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Old Jan 16, 2004, 10:58 AM
Bank & Yank !
Gary Dodds's Avatar
Sunderland, UK
Joined Jan 2002
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Quick question about Charging Li Polys

I have a few E-tec 1200 3s1p packs that ive been using for a little while.
I now have a need to use 2 of these packs together to make a 3s2p pack. I have just purchased a schultz charger to be able to charge them as one pack.

My question is: what is the best way to charge them together, ie do i need to discharge them individually with the scultz, before joining them and charging as one pack, or do i fully charge them individually before joining together as a 3s2p ?

Its probs basic stuff, but i want to be sure before i burn the house down

Regards
Gary
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Old Jan 16, 2004, 11:03 AM
luc
I plant balsa sticks too
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France
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plug them together, wait a couple of hours for them to equilibrate (it's automatic) and then you can charge them together.
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Old Jan 17, 2004, 08:25 AM
Bank & Yank !
Gary Dodds's Avatar
Sunderland, UK
Joined Jan 2002
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Thx Luc.,

so it doesnt matter what charge state the 2 packs are in? just joint them up (parralel of course) wait a while , then charge as a 3s2p (2400mah) .

Gary
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Old Jan 17, 2004, 08:40 AM
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Gary,

Just check the voltage on each pack. If they're within 0.5 volts or so of each other, it's OK to connect them in parallel.

Also, I have not found it necessary to wait for the cells to reach the same voltage (balanced condition) before charging in parallel. Balancing is accomplished while charging.

- RD
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Old Jan 17, 2004, 08:41 AM
Bank & Yank !
Gary Dodds's Avatar
Sunderland, UK
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Cheers RD,
ill do that before trying.

Gary
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Old Jan 17, 2004, 08:47 AM
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Gary,

Here's a thread demonstrating the flexibility and relative safety of parallel charging:

http://www.rcgroups.com/forums/showt...ks+in+parallel

- RD
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Old Jan 18, 2004, 09:12 PM
Keep the fun in it!
john8750's Avatar
Los Angeles
Joined Mar 2003
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Quote:
Originally posted by Gary Dodds
Thx Luc.,

so it doesnt matter what charge state the 2 packs are in? just joint them up (parralel of course) wait a while , then charge as a 3s2p (2400mah) .

Gar
y

Be very carefull charging in parallel.
Also, be carefull who you listen to.
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Old Jan 19, 2004, 07:01 AM
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Quote:
Originally posted by john8750
... be carefull (sic) who you listen to.
Good advice.

To appraise john's competence re parallel charging, see:

http://www.rcgroups.com/forums/showt...hreadid=188849

- RD
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Old Jan 19, 2004, 08:24 AM
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Walled Lake, MI, USA
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John8750, your assessment of the relative safety of Li-poly parallel vs. series charging is at odds with all of the experts in this area, as well as the experience of real people on this forum. Please do a little more research on this subject before dispensing misleading advice.
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Old Jan 19, 2004, 10:53 AM
Keep the fun in it!
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Los Angeles
Joined Mar 2003
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Dave--
I do agree, it is at some odds.
And I have upset at least expert with my explanations.
I dont know of any commerically available charger that can safely charge Li's in parallel.
I have explained that my own charger has a fuse to protect against over current, or over voltage because of too much current.
A voltage check before charging can detect a bad cell if connected in series, but not in parallel, unless it is shorted.
Two cells charged in parallel with one cell opened is a major problem.
In the same condition in series, the fuse will open, causing no problem.
I am trying to add some very thought out and tested theory I have done.
Again, I claim not to be an expert.
I would like to continue in a friendly manor to contribute to this forum.

I'm only trying to help here.
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Old Jan 19, 2004, 11:03 AM
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John8750, there are many technically astute people on this forum. I'm sure you will be able to have a good technical discussion about the pros and cons of series vs. parallel charging of Li-poly cells. In the meantime, it would be best not to recommend one or the other techniques to anyone until you have convinced the experts in engineering terms why you are right and they are wrong. The consequences of giving erroneous advice to someone that results in an accident is serious business. So please do take the time to discuss the technical reasons for your theory.
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Old Jan 19, 2004, 11:16 AM
Keep the fun in it!
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Dave--
That is exactly what I am doing.
I am not talking of cells not ballanced at charge, but of a damaged cell at charge.
What I say could not cause any danger, only prevent it.
I give no fulse info.
Charging any other configuration than 2s with a damaged cell could be dangerous.
I would think anyone would be interested in any thoughts of safety.
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Old Jan 19, 2004, 01:57 PM
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Arnold , Maryland, United States
Joined Nov 2002
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John, I appreciate your safety concerns. Charging with a damaged cell could cause problems, if charged in series or parallel.
The only question is which charging technique, might create the most hazzard, with a damaged cell in the pack.

I'm not even going to give my opinion here. Without controlled tests, it will still be an educated guess.

I wiil say, that it only becomes a problem, when you are charging packs. If you are charging a single cell, then the voltage is limited to 4.2, and the current is limited to the capacity of a single cell.

I don't think that these values are high enough to get you in trouble. Maybe not even with a damaged cell.
And cell balance never becomes an issue, because each cell is individually charged.


It may be more cumbersome, but I think it's safer.
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Old Jan 19, 2004, 10:36 PM
Keep the fun in it!
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I'm afraid to say anything anymore.
I agree about single cell charging.
Good luck and be careful.
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Old Jan 20, 2004, 01:10 PM
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Discussion and exchanging ideas should be encouraged. The thing to avoid is making categorical statements without offering any technical explanation or demonstrable proof that one has positively identified that all the experts are wrong and that things should be done a different way.

A healthy discussion about what happens when a series pack with a damaged cell is charged vs. what happens when a parallel pack with a damaged cell is charged would be beneficial to anyone considering which method of charging is safest. Everyone just needs to stick with factual data to back up their statements and avoid personal issues.

I'll even get things rolling here by saying, from my limited technical understanding:

A 3-cell series pack with a damaged cell will result in the charger's voltage for 3 cells (12.6V) being split equally between the 2 good ones (6.3V each), resulting in over-voltage frying the 2 good cells. However, the current being delivered by the charger at a 1C setting based on the capacity of 1 of the 3 cells in series would be as appropriate for the 2 good cells as for all 3.

A 3-cell parallel pack with a damaged cell will result in the charger applying the correct voltage to the 2 good cells (4.2V), as any parallel pack with no series connections will always be charged at 4.2V regardless of number of cells, eliminating the possibility of over-voltage. But if the charger's current setting is for 1C based on the combined capacities of 3 parallel cells, the charge to the 2 good cells would be 1.5C as they would be splitting the total current originally intended for the combined capacity of 3 cells.

Is any of that correct? What have I missed?
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