20 or 30A Discharge?
This is a good question and there is two distinct schools of thought on this.
1. You don't want to discharge your cells at too high a rate as you will shorten the life of the cells.
2. You want to discharge your cells at least at the same rate they discharge in the car to train them to give up their charge that fast.
I don't have any data on this one as it would take a long time be expensive to do. Maybe some of the matchers (or guys with more money and time
) who read this thread can check it out. I will say however that I don't see any noticable difference in cell life by discharging at 30A which I have been doing for nearly 2 years now. Up until then I was using a 20A discharge.
My own thoughts about this is that there is a difference between the heat caused by charging and the heat caused by discharging. When you charge you create heat and pressure in the cell which breaks down the chemicals inside. When you discharge you are releasing the pressure even though the heat is increasing. Heat is definitely the enemy for cell life however to get performance from your cells on the track you need to have some heat in the cells which works as a catalyst for the chemical reactions and increases voltage and lowers IR. As you can see there is a balance to get here. When I charge I like to charge to 110F when feasable. However I live in California, it can hit 110f ambient temp therefore temp charging is a little unfeasable so I just deal with it as best I can.
To digress just a little more Phill Haines (Pro Trak) did a test run on temperature gain in gp3700 cells during different ambient temperatures, he found a temperature gain of 25C (not sure what the conversion to F is) yeilds the best results and it also appeared that an ambient temp of around 25C (approx 78F) works well also. Most interestingly he found that using a peak detect of 0.05v for a 6 cell pack yeilded around a 25C temperature increase over ambient regardless of what that ambient temperature is.
I apologise for the digressions but the heat issue is quite important. If you are interested in the details of Phil's study the website address is in my info below.