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Power Supply to Batteries Changeover
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Please be positive and constructive with your questions and comments.

Power Supply to Batteries Changeover

by carpetball on Thu Jul 25, 2019 1:12 pm

I need to switch my Raspberry Pi and other electronics WITHOUT DISTURBANCE from a power supply to NiMH batteries for a brief mobile application. The computers must run continuously for setup. How can I do the changeover?

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Re: Power Supply to Batteries Changeover

by franklin97355 on Thu Jul 25, 2019 3:11 pm

The easiest(?) way would be to run the Pi from batteries and use a power supply to charge/maintain the battery.

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Re: Power Supply to Batteries Changeover

by carpetball on Thu Jul 25, 2019 4:42 pm

Thank you, Franklin. At your suggestion, I've looked into trickle charging at the same time as operation. This application draws a heavy current during an extended period of checking and initialization, a current far higher than a trickle charge rate, and then it wants to draw the same heavy current from fully charged batteries for brief mobile operation. So I don't think simultaneous can help me.

Also thanks: your suggestion covers an approach I'm holding low in the list because of its trickiness: use a high-current voltage follower to match, at the load, actual battery voltage. Disconnecting for mobile operation would be a non event for the computers. The voltage follower and not the batteries would supply full current before mobile, of course.

So I'm worried about a true changeover: having the supplies paralleled briefly to avoid a computer dropout, which could reverse bias the batteries or overcharge them because the voltages can't be matched. There are many ways to abuse NiMH batteries, but perhaps a brief overlap wouldn't affect battery chemistry. There would still be supply step changes to buffer.

carpetball
 
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Please be positive and constructive with your questions and comments.