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Battery Charging ?

Old 07-23-12, 11:52 AM
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Battery Charging ?

I have a 37V, 14AH, Polymer pack.
Wondering how low I should let it get before charging.
Do you watch the Volts, or the AH.
Thanks in advance.
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Old 07-23-12, 08:49 PM
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Did you get a manual? What does it read? You might do a search for your particular battery chemistry and see what wikipedia says.
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Old 07-24-12, 09:58 AM
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As far as I can tell just about every battery meter on the market measures voltage to determine the capacity. So logically, it's the voltage you would watch for when using the battery. Also note that voltage while under load will be different if then the voltage on an open circuit.
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Old 07-24-12, 10:57 AM
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Thanks Guys
I guess what I am really trying to figure out is how far I can go on charge, without actually draining the battery.
I understand that one should never completely drain the battery, but leave a certain percentage of charge in the battery.

Thanks
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Old 07-25-12, 12:17 AM
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what bike and motor do you use?
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Old 08-03-12, 05:21 AM
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On my other site that I am on, they recomend 80% dod. So for 37v, no lower than 29v. What kind of chemistry, Lipo or Lifepo4?

Lipo recommend range 3.6v to 4.2...for battery extended life, charge to only 4.1v per cell

Lifepo4 recommended range is 2.0 to 3.6v, discharge to only 29v for longevity.
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Old 08-03-12, 11:45 AM
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Refering to a battery pack as a Polymer pack doesn't really say what kind of pack you have. So it's dificult to give you a correct answer to your question. The most common are lipo. Lipo cells can be monitored the same way common flashlight batteries or lead car batteries are monitored. As indicated by chil6er you can simply monitor the voltage. However, if you have lifepo4 I wouldn't recommend this method. Lifepo4 cells tend to hold a more linear voltage until they are close to death. Therefore, the proper way to monitor lifepo4 cells is by the amount used not the amount left. To do this you need an amphour meter. You need to assume that the pack is full (12ah in your case) and the meter will record what you discharge. So if your goal is to discharge 10AHs you would just watch the AH meter till you discharge 10ah. This leaves you with 2ah remaining in the pack.

However, no matter what type of pack you have the lower you discharge it the shorter it's life. Also the faster you discharge it the shorter it's life. A good general rule is 50% discharge will increase the life of the pack 25 to 50% over an 80% to 90% discharge. Likewise, this is simular to the discharging at rate. Discharging at 2c will shorten the life by 50% over a 1c discharge rate.

Now lets get really deep. You should never trust any monitoring methods 100% at the "pack level". Monitoring the pack voltage for example only means the "pack" is still happy. But it does not mean the individual cells are happy. Therefore, you should always have an individual cell monitoring while discharging the pack. Some BMS monitor at both cell and pack levels but not all or even many. And you should never assume that all your cells are being properly charged to a full charge level.

You need to give us more info on your pack. A pic of it and your charger would be nice.

Bob

Last edited by dumbass; 08-03-12 at 12:04 PM.
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