DISCUS54

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I have gone over to NiMh on my Transmitter packs from Nicads. My pack is an 8 cell 2500mah pack ( aka nimh 2500mah tx battery). I have set up my charger (a Venom Pro) for min and max rates as follows:
7.2 volts min (.9min x 8cells = 7.2volts min)
discharge rate of .5 amp (is too low?)
charge rate of 1.3 (typically I charge via the 10 factor method 2500mah = 2.5 amp charge rate) however the pack is really heat up at this setting.
there is a default 120 minute shut off on the charge cycle.

My questions are:
Am I getting a deep cycle on the discharge if it only brings it down to 8.2 volts vs. something lower like 7.2 ?
Because the charge cycle is time limited is it fully charged? Stops around 10.8 or 10.9 volts with a measured capacity of 2489mah (that was at the 2.5amp charge rate-looks full). I'm currently trying the lower rate of 1.3
Do I bypass the 120 minute charge shut off function? (will it have enough time to top off at the lower charger rate?)
I have heard of false peaks, but don't know if that's the case here.
Hate to fly without knowing what is going on with the chemistry of the NiMhs

Thank you in advance for your helpful suggestions

bkfamily1

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Hey discus54,

Here is a pretty good article I found previously. [link=http://www.powerstream.com/NiMH.htm]http://www.powerstream.com/NiMH.htm[/link]

I am not much of a battery expert - I have been reading and learning in prep to change my electronics over to NiMH. The only thing that struck me about what you said is starting with a 1C charge rate instead of C/10 on a new pack. In a previous thread I was asking questions about this, and Red recommended at least 2 or 3 charge cycles to form the pack at C/10 for a 150% charge cycle for new packs. [link=http://www.rcuniverse.com/forum/fb.asp?m=8900152]http://www.rcuniverse.com/forum/fb.asp?m=8900152[/link]

You already sound like you know what you are doing, but I thought I would share that thought. Good luck.

ALWAYSPDG

My Feedback: (1)

You need to format your batteries especially NiMh type. Do three cycles of discharge and charge. You can do a max discharge rate of .500 mAh at .9 volt cut off but I usually do around .300 mAh. Then charge at .250 mAh, you want to use peak detection and NOT have the charge timer set to turn off the charger. It might take you 10 hours to charge the battery. If the battery is getting HOT you are charging at to high of a rate or to long. The battery can be warm to the touch which is fine. HOT is NOT good!

Hope that helps, Mike

bkfamily1

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Mike - is the max discharge rate a function of the pack capacity (mAh), the number of cells or something else? Or is 500 mA a good max rate as a rule fo thumb for any pack?

Thanks

DISCUS54

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Mike,
I thought the default 120 minute shut off was an issue, must be a liability thing. I have been discharging at .5 and will change that to .35 and the the charge to .250 and see how they cycle-thanks for the input!

DISCUS54

My Feedback: (211)

Also I see that it is not recommended to exceed 120 degrees F on the temp when cycling. I have set up a small fan to circulate air around both chargers and the packs, seems to be helping in reducing the heat, as they are only warm to the touchnot hot.

DISCUS54

My Feedback: (211)

bkfamily1, Excellent article at Powerstream. I see the C/10 is critical to establish proper memory. Thanks!

ALWAYSPDG

My Feedback: (1)

Sounds like you have things under control! You want to charge your batteries using peak detection and NOT by a timer.

Mike