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Old 03-07-2005, 01:10 AM   #31
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Quote:
Originally posted by KilRuf
Cole, to help try and answer your question... a guy here at the track was wondering the same thing about voltage curves and all. He started 2 new packs. 1 dead shorted... one not. Through out the life of the battery, he found that the dead shorted battery did indeed have a higher average voltage when cycled on his GFX at 30amps. But at the end of 300secs discharge (using the graph feature on the GFX) he found that the non-dead shorted battery had a higher voltage at the end of 300secs than the dead shorted one. So this told him that the DeadShorted battery will give him more voltage for the first 2 minutes of the race. But after that it will drop off more than the nonDeadShorted one. So the delima was... do you dead short for more punch at the start with higher "average" voltage. Or not dead short with a more consistant voltage throughout the race with more volts towards the end of the run?
This actually agree with the other post, I found. Hmmm. Two things plays a role: Performance on the track measured by the lap counter. The other thing is the psycological impression; Deadshorted speed might scare your competitors at the first minutes. But personally, I hate the feeling of loosing punch at the end of the race. And that factor means a lot to me, so I dont think I even try it out.
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Old 03-07-2005, 05:12 AM   #32
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Quote:
Originally posted by KilRuf
Cole, to help try and answer your question... a guy here at the track was wondering the same thing about voltage curves and all. He started 2 new packs. 1 dead shorted... one not. Through out the life of the battery, he found that the dead shorted battery did indeed have a higher average voltage when cycled on his GFX at 30amps. But at the end of 300secs discharge (using the graph feature on the GFX) he found that the non-dead shorted battery had a higher voltage at the end of 300secs than the dead shorted one. So this told him that the DeadShorted battery will give him more voltage for the first 2 minutes of the race. But after that it will drop off more than the nonDeadShorted one. So the delima was... do you dead short for more punch at the start with higher "average" voltage. Or not dead short with a more consistant voltage throughout the race with more volts towards the end of the run?
the best way to find out is actual testing on the track if everything's done right by the time it starts to lose punch the 300 sec have already gone by, that's if you run a stock motor I'm talking! remember a battery pack does not discharge at a continuous amp rate when racing, so it's way different than bench testing. we race on tracks not on equipment to test or discharge batteries..
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Old 03-07-2005, 05:25 AM   #33
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Originally posted by Quiet
the best way to find out is actual testing on the track if everything's done right by the time it starts to lose punch the 300 sec have already gone by, that's if you run a stock motor I'm talking! remember a battery pack does not discharge at a continuous amp rate when racing, so it's way different than bench testing. we race on tracks not on equipment to test or discharge batteries..
Maybe. But I dont have the money, and especially not the time, for doing these tests myself.

Anyway, you made me think of that the 300 sec limit equals 5 minutes In addition, the above test is done at 30 amps, while 20 amps are much closer to my use of juice in stock class.

When I discharge a fully charged pack at 20 amps, the discharge time is quite close to my track time with the same fully charged pack. So on average, this bench test, is quite close to my real world. But in the peaks (acceleration), a lower IR can have a great improvement.

So... I think I'll try this out with one pack for a start. Have to order a tray and a new pack, when I got the money
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Old 03-07-2005, 07:58 AM   #34
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BigDogRacing: If you would like background, I work for a battery corporation very close to entering the "toy" and the high performance R/C market pretty soon, at this time I cannot disclose any information, your information about NiMH having a memory is incorrect, NiMH batteries were designed to hold "dead" charge so when the battery gets to the end of it's run it gets soft to make your the drive feel that the pack is dead. The only thing we found with dead shorting was that the battery pack did hold more charge (due to no dead charge in the battery) and only had better performace during the final 20 seconds before it was done. It also decreases battery life.

I have unmatched GP 3300 cells, I normally run off-road and for stock on-road sedan I can see where matched batties might give an edge, but for stock racing I charge my batteris at 8 amps and cut it off at 3000MAH, the battery pack at this point is just a little warm maybe 100 degrees. The old NiCADs liked to be over charged so you could peak them outa few times to get max performance, but NiMH cells do not benefit from this.

BigDogRacing-you didn't offened me, I just hope to give you the correct information.
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Old 03-07-2005, 08:10 AM   #35
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Quote:
Originally posted by David Alberico
BigDogRacing: If you would like background, I work for a battery corporation very close to entering the "toy" and the high performance R/C market pretty soon, at this time I cannot disclose any information, your information about NiMH having a memory is incorrect, NiMH batteries were designed to hold "dead" charge so when the battery gets to the end of it's run it gets soft to make your the drive feel that the pack is dead. The only thing we found with dead shorting was that the battery pack did hold more charge (due to no dead charge in the battery) and only had better performace during the final 20 seconds before it was done. It also decreases battery life.

I have unmatched GP 3300 cells, I normally run off-road and for stock on-road sedan I can see where matched batties might give an edge, but for stock racing I charge my batteris at 8 amps and cut it off at 3000MAH, the battery pack at this point is just a little warm maybe 100 degrees. The old NiCADs liked to be over charged so you could peak them outa few times to get max performance, but NiMH cells do not benefit from this.

BigDogRacing-you didn't offened me, I just hope to give you the correct information.
Hmmm.

First of, I think the term "memory" in combination with batteries, aint defined.

It appears to me, that "memory" to most people is a voltage depression. And if that's what we're talking about, I will claim that NiMh batteries DO have a memory, meaning that they produce higher voltages, if discharged to (almost) zero, followed up by a full straight charge.
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Old 03-08-2005, 07:42 AM   #36
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Old 03-08-2005, 08:08 AM   #37
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Quote:
Originally posted by David Alberico
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.


I'm sorry, I don't understand, why would you want to under charge your pack ???
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Old 03-08-2005, 12:04 PM   #38
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Originally posted by cr250
I've dead shorted many different packs, many times and I've never seen a discharge voltage curve improve as a result. The dead shorted curves are always similar or lower on the graph than the non-dead shorted ones. The runtime is always less. I then calculated by hand the average voltages for the dead shorted packs and their average voltages were calculated higher, but only because the runtimes were less. Graphed, discharge voltage curves are far more accurate than calculated averages for determing pack performance.
That nails it - then it's not worth the work, the risk and fact that a pack only can be used once a day.

Have you made similar test on a pack used twice a day? Trackwise, I find it's very punchy, but if I do a cycle and compare average voltage and IR, there dont seem to be a noticable improvement.

Thanks for all of your guys comments - I find this is one of the best threads recently - serious, no fool talk and a nice approach from all of you
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Old 03-08-2005, 12:06 PM   #39
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Quote:
Originally posted by jag88
I'm sorry, I don't understand, why would you want to under charge your pack ???
Not that I'm sure, nor have any data on this, but I'll gues (spelling???) the idea is, that a overcharge, even sligthly, will short cell life.
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Old 03-08-2005, 01:27 PM   #40
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Seems like everybody has a theory on care for these cells.

Lately I found that by bench testing was the only way to put some of these myths to the test.

The funny thing with GP3300s is they do like to be used. I have cycled 1 pack 5 times in a day, of corse with adequate rest (usually 25 min), the numbers got better and better. So if you have that killer pack, with adequate care you can run it 4 to 5 times a day.

Dead shorting can slightly diminish the voltage and slightly increase IR if multiple uses of a pack in a day. I don't worry about runtime because I mostly run stock. Although I have not seen how deadshorting has bettered my packs being that I started playing around with it before really testing it or doing a before and after.

Some guys even will charge their batteries the night before. If you peak these batteries the next day it would be like charging a pack, letting it sit for 25 min or so and then racing without a repeak. They fall off that much voltage wise and increase in resistance.

I have not been traying through most of these tests, only a few. After some abusive test, the batteries do bounce back to around the same numbers with normal charge/discharge techniques. I have not seen a drop-off because I have not been traying.

If your packs are pretty lousy voltage wise & resistance wise. Try dead shorting them on a tray. I am leery about storing NiMh deadshorted, usually I leave mine shorted for 30min to an hour. Charge at 6amps, dump to 5.40 a pack and store in that fashon.

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Old 03-08-2005, 06:18 PM   #41
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Quote:
Originally posted by A-Ko
Seems like everybody has a theory on care for these cells.

Lately I found that by bench testing was the only way to put some of these myths to the test.

The funny thing with GP3300s is they do like to be used. I have cycled 1 pack 5 times in a day, of corse with adequate rest (usually 25 min), the numbers got better and better. So if you have that killer pack, with adequate care you can run it 4 to 5 times a day.

Dead shorting can slightly diminish the voltage and slightly increase IR if multiple uses of a pack in a day. I don't worry about runtime because I mostly run stock. Although I have not seen how deadshorting has bettered my packs being that I started playing around with it before really testing it or doing a before and after.

Some guys even will charge their batteries the night before. If you peak these batteries the next day it would be like charging a pack, letting it sit for 25 min or so and then racing without a repeak. They fall off that much voltage wise and increase in resistance.

I have not been traying through most of these tests, only a few. After some abusive test, the batteries do bounce back to around the same numbers with normal charge/discharge techniques. I have not seen a drop-off because I have not been traying.

If your packs are pretty lousy voltage wise & resistance wise. Try dead shorting them on a tray. I am leery about storing NiMh deadshorted, usually I leave mine shorted for 30min to an hour. Charge at 6amps, dump to 5.40 a pack and store in that fashon.

Jeff
Very interesting A-Ko ...

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Old 03-09-2005, 01:59 AM   #42
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Quote:
Originally posted by A-Ko
The funny thing with GP3300s is they do like to be used. I have cycled 1 pack 5 times in a day, of corse with adequate rest (usually 25 min), the numbers got better and better. So if you have that killer pack, with adequate care you can run it 4 to 5 times a day.
Do you mind sharing some numbers, and a detailed explanation about how you did the test, and on which equipment?
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Old 03-09-2005, 02:07 AM   #43
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Originally posted by cr250
How do most racers determine average voltages improve as a result of dead shorting? If by using a charger/discharger like a Turbo 30 or GFX 35, the average voltage would appear better. Why? Because the average voltage is calculated by summing up all the voltage readings during the discharge cycle and dividing that sum by the total number of readings. If the runtime went down as a result of dead shorting, the total number of readings was also less. Since the denominator is now smaller the answer (average voltage) appears larger.
I re-considered this; Yes, the runtime will be shorter. But since you add the measured voltage for each sample made, the accumulated voltage will also be smaller, thus reflecting the shorter runtime. So I dont get there should be a big difference compared to the graphs?

BUT:

WHat do matter, is the graphs for the first 5 minutes. Everything after 5 minutes dont matter. And thats why the average voltage dont matter as much, as graphs.

So...

If deadshortning raises the voltage during discharge for the first 5 minutes... it's worth it. But if the discharge curve will be too steep, meaning a lot of speed the first 1-2 minutes and slow at 4-5 minutes, it might not be worth it anyway...

Are you able to post the Excel graphs?

Thanks for your time.
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Old 03-09-2005, 06:28 AM   #44
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Old 03-09-2005, 07:36 AM   #45
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Cole: Memory is pretty much exactly how it is said, for instance if you take some 2000 cells and charge them run them like 3 min, then just put them away, charge them up and run them another 3 min....etc without discharging them, the cells remember this treatment so when you go to discharge the pack and actually start to take care of them on the track once you hit the 3 min mark you will start to feel the poor performance of the pack. this is memory.


jag88: I mostly run mod off-road and runtime is not a factor, so I cunder charge my packs so they last as long as possible.
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