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Reverse-protection for NiMH (during discharge)

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csdave

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Hi all,
I was wondering what you guys do when you need to design a device operated by several NiMh batteries in Series.
To minimize the risk of reverse charge the batteries should be as similar as possible. However this does not guarantee that reverse charge will be prevented.

The simplest solution I can think of is to monitor the voltage: either total or individual cell voltage. In this case, how much can I safely discharge a battery?

Do you have other suggestions?

thanks
 

Syncopator

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Assuming that you use good cells, i.e. either new ones or cells which have been well treated, discharge a battery of them to 1V per cell.

It is sufficient to measure the battery voltage and not that of each cell.
 

csdave

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so, if I understand correctly, say I have 6 1.2V batteries, I should switch off the circuit as soon as the total voltage goes under 6V, right?
 

Syncopator

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Yes.

The first word, above, was to be my answer, but the system said that it was too short and wanted at least 10 more characters. Bloody stupid system.
 

umesh49

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Its depends on current drawn from battery. I had some pratical experiance with batterries, and I did some testing. First observation was if you are usng a battery around 2000mAH capabilltiy and drawing a current of around 150mA then actual mAH delivered will be only 85%. Battery will take less than half a minute to go from 1.1V to 1V. So if current drwan is more then better switched off the batterries below 6.6V.
 

Syncopator

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Battery will take less than half a minute to go from 1.1V to 1V. So if current drwan is more then better switched off the batterries below 6.6V.

If the monitoring circuit takes more than a second or two to react, then it should be redesigned!
 

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