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Old 10-09-2007, 08:22 PM   #1
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Default Can I "pre-chill" my packs before charging?

I have two packs of IB 4200s, VisPro and matched. after i completely discharge and equalize them, it takes forever to charge them up at the same and recommended 5.0A current. they do heat up considerably by the end of the cycle, even when they are placed over a 120V turbo fan. they get up to about 130f sometimes, and i know that's not good. is it safe to put my packs in the freezer to "pre-chill" them for about 15 minutes before i throw them on the charger? or should i just kick it up to 6.0A? i'd like to keep these cells in good shape, so i do not want to risk hurting them by charging up too fast or overheating them.
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Old 10-09-2007, 09:06 PM   #2
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Yes, charge them at 6.0 A. However, DO NOT use a fan on the packs when charging them. This can lead to overcharging the packs. Also, keep them at room temperature whenever possible. You don't want to chill them down for the same reason as not putting a fan on them.

6 amps is a pretty standard charge rate for IB's. You could even go up to 6.5.
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Old 10-09-2007, 09:22 PM   #3
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You don't want to chill your packs. I'm in Canada and it gets pretty cold up here. I've thrown my stuff into my car in the morning before leaving for work and headed straight to the track after work. I've tried charging my packs that were cold and get nothing but false peaks and batteries that won't take a charge. I now let them sit until they reach room temperature before charging and haven't had any issues.
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Old 10-09-2007, 10:27 PM   #4
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Never pre-chill your cells! I am also from Canada, and as most Canadian knows, your car cannot start because batteries don't work well when they are cold!

Ok... maybe chilling to 10 degrees celcius chilling is ok, but below that... and you may have problems as mentioned before... or a dead battery that will never accept charge again!
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Old 10-10-2007, 12:43 AM   #5
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Right, all NiCd & NiMh cells rely on a chemical reaction to store & release electricity, & if you chill them, that slows down the chemical reactions inside the cells, reducing their capacity/performance. That's also why if you look at lead-acid car batteries, you'll notice a figure called CCA, which stands for Cold Cranking Amps, that's how many amps it can supply in freezing conditions, & it's considerably lower than the other amp number on it, that's what the cold does to it. And with low capacity batteries like what we use, that'll pretty much wipe out everything a Sub-C cell can do, so it's best to keep them at more "normal" temperatures, the chemical reactions will be at their best, & the battery will perform properly as a result. Also, while 130F might be a bit warm, it's not THAT bad, as long as they stay under 140 they should hold up fine....
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Old 10-10-2007, 12:47 AM   #6
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All you do is lower your Delta peak to bring down the pack's final temp when it charges.
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Old 10-10-2007, 01:40 AM   #7
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what minimum temp to per-chill those packs??
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Old 10-10-2007, 06:00 AM   #8
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i've only done this twice so far, and i better stop doing it. the pack (external temp) was only just above 60f, which is about 15f less than room temperature in my house. i have tried charging my packs at 6.0A at the track when i am in a time cruch, and they were fine and did peak a lot sooner than expected. i will get a temp probe for my ICE so that they do not overheat.
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Old 10-10-2007, 06:39 AM   #9
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You might want to invest ina temp gun of some sort. I have found that both of my ICE chargers are off by 5 to 12 degrees on the probe. The ICE would say 120* and the actual temp would be 130*. So just get a back up temp gun to back up the temp probe on the ICE.
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Old 10-10-2007, 07:32 AM   #10
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Dont Chill them, Much more even do a battery warming tray to get packs warm pre-charging for cold weather
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Old 10-10-2007, 07:44 AM   #11
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If you look at SMC and other experts recommendations you will find details on exactly the temps they recommend, etc. Try a search like charge peak detect temperature or something like that. Or if you're lazy, just go to web sites like

http://www.smc-racing.com/ and look under SMC charging
http://www.promatchracing.com/ and look under Tech Support, then Charging

You will see they have good information and instructions there.

My good 4200's peak close to 130F at 6 to 7.5 amp charging. I check them cell by cell with a temp gun (Ice reads surface temps by conductance, and it's usually about 10F or even more off on the low side of the surface temp by temp gun. However set the temp at say 120F on Ice is not a bad safety thing as a backup. In hot weather sometimes that has stopped my charging when the cells were getting hot.

In hot weather I run peak detect at 3mV which is the lowest (non-zero) offered. However it's a bit too high in hot weather, 2 or even 1 would be better, and I would use that if I had a Checkpoint or another charger that allowed lower peak detect. In cool weather if the cells don't hit 120F I raise the peak detect until they do... maybe 5 or 6 if it's 60's and windy.

Batteries work better when hot... almost up to the point where they are too hot, life shortens and the moisture evaporates or the battery even vents badly. There is a chemical engineering rule of thumb that chemical reactions often proceed at roughly twice as fast for every 10C increase in temperature (18↕F). Cold takes the punch and runtime out of batteries.
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Old 10-10-2007, 08:01 AM   #12
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so why should i not charge them over a fan?
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Old 10-10-2007, 08:09 AM   #13
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For a start all u will cool is the outside and the core can still overheat.
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Old 10-10-2007, 11:01 AM   #14
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Hi just reading all the notes above I use the Much-More Battery Heatsink 2 when I charge my cells is this not a good idea?
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Old 10-10-2007, 11:43 AM   #15
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It isn't a good idea to do anything that cools the exterior of the cell only. The temperature in the core of the cell is still what counts, so if you cool the outside you have no real idea what's happening inside. The inside can get too hot, and that's when the damage is done. HTH
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