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Old 09-26-2001, 06:05 AM   #1
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Unhappy my nimh 3k's are only taking 2000mah! please help!

i have a few packs of 3k's, 2 SMH's, 2 sanyo's and a old panisonic.

anyway they all are taking around 2000mah. i have been using a novak milllenium, running them each only on sat. (since thats when i race) and running them each 2-3 times. i used my temp gun and found they were running at up to 170f at the end of a run. i let them cool down completly with a fan blowing on them, and then charged them about an hour later.

i just got a turbo 35bl and its the same situation. i charge them, they are warm out of the charge, however now, it says on the discharge of how much they really took. i do a 25amp discharge, and none of the packs have more then 2200mah.

what i am doing wrong here? i set my cut off to .02 i dont use trickle, did i fry my packs or something? i also use deans connecters (all of them in are very good shape, and i use a ungar soldering iron and i know that all of my connections are good)

any suggestions or advice would be greatly appreacated, thanks!
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Old 09-26-2001, 06:09 AM   #2
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what amp are you using?
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Old 09-26-2001, 06:37 AM   #3
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How many runs have these packs had???

Some tips:

1. Discharge the packs on a tray .6 cut off per cell (5.4 for the pack) prior to charge, this is importaint!

2. Give the packs a longer period between charges ... say 2 hours

3. Charge the cells with some sort of cooling, i.e under a fan

4. Charge at 3.5 - 4.0 amps use a .03V perc cell cut off.

note: Sanyo cells will loose capacity after 30-40 runs
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Old 09-26-2001, 09:58 AM   #4
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I was under the impression that NiMH's don't like to be on a discharge tray, especially down as low as you guys are saying. In fact, aren't NiMH's supposed to be stored partially charged? That is what all the battery manufacturers say anyhow. I too have experienced severely short life spans for NiMH's. Approximately 100 charges until they are "practice packs", whereas properly maintained NiCd's can be charged around 400-700 times before they aren't cutting it anymore.
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Old 09-26-2001, 10:54 AM   #5
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I have been told to put them on a tray untill the lights start to dim, then put about 20% charge in them. I personally just run them down and just let them sit. I leave charge in them... But my packs arent nice $80 3000's. I got these for practice only..
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Old 09-26-2001, 01:29 PM   #6
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You have to treat NiMh just like NiCd or otherwise they will become practice packs after 30-40 runs. Don't leave them partially charged.
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Old 09-26-2001, 01:39 PM   #7
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NiMah DON'T like to be discharged to or close to zero. Dead shortening is even worse for them. I will dig up some online articles for you.
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Old 09-26-2001, 01:43 PM   #8
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http://www.rccaraction.com/articles/NiMHbatcare1.asp

Quote:
RC Caraction: If a pack is at a nearly zero discharge state and is put away for a week, it can easily bleed off the remaining charge and reach dead zero. If the pack is allowed to bottom out, it could be harmed.
Quote:
RC Caraction: A note for those who use battery "bugs," or cutoff devices: if they're designed for use with Ni-Cd batteries, they will discharge a NiMH pack to below a safe level.
Quote:
Team Orion: Cells must be stored in a partially charged state, if the cells are stored empty, the electrodes can oxydize and the cells be damaged.

-Because Ni-Mh cells do not peak like Ni-Cd cells do, the use of special chargers that have adjustable or very low delta-peak value are recommended for charging these batteries, like our D67 charger. If you have a normal charger and want to use it to charge your Ni-Mh cells, it is recommended to use a charge current between 2 and 3 amps, exceeding this value can damage your cells.

-The battery should not get hot like a Ni-Cd battery does while charging, this means that the charge current or delta-peak is too high and can result in damage to the cells or very low performance.
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Old 09-26-2001, 01:49 PM   #9
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i was charging the pack at 4.5 amps, and i do have a fan on my batts, but not right next to the pack since it might false peak.

i have around 50 runs on them.

i have a deans bulb dicharger that i used before i got the turbo 35.

now i discharge them to 5.4v for the whole pack.

they do get rather warm, like 120 after charging without the fan.

i always store them with a full charge, the longest i wait is one day, or the next day after racing to charge them all up.
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Old 09-26-2001, 01:55 PM   #10
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Storm - I charge mine at 4.5 & 5.0.. It doesnt seam to matter much...
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Old 09-26-2001, 03:53 PM   #11
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TRS6-I am the Manager at Schumacher USA. I talk to Danny Sullivan from SMC, Troy and Jeff Schroder from Fantom, Mike Reedy and Sean Corcoran from AE, Mike Dieter from Trinity and Oscar Jansen from Orion all the time. I help Paul Wynn, Mike McMahon and over 50 partially sponsored driver keep up to speed as to how to take care of their cars and batteries so they can keep winning with Schumacher Sedans. Based on my conversations with all of the above all of the info that was initially available as to how to take care of NiMh cells is entirely incorrect as was most of the info in the R/C Car Action article.

When the first NiMh cells came out we did not have any experience with them. We had to rely on what Panasonic and Sanyo engineers were telling the battery matchers as to how to take care of the cells.

We all stored our cells partially charged, charged at 3.5 to 4 amps and we all ended up losing 100sec plus in run time within 3 months of racing. A solution to this came from oval racers. There aren't many of them anymore but no one group of racers spend more time obsessing on batteries and motors than the oval guys. They had packs that were garbage after 10-20 runs so they experimented on ways to get them back. They started dead shorting and found out they could get 50% of the lost time back. My own experiments confirm this.

When the SMH cells came out everyone in my area started deadshorting right from the start. It turned out that shorting wasn't needed. It did not harm the cells but it did not help keep the capacity either. The cells survive the longest if you store them fully discharged. I run my pack, dump them on lights then leave them in a discharge tray until another pack is ready to go into the tray. My results are exactly the same as the guys that are shorting their cells. One more thing. You have to cycle your packs once every 2 weeks if you are not racing once every two weeks. If you let them sit during the off season you will have to buy all new packs when you start racing again. They will not take a charge and if they do, the runtime and voltage will be too bad to even practice with.

Within 10-20 cycles EVERY NiMh pack WILL lose 30-40sec of run time. The packs average voltage will increase and the IR will get lower. There is NOTHING you can do to prevent this. So far no one has figured out a way to keep NiMh at their rated capacity beyond 10-20 cycles.

If you race Stock, no big deal. You will go faster after the packs run time falls off due to the higher voltage and lower IR. If you run Mod in most places, with 9-12T mods, the lower run time should allow you to still run for 4-5min. If you race with 8-9T mods you should be able to make 4min. If you race 7-9T mod in competitive areas with Factory pros be prepared to get new packs every 10-20 runs or get a battery sponsor to remain competitive.

If you arent raving guys named Baker, Pavidis, or Lemieux you don't have to worry about losing 40 sec. Go out an have fun. If you run Stock SMH is the bet battery going regardless of run time.

I charge at 4.0 amps, repeak at 5amps for club races and 6amps at Nationals. I run my pack, dump them on lights then leave them in a discharge tray until another pack is ready to go into the tray. I cycle at 20amps to reduce cell stress during bench cycling. This is the best advice we have from the guys that know the real deal.


StormPerson-Dump your cells, put them in a discharge tray for 30min, solder a wire from the (+) to the (-) terminal and let them sit for a week. Cycle the the cells after a week and repeat the process again. After 2 shorting cycles you should regain 50% of your lost time. This works for SMH cells only. Your out of luck with Sanyos.
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Old 09-26-2001, 04:04 PM   #12
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Ok, Thanks for the correction. I was still going off the info i had seen in RCCA, and around the track...
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Old 09-26-2001, 04:47 PM   #13
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AdrainM is right about storing them in a discharged state. I dead-shorted my first 2 SMHs following what others done out there and end up losing a significant amount of runtime. My 3rd SMH pack is stored at 5.40V after runs and it's becoming better. Capacity stayed at around 2950mah to 2980mah and voltage is slowly increasing from 6.95V to between 7.01V and 7.05V @ 20A discharge.

Storm, just use your turbo 35 to bring the pack down to 5.40V will do, as for the fan I find no harm in allowing it to blow directly on the pack that is charging. I use a 5A charge and a 0.03V cutoff without any false peaking problem.
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Old 09-26-2001, 06:21 PM   #14
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What we need is 3000 ni cads...how good would they be!
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Old 09-26-2001, 06:49 PM   #15
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Quote:
Originally posted by black-knight
What we need is 3000 ni cads...how good would they be!
Yer I agree, I'm for 3000 nicd's.
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