Author: Red Scholefield
Edition: Model Aviation - 2008/09
Page Numbers: 91,92,95
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The Battery Clinic

Red Scholefield | [email protected]

Is my charger working?

I am still perplexed by the number of people who depend on batteries to fly their models, yet lack even the most basic battery test equipment. It is not as if it costs a fortune.

You can purchase adequate digital multimeters for less than $5 apiece. Harbor Freight has them for as low as $3.99 ($2.99 when on sale, which is frequent). See the sources list for contact information. Northern Tool and Equipment, RadioShack, and eBay are other sources. RadioShack has a multimeter that interfaces with your PC to allow you to record discharge voltage/current and print it out. These tools are a great way to check your batteries, and at a cost that is significantly less than you will pay for some of the hobby-specific devices.

Check out the photo with the multimeter connected to a servo. I have found this invaluable when setting up a model to check for servo linkage dragging.

Cut the red wire in the middle of a servo extension (about 12 inches). Add banana plugs to the ends of the red wire, and plug these into your digital multimeter. Polarity makes no difference, because most meters will read in either direction. Plug in the modified servo extension between the battery and the receiver or between the receiver and any servo under investigation.

How High and See How

How about a new fun-fly event? How high can you get your model in a certain number of seconds from takeoff? Winged Shadow Systems' neat little gadget called the How High allows you to get the exact altitude by hooking up to your receiver and flying the 2-gram device to altitude. While you can get a single reading—the maximum altitude—by waving your fingers over the LED and counting its blinks, the See How that the company sells lets you take multiple altitude readings in the same flight and displays the actual number. Simply mate the See How with the LED on the How High and press the button.

In less than a second, the See How downloads the altitude data and displays it for each segment of the flight. As many as 10 readings and nine individual flights can be displayed.

I learned something else. At 1,000 feet, your typical trainer is getting to the point where orientation becomes a problem. Most of our flying, it turns out, is done at about 200–300 feet of altitude—at least that is what How High told us.

Winged Shadow Systems' How Fast components were fastened to 1/32" plywood to allow them to be moved from aircraft to aircraft. This is achieved by temporarily taping the plate to the bottom surface of the wing and running the leads to the receiver for power, and acquiring different altitudes by toggling the retract switch.

The RC Reporter, also from Winged Shadow, gives you battery voltage on the fly. Installing this 2-gram device in your model allows you to check the voltage while in flight. The unit gives you audible beeps as your airplane flies by while actuating a spare channel on your transmitter. That's another reason to fly electric; you can hear these. It gives you the present voltage and the lowest voltage your pack sees during the flight.

A similar device for glow/gas-powered models measures the receiver-pack voltage and gives you an audio readout, but you would not be able to hear it with the engine running. It's still a nice feature: taxi back to the pits, shut down your engine, flip the retract switch on your transmitter, and find out if you have enough battery for your next flight.

Another feature is that if you turn off your transmitter without turning off your model, it will warn you with an audio alarm. In addition, it's useful as a lost-aircraft finder.

Propeller Pitch Speed

I received a simple formula from Paul. Someone always has a better way.

"Red, I just finished reading your column in May 2008 MA. Learned considerably. You gave us a location for a propeller pitch speed calculator. I find it much simpler and quicker to use the equation:

Pitch (inches) x kRPM x 0.95 = Speed (mph)."

kRPM means thousands of RPM; for example, 12,450 rpm would be entered as 12.45. I checked several calculations against the online calculator with the same results.

Hughes Spectra 4 — A Charger for All Reasons

Remember when the Litco Alpha 4 was the hottest item in charging? It was so hot you literally had to win the Litco raffle to even get one and then be willing to part with $300. This bought you the capability of charging four packs at the same time.

While the Alpha 4 has essentially disappeared from the market, the need to charge/cycle various kinds of packs has not. Hughes RC has stepped forward to fill that gap. There are other multiport chargers available, but few, if any, give you the charge/discharge/cycle control that the Hughes Spectra 4 offers for all the battery chemistries we are now employing.

One of the first things that struck me when I got the charger was the size. This is not a wimpy little charger you can lose on your charging bench. Its commanding appearance with the large heat sink on one end says serious charging.

Turning on the Spectra 4 for the first time is another surprise, because the display, after showing the Hughes welcome statement with firmware version, scrolled to "Property of Red Scholefield, Newberry, FL (352) 331-8410." The people at Hughes RC program the owner's information into each charger sold and can change it if the original owner requests it.

Following are the Spectra 4's specifications:

  • Four outputs allow you to manage as many as four batteries at one time:
  • One- to 10-cell Ni-Cd/NiMH
  • One- to four-cell Li-Poly/Li-Ion/A123
  • One- to six-cell lead acid
  • Serves as charger/cycler (for two or more cells)/loaded voltmeter
  • 50 mA–1000 mA per port (charge or discharge)
  • Input: 11–15 VDC
  • 80-character, four-line backlit LCD
  • Reverse polarity protection on input and output
  • Memorizes up to 20 battery-pack charge settings for "Automatic Charging"
  • Remembers packs by name (up to 16 characters each) — examples: "Futaba TX", "Extra 300 RX", "CAP 232 ignition"
  • Charges multiple batteries with common grounds
  • Simple four-button, menu-driven operation
  • Detailed monitoring of all ports
  • Audible alerts
  • Battery backup in case of power failure
  • Built-in loaded voltmeter
  • Fast charge with peak detection (selectable rates)
  • Timed charge (selectable rates)
  • Topping-charge option (selectable rates)
  • Trickle-charge option (selectable rates)
  • Accurate battery management
  • Rugged all-metal enclosure
  • One-year warranty
  • Weighs 2 pounds
  • Size: 8 x 5 x 3 inches

All the charge parameters measured and recorded appeared to be well within the accuracy limits expected for this type of equipment. The simple display gives you all the information about the pack.

A photo in this column shows the "END" display for three cycles on a four-cell Ni-Cd pack that had one flight on it in the morning before cycling. "P3" is for Port 3, "CYC" indicates that there were three cycles, and the last charge was 1:07:33 with 736 mAh input. The readings at the bottom were for the capacity delivered on each discharge. The Spectra 4 discharges and then charges in the cycle mode.

The Spectra 4 is shipped with a battery-backup lead. Connect a 7.2- to 12-volt Ni-Cd or NiMH pack to the jack on the left end, near the power wire. In the event of a power failure, the backup battery will continue to power the microprocessor and LCD while terminating all other functions. When power is restored, all functions will pick up where they left off.

Battery backup can save you a lot of headaches, especially if you are powering your unit from an AC-driven power supply that is subject to reliability issues. Your backup battery pack does not need to be large; a 500 mAh pack should keep you going through more than a 10-hour power failure. When you are doing multiple cycles, battery backup can keep you from having to start over.

Need more power? Connect two or more ports with a simple-to-make harness (details on the Hughes RC website), and you can charge/discharge at up to 4 amps for a single pack or two packs up to 2 amps. Just set the ports to the charge amounts you want. If you want 3,500 mA, set three ports at 1 amp and one at 500 mA.

A Caveat of All Chargers

This is the first time I've seen any charger manufacturer admit the following. The Hughes owner's manual states:

"Batteries should be disconnected from the charger within a reasonable period of time after all functions have been completed. Once 'END' is displayed there will be a small discharge (less than 5 mA) on the battery."

I knew this was the case with some chargers, such as the old ACE DVM/C. My curiosity was aroused, so I checked a number of other chargers in the lab. Every one puts a small load on the battery when the charge is complete.

So if you are using chargers that do not have a continuous or pulsed trickle charge, you could find a pack somewhat discharged if it were left connected to the charger for an extended period (such as four or five days for a 500 mA pack).

Readers' Conversions (Which Some Refer to as Ugly Models)

Brayton Paul seems to favor Axi motors, as I do. It looks like he is taking no chances on overheating his ESC.

With all my batteries charged, I'm going flying. You can write to me at the street address for "The Battery Clinic," but e-mail is faster.

Sources

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