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Old 04-08-2015, 10:47 AM   #1
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Default High charge rates and heat

I do not practice it myself, but I know the big thing in stock racing evidently is to charge the batteries at 40 amps or so. From what I've kind of picked out of the different threads on it, it's not necessarily about putting more power into the battery, it's about building heat. something about the higher temperature makes for a lower internal resistance and more power I guess. my question is, what kind of actual temperatures are they trying to reach? And instead of overcharging them to build heat, why could you not use a charging bag sitting on top of a heat pad? I do a stock in all three classes, and while I am just as much about getting more power as the next guy, I am in no hurry to overcharge the hell out of my battery.
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Old 04-08-2015, 11:11 AM   #2
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You discharge the pack at a high rate (20-40amps) to build heat in the pack (i go down to about 3.5v per cell), then start the charge cycle at a high rate to keep the heat in the pack (30-40amps). Charging a pack that you just ran (no significant discharge) at 5amps on a heating pad will do next to nothing other than put some heat in the case...not the actual cells. I have not temped my pack but i will try and remember next time (it was definitely warm though). By doing the above you can discharge the pack and re-charge it in about 12-15 minutes...if not less.

disclaimer...all this means next to nothing if you have a hard time keeping shiny side up.
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Old 04-08-2015, 12:00 PM   #3
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I am seeing temps of about 120-125 deg normally. the problem with inducing external heat, is that you need to get into the cells. And that can take a while trying to push heat through the case and into the cell. think about cooking something. have you ever cooked thick burger on the grill at too high of a heat? the char the outside and leave the center raw. Same principle. can you add heat to the pack for a long time to bring the temps up sure, takes longer and....if you already charger your pack, then add heat, the voltage can creep up and cause other issues. But the cycle method generates here directly where you want it..into the cells. and voltage is controlled by the icharger so no creep. They say you need to leave the packs at 72 deg for 1-2 hours to allow the heat to become even for battery testing and comparison. If I check my IR at 80deg and you check yours at 65, our numbers mean nothing. for like for like comparing, you need to create a baseline env. Typically that is around 72.
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Old 04-08-2015, 01:40 PM   #4
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yeah, with plastic not being a very good conductor of heat it would be more of a slow warm up with a heat pack vs hi charge rare. the heat pad method would almost have to totally surround them and have something to seal in the heat to be effective but it would take longer.

I have a brand new chassis on my B5m short course with an old body, so technically the shiny side is down. Haha
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Old 04-08-2015, 07:05 PM   #5
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Another reason is a hope to avoid detection. Roar events and some other races check battery temperature, it can't be more than 5 degrees above ambient temperature (Roar doesn't appear to specify F or C?). Heating and cooling devices are also against Roar rules.
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Old 04-08-2015, 07:07 PM   #6
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Quote:
Originally Posted by Dave H View Post
Another reason is a hope to avoid detection. Roar events and some other races check battery temperature, it can't be more than 5 degrees above ambient temperature (Roar doesn't appear to specify F or C?). Heating and cooling devices are also against Roar rules.
they tried to tech this at cactus, but some guys were pitting inside and some were pitting outside. Guess who had natually higher temps....they guys outside in the 90 deg weather. The guys inside were in 75 deg ac
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Old 04-08-2015, 07:19 PM   #7
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That would complicate matters no doubt. What did they end up doing?
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