Q-96: I’ve read a lot about the fact that the new Li-Poly battery
cells should not be discharged below 2.8 to 3.0 volts. Failure to observe that
caution can greatly reduce the life of these cells. I know most new ESCs can
either be selected for the proper cutoff or better yet will automatically set
themselves to the proper cutoff voltage.
My problem is that I have an older-designed ESC with a fixed cutoff of 5 volts
that was fine for my Ni-Cd and NiMH packs, but certainly not for Li-Poly
batteries. Is there any add-on device I can buy that will provide the proper
cutoff and still allow me to use my older ESCs?
A-96: There are several such devices on the market, and they range in
price from roughly $20-$25. I recently received one such product from FMA Direct
called the Automatic Cell Detect, Low Voltage Cutoff Device--part AVC1AIR.
This add-on enables proper low-voltage cutoff for Li-Poly, Ni-Cd, and NiMH
battery packs when used with older-style ESCs that don’t provide the proper
cutoff. This device is extremely small and weighs only 0.11 ounce, so it can
easily be installed in even parking lot-size models with no real weight penalty.
Installation is easy. The servo cable exiting your ESC is plugged into the
connector located on one end of the device. The cable exiting the device plugs
into the throttle port on your RC receiver. There is one additional wire that
must be “spliced into” the positive (+) battery lead wire as it exits the ESC.
Installations instructions are extremely detailed.
Once installation is complete, you choose from two modes of operation, the first
of which provides automatic cutoff based on a sampling of the particular battery
pack you employ. The second mode is a custom cutoff, in which you establish your
own voltage-cutoff point. Once it is determined, that level (of your choice)
remains in the device's memory until you change it.
You can find out more about this product at: www.fmadirect.com. In the "Search"
option, type in “AVC1AIR” and then click on the product name.
A similar product is available from Diversity Model Aircraft Inc. in San Diego,
California, called the Li-Saver. It sells for $24.95. You can learn more about
this device at
www.flydma.com/flydmahome.asp.
No matter which product you choose, the addition of this kind of device will
guarantee that your Li-Poly batteries are not discharged to less than the
minimum recommended 2.8 volts per cell.