Headways ma all over the place

[BIG BEAM]

I just got some headways 10ah and the ma when discharging vary a lot My charger discharges to 2.5 volts so I didn't think they would be the same as factory specs but the variance seems like a lot.I've cycled them 3 times now and they are the best 9788 to the worst 9291.This is with 12 batteries.Is this in line with what i should expect?
DON

 

[scoot]

I think that is pretty typical for a new batch. I wouldn't worry too much. I think after you cycle them more and more, you'll find their capacities continuously increasing up to a point, with better comparibility as well. At least, that has been my observations thus far. When I was bench testing and breaking in my cells, I was more concerned with the discharge voltage levels so I could pair them up effectively... I am running a string of paired cells on my scoot.

 

[cell_man]

The cutoff at 2.5V will reduce the measured capacity by a few %. They'll need to be charged to 3.65V and discharged to 2.0V to get to their spec and I do believe the 10Ah figure is a nominal figure rather than a minimum. A variation of 5% capacity which you are seeing, is to be expected if they haven't been matched. It shouldn't make any major issues when it comes to putting a pack together IMO. You still want to Balance them to 3.6-3.65V and limit the DOD to about 80%, so 7.5-8Ah in your case to keep them playing together nicely.

I'm interested to know how much capacity is gained by cycling a cell. I believe you can maybe get a small gain in capacity, but I think in most cases what people are seeing is an unbalanced pack that balances in time. It takes a long time for a typical BMS to bring the cells within a pack to the same SOC.

 

[BIG BEAM]

I cycled them 3 times one at a time.The second cycle I saw a gain of between 100-70ma and the third discharge was between 25 and 45ma so it was climbing much slower the last time.

My charger terminates at 3.6v and discharges to 2.5v.

The highest one after 3 cycles is 9.888amps and the lowest is 9.355amps

My charger charges at 8 amps and discharges at 3.
DON

 

[velowatt]

Forgive a stupid question- how does the charger discharge the cells. Mine charges them up.

 

[scoot]

... how does the charger discharge the cells. Mine charges them up.

There are a number of "hobby charger" brands and models that can do both, but most are very limited on the amount of current they can discharge. For example, an icharger 208b can only dissipate a mere 30 watts on its own in discharge mode, yet can charge at 300 watts or more. A dummy resistance load (light bulb arrays or giant resisters) can be used with them to increase the amount they can handle.... up to 600 watts with the 208b.

 

[cell_man]

I cycled them 3 times one at a time.The second cycle I saw a gain of between 100-70ma and the third discharge was between 25 and 45ma so it was climbing much slower the last time.

My charger terminates at 3.6v and discharges to 2.5v.

The highest one after 3 cycles is 9.888amps and the lowest is 9.355amps

My charger charges at 8 amps and discharges at 3.
DON

That's interesting that you are seeing that sort of gain in the first few cycles, but it's still a relatively small percentage gain. It's not the sort of gains that many people claim they see from "breaking in" a new pack. As far I can see it's more a case of balancing an out of balance pack than anything else in these cases.

If you were to change the charge, discharge to 3.65 and 2.0V I think you'd gain another few hundred mAh which would put the max to just over 10Ah and the lowest to just over 9.5Ah. I would imagine that is fairly typical and nothing to worry about IMO.

 

[scoot]

In my particular case, cell conditioning and charging/discharging has been achieved via a couple of methods. Repetitive parallel charging/discharging of numerous cells (8 or 16 at a time), or by balance charging & discharging in 8s configurations with CellLog monitoring.

Scoot - One of the "people", I think

 

[cell_man]

In my particular case, cell conditioning and charging/discharging has been achieved via a couple of methods. Repetitive parallel charging/discharging of numerous cells (8 or 16 at a time), or by balance charging & discharging in 8s configurations with CellLog monitoring.

Scoot - One of the "people", I think

Sorry, didn't mean to imply anything against you Scoot

I'm genuinely interested in the sort of gains in capacity that is seen when it's done in a controlled way as you have done. It's just when i hear things like my Ping has increased 15% capacity through the first 5 cycles, that can't be all down to cell conditioning or breaking them in. I can believe you'll gain 2 or 3%, maybe a little more but I can't see the cells improving much beyond that. It's just my thoughts, it's not a fact and if there is reasonably scientific data to show it can be more than that I'm all ears.

 

[scoot]

:? Whew... thought I was gonna have a lot of hard explaining to do LOL :lol:

I'll try to recall and convey my experiences more completely Cellman ... but, back to the slave pit for now.

 

[dogman dan]

A 15% gain would be explained by the pack being pretty out of balance on the first charge, so it's actually a matter of some of the pack being undercharged on the first few cycles. If they were discharging 100% on those first cycles, they were screwing up anyway.

 

[snowranger]

My headway pack had less than 50% capacity after the first charge. I was sweating bullets at that point.

With single cell balancing the next cycle had 95%. It's been good ever since.

 

[texaspyro]

I added a battery analyzer mode to my capacitive discharge welder and have been playing with it on some A123 cells. There is a fairly trivial amount of usable power below around 2.8V when discharging at 4C. The negative impact on cell life running them below that is not worth it. The voltage cliff is so steep there is almost no difference between a 2.8V cutoff and a 2.5V cutoff.

See the srceen shots at: http://endless-sphere.com/forums/viewtopic.php?f=2&t=2633&start=690#p300329

 

[999zip999]

Hay snowranger, How much faster is your headway than your old ping, how much faster up the hills. Is the 600w h.s. faster then the 400w BMC hub ? How much money do you have in your headway pack with bms ? How how how.

 

[snowranger]

Top end is about 1 mph faster on the flats and not as much sag under load. As to hill climbing, I can't really tell since the controller limits current to 25 amps. The main difference is that there aren't any cut-outs under load. I've got about $632 total invested in this battery.

 

[velias]

what the hell is a ma?

 

[texaspyro]

what the hell is a ma?

What pa sleeps with What you came out of

Ok.. milli amp, 1/1000 of an amp, not a whole lot of current. mAh is milli-amp hour. how many milli-amps a battery can supply over a 1 hour period.