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Old Feb 04, 2013, 03:45 PM
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Originally Posted by mrforsyth View Post
Are you sure that your chargers balance during storage charge mode? None of my chargers do such and doing so is unwise in my experience.

Charging multiple lipolys in parallel is generally far safer and wiser than attempting to charge in series.

See the following thread for a tremendous amount of information regarding charging multiple lipolys at the same time on single channel chargers:

http://www.rcgroups.com/forums/showthread.php?t=932319

Mark
When using A6 storage charge, I never have to balance my packs so yes, I think it balances. What's wrong with balancing to 3.8V per cell? I like it

IMO charging lipos in series is a no brainer, although it could be time consuming. Charging in parallel easily leads to the magic smoke (when one of your cells is bad), unless you're cautious enough and check all cells beforehand. I'm never in a hurry so I keep on charging in series if you don't mind .

I've read the thread globally, but I'm not really convinced. Really not I must say

Martin
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Old Feb 04, 2013, 04:03 PM
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When using A6 storage charge, I never have to balance my packs so yes, I think it balances.
As I see it, this merely means that your packs are comprised of matched cells, not via any intervention from the balance circuitry of the charger.

One would need to deliberately create an imbalance in a pack and then perform a storage charge / discharge to verify for sure.

Some chargers may balance throughout the charge cycle but most higher quality chargers do not do this as a default.
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Old Feb 04, 2013, 04:13 PM
That's a funny word
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A while back there was talk that the accucel 6 balanced ANY time the balance lead was plugged in and a charge function was started. It was supposedly balancing even though "balance" charge wasn't selected. I think I even did the test , but I'll be darned if I can remember what the conclusion was.
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Old Feb 04, 2013, 05:15 PM
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I was inquisitive myself so I dug out the manual. On charging, you to pick Balance Charge, but on discharge it does the balance discharge. It says word for word."BALANCE INDIVIDUAL CELLS ON DISCHARGE. It also can monitor and balance individual cells of the lithium battery pack during the discharge process. If the voltage of any one cell varies abnormally, the process will be stopped with the error message."

Gord.
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Old Feb 04, 2013, 05:46 PM
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I was inquisitive myself so I dug out the manual. On charging, you to pick Balance Charge, but on discharge it does the balance discharge. It says word for word."BALANCE INDIVIDUAL CELLS ON DISCHARGE.
Wow, that makes no sense at all. Further evidence that whomever developed the firmware for this family of chargers did not have a firm grasp on the nuances of rechargeable lithium chemistry.
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Old Feb 04, 2013, 10:58 PM
wjs
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Originally Posted by mrforsyth View Post
Wow, that makes no sense at all. Further evidence that whomever developed the firmware for this family of chargers did not have a firm grasp on the nuances of rechargeable lithium chemistry.
Not sure what does not make sense. In balance mode, the charger balances the cells during charge cycle. Fast and Charge mode, do no balancing, just a V cutoff selected by user. Discharge and Storage mode balance cells during discharge cycle. It all seems to work pretty well. I only use Balance for charge and Storage to store. The other modes I have less real need for.
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Old Feb 05, 2013, 12:43 AM
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Discharge and Storage mode balance cells during discharge cycle.
This is what makes no sense to me. A pack that is balanced during a discharged state will then show an imbalance when the pack is charged if all cells are not carefully matched. This makes the balancer work a lot harder when the pack is charged and may greatly extend the charge cycle.

Our planes, cars, boats, etc., do not balance during discharge as doing so can create more issues than it solves.

I guess the simple way to avoid this is to simply not plug in the balance tap during storage discharge, or use another means altogether...
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Old Feb 05, 2013, 12:50 AM
wjs
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Originally Posted by mrforsyth View Post
This is what makes no sense to me. A pack that is balanced during a discharged state will then show an imbalance when the pack is charged if all cells are not carefully matched. This makes the balancer work a lot harder when the pack is charged and may greatly extend the charge cycle.

Our planes, cars, boats, etc., do not balance during discharge as doing so can create more issues than it solves.

I guess the simple way to avoid this is to simply not plug in the balance tap during storage discharge, or use another means altogether...
"A pack that is balanced during a discharged state will then show an imbalance when the pack is charged if all cells are not carefully matched"

Why would this be? Cells that are stored balanced with have less work for charger to balance. Balance is only going to kink in toward the end anyway as max volts is reached and cells will seek level on the bus getting to that point.
They don't give specifics, but by my read it is not doing careful balance on discharge, only looking for major swing that can point to an issue with a cell. But I could not find any +-V margin that it looks for.
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Old Feb 05, 2013, 01:02 AM
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Why would this be? Cells that are stored balanced with have less work for charger to balance.
Only if the cells in the pack have the exact same capacity, which is increasingly rare these days. If one cell has lower capacity than the rest and the pack is balanced during a discharged state, this one cell will then need to be balanced when the pack is charged or it will be at risk of overcharging. If balancing during the discharged state is avoided altogether, no balancing will be needed when the pack is charged.

It's for this reason that many of the higher quality chargers with carefully considered charge algorithms do not engage balance circuitry until the charger transitions to CV stage.

Cheers,
Mark
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Old Feb 05, 2013, 03:18 PM
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That's interesting, I get the point. But then why should I ever balance my packs? What do you mean with CV stage?

Up to now I always balance my packs after flight at 40% charge level (3.8V per cell) because I think that keeps the cells in good condition. But should I instead store the weakest cell at 3.8V and let the better cells of the pack at a higher level? The better cells then get worse but I'm afraid that they will have higher internal resistance, not lower capacity.

Martin
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Old Feb 05, 2013, 03:50 PM
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Originally Posted by Martin. View Post
What do you mean with CV stage?
Charge the lipos to the correct voltage, then back off amps slowly until the voltage of the cells stays at the correct voltage. CV = Constant Voltage.
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Old Feb 05, 2013, 04:56 PM
wjs
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Originally Posted by mrforsyth View Post
Only if the cells in the pack have the exact same capacity, which is increasingly rare these days. If one cell has lower capacity than the rest and the pack is balanced during a discharged state, this one cell will then need to be balanced when the pack is charged or it will be at risk of overcharging. If balancing during the discharged state is avoided altogether, no balancing will be needed when the pack is charged.

It's for this reason that many of the higher quality chargers with carefully considered charge algorithms do not engage balance circuitry until the charger transitions to CV stage.
Cheers,
Mark
Thank you, but I am still missing the point. Storage and charge is relative to voltage not capacity as we know. If you want to store at 3.8v+- then you want all cells at 3.8v, regardless of slight cell capacity difference. So you want at least some form of balance on the storage cycle. At least you want an error on major swings to flag a bad cell or bad connector. If it a cell, you want to really check that pack anyway and possibly toss it. That is a good thing and what is does (actually you can run storage without the balance leads it stops on pack volts if that is what you want). Same with charging. You want all cells to charge to 4.2v+-. All cells will charge slightly different regardless. If it takes another minute or so to match, that is the price we pay to balance. If you just want to charge with no balance, you have that option. From my chair, it works pretty much the way you need in most cases and might error on the side of caution. The actual algo would be nice if we have the firmware programmer out there :-)
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Old Feb 08, 2013, 04:19 PM
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A neat thread with so much so details explanation. Thanks Mark.
Also thanks HB and Martin for the helpful and informative guide to lipoly.
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Old Feb 08, 2013, 05:25 PM
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Originally Posted by mrforsyth View Post
This is what makes no sense to me. A pack that is balanced during a discharged state will then show an imbalance when the pack is charged if all cells are not carefully matched. This makes the balancer work a lot harder when the pack is charged and may greatly extend the charge cycle.

Our planes, cars, boats, etc., do not balance during discharge as doing so can create more issues than it solves.

I guess the simple way to avoid this is to simply not plug in the balance tap during storage discharge, or use another means altogether...

Well, when storing a pack for an extended period, shouldn't one have the pack "balanced" at the storage voltage, rather than have one or more cells significantly higher or lower than the rest? If in storage, and one cell is much lower in voltage than the rest, is it not more likely to drop below the safe minimum during storage?

I prefer to have my packs balanced at the storage voltage when I am going to store them for a significant period of time, such as our lovely winters... Depending on the initial state of the pack (charged or discharged), balancing would be required either way... I do not see this as a problem, but rather as a desirable feature. We should not be using the discharge function for the fun of it, but rather only for extended storage. If we need to check the capacity, we won't be using the storage function, but rather the regular discharge function (and while we set the minimum total voltage to drain to, it would be nice if each cell is monitored (in case one cell drops it's voltage faster than the rest, and is in danger of going too low). If a pack is fully charged, then the charger SHOULD drain each cell to the same voltage, when doing so for storage. If the charger drains the pack based only on the total voltage of the pack, then one cell could possibly drop below the minimum safe voltage while the others remain much higher before even reaching the ideal total storage voltage.

Granted, a pack with this problem is hardly "a great pack", but hey... we like to get as much safe use out of a pack as possible before having to dispose of it.

Regards

Christian
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Old Feb 08, 2013, 06:12 PM
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Any lipoly pack that is properly balanced at full charge and then discharged to ~3.85 V/cell storage level should not be out by more than 1-2 mV, which is perfectly acceptable for long term storage. If it is out by much greater than this, it is a candidate for the trash bin as I see it.

At least there's an option for both balancing and not balancing during discharge to storage level. Since balancing during storage discharge masks potential problems with a pack, I would personally avoid such.

Mark
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