RC Car - How Should I Discharge My Cells?

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How Should I Discharge My Cells?

Comments: I am wanting to get a discharger but I am considering making one. I know that I am supposed to use 1157 signal light bulbs but why, and how many? I saw in the HPI tips page that you only really need one light bulb to discharge a battery, what's up with that? I think I may just stick to the "run my car dead" method for now.

Response: The HPI site is correct, you can use one light bulb to discharge your battery but it is not the best method.

Your main goal it to discharge your battery after the race at rate that is very close to the current draw your car has while racing. This will increase battery performance since the battery is discharged in a uniform manner. If you were to discharge your battery in the car at 20 amps for 4 minutes then discharge any remaining current by drawing 2 amps from the battery, the battery will realize that there is a lower current being drawn from it and, almost like a memory, will have a lower output at that point in the discharge curve in the future. Just like a battery can remember when it wasn't discharged, it can also remember at what rate it was discharged at. This is why it is possible to condition your batteries for specific applications (for example, high current draw or longer run times).

The method you mentioned of discharging the battery in the car is the absolute best method since the cells will be discharged just as they would be in a race. Some people find this method to be inconvenient. Therefore, many people make a discharger that discharges the battery similar to the car.

On average (this is a very rough estimate) an RC car draws about 20 amps. Each 1157 automotive light bulb draws about 2 amps. This is why most people solder 10 bulbs in parallel, to draw approximately 20 amps. This is also why it was not the best idea to only use one light bulb.

Don't get me wrong, obviously if you discharge your batteries they will be in better shape than if you didn't but if you want the optimum performance, try to keep the car drawing rates similar to your discharger drawing rates.

Let's take off a few tenths per lap,

"PRO"
Pro Racer Secrets

Also see Question About Your "discharge" Advice