Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Feeding DMM with 5V source instead of batteries.

Status
Not open for further replies.
T

treez

Guest
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
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
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
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
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.
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
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.
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
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.
 
  • Like
Reactions: treez

    T

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top