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output of power supply reads 24V should be 12V

salp

Nov 21, 2021
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I am using an old power supply (Power-One MPB125-2012G) on a project that needs 12V.
According to the data sheet this unit should put out 12V, but when I read the output with no load it reads 24V.

AM I testing the power supply correctly? or do I need a load on in in order to get the correct voltage reading?

Thanks,
 

bertus

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Nov 8, 2019
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Hello,

Is this the model:
mpb125_2012_connections.png
If so, are the sense connections made?

Bertus
 

salp

Nov 21, 2021
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Yes thats the model, pins 1&2 on J3 are jumpered toghether.
 

bertus

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Nov 8, 2019
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Hello,

The connection of pin 1 (RTN) and pin 2 (- sense) sould be OK.
Pin 3 (+ sense) of J3 should be connected to one of the +12 V too.

The sense pins are there to compensate losses on power cables and are connected direct at the load (after the power cables).
They can be thinner wires to sense the voltage at the load.

Bertus
 

salp

Nov 21, 2021
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Thanks for the information, I looked around but could not find much on the power supply other than the standard data sheet (same as the one you posted).

I will jump the J3 Pin3 to the 12V pin and try it again.
 

salp

Nov 21, 2021
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I connected J3-Pin3 to 12V in J2-Pin3.
The readings across J2 Pins 3-4 are still 24V
J4 Pins 1-2 read 12V.

I thought of using J4 output since it reads 12V, however from the data sheet I dont know how much current J4 can handle
It's going to power a DC motor that can draw up to 4 amps.

Thanks for the help.
 

bertus

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Nov 8, 2019
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Hello,

The secondary power can only supply 0.5 Amp:
mpb125_2012_specs.png
Bertus
 

salp

Nov 21, 2021
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I think I'm going to use a different power supply, I'm just getting into electronics as a hobby and dont have enough knowledge to troubleshoot.

Thank you you for all you rhelp.
 

crutschow

May 7, 2021
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To add to the info on the sense lines, they are the feedback connections that determines the output voltage, so they must be connected to the output terminals to get the correct output voltage.
If they are not properly connected than the output will go to the maximum voltage the supply can output.
 

Minder

Apr 24, 2015
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Normally pin 2 & 3 of J3 would be ran to the final destination using small gauge conductors, these would be connected to the final load, these would sense any voltage drop at the load end and raise the supply output in order to compensate.
As already noted, if not used, then each should be connected to the output at the source in order to simply output the normal supply without load regulation.
 
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