Feeding DMM with 5V source instead of batteries.

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treez

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Hi,
We have a mastech MS3229 DMM.
It uses 3 AAA batteries, but doesn’t indicate when the batteries are going flat, -the readings just get inaccurate.
We want to supply it with a DC power supply instead. We don’t have a schem for the meter, but do you reckon we’ll be ok feeding it a 5V source, with a single diode to drop down to approx. 4.5V?
Its difficult to say when we don’t know whats inside it.

https://www.amazon.com/MASTECH-MS8229-Multimeter-Temperature-Humidity/dp/B0094DH8UO
 

Hi,

Its difficult to say when we don’t know whats inside it.
Click to expand...
I agree.

Thus I recommend to use an DCDC converter to get high impedance isolation.

Klaus
 
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Agree with the isolation that Klaus has mentioned. Particularly if you are attempting to measure mains referred voltages while powering from the DC power supply.

Medical-grade supplies have very low leakage currents
 
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A transformer style "wall wart" and a LM317 ought to do the
job for the cost of scrap and a shilling (do you guys still have
shillings?). Might want to test what the accurate-as-spec'd
supply voltage range realli is, and tweak the LM317 feedback
network to center up. If you do this first then maybe it says
a 78L05 is am even cheaper option. Maybe check supply draw
across operating modes (like resistance, low range) while
you're at it.
 
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Batteries are isolated and low noise. I wonder how well it will adapt to a supply with common mode and differential noise it would otherwise never see.

For medium cost DMM’s extech or BK Precision would be my choice.

We have a plug-in Mastech that drives me insane with its 15-minute power-down feature that cant be disabled. I swear it shares a board with a handheld and they couldn’t be bothered to make this single change.
 
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It uses 3 AAA batteries, but doesn’t indicate when the batteries are going flat, -the readings just get inaccurate.
Click to expand...

True; very annoying but it is also messy to use an external power supply. I do not understand why they cannot incorporate a low-bat indication.
 
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