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NiCd/Nimh Battery Tech Info
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chris



Joined: 18 Jun 2004
Posts: 160
Location: Brisbane


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hmmm, i dont know much about NiCDs but is it a possiblility that you initially charged them with far too much current killing some cells? I dont know if it is possible but thats my 2 cents
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Post Sun Aug 15, 2004 6:27 pm 
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kkeerroo
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Aocording the bloke who wrote this site bellow you may have damaged your cells by charging them at too high a current.
http://www.angelfire.com/electronic/hayles/charge1.html

for those who don't want to skim through the site to find the relative info here it is:
"Rechargeable battery capacity is rated in mAH (milliampere-hours). The total capacity of a battery is defined as "C", that is it can supply C mA for 1 hour, or 2C for 30 minutes etc. Charge rates can vary from trickle charges to keep the battery 'topped up' of 3.3% of C to 5% of C, a slow current charge of 10% of C to 20% of C or a fast charge of 50% of C to 100% of C. Slow charges are not meant to be continually applied, and since NiCd/NiMH batteries are about 66% efficient, they normally last about 8-15 hours. Fast charges such as 100% of C should be terminated after about 1.5 hours, providing the battery is flat to begin with. Once a battery is fully charged, the battery produces gas creating a high internal pressure, and a sudden rise in temperature. The charge should be switched to a trickle charge at this point or the battery will begin to vent and release its electrolyte. My old battery was rated at C=1300mAH and my old charger was rated 400mA (30% of C) so the charger should have been switched off after about 4 hours, provided that they were almost flat to begin with. However there is no way of knowing if C was actually 1300maH or if it had decreased a bit, and once the a battery starts to deteriorate, I suspect this becomes a vicious cycle and the battery deteriorates rapidly due to more and more overcharging. The manufacturer suggests these cells should be good for 500 to 1000 cycles if properly treated!"

I am sure cutting and pasting like that will annoy many people but it is all good info. The above site also has good stuff on "memory effects" as well.
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Post Sun Aug 15, 2004 6:38 pm 
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ffej
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Joined: 22 Jun 2004
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Location: Kurrajong, NSW


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Well, having charged drill batteries at 5A, I really doubt you killed them with 2A. The GWS charger is a peak detection charger, meaning it senses the slight drop in voltage that occours in NiCd and NiMh batteries when at the end of the charge of the cycle due to gas build up in the cell. Unless the charger was set up wrongly, its pretty hard to kill batteries.

Toward the end of a charge cycle, the pack will get pretty warm, but not too hot to touch(55^oC or so, depends on the batteries). If the packs arent warm at all then the charger is stopping to early, either detecting a false peak, or for some other reason. If they were hot, then most likely they have overheated and lost gasses, reducing the capacity.

Have you tried to charge the bot with the 400mA charger? If they do still charge up fine when using it, then your charges set up wrongly, if they dont, then either your charger was set up wrongly and didnt detect the peak, hence overcharging and killing the batteries, or for some reason one or more cells have collapsed, screwing up the packs capacity( cheap batteries will do that too you, I mean, the whole drill is only worth $17, you cant expect too much ).

Also, the drill batteries seem to take a lot more power when being charged more slowly. At about 2.5C, ive had them only take 600mAh, and remember you have to put 140% in to get 100% out.
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Post Sun Aug 15, 2004 10:49 pm 
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kkeerroo
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Joined: 17 Jun 2004
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did you read my last post?
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Post Mon Aug 16, 2004 3:22 pm 
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Waddy the phoenix



Joined: 16 Jun 2004
Posts: 971
Location: sydney


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well jeff the drills are probably worth about 10$ because the company has to make a profit so yeah
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Post Mon Aug 16, 2004 3:52 pm 
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chrisjon65
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Joined: 15 Jun 2004
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ive been using drill batteries from day 1 and all you gotta do is discharge all of them after a days battling recharge them to full power a week before the next round and give them all 1 hour recharge 1 day before the event ......ive been using drill batteries for 20 years in my trade and you get to know a few tricks Wink
heres one .....if a drill pack is not performing well ,freeze it when flat ,let it thaw out ,charge it up full ,and itll be perfect for a lot more battles ..............just a little secret on how to get a 9 minute battle out of a drill batteries Very Happy ...cheers sarge
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Post Tue Aug 17, 2004 6:59 pm 
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timmeh
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Thats a nice looken bot sorry'2 what do you use for drive motors and the weapon motor?
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Post Thu Aug 19, 2004 7:57 pm 
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JohnMuchow



Joined: 25 Aug 2004
Posts: 21
Location: New York City, USA


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Re: NiCd/Nimh Battery Tech Info

quote:
Originally posted by Spockie-Tech:
Some very useful information on up-to-date battery tech is here.


Thanks!
Just wanted to let everyone know that our site has recently moved and those two PDF documents are now at:

http://www.camlight.com/techinfo/camlight_whydischarge.pdf
http://www.camlight.com/techinfo/camlight_techtips.pdf

Or you can view them on the Why Discharge? or Tech Tips pages on our site at www.camlight.com

With most of our products now in production, we have a bit more time to visit the forums more often. Feel free to contact us with any questions you might have regarding these documents.

Thanks!

Post Wed Aug 25, 2004 3:11 pm 
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JohnMuchow



Joined: 25 Aug 2004
Posts: 21
Location: New York City, USA


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quote:
Originally posted by andrew:
I bought a gws charger for 75 and charged them with it and for some reason it does really bad. lasts about 30 secods then slows down to dragging point.

I agree with nightshade....
Peak-detecting chargers can often "false-peak" and shut off too soon leaving your packs only partially charged....especially with certain NiMH packs.

If you have a watt-hour meter (like the Astroflight Whattmeter), you can double-check the pack's charge and if the charger false-peaked, just restart the charge (noting the accumulated AH being put into the pack). For new cells, this can often occur several times during each charge. With our Astro 112D's we sometimes have to restart the charge half a dozen times with NiMH packs....very frustrating. But, with proper forming/conditioning of the cells when new, and regular conditioning of the cells over the years, there should be very little (if any) false-peaking occuring again.

If you don't have a whatt-hour meter, just test the packs after charging with a known current source. You can try a 1/10C rate charge to 110%-120% of capacity, or charge to about 100% at higher current levels. But, monitor the temperature of the cells. The outside of the pack might be just warm, but the cell could be way too hot due to localized heating and the insulation prpvided by wrapping on the cell, pack shrink wrapping, etc. Check the temperature of the cells a couple of minutes (up to 5 miutes for larger cells) after the charge is over. It's a better indicator of what heat is being generated inside the cell during charging. Our cells get abused enough during use, we should be kind to them during charging. Wink

We often find that, after initial low-current forming/conditioning of the cells, that a higher current charge is better at preventing false peaking with problematic packs. Unfortunately, lots of experimentation is the best way to see what works for your packs.

Post Wed Aug 25, 2004 3:46 pm 
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Spockie-Tech
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Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


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Re: NiCd/Nimh Battery Tech Info

quote:
Originally posted by JohnMuchow:
Thanks!
Just wanted to let everyone know that our site has recently moved and those two PDF documents are now at:
http://www.camlight.com/techinfo/camlight_whydischarge.pdf
http://www.camlight.com/techinfo/camlight_techtips.pdf


Thanks for the updated links John, I've edited the original messages to reflect the new URL addresses.

Welcome.. nice to see you here downunder on our Forum, I've often seen your posts of the BattleBots and RFL forums. we're a few years behind you guys down here with our first 12Kg (30lb) arena's just starting to appear, but we're having fun and the sport is gradually growing..
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Post Wed Aug 25, 2004 10:02 pm 
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timmeh
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Joined: 20 Jul 2004
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Location: Victoria


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HOOORRRRAAAAYYY!!!!!

I got my triton charger today Very Happy benn playing with my battery packs i made
going well Very Happy

BUT!! I was a little disapointed when i found out that the triton can only charge at 5amp max "i found that out when i read the instructions Laughing Yes i read the instructions "normally i just throw them aside and tinker with my new toys but this time i thought i should anyway if i had of known that when i brought my power supply i wouldent have brought a 12amp one i would have just got a 6amp one Smile

But im still happy with it as it is very easy to use and charges all battery types
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Post Fri Aug 27, 2004 5:33 pm 
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Nexus
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Joined: 17 Jun 2004
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Actually you did the right thing. Just because it only supplies 5 amps out doesnt mean you need 6 amps in, thats a bad assumption.

Even at 12 amps the triton might error when you charge 24 volt packs.

The thing you are not considering is the voltage because if the triton is running off 12 volts and you are charging a 24 volt pack then the amps are not the same.
You will generally find that the triton pulls in more amps than it is putting out regardless so dont despair and hopefully 12 amps will be enough. I have been using a 5 amp charger so do know its limits and want a bigger power supply already.
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Post Fri Aug 27, 2004 5:43 pm 
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timmeh
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Are cell capacitys normally more then they are rated?
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Post Fri Aug 27, 2004 6:03 pm 
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Philip
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Joined: 18 Jun 2004
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Location: Queensland near Brisbane


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Please read this

http://homepages.which.net/~paul.hills/Batteries/Batteries.html

http://www.teamtornado.co.uk/batt.htm

Post Sat Aug 28, 2004 6:47 am 
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timmeh
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Why i wanted to know is because my triton charger was charging a 4500mah pack and it was still charging when it had reached 5amps in the pack or so it sed thats how much it had put in.

It was still going and i didnt know if i should stop charging or if it was because the cells have more then what they are rated?
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Post Sat Aug 28, 2004 12:36 pm 
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