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Old Jan 31, 2005, 06:09 AM
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Help!
How to balance Lipo cells without balancing tabs?

Hi,

I am just starting out on RC and after reading so many horror stories about Lipo packs, is regretting on my decision on jumping onto Lipo packs right away.

Anyway, since I have already bought them, now it is to find out more and make sure I handle this unstable power units properly.

Please advise.
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Old Jan 31, 2005, 06:18 AM
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What brand are your packs?

- RD
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Old Jan 31, 2005, 06:37 AM
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Have not received them, they are on the way. They are the ones call E-Power from China.
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Old Jan 31, 2005, 06:54 AM
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If they dont have tabs, the only way to balance them is to remove the covering and install your own, but this can be tricky and should not be tried if you are not competent/confident about what must be done.

Assuming the cells are all ok to start with the best way to keep them in balance is to charge at less than 1C (i.e. 0.5C or 0.7C) and do not discharge to the limit of capacity or current.

so if the pack is a 10C rated 2 cell 1200mAh : charge at about 600-800mA and discharge at no more than about 7 or 8C and dont drain every last mAh out of the pack.

All of this advise WILL NOT stop a bad pack (or even a good one) from going out of balance, but it will slow down the process.

A good check to do is to fully charge the pack and record the voltage, then let it rest for a day and re-check the voltage. There should not be a significant difference between the two levels as healthy lipos have a very low leak current. If the voltage is much lower there may be a bad cell(s) in the pack and it may need balancing or disposing of.

Stuart
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Old Jan 31, 2005, 07:18 AM
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Thanks for the fast reply. BTW, is it advisable to store the charged Lipos in the freezer?

I plan to put the Lipos individually in Ziplocs with a handful of silica gel and throw them into the freezer.
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Old Jan 31, 2005, 07:56 AM
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Before we talk about balancing, let's have a look at those packs.

First, they are shipped in retail packaging of unknown characteristics by ordinary airmail. I would rather not ride a commercial airliner out of Hong Kong until this practice is thoroughly investigated.

Second, the buyer is warned:
if you will discharge it over 9A, please change suitable battery plug before !!!

It's anybody's guess how the wiring is attached to the tabs. That will have to be discovered before individual cell voltages can be checked for pack balancing.

These packs are quite risky for newbies, IMO.

Pictures of the 3S 2200 with discharge graph appear below.
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Old Jan 31, 2005, 08:04 AM
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Vendor's Discharge Graph:
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Old Jan 31, 2005, 10:36 AM
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Tanic

Not practical without the balancing connectors built-in the pack like Tanic packs, each cell can be checked thru the JST 2 pin female socket
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Old Jan 31, 2005, 10:52 AM
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Try charging them at a low amperage over a period of many hours. This works sometimes.
**** Don't do this! That's the fastest way to have a puffed pack. You cannot trickle charge a Lithium pack of any kind. -Jim McPherson, Moderator****
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Last edited by Jim McPherson; Jan 31, 2005 at 05:07 PM.
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Old Jan 31, 2005, 07:32 PM
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Thanks, Jim.

Wish the new folks would read your sticky before embarking on their quest for LiPo power.

- RD
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Old Feb 01, 2005, 03:25 AM
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Quote:
Originally Posted by ptglass
Try charging them at a low amperage over a period of many hours. This works sometimes.
**** Don't do this! That's the fastest way to have a puffed pack. You cannot trickle charge a Lithium pack of any kind. -Jim McPherson, Moderator****
Jim,

Sorry to get a little off topic, but what is the harm in charging an 1800mAh lipo pack at the 250mA setting on my Apache 2500? All I have read indicates that this may indeed extend the life of the battery.

If you mean trickle charge on a nicd style charger, then I completely agree with you.

Back on topic:

From what I have read on these boards slowly charging (<1C) a lipo will help it to stay in balance, but will NOT re-balance an out of balance pack.


Stuart
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Old Feb 01, 2005, 03:48 AM
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Ok...now I have already done it...bought 4 of these. What will be the best approach? Break them up, reconfigure and solder the tabs? I am quite adept at soldering.
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Old Feb 01, 2005, 04:49 AM
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Solder on your own taps if you really want to, but if I were you, I would treat them well i.e. don't run them to their limits and monitor for any significant drop in capacity or voltage and for puffing/deformation.

I have some original e-tec1200 packs without taps and they are still running strong after more than a year. I took the wrapping off one and the cells read 4.19v and 4.20v after a full charge. Always charges at 0.7-1C and discharged at about 6-7Amps, NEVER balanced!

Packs usually go bad for one of two reasons: Abuse or defective cell(s).

either way, you should notice a drop in capacity or voltage and/or puffing/deformation before they explode in a ball of fire.

In my personal opinion taps are a great thing to have, but if you take the proper precautions (Don't abuse them, never charge unattended, charge in fireproof container etc etc) they are not absolutly necessary for safe use of lipos.

Next time buy packs with taps!

Stuart
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Old Feb 01, 2005, 04:53 AM
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Dont stress. The packs would be balanced when you get them.

I just checked 5 packs,all 3S They are 6 months old and have between 20 & 50 cycles each. Cells in one pack differed in voltage by a of half volt.ie the highest 12.4v, lowest 11.9v. the others only had a range of 0.02v. I just charged each cell individually and all is fine again. I used alligator clips on the tabs.
I will add that I baby these lipoly. Only discharge to about 11.2volts and draw 10C wot on a 3d ship that doesnt see much wot(10C batts).

Use them, be sensible and I doubt you'll be sorry, nothing lasts forever anyway
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Old Feb 01, 2005, 05:42 AM
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Quote:
Originally Posted by stu78
Solder on your own taps if you really want to, but if I were you, I would treat them well i.e. don't run them to their limits and monitor for any significant drop in capacity or voltage and for puffing/deformation.

I have some original e-tec1200 packs without taps and they are still running strong after more than a year. I took the wrapping off one and the cells read 4.19v and 4.20v after a full charge. Always charges at 0.7-1C and discharged at about 6-7Amps, NEVER balanced!...
Trouble is, Stuart, these aren't e-tecs. A vendor whom you would recognize has told me he has tested many new entries in the LiPo ratrace and some are "real junk".

I hasten to add I'm not implying that E-Powers are, just that we don't know much about them yet. Personally, I welcome the introduction of commodity-priced LiPos, but my point is that I think they should be tested by knowledgable e-fliers before they get widely distributed.

- RD
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