ebay power supply

[HankMcSpank]

Thanks for the feedback - have you measured how much the 'out of regulation' 42.7V moves when your stepper motors are going at full tilt?

[Tom]

It doesn't flinch at maximum speed. I can't measure it under cutting load at the moment because there's some dust-sensitive stuff in the room, but jogging at max speed I can't even measure 0.1V variation on the output pins of the supply. Steppers under load should only consume marginally more power i'd have thought.

I'm running with the 3Nm steppers that everyone sells, along with the 4.2A drivers.

One test I can't do is a hardware e-stop, to see what voltage gets pushed back through the drivers with a sudden stop. I'm still only wired into software e-stop circuit (not good), so I can only decelerate at the max values EMC2 allows. Still, with 7V of headroom to the 50V max which the drivers can cope with, hopefully no problems...

[John S]

Tom,
You say 42.7 volts but the spec says 50v ?
Is this with it turned down as far as it will go ?

[irving2008]

John,

The PSU is variable 50 - 56v but with no control input it runs in a 'unregulated' state at a fixed 42.8v +/-0.5v. it appears this isnt unregulated as such, just outside the voltages for which the very low noise/ripple spec is guaranteed (these PSU were originally intended for telecoms phone lines so are very low noise).

[Tom]

Hi John,

Yeah, basically. Plug it in and it'll whirr away at 42.7V happily.

I think they were originally intended to be used by some sensitive rack-mounted equipment, which needed really close voltage control somewhere between 50V and 56V. The exact voltage within the 50V to 56v range can be adjusted with a control voltage to pin28. I guess some closed-loop control (in a different box) would increase the control voltage slightly when the unit was under peak load, to keep the voltage seen by the sensitive equipment stable.

We're all using them in "cheap whacking great power supply" mode, without any need for the regulation voltage on pin 28. I've just bought 2 more (in case they run out! one for the lathe and one spare).

[ecat]

Just bought two :)
I may be away next week but I'll have the cover off them as soon as I can :)

[GeorgeD]

Was thinking of going for one of these? thats not too bad considering its amperage and some 15amp jobs are getting knocked out at around £35 to £40
http://cgi.ebay.co.uk/21-30volt-powe...item23089231e7

[John S]

Why do you need all those amps at a puny voltage ?

[GeorgeD]

WellI'monly going to un my drivers at 24volts so thats adequate and the amps are there if and when its needed.

[irving2008]

It will never be needed... you wont find a driver capable of more than 4A tops thats limited to use at 24V so the most you'll ever need is 3 * 4 *.66 = 8A unless you plan a 4th or 5th axis... but by then having only 24V will be a serious limitation anyway...