PSU works with a multimeter attached, but trips the safety without it.

[sebas96]

Hey,

I want to use an old xbox 360 PSU- 12V 175W output- for my 12V sup pump (pump/air compressor).

When I connected the PSU to the pump directly the SUP pump worked without a problem until it switched to the air compressor( it does it automatically after the pressure reaches 1 psi. The moment it switched the indicator light on the PSU turned red(green is good, orange-standby and red-fault alarm) and stoped working.

I thought, that it must draw a higher current then the PSU could safely put out so I connected my multimeter to it. For some reason the SUP pump works without a problem after it switches to air compressor mode when connected to the mulitmeter.

The thing is tho, that the SUP pump draws 7,7 A (max. 11A) in pump mode and only 6,3 A (max. 8,5A) in compressor mode.

So my problem is, I don't know what is tripping the safety feature of the PSU and why it is working when the multimeter is hooked up. Does anybody know how to fix this?

FYI

1. I cleaned and oiled the fan.
2. The SUP Pump works with other PSUs with a similar output.
3. The Xbox PSU works with another aircompressor(specs in image 3)

 

[Avo Mk8]

The power supply is likely built as a high frequency switch mode device with decent voltage stabilisation for its normal electronic load.
You are using it with quite a 'dirty' load, which could have a nasty transient starting current. I don't think it is the ideal supply for this job, but since it's there I get why you are using it!
If you are putting your multimeter in the circuit to measure current, you are adding a bit of series resistance, apparently enough to stop the PSU tripping out from the motor transient current when it starts.
Well, that's my guess

 

[sebas96]

The power supply is likely built as a high frequency switch mode device with decent voltage stabilisation for its normal electronic load.
You are using it with quite a 'dirty' load, which could have a nasty transient starting current. I don't think it is the ideal supply for this job, but since it's there I get why you are using it!
If you are putting your multimeter in the circuit to measure current, you are adding a bit of series resistance, apparently enough to stop the PSU tripping out from the motor transient current when it starts.
Well, that's my guess

Thanks for your replay. Probably a stupid question, but is there anything I could use, like a resistor to mimic the multimeter or will it eventually damage the PSU and/or appliance?

 

[Avo Mk8]

Thanks for your replay. Probably a stupid question, but is there anything I could use, like a resistor to mimic the multimeter or will it eventually damage the PSU and/or appliance?

The ideal solution would be a 1 or thereabouts ohm NTC thermistor rated at say 10 or 15Amps. It would get hot so you'd have to have it safely shielded etc.
It's 1 ohm cold, but heats up to be 0.03ish of an ohm, (or ideally less if you choose the right one) at full load while the load runs.
Just an example: NTC Thermistor Inrush Current Limiter 1 Ohm 16A TDK B57364S0109M000 Cross - AMWEI Thermistor Sensor - https://amwei.com/icl-ntc-thermistor-inrush-current-limiter-1-ohm-16a-tdk-b57364s0109m000/

Health warning: I haven't done any sums, so you might give some thought to exactly which rating of device to use