Author Topic: Assembling NiMH battery  (Read 721 times)

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Offline pcm81Topic starter

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Assembling NiMH battery
« on: January 04, 2023, 12:26:35 am »
I have, hopefully the last, question about assembling NiMH battery.
I have cycled the cells and selected the cells with matching IR and capacity.
My question is: do i want to fully charge the cells or have them fully discharged to 1V before assembling them into a battery in order to make sure i have a SOC balanced assembly? I won't be able to charge individual cells after the assembly is done.

Thanks ahead
 

Offline ConKbot

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Re: Assembling NiMH battery
« Reply #1 on: January 04, 2023, 03:35:36 am »
Ni batteries are balanced by putting them on a trickle charge.  The classic NiCd charge routine of 0.1C for up to 24Hr would balance the pack by driving every cell into overcharge, where excess energy is dissipated as heat, and nothing horrific happens for charging like this.
NiMH can vary in its ability to be overcharged for a long time, and their capability to burn off the overcharge without building excessive pressure internally, so 0.1C is not always safe. Especially in low self discharge NiMH cells. If your cell manufacturer gives a trickle charge recommendation, follow that. If not, personally, I'd go for 0.05C and let it sit for 25-30 hours, while making sure it's not getting too warm while doing such.
 
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Online bdunham7

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Re: Assembling NiMH battery
« Reply #2 on: January 04, 2023, 03:41:44 am »
My question is: do i want to fully charge the cells or have them fully discharged to 1V before assembling them into a battery in order to make sure i have a SOC balanced assembly? I won't be able to charge individual cells after the assembly is done.

If you were concerned about imbalance and you weren't going to equalize them afterwards, you might want them to be dead when you assemble them.  This way if they are all subject to the same charge/discharge, they would go dead together, which is what you want since the best way to kill NiMH batteries is to reverse-charge the weaker cells by discharging the pack beyond dead.  If they are all bottom-balanced, they'll all go dead at once.  However, it probably doesn't matter in your case since they are all nicely matched.  Also, charging will tend to equalize them anyway so they'll become top-balanced by natural operation.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline IanB

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Re: Assembling NiMH battery
« Reply #3 on: January 04, 2023, 04:40:53 am »
I would agree with what ConKbot says. You balance an NiMH pack after it is assembled, and periodically thereafter. Balancing is done by doing a long slow charge, such as 0.1C for 16 hours. Read the manufacturer's data sheet for recommendations on this, but if these are the same cells as from the other threads, then 0.1C for 16 hours is what that data sheet recommended.
 


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