Charging my transmitter from my car battery

[Chatenever]

I've been field charging my Hitec transmitter battery pack by hooking it up directly to the cigarette lighter on my car. It charges much faster than the factory-supplied wall wart (25ma max), but the rate is well below anything that would heat up the cells (I measured less than 1.5C). I would like to make some sort of a circuit that would give me an LED or other indicator of when current is actually going into the battery, but I'd like it to cost less than an in-line amp meter. Suggestions?

[jeffs555]

If you are connecting a 9.6v battery pack directly to a car cigarette lighter with nothing to limit the current you are playing a dangerous game. The only thing limiting the current at the cigarette lighter is its fuse, and that is usually around 15 amps.

At a minimum you need a series resistor, but a real field charger would be much better and would get you your LED indication. Here is a page with some charger circuits, and there are probably some simpler designs floating around. http://davesrcflight.mysite.wanadoo-members.co.uk/frame_pages/circuits_frame.htm
Here is another one.
http://www.uoguelph.ca/~antoon/gadgets/carnc12.htm

[quax]

In former times it was an open secret ;) , that 8 NiCd cells can be charged directly by a 12V car battery, provided that the motor is not running and that the accu is not connected continuously for many hours. For a fast refresh in the field you can do it. Simply use a long cable (2m) with low diameter to limit the high start current.

cul
quax

[gnofliwr]

Yes, you can charge 8 NiCd cells off of a car battery, but a word of caution about Tx NiCd packs. These are not intended to be fast charged like motor batteries, nor fast discharged. They're supposed to be charged at C/10. Fast charging them will shorten their life. If you going to "cheap charge" them, best to keep an eye the pack temp.

Having said that, I've been known to recharge a Tx at the field at 1-2C using a peak charger on ocassion, but not as a general practice.

- Roger

[Acetronics]

Hi,

You can make a simple current indicator ...

by Winding 20-30 turns of 1mm enammelled copper around a reed switch.

when current flows ... switch is closed !!! ( you can then power a LED from the 12v car batt ... or short it ( the led ...ROFL ) if showing end of charge ! )

just try it !!!

sooooooo simple.

Alain