Author: Red Scholefield
Edition: Model Aviation - 2007/11
Page Numbers: 81,82,84
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Put your charger to work

Red Scholefield | [email protected]

Also included in this column:

  • Uses for old computers
  • Battery specs: where to find them
  • Bob Lloyd goes electric
  • What an electric propeller can do to you
  • Winter battery storage
  • Electric gift suggestions
  • Battery questions and answers
  • Battery education sources

The charger you bought to take care of your hobby needs can do many other charging/cycling tasks on cordless appliances, cell-phone batteries, MP3 players, and almost anything that uses batteries. Has the charger gone south on your cordless drill? Are you suspicious of the capacity delivered by your cell-phone battery? Your hobby charger can come to the rescue. The only catch is how to make the connections to the battery or device itself if the battery is inaccessible. If the charger has gone bad you can salvage the part that interfaces with your battery and simply add leads with banana plugs to go into your hobby charger. Others require that you get a little more creative and make an adapter.

Don't trash that old computer. Give it a new purpose in your shop as a data logger/programmer. Several battery maintenance devices are being offered with computer interfaces that enable you to set up the test and/or monitor them. Devices such as the West Mountain Radio CBA II discharge analyzer, the Orbit Microlader, the recently introduced FMA Direct BalancePro and Cellpro, and the TME Xtrema, with its latest update, take advantage of a computer interface. The handy RadioShack digital multimeter also comes with a computer interface, enabling you to record voltage or current and graph it.

Then you have programming devices for Castle Creations' Phoenix ESCs that greatly simplify setting them up, with brake on/off, cutoff voltage, hard/soft timing, etc. Plus the computer will give you a place to keep all your modeling notes that you are forever filing and forgetting where. And if you do decide the computer has no further use, pull the hard drive and take out the two crescent-shaped magnets. They are great for holding tools, hanging up plans while you are building, etc.

Where to Find Battery Specs

My favorite source is the Sanyo site. Another manufacturer is Yuasa (field box and lead-acid starting batteries). Some battery suppliers, such as FMA Direct, have taken the bold step of providing battery performance curves for Li-Poly packs on their web sites. If you know the name of a manufacturer (not the distributor, which can seldom give you any meaningful information), you can type it into the Google search engine. That will usually lead you (albeit on a somewhat tortuous path through all the marketing hype) to some useful information if you are patient.

Another Old Faithful Gets Electrified

Bob Lloyd, a member of the Staten Island NY RC Modelers, sent in a picture of his Goldberg Eagle 2 designed for a .40 glow engine. He is powering it with two six-cell, 3300 mAh NiMH packs. An E-flite 46 brushless motor is controlled with a Phoenix 60-amp ESC. Bob claims that the Eagle 2 is a great success. Why am I not surprised? It has great breeding.

Something that constantly bothers me at the field is seeing electric-power fliers hover over models with the surgically efficient APC E propellers only millimeters away from a wrist, throat, or other vulnerable part of the body while twiddling with airplanes and having the battery plugged in. Maybe what Brad Faul (aka Tommygun@RCU) submitted will get their attention. Included is a picture of what a small outrunner can do if you are careless during setup. Always remove the propeller before setting up a computer radio and hooking up the connections.

The throttle channel was reversed, and an inadvertent arming sent Brad to the emergency room. He received nine stitches—worse than any glow engine he can remember.

Some people don't realize that unlike with a glow engine, an electric-powered propeller will keep slicing away like a blender—unless the propeller breaks. Hell hath no fury like a runaway electric with only one propeller blade.

As some of you are reading this it is time to put your models away for the winter. (Shudder!) Your batteries will hibernate fine in most cases. It does not matter in what state of charge you store your Ni-Cd or NiMH packs. However, it is best to remove them from your model in case a cell shorts out during storage and leaks electrolyte. You have probably heard of black-wire disease so I won't go into it here, other than to point out that it can cost you a wiring harness or worse if it makes its way into any of your electronics.

According to the manufacturers, lithium packs should be stored 40%–60% charged for best results. How do you get to that level? Discharge the packs in your model, checking the voltage occasionally. When they get to roughly 3.7 volts (open circuit) they are good to store. An easier way is to use a discharger that will let you set the voltage, such as the CBA II.

A couple chargers will let you set the charge voltage (after complete discharge) to a storage level. There are the Cellpro and the Xtrema. You can even use other chargers if you monitor the voltage while charging and shut down the process at the desired level.

Li-Polys should never be left in the airplane after use. My shop refrigerator is a good repository for packs that are not going to be used for a while, even if we don't enjoy your nice, long building season.

People have asked about leaving models in an environment where they are frequently dropping below freezing. Ni-Cd and NiMH specs give −40° (C/F) as the low-temperature storage level. Lithium can be stored to 20°C (−4°F) per some manufacturers' specs. It would probably be better to store them where there are fewer broad temperature swings.

As the number of people going clean (electric) increases, many are still operating blind in regards to the abuse they are giving their equipment and batteries. Yes, they can detect the smell of overstressed components, but by then it is too late.

Motors and batteries have limits. If they are frequently pushed beyond those limits, they become unhappy. A wattmeter of some type would make a great Christmas gift.

The AstroFlight Super Wattmeter (part 101) has been a popular unit. Although I have never used one, Medusa Research also has some nice units: one standard and one with several options for more bells and whistles. Give your family a clue; leave the magazine open on this page with this item circled.

The Hard Ones

The following are battery-charging questions.

"Hello, I have a question about battery charging and I can't seem to get a straight answer. Can a 1600 mAh battery be charged safely with a 2 amp charger?

One thing I saw was that each cell can be charged at .5 amp (this is a five-cell hump pack), which would mean that the pack can handle rates up to 2.5 amps. Another thing I saw was that the battery shouldn't be charged at more than 10% of its mAh rating, so the 1600 mAh battery shouldn't be charged at more than 1.6 amps.

Please help, I have a 2 amp charger and I want to know if I would be ok using it. Thank you."

That is not how it works. (Not that I had the slightest clue what his 2-amp charger was.) The pack charge rate is the same as a single cell when they are connected in series. Ten percent of a 1600 mAh pack would be a charge rate of 160 mA (0.16 amp) — not 1.6 amps.

What kind of a charger do you have? If it is a peak charger, yes, you could charge the 1600 mAh pack (Ni-Cd) at 2 amps. Maximum for a NiMH pack would be 1.6 amps.

Back to Basics

There are many good sources for basic battery information, including The R/C Battery Clinic, BatteryUniversity.com, and Hangtimes Hobbies. For electric flight in general there is no better resource than the Electric Flyers Only web site. For lead-acid batteries check out BatteryStuff.com.

Space here doesn't permit my going into the detail necessary to give you even a minimal battery education. The basic seminar on my web site exceeds 5,000 words.

For those without computers, your local library has them for your use. It might cost you a few nickels to print out all the information you are going to find that you might want, but you won't have to buy a computer to get it.

Lithium battery pricing is coming down. The cost of battery packs has a significant impact on the cost of electrics, but it appears that there is some light at the end of the tunnel.

Following is a survey of the market as of July 2007. I picked a typical pack to use as an example.

  • Air Thunder — 3S2200 mAh, 25C — $69.99
  • Amodotech — 3S2100 mAh, 10C — $49.75
  • Apogee — 3S2200 mAh, 20C — $51.99
  • Common Sense RC — 3S2100 mAh, 15C — $69.95
  • DN Power — 3S2150 mAh, 15C — $74.96
  • Flight Power — 3S2100 mAh, 18C — $62.99
  • FMA Direct Cellpro — 3S2100 mAh, 18C — $47.95
  • Hurricane Flight Systems — 3S2000 mAh, 12C — $40.20
  • Max Amps — 3S2100 mAh, 20C — $57.95
  • Poly-Quest — 3S2150 mAh, 20C — $79.90
  • Thunder Power — 3S2100 mAh, 12C — $69.95

That's it for this month. I'm still at 12219 NW 9th Ln., Newberry FL 32669, and my computer still accepts e-mail on a regular basis.

Take care. MA

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.