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Old 03-09-2006, 05:59 AM   #1
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Default How to discharge pack properly without damaging pack

Hi. I have been using my teamwave equlizing tray, it has given me a great deal of information about when i discharge me cells and would thought i will share with you all.

Basically i hook my pack to the teamwave, and will tell me the volt of each individual cell.

My charger can discharge up to 20Amps.

I found that if you use 20Amp discharge you should cut off the discharge at 6V. (average 1v per/cell) Any lower than this you will risk some cells going below 0.9v...

If you have unmatched packs then the cutoff should be higher, coz the variances in runtime would be more significant.

Also I have found that the lower the discharge rate, the higher the cutoff voltage should be set to to avoid going below 0.9v percell.

Moral is, never discharge your cells down to 5.4volts on your charger.your cells will definitly go below 0.9v when you do.
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Old 03-09-2006, 09:22 AM   #2
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Whats so bad if the cells go below .9v? You act like it will ruin the cells when in fact it wont.
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Old 03-09-2006, 03:16 PM   #3
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Quote:
Originally Posted by rcguy2477
Whats so bad if the cells go below .9v? You act like it will ruin the cells when in fact it wont.

well a few reasons...

1. its widely accepted that IB should NOT be taken bleow 0.9v.

2. it could be any figure below 0.9, in fact for older matched or unmatched cells, the variances in runtimes/voltages between cells could be much more significant and in fact could cause cell reversal.

3. if you have your equilizing tray set at 0.9volts, and some cells have already reached say 0.5volts... then puttin it on your smart tray at 0.9v cut off will not equilize the cells, coz the cell has already gone below 0.9 anyway.

anyway you can take it or leave it, just giving some friendly advice.

cheers
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Old 03-09-2006, 05:04 PM   #4
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So are you saying that if my IB cell goes to 0.89v it's gonna hurt its performance? Bullplop. 0.9v/cell is a safe cutoff if you are discharging at a high rate in series. Once you are individually discharging cells, you eliminate the risk of certain cells going into reversal because other cells are still discharging. IB cells have no problem being taken down to low voltages, so long as you know what you are doing. You can charge down to 0.5v if you want, just discharge at a low rate, like 2A. Hell, I used the CTX-D's zero-volt function to discharge my IB packs, didn't seem to ruin my packs at all.
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Old 03-09-2006, 05:35 PM   #5
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Quote:
Originally Posted by XrayFK
So are you saying that if my IB cell goes to 0.89v it's gonna hurt its performance? Bullplop. 0.9v/cell is a safe cutoff if you are discharging at a high rate in series.
did i say 0.89v? very rarely will you get a pack that will discharge evenly at .89 .91 .90 .90.90.90.

yes 0.9v/cell is ok but what happens is that its 0.9v/cell AVERAGE. each cell doesnt cut off exactly 0.9v. some are over 0.9 and some are under 0.9v. however average is 0.9v.

Also note that once the cell reaches anything below 0.9v the cell drops voltage to zero very quickly with any load applied to it.

Quote:
Originally Posted by XrayFK
Once you are individually discharging cells, you eliminate the risk of certain cells going into reversal because other cells are still discharging.l.
yep my point exactly. you need to tray to 5.4, but do not discharge in series to 5.4


Quote:
Originally Posted by XrayFK
IB cells have no problem being taken down to low voltages, so long as you know what you are doing. You can charge down to 0.5v if you want, just discharge at a low rate, like 2A. Hell, I used the CTX-D's zero-volt function to discharge my IB packs, didn't seem to ruin my packs at all.
well then the battery matchers must be wrong, they tell me to keep IB above 0.9v
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Old 03-09-2006, 06:15 PM   #6
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Of course manufactures and matchers are going to say do not go below .9v as the person doing the discharging may not know what they are doing. If you are aware of what you are doing, you can discharge to much lower voltages without any risk.
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Old 03-09-2006, 07:51 PM   #7
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well of course lol
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Old 03-09-2006, 08:46 PM   #8
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Hi guys, I get a question. I just bought the smart trait by Novak. When I put my batteries on the smart trait all the red lights light up on the bottom of the trait. And after a minute or so one light or may be two lights go out. And the other ones are still red. Does that mean that the lights that went out those cells are still discharging because the other lights of still red and they didn't go out yet. Anybody know about this. Thank you
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Old 03-09-2006, 08:55 PM   #9
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red lights mean they're still discharging...when all lights go off you're set.
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Old 03-10-2006, 12:25 AM   #10
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I know when the lights are on its still discharging. On talking about the lights that go off and I'm still waiting for the other lights are the ones that went off still discharging waiting for the other ones to go off
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Old 03-10-2006, 01:06 AM   #11
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Bob, it is an equalizing tray, the cells discharge and charge at different rates.
leave the cells in the tray until all lights go out. Set the cut off at 0.9v as discussed previously.

Mentioned in an earlier post, 20amp discharge at a cut off at 5.4v is bad as the cut off is too low for the discharge rate. as the Novak Tray has a discharge rate of 2V it is safe to place you cells that have been discharged to 5.8v - 6V in the tray and leave them until all the lights go out.
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Old 03-10-2006, 01:01 PM   #12
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When cells are discharged, they develop a layer of gas around the internal components. This will make the battery appear(and sometimes it will be) dead. When discharging at a lower amperage, this gas has time to disperse so it really takes out more than a higher amperage would. When charging at a high amperage rate, this gas builds up quite quickly, and the cells will drop off sooner than if a lower amperage rate were used. If you discharge at 20 amps with a 5.4 cutoff, it should be find so long as the cells are generally equal. It wont hurt the cell if it drops down to .5 or lower, as it will "bounce back" quickly after the load is taken off. People often say that you have the possibility of reversing the cell if you dicharge the pack without equalizing it to very low levels. While this can be true, it is highly unlikely to occur. With the release of the Nimhs, the occurance of this has reduced dramatically.
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Old 03-10-2006, 04:44 PM   #13
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Thank you
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Old 03-11-2006, 12:16 AM   #14
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after 20A dischg then tray, then keep about 10 min, I measure each cell voltage, I found one cell bounce back higher voltage than others in those 10 minutes, but this cells is also the fastest lamp off on tray,
is this cell damaged?
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Old 03-11-2006, 01:19 AM   #15
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Quote:
Originally Posted by Faiz
after 20A dischg then tray, then keep about 10 min, I measure each cell voltage, I found one cell bounce back higher voltage than others in those 10 minutes, but this cells is also the fastest lamp off on tray,
is this cell damaged?
not necessarily. it may just have less run time than the others.

whats also important is its internal resistance.

charge up the pack and moniter the temperature of that cell. if it has much higher temperature than the others, then yes it should be replaced.
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