HELP!!! Power Supply Troubles!!!

Switching power supplies sometimes need a load to 'turn on'. I had a similar problem with a brand-name PS where it wouldn't turn on if I didn't have enough of a load attached (a single LED or relay coil wouldn't do it).

Solution was to add a big resistor to the output and just ground the resistor. Calculated the resistance needed and got a 2W one which could deal with the heat - looks like one of those big power resistors built in to a heatsink.

Check the power supply minimum current spec - that's what you need to provide as a load before it turns on.

And, as usual, Jim is on the money. If you can swing it you want a toroidal power supply for the drives. They turn on without issues and handle back EMF (decel of an axis) better.

-R
 
I'm going to see if I can return these and replace with the unregulated 625 W power supply.
 
spumco said:
Switching power supplies sometimes need a load to 'turn on'. I had a similar problem with a brand-name PS where it wouldn't turn on if I didn't have enough of a load attached (a single LED or relay coil wouldn't do it).

Solution was to add a big resistor to the output and just ground the resistor. Calculated the resistance needed and got a 2W one which could deal with the heat - looks like one of those big power resistors built in to a heatsink.

Check the power supply minimum current spec - that's what you need to provide as a load before it turns on.
Click to expand...

I looked at the datasheet and I couldn't find a minimum current spec.

However, I had them connected to the motor drivers and they still wouldn't reliably turn on. Maybe, the motor drivers have a very light load on the power supplies until the motors are activated?

In any case, I'm ready to switch to the unregulated power supply.
 
devils4ever said:
I looked at the datasheet and I couldn't find a minimum current spec.

However, I had them connected to the motor drivers and they still wouldn't reliably turn on. Maybe, the motor drivers have a very light load on the power supplies until the motors are activated?

In any case, I'm ready to switch to the unregulated power supply.
Click to expand...
It sounds like something might be wrong. My supplies powered up without problems when nothing was connected and I never had an issue with them not turning on. Can you post pictures of your connections and check that the polarity is correct?
 
Hmmm. I already pulled them out.

But, I connected the 120 VAC to the proper terminals (line and neutral) with ground to the proper terminal. I used my Fluke DMM to make sure the L and N terminals were getting 120 VAC. I got nothing on the 48 VDC terminals and the little LED was off. This was without load and with load.
 
If the sense terminals (+,-) are strapped properly on the output then there really isn't anything else you can do except return them
-mark
 
I don't think there are sense terminals. Here's the link to the power supply I'm using.
 
It sounds like an intermittent short in the wiring. Have you tried powering the supplies up with nothing attached to the output terminals?
 
Well, I tried and tried just now and I could not get the power supplies to fail!

I did it at least 25 times on both power supplies and they came on every time. They were on my bench with no load and I waited different amounts of time between tries and it never failed. I don't get it. This is so frustrating.

I'm sure if I put them back in, they will start acting up. They did fail on my bench before though.

ARGH!
 
If they work Out-of-Circuit and fail In-Circuit. then I would suspect that you have a short and the pwr supply protection circuit is kicking in.
 
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