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nimh batteries

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moe7404

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moe in wichita ks next week iam getting a rc nitro car. i bought 8 nimh aa bats, rated at 2000 mah, die hard brand, also bought same brand charger. seams to workfine. but should i discharge down to or near 0.0 volts before recharging? if so whats the best way to discharge it?
 

audioguru

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Old fashioned Ni-Cad cells had a "memory" that is erased by a complete discharge. If the cells are still in series when they are deeply discharged then some are destroyed.
Each cell needed to be discharged separately.

Ni-MH cells do not have a "memory" so they do not need to be completely discharged.

You need to use a smart charger so that your battery is fully charged but not over-charged. A cheap charger only has a timer and if your battery is not low then it will be over-charged.
 

HarveyH42

Banned
You should search for an R/C forum (plenty out there, into R/C Helicopters myself). Easy way to sort out the good, bad, and affordable. If the batteries and charger came from the same place as the car, should probably work well, since most hobby place make their money off repair parts and upgrades. The longer you run the R/C, more likely you are going to need some parts, plus you'll get hooked, and go for something bigger, faster...
 

Sceadwian

Banned
2000ma pack for a nitro car? Well your receiver and servo's won't be running out of power anytime soon =)
 

moe7404

New Member
nimh batterys

thanks for the help. i dont know why i didnt think of r/c fourm. oh yea iam looking foward to faster and so on. in wichita we have two tracks, one is less than 4 miles away. thanks again.
 

Sceadwian

Banned

moe7404

New Member
moe in wichita ks well Sceadwian when i read your post i thought i may have put down the wrong number, so i checked the cardboard that came with the aas, i keep everything. the way it is writen its saying that 4 aas are 2000 mah. one needs to read it carfuly. yea 2000 in one aa would be great. so what i have is 500 each aa. but i cant remember how many aas gos in the car. when i get the car, thursday ill post how many aas it takes. i realy love this site. also i did a lot of reading on the net. it sounds like it realy doesnt mater if you totaly discharge a nimh bat. thanks everyone
 

audioguru

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The latest Energizer AA size Ni-MH cells are 2450mAh each.
Duracell does not post spec's for their Ni-MH cells on their website.

My cheap Chinese solar garden lights have toxic old 500mAh Ni-Cad cells.

You must not totally discharge Ni-MH cells that are in series. Then the weakest one goes dead first and the other cells charge it in reverse while they continue to discharge. Stop discharging Ni-MH cells that are in series when the voltage of each cell drops to 0.8V to 1.0V.
 

Sceadwian

Banned
audioguru, what is the discharge rate the mah rating is based off of?
 

audioguru

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audioguru, what is the discharge rate the mah rating is based off of?
The capacity of a Ni-MH battery cell does not change much with the current. The energizer 2450mAh AA cell is rated at 0.2C which is 490mA.
It is also 2450mAh at 2.45A and is slightly less at 4.9A.

The internal resistance is 0.03 ohms when fully charged which increases to 0.04 ohms when half discharged which reduces the voltage a little at high currents.
 

Sceadwian

Banned
Wow, really low internal resistances, I didn't expect that. I'll consider this relativly standard for 2000+ mah cells. What's the self discharge?
 

audioguru

Well-Known Member
Most Helpful Member
"Old" Ni-MH cells discharged fairly quickly. "New" ones are sold fully charged and a charge is still good after 6 months.
 
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