Thread Tools
May 01, 2002, 01:15 PM
soft yummy goodness.
freq's Avatar
Thread OP

slow charge equalizing after the fact


The general consensus, though frequently debated, is that a C/10 charge will equalize the cells in a pack. It's commonly recommended to do this for the first charge on a pack to get all cells to an equal level (also debated). After the initial C/10 charge, the user may fast charge (3C or whatever is appropriate for the type of cells), with an occasional (say, every 20 cycles or so) C/10 charge to re-equalize the cells.

So far, the above statements make perfect sense to me. Feel free to debate 'em, though.

Here's my question: suppose a modeler got a few new packs (not matched) and didn't have the patience to do a C/10 charge at first, but instead fast-charged the packs right away at, say 2C. For this example, I think it's safe to assume that the cells in the pack are at slightly different levels, but the pack flew just fine.

What if said modeler cycled his packs several times at a fast rate, then decided to take the time to slow-charge at C/10? Would this be an effective means to equalize the cells in the pack? Would it have been any better to charge them at C/10 the first time? Does the C/10 charge have to be done the first charge to be most effective, or can this be done any time?

All input, even bashing the heck out of my assumptions gathered from various sources, is appreciated.


-chris
Sign up now
to remove ads between posts
May 01, 2002, 02:29 PM
Registered User
Tim K's Avatar
Chris,

A C/10 charge is a good idea anytime. By not doing it first, you run the following risk. When fast charging an unbalanced battery, the cells at the higher states of charge will become fully charged too soon. At low levels of overcharge, the only result will be that the cells will heat up more than the rest due to excessive oxygen generation. That oxygen will recombine in a few hours, so all will be well. At moderate levels of overcharge, the internal oxygen pressure may increase to the point that the cells vent. One vent episode is not critical, except for the fact that the vents don't ever seem to reseal perfectly. At high levels of overcharge, venting will be extreme and there will be significant loss of electrolye and capacity. Worse than that, losing any oxygen out of the cell can cause the relative states of charge of the positive and negative electrodes to become out of balance (called pre-charge). If this continues, the cell will eventually lose its overcharge protection and it will start generating hydorgen on charge. There is no ready recombination mechanism for hydrogen, so this leads to pretty rapid cell failure.

With all that said, 2C is not all that high. If the cells were close, I would guess that you did no permanent damage. Also, if the cells were new from the factory and had been sitting for any length of time, they likely had self-discharged down to almost no capacity anyway, and so were pretty close to being balanced. That argument assumes they come from the manufacturer discharged, which I believe is the case due to shipping regulations.

Tim
May 01, 2002, 02:43 PM
Registered User
Andy W's Avatar
What Tim said..
..a
May 02, 2002, 02:51 AM
The initial C/10 charge used to be absolutely vital years ago because cells came from the manufacturer "unformed" i.e. basically had never taken any charge at all. They needed a long slow charge to sort of settle the chemistry down. An initial fast charge could make a real mess of them.

AFAIK no manufacturer has delivered unformed cells for many years now so it's much less important. It's not a bad idea to be kind to your cells every so often to stop them getting too far out of balance but that's about it. Many of us are too lazy to bother often, if at all, and still manage to keep flying somehow

Steve
May 02, 2002, 03:27 AM
soft yummy goodness.
freq's Avatar
Thread OP
Interesting. So I guess it's safe to say that all cells are shipped formed, these days.

What is the likelyhood of individual cells in a pre-built pack being at significantly different states of charge as shipped from the manufacurer/ pack builder, nowadays?

In my experience, nearly every pre-built pack I've bought has been shipped discharged. However, I recently purchased 6 individual cells that had a fair amount of juice in 'em (around 50% if memory serves), as reported by my SuperNova on first charge after assembling the pack. Unfotunately, I didn't check the cells individually, so I don't know how out of balance they were in relation to each other. I seem to recall getting some partially-charged cells in the past, as well.


-chris


Quick Reply
Message:

Thread Tools