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Old 02-01-2005, 07:20 PM   #1
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Default Battery question

Right now I charge my packs at 5 amps and want to know what the advanteges and disadvanteges are of charging your packs at 6-6.5 amps. I race touring car carpet stock. just looking for as much as an advantege as I can get.
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Old 02-01-2005, 07:24 PM   #2
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Charging at 6A will give your packs more punch, which is important in stock racing. I read that the best is to have a higher input amperage and a lower input voltage. Normally, it would be 6-6.5A and 14-15V, but 7A @ 11V supposedly doesn't get the pack as hot.
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Old 02-01-2005, 07:27 PM   #3
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Since your running stock, I would charge around the 6.5 amp range. The general rule would be higher charging amprage would mean higher voltage in the pack which leads to a punchier pack. The only disadvantage would be a decreased amount of runtime which isn't really a concern for stock. Another advantage would be to "dead short" the batteries. This is a whole other topic but it would increase voltage and decrease runtime.
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Old 02-01-2005, 09:12 PM   #4
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how much run time am i looking at losing? does higher imput amperage increase internal risistance?
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Old 02-01-2005, 11:14 PM   #5
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Hi mcc,

Don't believe the hype. I have been hearing this for such a long time. So I did a test, according to my own discharge data, there is no difference between charging at 4 amps or charging at 6 amps. NONE!!

I have tried both ways, it makes no difference whatsoever on punch, average voltage or run time. Now there is some reason to believe that charging at a higher amperage will reduce the lifecycle of the cell, I think this is highly likely. Maybe there is an improvement by charging at really high amps like 9 or so but I think your cells will be trashed in a few weeks.

Now of course you have to make your own decisions, you can either believe everyone else (pretty much) who think that they get more punch from more amps or who have heard it said that this is the case. Or you can believe me, someone who has done the tests. I charge at 4.5A, the only time i go higher is when I need to charge faster.

You will get better results by working on your motor cutting and brushing every run or working on your drive train, having cells with better voltage (but be carefull with this one) and lower internal resistance etc etc.

have fun with this one.

Chris
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Old 02-01-2005, 11:19 PM   #6
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From actual track experience, I've found that repeaking a pack at 6-6.5A before the race gives you a little extra punch.

crimson eagle- for your tests, are these just numbers from a machine, or from race experience? For me, packs charged higher always yielded better punch, especially fresh packs.
(I'm not attacking your claim, just curious )
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Old 02-02-2005, 12:17 AM   #7
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Micros,

Actually both, I have found that my machine data backs up what I see on the track as far as I can tell. The reason I say this is there is so many things that can affect track performance greatly that the very slight differences (if any) from charging at a higher amperage is virtually undetectable in the car.

I can understand that you will feel a little more in the pack when you repeak, this is because when you repeak you are making your cells warmer (and overcharging). Now heat has a very big impact on cell performance but this depends on how you define performance. As you know there are two main aspects to performance, on track performance and the cell lifecycle performance. I don't know about your financial situation but I cannot afford to buy new cells every 3 months so cell lifecycle is important to me. Heat has two effects, it speed up the chemical reactions in the cell (chemical transfer time) and it speeds up the rate of chemical breakdown in the cell.

A faster chemical transfer time is good, it allows the current to get out of the cell faster which means a lower internal resistance. This also means that the cell voltage can recover faster which helps the average voltage. All good things particularly for stock racing.

As you can imagine, chemical breakdown is not a good thing, if the chemicals break down there is obviously less available to supply current and therefore the run time will be reduced.

I have spoken to many people about these thing including General motors engineers and cell matchers. There is a lot of different opinions out there, and these ones are just mine but I do have some data to back it up.

Chris.
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Old 02-02-2005, 12:28 AM   #8
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Hi Crimson Eagle,

I wanted to ask a question regarding your battery test. Does deadshorting really decrease internal resistance. Were you able to confirm this in your tests?
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Old 02-02-2005, 06:40 AM   #9
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rough,

I dont really dead short, I equalise to 0v and usually have the cells on the tray for a while when they get there but there is a resistance accross the cell. You can argue a little that it is effectively dead shorting (i've made that one myself) but it's not really. I've heard of many stories of different things happening when you dead short and i believe that most are probably true. This leads me to think a couple of things. Firstly that many things could happen good and bad and you don't reall know what it will be. I think it depends on the condition of the cell before you start. And also I think no-one really knows for sure.

I apologize if i have just made it more confusing but I've heard so much contradictory stuff. I don't do it, I have a lot of success with what I already do so i don't need to.

Chris
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