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Li-po charging question

Li-po charging question

Old 09-30-2012, 01:33 PM
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I recently started getting into electric r/c. I've been looking to upgrade to li-po. I purchased the passport ultra charger and batteries from Hobby King. The batteries are Turnigy 1700mAh 2S 20C li-po packs. I set the charger to li-po and the capacity cutoff to 1700 mah. On the balance charge setting I set the charger to 1.7A and 7.4v (2s).

When I go to charge the batteries one series is at 3.54 and the other at 2.57. I was under the impression they should be closer balanced and shouldn't be allowed to drop under 3.0. After allowing the balance charge cycle to finish the series were further out of balance then at the start.

Am I doing something wrong? I ordered 4 packs and the results are similar across the board. Is there something I should be doing with new batteries? I tried one set in my brushless rc18b2 and couldn't get it to do anything after initial startup. I'm assuming that is because one series is under the 3.0 li-po cutoff?
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Old 09-30-2012, 01:48 PM
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You should charge your batteries with 0.1C or a bit higher the first times. But your celldrift is reaally bad, i dont think it's because of the charging. Maybe you just got some bad batteries. Normally they only drift that much if one cell has a much higher inner-resistance than the other.

PS: you dont need the capacity-cutoff, its just a control-function for the charger. The charger always charges until the batterie reaches 8.4V, or the capacity-cutoff is reached. You should make it higher so the charger can charge the batterie full even when it has a bit more than 1.7Ah.
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Old 09-30-2012, 02:00 PM
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Originally Posted by Cody227 View Post
You should charge your batteries with 0.1C or a bit higher the first times. But your celldrift is reaally bad, i dont think it's because of the charging. Maybe you just got some bad batteries. Normally they only drift that much if one cell has a much higher inner-resistance than the other.

PS: you dont need the capacity-cutoff, its just a control-function for the charger. The charger always charges until the batterie reaches 8.4V, or the capacity-cutoff is reached. You should make it higher so the charger can charge the batterie full even when it has a bit more than 1.7Ah.
you mean 1C not .1C
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Old 10-07-2012, 11:41 AM
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Thanks for the information about the capactiy cutoff. I thought the charge rate of 1.7a was equal to 1c? That was how it seemed when I read the battery manual. So it would seem like I got 4 bad battery packs? I had read good reviews about these batteries are there any other packs/vendors I should look into? At this point I really want to get this thing running. I went to my lhs and they didn't carry any packs with the proper ends.
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Old 10-07-2012, 12:26 PM
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1.7a is 1c, in this case. EG: 1700mah = 1.7ah so 1c = 1.7a. If you've got a cell that's dropped down to 2.57, consider buying a new battery, or have someone who knows how to fix it have a look. The cell can be isolated and revived, but there is a little danger involved.
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Old 10-07-2012, 12:43 PM
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Thanks for clearing that up that is what I thought. These are brand new batteries bought from hobby king. This is how they were when first opened and put on my charger.
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Old 10-08-2012, 03:32 PM
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Minimum resting voltage for lipo cells really should be no less than 3.5 volts. If more than one pack is showing this low voltage and ESPECIALLY if the same cell in the pack reads lower then the readings from the charger are very suspect. Generally lipos arrive at about 3.85 volts per cell.
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Old 10-08-2012, 04:01 PM
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Oops, wrong thread!
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Old 10-08-2012, 05:15 PM
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Are all 4 lipo's showing 1 cell at 2.57V? I've ordered many batteries from HK and sometimes I get the odd one showing below 3V but never 4 in a row. I would try another charger just to confirm.

Just a FYI, if your charger wont allow you to charge it, a quick fix is switch to Nihm mode and slowly build up the low cell to over 3V and then back to lipo mode to charge it fully. I've done that to a few lipo's and they've turned out fine.
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Old 10-10-2012, 02:33 PM
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The packs read as following:

Pack 1: s1-2.78 s2-4.15
Pack 2: s1-2.57 s2-3.84
Pack 3: s1-2.40 s2-3.58
Pack 4: s1-2.57 s2-3.84

I let the first pack go through the full charge cycle hoping they would level out. Obviously they didn't. Thanks again.
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Old 10-10-2012, 02:46 PM
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The charger may be faulty. I would ask a fellow racer to cycle(charge fully and then discharge to no less than 3.7v per cell) all four packs. Hopefully your packs are recoverable. Shoot hobbyking an email or contact them and ask how you should proceed. hate to see your money go to waste.
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Old 10-10-2012, 02:53 PM
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Static voltage per cell should never go lower than 3.3(3.0 at the extreme) volts per cell. If those packs are recoverable, its going to take a long long time seeing how out of balance they are. i know most packs are made in China but I don't ever buy turnigy. I tend to buy top shelf brands cause being that some can handle 2+C charge rates, tend to be more robust. My cells never go more than .02 difference and those packs are 1.5 years old. My newest packs are about .001 difference.
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Old 10-10-2012, 04:44 PM
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Sounds good. I'll be heading to my lhs tomorrow to try to get some help. Hopefully we can figure something out. Thanks for the advice.
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Old 10-10-2012, 05:14 PM
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You are welcome. I know this hobby is and can be expensive. But all of us were beginners at one point and we don't want to break our wallets over a hobby. Ask the local fast guys or be observant of what equipment they are using. If the equipments is good and on the expensive side, save up and try to find a happy medium or try to duplicate equipment. The good stuff will cost more but if taken care of, can last quite a while. i used to buy the cheaper stuff but find myself in the same situation as you. Premature failure or lack of speed. Now i just save and get the good stuff right off the bat and the equipment tends to be more robust and last much longer.
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