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This is the new Sirius Electronics SuperTest PRO precision battery tester. With this unit you can select any cutoff voltage in increments of 0.1 volt from 1 to 14 volts. This enables you to test Ni-Cd, NiMH, and Li-Poly battery packs and cells. The unit sells for $99.95 plus shipping and handling. |
Q-25: I acquired a Global Hobbies ProMax Activator peak digital charger. I am just getting into electric power, but would like to use this charger on my regular RC transmitter and receiver batteries. It states in the instructions that you should set the charge current to two or three times the rated capacity of the battery pack. Is that okay?
You also said in your "Battery Basics" article (October 2003 Model Aviation) that a battery pack is bad when it is depleted to 20% of its rated capacity. How do I know when I get there? Can you straighten me out?
A-25: Several answers are necessary, and this is an important subject. The ProMax charger works well, and I have no problem with it. The basic charging circuit was designed with the electric-power enthusiast in mind.
You can charge one to eight (Ni-Cd or NiMH) cells at selectable charge currents ranging from 0.5 to 6.0 amps. It is essentially a fast charger with peak-detect cutoff. There is also a "Slow Peak Mode" that applies a fixed 0.2 amp (200 mA) charge current to the smaller battery pack.s There are no discharge testing capabilities in this unit.
I do not recommend that you fast-charge your RC transmitter battery. Most of these cells are rated at 500-600 mAh. If you apply a 3C charge current (600 X 3 = 1,800, or 1.8 amps) you might blow out the internal charging-circuit wiring inside your transmitter.
I recommend that you charge your RC transmitter battery pack with the system charger that the manufacturer supplied. That will always be at the overnight rate (or for at least 10-12 hours). You can do this every other day and never overcharge the battery.
For the most part I also favor charging the RC airborne receiver/servo battery pack with the system manufacturer's charger at the same overnight rate. Unless you want to fly for more than two hours at a particular flying session, there is no need to fast-charge these batteries. Most RC-system batteries were never intended for fast charging in the first place. I recommend that you save your ProMax charger for your electric-power battery packs. It will do a fine job.
In the next part of his question, the reader indicated that I my article stated that a battery needs replacing when it falls to 20% of its originally rated capacity. He then wondered if he could interpret data from the ProMax charger that would allow him derive battery capacity.
Here we go again with the fine print! In that article I wrote that I discard battery packs when they drop down 20% from their original capacity rating. As an example I wrote that a 600 mAh pack should be discarded when the capacity reaches 480 mAh (600 less 20%). I referred to when it goes down 20%—not down to 20%.
The peak voltage and time showing up on the ProMax display will not directly tell you anything about the battery's capacity. You need a simple battery discharge tester. This device applies a load to the battery, usually taking the voltage down to 1 volt per cell. The amount of the load and the time it took to get to the 1 volt per cell is integrated into a single capacity reading in mAh.
I’ve included a photo of the new Sirius Electronics (a division of Peak Electronics Inc.) SuperTest PRO precision battery tester which can handle as many as 14 battery cells. You can set the voltage cutoff point in 0.1 volt increments up to 14 volts. This will enable you to test Ni-Cd, NiMH, and even Li-Poly batteries. The Web site for this new battery tester is www.siriuselectronics.com/supr_tst.htm.