[Typefighter01]

Hey guys,

As part of the checks during the build of my CNC control box, I thought I should confirm the voltage of my 48v power supply. It is an S-350-48v with 7.3A output. When I first measured, it was in the 50's, something like 52.5v, so I adjusted the pot to read 48.5v (close as I could get it as I mounted it in a real inconvienient location). My question is, did I do the right thing in adjusting it closer to spec or do they normally ship high to account for voltage drop under load? I haven't got to the point of sending power to the drivers, so no harm done, but if you guys normally run your power supplies a little hot, please chime in and let me know why and any other tips on setting the voltage. The drivers are Wantai DQ542MA, breakout board is a generic DB25-1205, steppers are 57BYGH633.

Thanks...

[john-100]

a 48V switch mode power supply should have an output within 0.5% of the expected 48V
at full load expect it drop by 1.5%
thats when paying £100 for an original power supply from a trusted supplier

if its a £ 30 copy via e**y its any body guess what you will have

as the Wantai DQ542MA is designed to work with a 18 to 50V supply
not knowing the absolute voltage they can survive
I'd ensure the supply never goes over 50V

John

PS
Gecko Drive have had drives returned for repair thats been damaged by faulty 48V switch mode power supplies
even though the Gecko drives can survive 70V instead of the drives design maximum of 50V

[Al_The_Man]

Servo's and steppers do not really need a switching/regulated supply, the linear type, although not always regulated are much more rugged, and in the rare case of failure, are easily fixable.
Al.

[Typefighter01]

Thanks for the info guys. I will keep the PS at the 48.5v to ensure I don't screw the drivers and if there are any problems down the road I will revisit the output.

[Dylwad]

Adding a beefy capacitor to the Output might make the drives happier too if it's not a real solid switching supply. I believe gecko has some info about this.

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[jt4897]

I have had a few telecom grade 48v power supplies and I run an old linear one for my mill with Gecko G203V drives - I forget what it comes in at but easily over 52v. It makes that annoying 60hz hum but is rock solid. It's not uncommon for them to be over 48V since telecom batteries are charged at something like 2.30v per cell so that can be something like 55V for a bank. There are different ways to run them ("float" and "equalize") and because temperature is critical in charging better systems monitor and adjust that 2.30V per cell up or down. So basically it could be anything in that zone and may even change. Many telecom boards use a DC-DC converter in the power supply with an input range of something like 35V-70V. Where I live (Quebec) line voltage is allowed to vary by something like 6% (I forget) which means 112VAC-128AVC and still be acceptable (I think 109-130 is the limit). That's where that tight regulation comes in, the ps holds output and ignores the input. My linear ps won't.

So I recommend you add 10% to whatever your ps is putting out and check the acceptable input range for your drive (another poster said 18-50V)

Also, with a 30V ps I've blown a drive rated at 35v because of back EMF from the motor. Mariss from Gecko drive has a schematic for a "returned energy dump" - I built it and never blew the 35v drives ever again.