24v dc pwr supply

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
New customer via a pump installer that sends me "opportunities" on occasion.

An external power supply for a transducer to his well VFD fails about once a year. He pointed it out to me thru the ventilation slots in the VFD. Sure enough a RH___ power supply directly connected to L3 of the VFD and the EG. Lead length may be 6" of #14. L3 is the hi leg of a 240 Delta. Approx 212 volt to grnd. The supply is rated 100-240AC. I have used these power supplies and have yet to have a failure. Could the proximity to the vfd be a factor, the high leg in general or both?

Why the external power supply? Don't know. I was to befuddled as to who and why anyone would hook up a power supply the way they did.
 
The connection to the EGC rather than the nonexistent neutral is a code violation IMO. (Even if done at the factory rather than in the field.)
Could the temperature inside the enclosure be too high for proper cooling of the supply?
 
Beats me as to what kills the supply but I would put it on it's own breaker and come up with a neutral. If that's not an option then find a power supply that
will run off 2 legs. Maybe a line reactor on the line side of VFD but I don't think you would need that. We don't do that and never lose supplies.
It all depends on available room in the box but move it farther away if you can.
 
Why isn't the power supply connect to a second phase, (L1 or L2) as it is rated for 240 volts. Are you certain that you can't see the other connection and the EGC is just that. How is power fed to the VFD, does it come from a two pole breaker?
 
Aleman said:
Beats me as to what kills the supply but I would put it on it's own breaker and come up with a neutral. If that's not an option then find a power supply that
will run off 2 legs. Maybe a line reactor on the line side of VFD but I don't think you would need that. We don't do that and never lose supplies.
It all depends on available room in the box but move it farther away if you can.
Click to expand...

I checked voltage on the VFDs low voltage control and it appears to be functioning. Once I get a look at the manual we will most likely do away with the external supply.

The power supply would run off two legs.
 
ptonsparky said:
Why the external power supply? Don't know.
Click to expand...

Many VFD's do not have a large enough 24V power supply to power anything but their own inputs. You did mention that this power supply powered an external transducer, right?

ptonsparky said:
I checked voltage on the VFDs low voltage control and it appears to be functioning. Once I get a look at the manual we will most likely do away with the external supply.

The power supply would run off two legs.
Click to expand...

My suggestion would be to use a small control transformer between the VFD incoming power and the 24V power supply input. The transformer would block a large quantity of electrical noise from the input of the 24V power supply. VFD's create a lot of noise (electrical), and most of this noise wants to return to either the VFD or the transformer feeding the VFD. My guess is that this noise is what is killing the power supplies.
 
So what did you mean by "a RH___ power supply..."?

Inexpensive power supplies with all plastic housings, such as the "wall wart" type, have zero shielding from EMI/RFI and inside of their own box, VFDs are like very powerfully local radio transmitters. There are better quality industrial grade power supplies, some with metal housings, that are specifically designed to shield them, but people look at the price and immediately dismiss them, because if all you look at are the output specs, they are the same.

You get what you pay for.
 
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