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Old Jul 21, 2012, 01:13 PM
That's a funny word
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Originally Posted by everydayflyer View Post
Just a heads up and yes I knew better but forgot.

I have been using my 306B to parallel balance charge 4 each 300 mAh 2S Lipolys for my Blade 130X and today they seems a bit weaker than normal. I decided to check them on another charger and found that they were indeed out of balance by 0.3V which really surprised me until I checked its' setting and found that I had left it set to Balance at CV stage. 4 LiPolys of 300 each equals 1.2Ah and I charge them at 2 to 3C so 2.4 to 3.6A and it turns out that the 306B's balancing power just is not enought to balance these mixed packs during the CV stage only. After I set Balance to Start at Storage all is well again with the 306B.

I normaly set Balance to Start at Storage but had changed it many months ago when I was charging mostly 3S Lipolys which in fact rarely required any balancing at all. Just goes to show that one needs to keep an eye on things.
Does this mean that 2 or 3 or 4 packs were out of balance seperately (ie cell 1 and 2 of same pack are .3 volts difference)

Next question is if it was 2 or 4 packs were they opposite cells? (ie cell 1 in one pack was highest , yet cell 2 in other pack was highest)

Concluding that the charger didn't know of ANY imbalance whatsoever. Depending upon how these were wired this makes no sense if all balance taps were paralleled, does it?

I'm curious as to what the cell's voltage screens read perhaps at the start of charge and maybe half way through because as you know this is a gross imbalance especially at the end of charge.

It seems it would be very difficult to duplicate this condition even if one tried to.
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Old Jul 21, 2012, 01:15 PM
That's a funny word
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oops , I forgot my own question:
(not on charles set-up , but on any setup with 306B)

Does the balancer continue to balance after charge has ended?
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Old Jul 21, 2012, 01:52 PM
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Nope. Balancing stops at charge termination.

Mark
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Old Jul 21, 2012, 02:02 PM
That's a funny word
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Thanks, I don't like that. It would be nice if it was adjustable. So maybe that is charles' problem?

Charge ended long before cells were in balance , but then that begs the question of why the cells were imbalanced to start with?
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Old Jul 21, 2012, 02:21 PM
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but then that begs the question of why the cells were imbalanced to start with?
Bingo. If I have packs that are getting imbalanced with every discharge and cannot be easily balanced during CV mode, I keep a very watchful eye on them and consider them as candidates for disposal.

Mark
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Old Jul 21, 2012, 03:00 PM
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gulio I can not accuataretly answer your questions other than yes all balancing / charging leads were in parallel,they were mixed batteries . one 2S 35C 300 (not accurate ratings) one nano 35C 360 which was in fact two 2S 180 hard wired in parallel and one Nano 25C 2S 300 which is in fact two 1S 300 hard wired in series. All flown for 4 min. active flights in Blade 130X plus total of approx. 30 to 45 seconds total spool up and landings.


One of the members here did rarther extensive testing of mixed LiPolys charged in series aat greater than 1C rates and found some rather wide inbalances and I have noticed the same myself. I have not been a big fan of parallel charging since chargers / balancers have became more afforable and most persist in using what I term very limited balancing power.

As long as the cells are closely matched, all cells and all packs are fairly close to same IR there are no issues. If one charges slow there are few issue if one charges mix unmatched packs at greater than 2C there can be issues. I found years ago that starting balancing at 3.85 per cell would go a long way in maintaing the limited balancing power the ability to keep thing in reasonable limits.

Note: Limited balancing power is relative.

If one is charging at 300 mA rate then a 300 mA balancer is a 1:1 ration and should have no problems keeping up however charge 4 300s at 2C and now balancing power is down to a 1:8 ratiocharge those same at 3C and ratio is not 1:12. Just think about when one is charging 6ea. 50000 mA in parallel.

We keep getting more and more powerful chargers but not balancers to match. Once again if one charges at 1C or less and does not mind using Trickle Balance or Hyperions balancing until charger has it Stop buttom pushed most often cells stay reasonably balanced.

-----------------------------------------------
Mark these are small 2S Lipolys which are relatively inexpensive and I charge at high rates so that I can get multi cycles on them per flying session as I am per usual also testing the LiPolys. I could more easily charge 10 or so at home on a charger which has no issues balancing them and not bpther with filed charging at all. I could also make a series charging / balancing harness so that each cell would have the full limited as it may be balancing power available and with all being at between 3.75 to 3.80 after the typical flight ther should be no issued, I could also just ue my DN Power charger and charge only two at a time and it charges each cell seperately ( true multi channel outputs) and have no issues. One should try and remember that often that how I charge / treat a LiPoly is not what I consider ideal but more toward what the average purchaser may subject them to. I have even been known to leave some of thge micro Lipolys both 1S and 2S from 120 to 360 mAh charged overnight.

Charles.
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Old Jul 21, 2012, 03:10 PM
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Originally Posted by gulio View Post
oops , I forgot my own question:
(not on charles set-up , but on any setup with 306B)

Does the balancer continue to balance after charge has ended?
Not exactly, but if you enable balance trickle, it will charge until pack is balanced .
Making terminating current lower than max bleeding current of the balancer helps too. If you select "slow balancing". it will terminate when current drops to 1/20 of initial current. If current is set to 5A. it will terminate at 250mA. If bleeding current is 300mA, charge current will throttle down to 300mA when first cell reaches 4.2V, but charge will not terminate since this is above 250mA. So it will continue to charge the other cells until they all reach 4.2V, then it will lower current until 250mA is reached and charge is terminated.

The problem with parallel charging is that badly matched packs will be unbalanced the moment they are connected in parallel when discharged. If charged alone, a badly matched pack will normally end up in perfect balance at the end without any balancing. If charged in parallel, balancing is needed.
'
Fred
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Old Jul 21, 2012, 03:21 PM
That's a funny word
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Your pack configs should pose no problem as far as balancing goes. The 500 ma capability really should be more than capable of dealing with a reasonable amount of imbalance for the rate of charge too.

I'm thinking that this was a cumulative out of balance condition that went on for more than just this one single charge. It seems that both Mark and Charles are thinking along the same lines too.

Charles , is it too late to verify this? Could you now check all cells in each pack when discharged or perhaps you have balanced them already and it is too late to check them. I must admit that I rarely check individual cells voltages at the discharged state , and this may have been an early tip-off had you read the cells before charge , right?

Oh well, maybe we never know.
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Old Jul 21, 2012, 04:48 PM
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Pleas see post #1 #12 and #15 here

http://www.rcgroups.com/forums/showthread.php?t=1315548


FWIW I do not whole hearttey subscribe to the accumulated inbalance theory unless one is using really sorry over the hill LiPolys.

FYI the 2S micros I posted about are allways balanced charged and allways on the 306B at the field but a different charger at home and before someone asks ,yes the chargers agree volage wise for the cells on all 4 batteries when discharged ( 3.7 to 3.8) and when blanace charged to 4.2 per cell ,that is when 306B was not set to Start balancing until CV stage..
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Old Jul 21, 2012, 05:56 PM
That's a funny word
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I couldn't agree with post 1,12,15 more. It proves that if cells were once in balance then they tend to stay that way. It sounds as if you are saying that this problem happened "on this one charge and only because the balancing was delayed until cv"

I am hard pressed to give an explanation to this gross imbalance other than you may have 1-3 cells that have very quickly gone belly up (like within the last 2-3 uses and recharges)

Subsequent use will easily tell if that's true or not.

Here's another question that may shed some light on the difference between balance start voltage. How long would you estimate the cv part was?
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Old Jul 21, 2012, 06:53 PM
BGR
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If the ICharger cannot charge through the balance port then ideally it should stop charging and drain the high cell to match the low ones and then resumes charging. Rinse and repeat until the battery is balanced.

Is this how it works?......It seems not because I have watched my 106B+ balance charge 3S lipos and the current never stops flowing until the charge is done.

I just can't imagine those tiny resistor banks holding one cell back sufficiently at high charge rates.
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Old Jul 21, 2012, 07:26 PM
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If the ICharger cannot charge through the balance port then ideally it should stop charging and drain the high cell to match the low ones and then resumes charging. Rinse and repeat until the battery is balanced.

Is this how it works?
Yes, nearly all balancing chargers will bleed current from the high cells during the charge cycle and if any cell gets a little too high, the charger will taper charge current until the cell is at or below the set cell termination voltage, and then continually adjust charge current such that the highest cell is held at termination voltage.

Mark
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Old Jul 22, 2012, 12:08 AM
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It proves that if cells were once in balance then they tend to stay that way.
Yes, but the moment one connects several discharged packs in parallel, that is not the case any more.

Fred
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Old Jul 22, 2012, 01:50 PM
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The saga started here

http://www.rcgroups.com/forums/showp...ostcount=12655

It turns out that one of the 2S LiPolys which was being charged in parallel decided for whatever reason to become just over 0.3V out of balance and it was in fact causing the other three in parallel with it to be out of balance but to a lesser degree. I have started addational test on the very suspect nearly new ,( 8 easy flights in a Blade 130X ) E Flite 35C 2S 300. Could prove to be just one more example of why I do not purchase E flite LiPolys. All I have ever had have came with B n F aircraft and all have been rather sorry.


Charles
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Old Jul 22, 2012, 08:38 PM
BGR
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I found E-Flite Lipos to be anemic.
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