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Old 03-03-2005, 03:12 AM   #1
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Default Dead shorting versus discharge voltage curve

If I choose to tray my batts to zero volts, or even deadshort, how will it affect the discharge voltage curve? Will it be steeper or more flat, or as it is now, just raised some?

Currently, I charge at 6 amps, race till the batts drops, discharge at 20 amps, and store the pack. Before next use, I equalize at one amp and auto cut off at 0,8 volt.

Will buying a zero volt/20 amp tray gain anything? I mean, most of the discharge is already done in the car and/or at 20 amps.

Thanks.
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Old 03-04-2005, 08:28 AM   #2
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Old 03-04-2005, 09:43 AM   #3
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Everyone has their own opinions on deadshorting. My .02$ start deadshorting only when packs are new. You can expect to loose 20 seconds or so of runtime and gain .2 volts over a cycle. So is the loss of runtime worth the gain in volts for me running mostly stock.heck yah. The discharge curve drops super fast at the end of a cycle as well. I store all my packs shorted some for 2 weeks or so. You will need a charger with a peak lockout (600seconds) or they may false peak.
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Old 03-04-2005, 10:17 AM   #4
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Quote:
Originally posted by schmelme
Everyone has their own opinions on deadshorting. My .02$ start deadshorting only when packs are new. You can expect to loose 20 seconds or so of runtime and gain .2 volts over a cycle. So is the loss of runtime worth the gain in volts for me running mostly stock.heck yah. The discharge curve drops super fast at the end of a cycle as well. I store all my packs shorted some for 2 weeks or so. You will need a charger with a peak lockout (600seconds) or they may false peak.



Do you solder short wires to each cell, then tie them together for your storage ? Is there any advantage for older 3300 packs ?
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Old 03-04-2005, 11:50 AM   #5
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Ok here's what I know about dead shorting. When you buy new packs and then run them a few cycles (5-10) the numbers will be significantly different. Run time should go down 20-30 seconds, IR should Go up some and Voltage may or may not change. When you Dead short new packs you are basically wiping that 30 seconds out then and there, but you are also Lowering IR (which is good). Voltage tends to go up some too but the main thing is the IR. Downside....you must continue to Dead short that pack or performance will be inconsistant and could fall off drastically. You must also now run that pack only once per day to get the full effect of the Dead Short, so that means one for each qual and a main.

Another positive of Deadshorting. If you have an old pack the just doenst perform like it used to try this. Charge it up at a high amp rate (8-10) and then discharge at a high rate(30-40). This will basically kick the pack's tail and really work it out. As soon as it is completely dumped solder a jumper wire and leave it sit for 2 weeks. Next time out charge it at 6 amps and see how it feels. You will be pleasantly surprised.
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Old 03-04-2005, 12:04 PM   #6
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Dead-shorting is dangerous and with the run times we have with NiMH cells it is really not needed. Ni-MH do not hold a memory, the stats you hear above from dead-shorting is from the lack of "dead-charge" (for example if you charge a battery and let it sit over night then just repeak it, it won't have the same voltage, it will feel dead), batteries will naturally recharge themselves which is how they are designed.

So if you want the longest and most consistant life out of your batteries I recommend discharging a 6-cell pack to 5.10 volts, it will then take it's designed charge, i.e. 3300GP will take 3300MAH of charge.
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Old 03-04-2005, 12:19 PM   #7
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Cole - what class are you running and does run time matter?

If run time isn't an issue with the class you are running (given the new 3300 batteries), at a minimum you should fully discharge (to lower than 0.9 per cell) and then charge at the maximum amps (up to 12 amps) your charger can provide.
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Old 03-04-2005, 12:22 PM   #8
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what you have to understand is that even if you have pleanty of runtime...let try to make it simple. 10 minutes of runtime. out of that 10 minutes of runtime you get the first 4 minutes blazing fast. then the pack slowly falls off. with higher capacity cells say 15min of runtime you will get 6 minutes of blazing fast performance then fall off. now obviously these numbers are just so you can see this easier. The idea is to push that "usable" amount and make it longer and faster. hopefully that will make sense.
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Old 03-04-2005, 03:21 PM   #9
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Does dead shorting mean the entire pack at once by connecting the + and - , or individual cells on the pack ???

Also does the battery have to be 0 volts first ?
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Old 03-04-2005, 03:25 PM   #10
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Yeah...deadshorting means connecting the + side to the - side via a connection, usually wire or solder

and YES!!! the pack needs to be at ZERO!!! connecting cells with voltage is a big NO NO!!!

Keep the cells in your discharge tray while soldering the lead on...becuase as soon as you remove the pack from the tray, voltage will start coming back in the pack
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Old 03-04-2005, 03:29 PM   #11
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Quote:

If run time isn't an issue with the class you are running (given the new 3300 batteries), at a minimum you should fully discharge (to lower than 0.9 per cell) and then charge at the maximum amps (up to 12 amps) your charger can provide.

Does charging at high amps (say over 6) overheat the packs ?
I have some GP3300 packs with around 40-50 cycles, and the "flat spot" is getting bigger. Will charging at higher amps improve this ? Is dead shorting better ?
I currently charge at 5a and use a Novak ST to 0.4v
They usually peak at around 9-9.5v and take around 3800 mil.
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Old 03-04-2005, 03:43 PM   #12
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no, some advanced chargers will even allow you to limit the amount of charge that goes into a cell. If I'm racing stock I will normally make sure that my battery is discharged to 5.1 volts at 10amps then limit the amount of charge to 3000MAH in my GP 3300's, this way it will under charge the pack. My packs just barely get warm and that's normally how I run it and as far as punch goes it stays about the same through the whole run.
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Old 03-04-2005, 05:20 PM   #13
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I can tell you in mod oval we actually dump our packs hard on the track all the time. When this happens runtime dies and so does voltage. This can happen after 10 or 15 cycles on the batts. And deadshorting will in many cases bring back runtime. Like at 35 amp discharge you have a 365rt pack at 4.68volt from the start and you dump it hard it falls to a 310rt 4.60volt. Deadshort it and it will go up in rt and in voltage. So you dont have to do it as soon as you get the pack. It may not work as well as doing it initially but you can bring the life back to a older pack. We then use them in 19t and stock.
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Old 03-04-2005, 05:29 PM   #14
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For stock and 19T 6 cell racing there is nothing I like better than a pack that has been dead shorted and chargerd at 8 amps and peaks at 135 deg.
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Old 03-05-2005, 10:51 AM   #15
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Quote:
Originally posted by John Tag
For stock and 19T 6 cell racing there is nothing I like better than a pack that has been dead shorted and chargerd at 8 amps and peaks at 135 deg.
Now, that would explain where you get some of your speed from
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