homemade discharger

[Kendodude]

does anyone know how to make a homemade discharger for a large battery since I don't own one and a little short on money and I heard someone say they read it in a article but never explained?

[ArmyHummer]

I just use a general cheap resistor that I got at my local hobby shop. It was 2 bucks and it is nothing but a 30 ohm ceramic resistor

[AlphaSix]

I use several 12v auto tail-light bulbs that I've soldered together, and just attach my batteries to that until the lights are out.. It works MUCH better and faster than that kooky tokyo marui discharger..

[TVCasualty]

Actually inside the TM discharger there is a ceramic resistor (ceramic to withstand the high amperage), a diode wired in parallel, and an LED in there too. The value of the diode is set so that it will cut power to the LED when a 8.4V pack reaches close to 7.5 volts (or whatever the recommended discharge value is – I forget).

HOWEVER the ceramic resistor continues to drain the battery beyond what it is healthy to drain you battery to and will eventually cause damage to your pack. There fore you need to UNPLUG the discharger as soon as the LED goes out!

Alpha's method will work also, just as long as you know how many light bulbs to use, how to wire them together, and when to take them off. The same over draining could result in this method so you need to know what you're doing.

[Koko]

Question..why is it necissary to drain your battery?

[Nitrous]

If you have a Nickel-Cadmium battery pack, it is best to discharge the battery so that it doesn't develop a "memory". This occurs when you charge the battery from an already partially-charged state a lot. This is not so prevalent in the newer NiCad batteries, but it is a good idea to discharge the battery as often as possible, especially if you are storing it for long periods of time.

With the Nickel-metal-Hydride packs, discharging can actually be harmful to the pack, so I would advise against it.

[Koko]

Oh okay. Thanks for explaining it to a newb like me! :D

[TVCasualty]

Another reason is so that the battery is 'dead' before charging it for the full recommend time stated on the charger. Since there is no way to determine how dead the battery is (unless you have a peak charger, but then it doesn't matter) it's best to kill it before slapping it on a charger. That way when it charges it gets just a full charge rather then being over charged, which prevents voltage depression or damage to the pack by excessive heat. Both of which are more serious then the memory affect in my experiences. (I have not discharged my NiCds in over 1 year of heavy use and have noticed no memory effect, I am able to not discharge because I have a peak NDV charger.)