720i balancing problem
 

I just noticed that once the charge is finished, say at ~20 mins, all cells are between 4.19 and 4.20v, balancer kicks in and tries to balance at end of charge, but it doesn't actually do anything. I will sit there for another 20+ mins trying to balance that 0.01v difference, but sometimes it just increases the cell gap, or takes forever to do it. Has anyone else here had the same problem with their HP charger? It is the older 720i (non-NET3).

This last charge took ~22 mins, and it's currently at 49 mins and still thinking about balancing... it's gone stupid it looks like.

yer..my e station 902 does this too....worse on older packs....

i have a theory...i think the charger draws off some current after the charge has finnished...so the balancer constanly tries to remedy this.
im sure if you left it long enough it would drain the whole pack down.
all i do is disconnect the pack as soon as it is charged and use it.
chris

my 610iduo is doing that too, im not sure if I clicked the alarm off on a channel, or its with my older lipos but it will sound the alarm on 1 i'll take it off and the other keeps screwing around with most cells at 4.2 then 1 screwing with it from 4.19 back to 4.2 down to 4.18 back to 4.2, I eventually just pull it off and run it

I've always noticed that Hyperion balance-chargers and stand-alone balancers tend to be very sensitive to pretty much ANY imbalance. While that's good to a degree, it can worry the inexperienced user that their pack isn't "right".

I don't have that charger, I have a cheap chinese one. It is not accurate when balancing and over time I beleive it has gotten slightly worse. Some packs it can balance to with in 0.02v, these are usually packs with less cycles, charged at less amps and don't require a whole lot of balancing to start with.

Other more dodgey packs I have (reclaimed A123's from dewalt battery packs) get to with in 0.05 - 0.07v and will not balance. I am not able to measure the resistance of the cells but I suspect that is what is screwing around with the charger.

That's how I understand it anyway. The different resistance causes the cells to relax to different voltages, when a cell will not hold 4.19 - 4.20v and others will, the charger/balancer is constantly working.

Well it looks like I am not the only one with the issue then. It never used to do this up until a few weeks ago, but I thought it was the older packs I had. But I have been trying to put a few light wake up cycles on some new 6s 2200mah 45c G3's. (which, btw, are tiny!)

Some of you are saying that the cells will go up and down; I have some old old A123 packs with balance taps that I tried and the cell imbalance will continue to increase... 0.03v gap....0.06v gap....0.10v gap, it's retarded. The only way I could get them within an acceptable balance was to use a resistor through the balance tap.

I bought a HP Sentry 2, so maybe i'll just use that for balancing the pack will charging, not that a G3 pack will need much balancing anyway.

Yes, I've acheived better results from an external balancer. Though I do lower the charge amps particularly with the A123's so as not to overcharge any cells. The charger will 'charge on' despite any cell differences until the desired pack voltage is reached.

I've never heard of using a resistor on the balance tap. Is that a resistor for every pin on the tap?

No, I just use a 10W resistor, plug it into the tap and use a volt meter to watch the voltage until it reaches where I want it, then I move to the next cell.

I was thinking of getting the new 1420i charger, 550w and 20amps, whats not to like... that is, if the sentry balancer cannot keep up with the charge rate

It's simply an out of balance cell. When charging the charger charges all of the cells all of the time, and then stops charging and bleeds off voltage from the highest cells until they are all even.

You will see that the output is switching back and forth from 0v to full pack voltage during this process.

The "bad" or "low" cell just takes a while to reach the full 4.2v, and the "good" cells with low internal resistance easily reach 4.2v. It does take quite a bit of time for this cell balance dance to take place.

This is where a charger with individual cell charging shines and the rest fall short.

It's not a low or imbalanced cell(s) in the pack, it is the charger. Like I said, it will UNbalance a properly balanced pack. It is doing it to brand new G3 45C packs I have hear just as bad as my old 35C G3 packs.

I just got the Sentry in the mail today and WOW, this thing is awesome, tells you everything about your pack, beautiful clear screen. I tested it out on a 4s A123 pack that had a low cell in it, total cell gap was over 0.200 volts, it balanced it out in about an hour, down to within 25mv. I will try doing some charging using this thing attached to balance port, seems to have a very decent balancing current.

Does anyone know if you can change the tolerance for cell balancing on the 720i NET? I have heard you can do it on the new NET3, but I am not sure on mine.

Oh wow. I guess I jumped to a conclusion. That sucks man. I've actually had good luck with the turnigy chargers from hobbyking.

Thanks for the words of encouragement bro :lol:

Well it seems like the charger is smartening up now, the more I use it the better it is working. I will only take a few extra minutes to balance off a pack, I don't understand this, but I like the fact.

wow...it looks like you stumbled across the worlds first self educating charger :lol:
you probably just had a bit of junk in the balancer plug/socket..
chris