Electronics > Mechanical & Automation Engineering

Two phase VS Three phase Din mounted power supplies



I wonder if anybody could clear out the confusion in regards to two phase power supplies.
I have an induction motor, running off a three phase VFD. I need to add a small 24VDC power supply, so that logic would be powered separately on the VFD.
On MeanWell website I have a choice between:
1. WDR series power supplies, which as I understand could be wired into two out of three phases and should support 24VDC. Example: https://www.meanwell-web.com/content/files/pdfs/productPdfs/MW/WDR-60/WDR-60-spec.pdf
2. TDR series power supplies, which just simply power off all three phases. https://www.meanwell-web.com/content/files/pdfs/productPdfs/MW/TDR-240/TDR-240-spec.pdf

Please ignore the current ratings of the PSU, question is about Uin side of things.

I really want to avoid have a five wire feed into the control cabinet and do not want to use the Neutral for the single phase power supply (not available as it is installed at the moment). Two phase Uin is half a price to three phase Uin. The feed into the VFD is 32A three phase.

Then only issue with two phase power supply I could see is unbalanced phase loading, but would that really matter, when VFD is 15kW and the PSU taps in half an amp? Or do I not understand something?

Maybe there is some white paper I could ready to build a better understanding? 

The "Two phase" PSU is actually just a regular single phase input PSU, except that it has a unusually wide input supply voltage range that lets it be powered from higher voltage between two phases.

You can simply feed neutral and one phase into that PSU and it will work fine. Phase imbalance also is not an issue since most loads plugged into single phase outlets are simply using one phase out of the three. So your little PSU is not going to matter if someone else can plug a 1.5kW space heater into the wall outlet.

The benefit of having three phase input for a control cabinet PSU might be to make sure the control cabinet keeps working if you loose a phase. Tho the VFD is likely to quickly become upset about that and safely shut itself down anyway.

It wouldn't make much of a different because the power supply doesn't draw sufficient power to cause phase imbalance. However, if I have 3 phase power in the cabinet I would use a 3 phase power supply.

You can use the first one without problems, just put in there a 2 pole circuit breaker to protect both phases. You can connect it between any of two phases as long as the voltage is in the specs, which i asume it is (400V?)
It is good practice to not use the neutral in the industrial cabinets. Even if you need some 230V for some auxilary circuits (cabinet lightning, service outlet, etc.) it's nice to use a 400V/230V transformer...


[0] Message Index

There was an error while thanking
Go to full version