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Powering a multimeter built into bench-top power supply? Answered

Recently I built a bench-top power supply from an ATX power supply (Like the one from here: https://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe). It works great but I'm looking to consolidate this and my analog multimeter into one box. I'd like to know how to power the multimeter using the power supply so I don't have to worry about changing the batteries. The multimeter uses two AA batteries and a 9V, and the power supply has voltages of 12, 5, 3.3, 0, -5, and -12. Thanks for any help.


I'm assuming that the two AA batteries are in series to give 3V and that the battery 0V are connected together. Check that this is the case.

Replace the three batteries with rechargeable equivalents and connect a 270R resistor from PSU +12V to the positive of the 9V battery and a 180R resistor from the PSU +5V to the 3V of the AA batteries.
Connect the 0V of the PSU to the 0V of the batteries.

This will give a continuous 10mA trickle charge to the batteries whenever the PSU is on.

(Usual disclaimers apply if the magic smoke appears!)

What type of rechargeable batteries then?


Standard NiMh - You can trickle charge these at C/10 or less indefinitely with no adverse effects. It's worked fine for me in a couple of situations.

. . . and if you connect the PSU via a stereo socket you can unplug it at will and use the multimeter away from the workbench.

I reckon the 3.3V should work for the AAs, voltage regulator on 12V for the 9V.