄8 plywood—1.2 x 1.5 inches
Feet, stick-on—package RS 64-2365
Standoffs, nylon—4-40, two pieces 561-TSP5
IC socket, 8 pin 571-26404634
#24 buss wire, bare, tinned RS 278-1341
#26 stranded, Sig assortment SIG. H328
#18 Stranded lamp cord, A/R
Knob, package RS 274-416
Banana jack, red, 1 each 530-108-0902-1
Banana jack, black, 1 each 530-108-0903-1
Banana plug, red, A/R 530-108-0302-1
Banana plug, black, A/R 530-108-0303-1
Battery pack connectors A/R
#4 Hardware, A/R
#6 Hardware, A/R
Solder, A/R
Glue stick or similar, A/R
LED holder 531-0003
Heat-shrink tubing Du-Bro Yellow size
Test Accessories:
DMM with mini-test clip leads
Jumper mini-clip leads
Resistor “Rt” see above
the board on the nylon standoffs and mount
with 4-40 x 1⁄4-inch screws. Install IC2—
correctly oriented!
Connect the ohmmeter to the banana
jacks and verify a reading of “Very High”
ohms to “Infinity,” depending on the polarity
of the leads and meter scale used. Push the
SW1 button and verify a reading of 3.5-4.0
K. The value should be the same with the
meter leads both ways.
If this checks out, it’s time to perform a
preliminary power-up test. For this test, you
need a charged seven-cell Ni-Cd or NiMH
pack, the specified 7.5-ohm test resistor (Rt),
and some assorted test clip/meter leads.
Connect Rt in series with the battery and
84 MODEL AVIATION
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the combination to Dump’r; i.e., Rt is in one
wire from the battery to Dump’r. Connect a
Digital Voltmeter (DVM) across Rt. The LED
should be off, and there should be no voltage
indicated across Rt.
Push SW1 button; the LED should come on
and the voltmeter should indicate 3.75 volts
nominal (1⁄2 amp x 7.5 ohms). If this is so,
advance the cell-count switch one step at a time.
The LED should go out at 5 or maybe 6,
depending on the exact pack voltage. The
voltmeter should drop to 0 when the LED goes
out.
If this test is okay, remove Rt and the
DVM, and connect the battery directly to
Dump’r. Set the cell-count switch to 7 and
push the button; the LED should come on.
Move the switch to 8 (or maybe 9), and the
LED should go out, depending on the exact
pack voltage.
Reset SW2 to 7, push the button, and allow
the pack to discharge. The LED should go out
eventually. You can watch the progress of the
discharge with a voltmeter on the battery. The
discharge should stop at the nominal 0.9 x 7 =
6.3-volt point. This will take less time with a
partly charged, lower-capacity pack.
For those so equipped and skilled, a labtype
variable power supply can be used to do
the same thing. It’s also informative to insert a
current meter and note the steady reading as
you vary the cell count/supply voltage!
When you’re finished testing, tuck the
dangling fuse inside the box and install the
box cover and cover screws. I use stick-on
rubber feet on the box bottom to make it
“slide resistant.” Your Dump’r is now ready
for actual use—and for show-and-tell at your
next club meeting!
If you experience any trouble with Dump’r,
I’ll be happy to assist in any way I can. As
with all of my published electronics projects, I
will not let you fail if you give me the
opportunity to help; that includes
troubleshooting and repair if need be, which is
free except for postage. Write me and we’ll
take it from there.
Happy dumping! MA
Bob Kopski
25 West End Dr.
Lansdale PA 19446
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ump’r is a relatively simple device that
safely discharges four- to 18-cell
Nickel Cadmium (Ni-Cd) and Nickel
Metal Hydride (NiMH) batteries at a fixed
1⁄2-amp rate. Discharge is initiated with the
push of a button and automatically
terminates when the pack reaches the
equivalent of .9 volt per cell. Dump’r
requires no external power and, other than
setting the “cell count” switch, needs no
adjustment or calibration.
Dump’r was designed for the Electrics
enthusiast, but it is easy for anyone with
batteries to discharge to use. It is fuseprotected
against polarity reversal. Only a
seven-cell pack, a Digital Multi Meter
(DMM), a test resistor, and some test/clip
leads are needed to check out proper
operation. All parts and supplies are readily
available, and anyone with electronic
soldering experience can build Dump’r.
Dump’r was conceived when it became
routine for me to charge more E-power
motor packs than I had the opportunity to fly
out. This happens easily with Electrics that
may have interchangeable packs.
I prefer not to store motor packs in
charged condition longer than a day or so for
a couple of reasons. One is that charged
packs can slowly self-discharge unequally
among the cells. Under
these conditions, it is
not good practice to
“top off” with a fast
refresh charge or use
the pack in subsequent
flight. A fresh, fast
charge from empty
seems to yield better
flight performance
anyway.
Aeromodelers do
have several ways to
run down packs,
including running
motors, using the
“discharge” function
that is built into some
chargers, using
“cyclers” in limited
cases, or using banks
of auto lamps and/or
power resistors that
vary with the cell count. Dump’r, being a
self-powered, one-size-fits-all alternative, is
more convenient than most of the preceding
approaches.
Since Dump’r was designed with banana
jack connectors, all that is needed to
accommodate any battery is a suitable
adapter cable. Short cables with banana
plugs on one end and the appropriate
connector on the other end will do the job.
I use Dump’r with 150-3000 mAh
batteries, but there is no upper capacity limit.
With the fixed 1⁄2-amp rate, the time needed
to discharge packs varies widely. The lowest
capacities take less than an hour and the
largest require hours. Cell count has no
72 MODEL AVIATION
Dump’r ■ Bob Kopski
Dump’r is a safe, one-size-fits-all Ni-Cd/NiMH battery discharger. Short cables adapt to any battery connector style.
Assembled circuit board shown is ready for nine flexible wires to
be added. All components are easy to obtain.
D
effect on discharge time. Whatever the time, it is inconsequential to
me; I just want “empty” packs before the next outing.
The cell-count range and discharge rate keep the power
dissipation and associated heating to safe levels. However, the heatsink
fins on Dump’r can reach 170° with a fully charged 18-cell
pack. That is fine, but you probably don’t want to touch it—just like
you wouldn’t hold onto a 7-watt night-light bulb! Keep this in mind
when you deploy Dump’r (or any other discharger).
Discharging to a nominal .9 volt per cell is generally considered
good practice. For a pack that is in good condition, that is a safe
target value that adequately drains all cells to approximately the same
state. All of the cells are equally empty, which is a great place to
begin a fresh charge the next time.
Discharging a pack without an appropriate cutoff point puts at
least some cells at risk of being “reverse charged,” which is a known
cell-killer condition. Dump’r can be well worth having!
How It Works: If you are one of the many readers who truly enjoys
knowing the operational details of projects such as this, this section is
for you!
Referring to the schematic, the discharge current is held stable by
operational amplifier IC2b, power transistor Q3, and some associated
passive components. This portion of the circuit—an electronic
“current source” configuration—holds the current steady no matter
the cell count.
IC1 is a precision 1.225-volt 1% reference diode. This reference,
in conjunction with some 1% resistors, establishes the current level
October 2003 73
Rotary switch SW2/resistor subassembly and 1⁄8 plywood spacer
plate. Assemble with resistors at solder lug height.
Copy full-size drill pattern, glue to metal box’s outer surface,
center punch, and drill as dimensioned.
Box subassembly ready for circuit board and rotary switch. Everything is wired, and SW2 and spacer is in place.
Dump’r is done! Tuck the fuse inside, install the box cover, hold
with four supplied screws, and have at it!
Photos by the author Graphic Design by Lydia Whitehead
76 MODEL AVIATION
and permits accurate representation by the “cell count” switch. These
precision parts are also the reason why no tune-up or calibration is
needed; put Dump’r together correctly, and it works correctly. Every
Dump’r should have the same discharge current under all conditions
within 5%.
Indicator LED (light-emitting diode) D1 is on when discharge is
in progress and goes off at the end of discharge. LED current is held
steady at roughly 6 mA by transistor Q4. This assures equal
brightness and safe operation throughout the wide cell-count range.
With the cell-count switch properly set, Dump’r operation
commences when a battery is connected and push button SW1 is
activated. Prior to this, circuit voltage V1 is 0, so nothing in the
circuit is operational. SW1 momentarily connects battery voltage to
circuit buss V1 for circuit “start-up.”
This initiative action results in operation of IC2 and all associated
circuitry including discharge operation. Comparator-configured
operational amplifier IC2a immediately goes “high,” thereby biasing
Q1, hence Q2 on. The latter allows continued presence of V1, which
is nearly equal to the battery voltage, after SW1 is released.
Basically, Dump’r is “latched on” after being put there with a
momentary push of SW1.
IC2a comparator operates as follows. The noninverting input is
biased by a fixed percentage of the battery voltage via divider R1/R2.
A precision inverting input is step-selected by rotary switch SW2.
Thus divider R1/R2 applies a voltage that declines with the discharge
of the battery while SW2 applies a stable voltage that is
representative of the cell count.
When the battery voltage drops so that the comparator
noninverting input voltage falls below the SW2 switch-selected level,
IC2a output goes “low” and removes drive from transistor Q1, thus
from switch Q2. This disconnects V1, and all control circuitry shuts
down. Discharge ceases and indicator LED D1 goes out. With no
current drain present, it is safe for Dump’r to
remain connected until it’s convenient for
you to attend to the matter.
The cell-count switch selects cells
individually from four through 12 and
thereafter by twos up to 18. Numerically, the
last three switch steps are electrically
equivalent to 131⁄2, 151⁄2, and 171⁄2 cells
respectively.
This is a satisfactory way to represent
“higher” cell counts because there is
diminished resolution of cell voltage
available as the actual total voltage gets high
enough. So in the worst cell-count position
of 13/14, the greatest “volts per cell” error is
only roughly 0.035 volt—which is
acceptable.
Building Dump’r: The circuit board is cut
from a standard RadioShack General
Purpose Component PC Board. It has a
specific conductor pattern as seen by “Xray”
view in the assembly drawings. It is
important to cut the board exactly to the
conductor pattern shown; count holes to get
it right. Drill the two 1⁄8-inch mounting holes
and the wire relief slot.
Install the nine solid jumper wires as
shown, beginning with the two small
jumpers that will be located under the IC2
socket. Put these two wires in the board,
install the IC socket over them, then solder
eight socket pins and two wire connections.
Make sure you get this right! Install and
solder the seven remaining jumper wires.
Again, count holes!
Now you can install the circuit-board
components in any order you want. Do keep
the parts close to the board; there will be
limited “headroom” in the aluminum box.
Verify the correct orientation of all
semiconductors. Finish with the nine flexible
leadout wires, leaving them a bit long for
now. Strip the wire ends approximately 1⁄4
inch to allow later subassembly testing.
Examine all solder work with a lens,
touch up as needed, clean the solder flux
with a brush and solvent (e.g., acetone), and
reinspect. Make sure everything is correct
and that there are no land-to-land shorts, and
that all component leads are clipped off near
the board. IC2 will be installed later. Set this
circuit subassembly aside.
Assemble the resistor string R14 through
R24 around SW2 as shown, making sure that
the “rotation” is correct. Visually inspect all
joints, then, using an ohmmeter, verify the
accuracy of this switched resistor assembly.
Connect one ohmmeter lead to the switch
wiper terminal and the other to the beginning
of the resistor string at the bottom lead of
R24. With a temporary knob on the shaft,
rotate the switch for a reading of 0 ohms. (A
fractional ohm may be indicated because of
test lead resistance.)
Rotate the switch clockwise (knob view)
one step at a time and verify that the meter
reads the progressive resistance value as
predicted by the schematic. All readings
should fall within 1% of the exact value.
Before removing the knob, preset the switch
position back to 0 ohms as in the preceding.
Set this switch subassembly aside.
The mechanical work is shown herein full
size and includes a drill pattern and labels for
the finished Dump’r. Make a photocopy of
this page, and cut out the drill pattern. Use
glue stick or similar to adhere this paper
pattern around the outside of the metal box.
Make sure you do this accurately, then
center-punch and drill as shown. If you do
this work carefully, everything from here on
will fit nicely.
Remove the paper, deburr all holes, and
clean the box with a suitable solvent. (Soapy
water or alcohol will work well on most
glue-stick material.) Cut and drill the 1⁄8
plywood switch spacer plate as shown. This
piece indexes SW2 and prevents it from
working loose and rotating inside the box.
78 MODEL AVIATION
80 MODEL AVIATION
Trial-fit this piece along with SW2 in the
box, then remove.
The box subassembly proceeds as
follows. Install the 1-inch nylon standoffs
using 4-40 x 1⁄4-inch pan-head machine
screws with inside star washers between the
standoffs and the box.
Install Q3 and the heat sink with 6-32 x
1⁄2-inch screws going through the transistor
mounting holes, the heat sink, 1⁄8-inch-thick
spacers, then the box. The spacers are 6-32
hex nuts drilled out to 5⁄32 inch. (The two
transistor screws are used to mount it and
the heat sink. The latter is spaced up off of
the box roughly 1⁄8 inch by the drilled nut
spacers.)
Inside the box, install one #6 inside star
washer and the specified solder lug over the
protruding screws followed by hex nuts, as
shown.
Next are the banana jacks, SW1, LED
D1/holder, diode D2 (observe polarity),
resistor R25, and any associated wire.
Delay soldering at the negative banana jack
and the solder lug until later.
Make fuse connectors using the clips
specified with leads of 18-gauge lamp cord.
I chose this material for ready availability
and mechanical appropriateness for this
particular task: supporting a dangling fuse.
Sweat-solder the wire to the “flat” of the
fuse clip, then fully cover the clip with
heat-shrink tubing. Make sure that the
wire/clip assemblies are thoroughly
insulated, as shown. Glue the labels to the
box, and protect them with clear tape or
similar. This completes the box
subassembly.
Subassembly Checkout and Final
Assembly: The circuit-board subassembly
is preliminarily tested with an ohmmeter
from lead to lead, as in the following table.
(Remember that IC2 is not in the socket.)
Use the meter on the appropriate scale
(range), and make each measurement twice;
measure, reverse the meter leads, and
measure again.
Although this test does not guarantee
total assembly perfection, an incorrect
result means that you must track down the
reason and fix it before proceeding.
Table of Ohmmeter Tests
Wire Pair Ohms
8-9 “Very High” to Infinite
2-4 3-3.3 K
2-9 9.5-10
4-8 “Very High” to Infinite
6-7 “Very High” to Infinite
6-9 “Very High” to Infinite
1-All “Very High” to Infinite
With the preliminary board checkout
complete, eyeball the final lead dress
needed, and trim and restrip the leads to
installation length. Solder six of the wire
leads to the proper locations in the box and
three to SW2. Insert the fuse. Inspect all.
Mount the switch plus the spacer plate
and knob setting the pointer at “4.” Position
Dump’r Versatile Battery Discharger Parts List
All resistors are 1⁄4 watt except where noted. Some must be 1%, and some need
only be 5%. It may be less costly to use the nearest 1% value for the 5% parts; see
catalog reference. All catalog numbers are Mouser Electronics ([800] 346-6873 or
www.mouser.com) except RadioShack, indicated as “RS ... ” All other items are
common and/or hobby shop/hardware-store supplies.
Item Part/Value Catalog Number
R1 16.9K, 1% 660-MF1/4CL1692F
R2 1.0K, 1% 660-MF1/4CL1001F
R3, 9, 11 10K, 5% (three pieces) 30BJ250-10K
R4 6.8K, 5% 30BJ250-6.8K
R5 681 Ohms, 1% 660-MF1/4CL6810F
R6 2.7K, 5% 30BJ250-2.7K
R8 6.81K, 1% 660-MF1/4CL6812F
R10 1K, 5% 30BJ250-1.0K
R12 1.00 Ohms, 1%, 1W 71-RS1A-1.0
R13 100 Ohms, 5% 30BJ250-100
R14, 15 200 Ohms, 1% (two pieces) 660-MF1/4CL2000F
R16 150 Ohms, 1% 660-MF1/4CL1500F
R17-R24 100 Ohms, 1% (eight pieces) 660-MF1/4CL1000F
R25 392 Ohms, 1% 660-MF1/4CL3920F
Rt 7.5 Ohms, 5%, 5W 280-CR5-7.5
C1 0.1 uF, 50V, Ceramic 80-C315C104M5U
D1 LED 351-5111
D2 1N5401 Rectifier 583-1N5401
Q1, Q4 2N3904 Transistor 512-2N3904
Q2 2N3906 Transistor 512-2N3906
Q3 2N3055 Transistor 511-2N3055
IC1 1.225V Reference 511-TS821AIZ
IC2 LM358 Dual Op. Amp. 511-LM358AN
SW1 SPST Momentary n/o 103-1012
SW2 1P12T Rotary, Shorting 10WW112
F1 ATO, 1 amp 5768-57001
Clips Fuse, two pieces 534-3522
PC holeboard RS 276-168
Chassis box 537-TF-770
Heat sink 532-500403B00
Solder lug 534-904
1⁄8 plywood—1.2 x 1.5 inches
Feet, stick-on—package RS 64-2365
Standoffs, nylon—4-40, two pieces 561-TSP5
IC socket, 8 pin 571-26404634
#24 buss wire, bare, tinned RS 278-1341
#26 stranded, Sig assortment SIG. H328
#18 Stranded lamp cord, A/R
Knob, package RS 274-416
Banana jack, red, 1 each 530-108-0902-1
Banana jack, black, 1 each 530-108-0903-1
Banana plug, red, A/R 530-108-0302-1
Banana plug, black, A/R 530-108-0303-1
Battery pack connectors A/R
#4 Hardware, A/R
#6 Hardware, A/R
Solder, A/R
Glue stick or similar, A/R
LED holder 531-0003
Heat-shrink tubing Du-Bro Yellow size
Test Accessories:
DMM with mini-test clip leads
Jumper mini-clip leads
Resistor “Rt” see above
the board on the nylon standoffs and mount
with 4-40 x 1⁄4-inch screws. Install IC2—
correctly oriented!
Connect the ohmmeter to the banana
jacks and verify a reading of “Very High”
ohms to “Infinity,” depending on the polarity
of the leads and meter scale used. Push the
SW1 button and verify a reading of 3.5-4.0
K. The value should be the same with the
meter leads both ways.
If this checks out, it’s time to perform a
preliminary power-up test. For this test, you
need a charged seven-cell Ni-Cd or NiMH
pack, the specified 7.5-ohm test resistor (Rt),
and some assorted test clip/meter leads.
Connect Rt in series with the battery and
84 MODEL AVIATION
DON’T LOSE YOUR
PLANE IN THE SUN!
• Fly close to the sun with
comfort, increased color
acuity and greater depth
perception.
• Can be worn with or without
prescription glasses.
• Maximum UV-A, UV-B and IR protection.
• Optically perfect, ultra clear vision.
•Total wraparound to protect from side glare,
UV, wind, debris and most hazards.
TO ORDER NOW, CALL
(800) 533-5665
www. z u r i c h s u n g l a s s.com
www. z u r i c h u s a . c o m
Available in Silver, Blue and Gold.
Glasses, belt clip, warranty $49.95 + S&H $6.95
All credit cards welcome.
Zurich International, 9418 Snow Lake Place, Elk Grove, CA 95758
NEW AND IMPROVED TO LAST
LONGER AND WORK BETTER!
CALL US OR VISIT OUR WEB SITE
TO FIND OUT HOW!
FREE!
$10.00 neoprene carrying case
when you mention this ad.
the combination to Dump’r; i.e., Rt is in one
wire from the battery to Dump’r. Connect a
Digital Voltmeter (DVM) across Rt. The LED
should be off, and there should be no voltage
indicated across Rt.
Push SW1 button; the LED should come on
and the voltmeter should indicate 3.75 volts
nominal (1⁄2 amp x 7.5 ohms). If this is so,
advance the cell-count switch one step at a time.
The LED should go out at 5 or maybe 6,
depending on the exact pack voltage. The
voltmeter should drop to 0 when the LED goes
out.
If this test is okay, remove Rt and the
DVM, and connect the battery directly to
Dump’r. Set the cell-count switch to 7 and
push the button; the LED should come on.
Move the switch to 8 (or maybe 9), and the
LED should go out, depending on the exact
pack voltage.
Reset SW2 to 7, push the button, and allow
the pack to discharge. The LED should go out
eventually. You can watch the progress of the
discharge with a voltmeter on the battery. The
discharge should stop at the nominal 0.9 x 7 =
6.3-volt point. This will take less time with a
partly charged, lower-capacity pack.
For those so equipped and skilled, a labtype
variable power supply can be used to do
the same thing. It’s also informative to insert a
current meter and note the steady reading as
you vary the cell count/supply voltage!
When you’re finished testing, tuck the
dangling fuse inside the box and install the
box cover and cover screws. I use stick-on
rubber feet on the box bottom to make it
“slide resistant.” Your Dump’r is now ready
for actual use—and for show-and-tell at your
next club meeting!
If you experience any trouble with Dump’r,
I’ll be happy to assist in any way I can. As
with all of my published electronics projects, I
will not let you fail if you give me the
opportunity to help; that includes
troubleshooting and repair if need be, which is
free except for postage. Write me and we’ll
take it from there.
Happy dumping! MA
Bob Kopski
25 West End Dr.
Lansdale PA 19446
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ump’r is a relatively simple device that
safely discharges four- to 18-cell
Nickel Cadmium (Ni-Cd) and Nickel
Metal Hydride (NiMH) batteries at a fixed
1⁄2-amp rate. Discharge is initiated with the
push of a button and automatically
terminates when the pack reaches the
equivalent of .9 volt per cell. Dump’r
requires no external power and, other than
setting the “cell count” switch, needs no
adjustment or calibration.
Dump’r was designed for the Electrics
enthusiast, but it is easy for anyone with
batteries to discharge to use. It is fuseprotected
against polarity reversal. Only a
seven-cell pack, a Digital Multi Meter
(DMM), a test resistor, and some test/clip
leads are needed to check out proper
operation. All parts and supplies are readily
available, and anyone with electronic
soldering experience can build Dump’r.
Dump’r was conceived when it became
routine for me to charge more E-power
motor packs than I had the opportunity to fly
out. This happens easily with Electrics that
may have interchangeable packs.
I prefer not to store motor packs in
charged condition longer than a day or so for
a couple of reasons. One is that charged
packs can slowly self-discharge unequally
among the cells. Under
these conditions, it is
not good practice to
“top off” with a fast
refresh charge or use
the pack in subsequent
flight. A fresh, fast
charge from empty
seems to yield better
flight performance
anyway.
Aeromodelers do
have several ways to
run down packs,
including running
motors, using the
“discharge” function
that is built into some
chargers, using
“cyclers” in limited
cases, or using banks
of auto lamps and/or
power resistors that
vary with the cell count. Dump’r, being a
self-powered, one-size-fits-all alternative, is
more convenient than most of the preceding
approaches.
Since Dump’r was designed with banana
jack connectors, all that is needed to
accommodate any battery is a suitable
adapter cable. Short cables with banana
plugs on one end and the appropriate
connector on the other end will do the job.
I use Dump’r with 150-3000 mAh
batteries, but there is no upper capacity limit.
With the fixed 1⁄2-amp rate, the time needed
to discharge packs varies widely. The lowest
capacities take less than an hour and the
largest require hours. Cell count has no
72 MODEL AVIATION
Dump’r ■ Bob Kopski
Dump’r is a safe, one-size-fits-all Ni-Cd/NiMH battery discharger. Short cables adapt to any battery connector style.
Assembled circuit board shown is ready for nine flexible wires to
be added. All components are easy to obtain.
D
effect on discharge time. Whatever the time, it is inconsequential to
me; I just want “empty” packs before the next outing.
The cell-count range and discharge rate keep the power
dissipation and associated heating to safe levels. However, the heatsink
fins on Dump’r can reach 170° with a fully charged 18-cell
pack. That is fine, but you probably don’t want to touch it—just like
you wouldn’t hold onto a 7-watt night-light bulb! Keep this in mind
when you deploy Dump’r (or any other discharger).
Discharging to a nominal .9 volt per cell is generally considered
good practice. For a pack that is in good condition, that is a safe
target value that adequately drains all cells to approximately the same
state. All of the cells are equally empty, which is a great place to
begin a fresh charge the next time.
Discharging a pack without an appropriate cutoff point puts at
least some cells at risk of being “reverse charged,” which is a known
cell-killer condition. Dump’r can be well worth having!
How It Works: If you are one of the many readers who truly enjoys
knowing the operational details of projects such as this, this section is
for you!
Referring to the schematic, the discharge current is held stable by
operational amplifier IC2b, power transistor Q3, and some associated
passive components. This portion of the circuit—an electronic
“current source” configuration—holds the current steady no matter
the cell count.
IC1 is a precision 1.225-volt 1% reference diode. This reference,
in conjunction with some 1% resistors, establishes the current level
October 2003 73
Rotary switch SW2/resistor subassembly and 1⁄8 plywood spacer
plate. Assemble with resistors at solder lug height.
Copy full-size drill pattern, glue to metal box’s outer surface,
center punch, and drill as dimensioned.
Box subassembly ready for circuit board and rotary switch. Everything is wired, and SW2 and spacer is in place.
Dump’r is done! Tuck the fuse inside, install the box cover, hold
with four supplied screws, and have at it!
Photos by the author Graphic Design by Lydia Whitehead
76 MODEL AVIATION
and permits accurate representation by the “cell count” switch. These
precision parts are also the reason why no tune-up or calibration is
needed; put Dump’r together correctly, and it works correctly. Every
Dump’r should have the same discharge current under all conditions
within 5%.
Indicator LED (light-emitting diode) D1 is on when discharge is
in progress and goes off at the end of discharge. LED current is held
steady at roughly 6 mA by transistor Q4. This assures equal
brightness and safe operation throughout the wide cell-count range.
With the cell-count switch properly set, Dump’r operation
commences when a battery is connected and push button SW1 is
activated. Prior to this, circuit voltage V1 is 0, so nothing in the
circuit is operational. SW1 momentarily connects battery voltage to
circuit buss V1 for circuit “start-up.”
This initiative action results in operation of IC2 and all associated
circuitry including discharge operation. Comparator-configured
operational amplifier IC2a immediately goes “high,” thereby biasing
Q1, hence Q2 on. The latter allows continued presence of V1, which
is nearly equal to the battery voltage, after SW1 is released.
Basically, Dump’r is “latched on” after being put there with a
momentary push of SW1.
IC2a comparator operates as follows. The noninverting input is
biased by a fixed percentage of the battery voltage via divider R1/R2.
A precision inverting input is step-selected by rotary switch SW2.
Thus divider R1/R2 applies a voltage that declines with the discharge
of the battery while SW2 applies a stable voltage that is
representative of the cell count.
When the battery voltage drops so that the comparator
noninverting input voltage falls below the SW2 switch-selected level,
IC2a output goes “low” and removes drive from transistor Q1, thus
from switch Q2. This disconnects V1, and all control circuitry shuts
down. Discharge ceases and indicator LED D1 goes out. With no
current drain present, it is safe for Dump’r to
remain connected until it’s convenient for
you to attend to the matter.
The cell-count switch selects cells
individually from four through 12 and
thereafter by twos up to 18. Numerically, the
last three switch steps are electrically
equivalent to 131⁄2, 151⁄2, and 171⁄2 cells
respectively.
This is a satisfactory way to represent
“higher” cell counts because there is
diminished resolution of cell voltage
available as the actual total voltage gets high
enough. So in the worst cell-count position
of 13/14, the greatest “volts per cell” error is
only roughly 0.035 volt—which is
acceptable.
Building Dump’r: The circuit board is cut
from a standard RadioShack General
Purpose Component PC Board. It has a
specific conductor pattern as seen by “Xray”
view in the assembly drawings. It is
important to cut the board exactly to the
conductor pattern shown; count holes to get
it right. Drill the two 1⁄8-inch mounting holes
and the wire relief slot.
Install the nine solid jumper wires as
shown, beginning with the two small
jumpers that will be located under the IC2
socket. Put these two wires in the board,
install the IC socket over them, then solder
eight socket pins and two wire connections.
Make sure you get this right! Install and
solder the seven remaining jumper wires.
Again, count holes!
Now you can install the circuit-board
components in any order you want. Do keep
the parts close to the board; there will be
limited “headroom” in the aluminum box.
Verify the correct orientation of all
semiconductors. Finish with the nine flexible
leadout wires, leaving them a bit long for
now. Strip the wire ends approximately 1⁄4
inch to allow later subassembly testing.
Examine all solder work with a lens,
touch up as needed, clean the solder flux
with a brush and solvent (e.g., acetone), and
reinspect. Make sure everything is correct
and that there are no land-to-land shorts, and
that all component leads are clipped off near
the board. IC2 will be installed later. Set this
circuit subassembly aside.
Assemble the resistor string R14 through
R24 around SW2 as shown, making sure that
the “rotation” is correct. Visually inspect all
joints, then, using an ohmmeter, verify the
accuracy of this switched resistor assembly.
Connect one ohmmeter lead to the switch
wiper terminal and the other to the beginning
of the resistor string at the bottom lead of
R24. With a temporary knob on the shaft,
rotate the switch for a reading of 0 ohms. (A
fractional ohm may be indicated because of
test lead resistance.)
Rotate the switch clockwise (knob view)
one step at a time and verify that the meter
reads the progressive resistance value as
predicted by the schematic. All readings
should fall within 1% of the exact value.
Before removing the knob, preset the switch
position back to 0 ohms as in the preceding.
Set this switch subassembly aside.
The mechanical work is shown herein full
size and includes a drill pattern and labels for
the finished Dump’r. Make a photocopy of
this page, and cut out the drill pattern. Use
glue stick or similar to adhere this paper
pattern around the outside of the metal box.
Make sure you do this accurately, then
center-punch and drill as shown. If you do
this work carefully, everything from here on
will fit nicely.
Remove the paper, deburr all holes, and
clean the box with a suitable solvent. (Soapy
water or alcohol will work well on most
glue-stick material.) Cut and drill the 1⁄8
plywood switch spacer plate as shown. This
piece indexes SW2 and prevents it from
working loose and rotating inside the box.
78 MODEL AVIATION
80 MODEL AVIATION
Trial-fit this piece along with SW2 in the
box, then remove.
The box subassembly proceeds as
follows. Install the 1-inch nylon standoffs
using 4-40 x 1⁄4-inch pan-head machine
screws with inside star washers between the
standoffs and the box.
Install Q3 and the heat sink with 6-32 x
1⁄2-inch screws going through the transistor
mounting holes, the heat sink, 1⁄8-inch-thick
spacers, then the box. The spacers are 6-32
hex nuts drilled out to 5⁄32 inch. (The two
transistor screws are used to mount it and
the heat sink. The latter is spaced up off of
the box roughly 1⁄8 inch by the drilled nut
spacers.)
Inside the box, install one #6 inside star
washer and the specified solder lug over the
protruding screws followed by hex nuts, as
shown.
Next are the banana jacks, SW1, LED
D1/holder, diode D2 (observe polarity),
resistor R25, and any associated wire.
Delay soldering at the negative banana jack
and the solder lug until later.
Make fuse connectors using the clips
specified with leads of 18-gauge lamp cord.
I chose this material for ready availability
and mechanical appropriateness for this
particular task: supporting a dangling fuse.
Sweat-solder the wire to the “flat” of the
fuse clip, then fully cover the clip with
heat-shrink tubing. Make sure that the
wire/clip assemblies are thoroughly
insulated, as shown. Glue the labels to the
box, and protect them with clear tape or
similar. This completes the box
subassembly.
Subassembly Checkout and Final
Assembly: The circuit-board subassembly
is preliminarily tested with an ohmmeter
from lead to lead, as in the following table.
(Remember that IC2 is not in the socket.)
Use the meter on the appropriate scale
(range), and make each measurement twice;
measure, reverse the meter leads, and
measure again.
Although this test does not guarantee
total assembly perfection, an incorrect
result means that you must track down the
reason and fix it before proceeding.
Table of Ohmmeter Tests
Wire Pair Ohms
8-9 “Very High” to Infinite
2-4 3-3.3 K
2-9 9.5-10
4-8 “Very High” to Infinite
6-7 “Very High” to Infinite
6-9 “Very High” to Infinite
1-All “Very High” to Infinite
With the preliminary board checkout
complete, eyeball the final lead dress
needed, and trim and restrip the leads to
installation length. Solder six of the wire
leads to the proper locations in the box and
three to SW2. Insert the fuse. Inspect all.
Mount the switch plus the spacer plate
and knob setting the pointer at “4.” Position
Dump’r Versatile Battery Discharger Parts List
All resistors are 1⁄4 watt except where noted. Some must be 1%, and some need
only be 5%. It may be less costly to use the nearest 1% value for the 5% parts; see
catalog reference. All catalog numbers are Mouser Electronics ([800] 346-6873 or
www.mouser.com) except RadioShack, indicated as “RS ... ” All other items are
common and/or hobby shop/hardware-store supplies.
Item Part/Value Catalog Number
R1 16.9K, 1% 660-MF1/4CL1692F
R2 1.0K, 1% 660-MF1/4CL1001F
R3, 9, 11 10K, 5% (three pieces) 30BJ250-10K
R4 6.8K, 5% 30BJ250-6.8K
R5 681 Ohms, 1% 660-MF1/4CL6810F
R6 2.7K, 5% 30BJ250-2.7K
R8 6.81K, 1% 660-MF1/4CL6812F
R10 1K, 5% 30BJ250-1.0K
R12 1.00 Ohms, 1%, 1W 71-RS1A-1.0
R13 100 Ohms, 5% 30BJ250-100
R14, 15 200 Ohms, 1% (two pieces) 660-MF1/4CL2000F
R16 150 Ohms, 1% 660-MF1/4CL1500F
R17-R24 100 Ohms, 1% (eight pieces) 660-MF1/4CL1000F
R25 392 Ohms, 1% 660-MF1/4CL3920F
Rt 7.5 Ohms, 5%, 5W 280-CR5-7.5
C1 0.1 uF, 50V, Ceramic 80-C315C104M5U
D1 LED 351-5111
D2 1N5401 Rectifier 583-1N5401
Q1, Q4 2N3904 Transistor 512-2N3904
Q2 2N3906 Transistor 512-2N3906
Q3 2N3055 Transistor 511-2N3055
IC1 1.225V Reference 511-TS821AIZ
IC2 LM358 Dual Op. Amp. 511-LM358AN
SW1 SPST Momentary n/o 103-1012
SW2 1P12T Rotary, Shorting 10WW112
F1 ATO, 1 amp 5768-57001
Clips Fuse, two pieces 534-3522
PC holeboard RS 276-168
Chassis box 537-TF-770
Heat sink 532-500403B00
Solder lug 534-904
1⁄8 plywood—1.2 x 1.5 inches
Feet, stick-on—package RS 64-2365
Standoffs, nylon—4-40, two pieces 561-TSP5
IC socket, 8 pin 571-26404634
#24 buss wire, bare, tinned RS 278-1341
#26 stranded, Sig assortment SIG. H328
#18 Stranded lamp cord, A/R
Knob, package RS 274-416
Banana jack, red, 1 each 530-108-0902-1
Banana jack, black, 1 each 530-108-0903-1
Banana plug, red, A/R 530-108-0302-1
Banana plug, black, A/R 530-108-0303-1
Battery pack connectors A/R
#4 Hardware, A/R
#6 Hardware, A/R
Solder, A/R
Glue stick or similar, A/R
LED holder 531-0003
Heat-shrink tubing Du-Bro Yellow size
Test Accessories:
DMM with mini-test clip leads
Jumper mini-clip leads
Resistor “Rt” see above
the board on the nylon standoffs and mount
with 4-40 x 1⁄4-inch screws. Install IC2—
correctly oriented!
Connect the ohmmeter to the banana
jacks and verify a reading of “Very High”
ohms to “Infinity,” depending on the polarity
of the leads and meter scale used. Push the
SW1 button and verify a reading of 3.5-4.0
K. The value should be the same with the
meter leads both ways.
If this checks out, it’s time to perform a
preliminary power-up test. For this test, you
need a charged seven-cell Ni-Cd or NiMH
pack, the specified 7.5-ohm test resistor (Rt),
and some assorted test clip/meter leads.
Connect Rt in series with the battery and
84 MODEL AVIATION
DON’T LOSE YOUR
PLANE IN THE SUN!
• Fly close to the sun with
comfort, increased color
acuity and greater depth
perception.
• Can be worn with or without
prescription glasses.
• Maximum UV-A, UV-B and IR protection.
• Optically perfect, ultra clear vision.
•Total wraparound to protect from side glare,
UV, wind, debris and most hazards.
TO ORDER NOW, CALL
(800) 533-5665
www. z u r i c h s u n g l a s s.com
www. z u r i c h u s a . c o m
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Zurich International, 9418 Snow Lake Place, Elk Grove, CA 95758
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LONGER AND WORK BETTER!
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$10.00 neoprene carrying case
when you mention this ad.
the combination to Dump’r; i.e., Rt is in one
wire from the battery to Dump’r. Connect a
Digital Voltmeter (DVM) across Rt. The LED
should be off, and there should be no voltage
indicated across Rt.
Push SW1 button; the LED should come on
and the voltmeter should indicate 3.75 volts
nominal (1⁄2 amp x 7.5 ohms). If this is so,
advance the cell-count switch one step at a time.
The LED should go out at 5 or maybe 6,
depending on the exact pack voltage. The
voltmeter should drop to 0 when the LED goes
out.
If this test is okay, remove Rt and the
DVM, and connect the battery directly to
Dump’r. Set the cell-count switch to 7 and
push the button; the LED should come on.
Move the switch to 8 (or maybe 9), and the
LED should go out, depending on the exact
pack voltage.
Reset SW2 to 7, push the button, and allow
the pack to discharge. The LED should go out
eventually. You can watch the progress of the
discharge with a voltmeter on the battery. The
discharge should stop at the nominal 0.9 x 7 =
6.3-volt point. This will take less time with a
partly charged, lower-capacity pack.
For those so equipped and skilled, a labtype
variable power supply can be used to do
the same thing. It’s also informative to insert a
current meter and note the steady reading as
you vary the cell count/supply voltage!
When you’re finished testing, tuck the
dangling fuse inside the box and install the
box cover and cover screws. I use stick-on
rubber feet on the box bottom to make it
“slide resistant.” Your Dump’r is now ready
for actual use—and for show-and-tell at your
next club meeting!
If you experience any trouble with Dump’r,
I’ll be happy to assist in any way I can. As
with all of my published electronics projects, I
will not let you fail if you give me the
opportunity to help; that includes
troubleshooting and repair if need be, which is
free except for postage. Write me and we’ll
take it from there.
Happy dumping! MA
Bob Kopski
25 West End Dr.
Lansdale PA 19446
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