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View Full Version : eBay: A good quality but cheap 48v 30A+ power supply ideal for CNC



Wobbin
05-07-2014, 10:45 PM
Just thought I'd share this with you guys and girls in case anybody is in the market for a power supply to run their CNC mill conversion ?

http://www.ebay.co.uk/itm/181443785558 - this is an Eltek 1800si psu, originally designed for rack mounting but easy to connect to and there is data available on t'interweb showing which pins are which. Note these are used but tested with some load (not full load) originally I believe that these were used to charge backup battery systems on communications devices.

The output voltage is adjustable from the front panel. Internal construction is exceptionally good with quality electrolytic capacitors (Elna / Nichicon / Rubycon) - none of the junk that seems so prevalent in the Chinese psu's.

Please note that I am not the seller of these, but I've just bought one and tested it and it is absolutely fine. For the record, I have no connection whatsoever to the seller, other than being a happy customer. There are still two of these left up for grabs at 35 each (but worth a best offer :encouragement:)

Hope this helps someone.

Cheers
Robin

Lee Roberts
05-07-2014, 11:55 PM
Thanks for sharing !

Jonathan
06-07-2014, 10:52 PM
Bought one, thank you :)

Do you want to swap yours for a suitable linear PSU (toroidal transformer wired to capacitors etc)? Seems a waste to me to use such a nice PSU for a few stepper motors! If you're interested let me know - looks like we're not too far from each other, so shouldn't have to post.

JAZZCNC
07-07-2014, 12:11 AM
Do you want to swap yours for a suitable linear PSU (toroidal transformer wired to capacitors etc)? Seems a waste to me to use such a nice PSU for a few stepper motors! If you're interested let me know - looks like we're not too far from each other, so shouldn't have to post.

I would take Jonathan up on that offer because toroidal setup will be much better for use with steppers.!

Wobbin
07-07-2014, 06:57 AM
Thanks Jonathan but I'll pass thanks. I agree that the Eltek is overkill for the job in hand but it will have loads of headroom and probably still be as efficient as a linear psu.

I am intrigued though by your comment Jazz - why would you feel that a linear psu would suit steppers more ?

Cheers
Robin

JAZZCNC
07-07-2014, 02:50 PM
I am intrigued though by your comment Jazz - why would you feel that a linear psu would suit steppers more ?

Because the capacitors in the toroidal system handle back EMF better and chances are this supply as protection circuitry built into it to shut down if it detects back EMF which isn't what you want as steppers produce electricty when de-accelerating.!

Wobbin
07-07-2014, 05:15 PM
Good point, I hadn't considered a regen situation.... we'll see what happens. I've got hold of a Axminster (Sieg) X2 which has ballscrews on the X & Y axes already, plus a set of drives and motors, just setting about sorting out the motor mounts and the Z axis bits. Just need 28 hours in the day at the moment....

Cheers
Robin

Jonathan
07-07-2014, 08:44 PM
That won't be an issue with these power supplies - if it was then it's quite easily mitigated anyway.


I've got hold of a Axminster (Sieg) X2 which has ballscrews on the X & Y axes already, plus a set of drives and motors

This one (http://www.ebay.co.uk/itm/Axminster-X2-Hobby-Mini-Milling-Machine-Model-Engineering-/201116186613?pt=LH_DefaultDomain_3&hash=item2ed37577f5) I presume? The motors look like the common 3Nm ones, in which case they would run faster on 75V, but you're limited to 48V by the m542 drivers so that's not an option without replacing the drivers and power supply. Should you decide that that's worthwhile, my offer still stands. Edit: Also, take the handles of when you use it as CNC, otherwise their inertia will significantly limit the acceleration you can get.

Do you know if the output of the power supply you have is isolated? If not could you do me a favour and check it? Given the intended application, I suspect they are, but would like to be sure...The manual doesn't say.

Wobbin
07-07-2014, 10:07 PM
Yup, that's the one. Re the psu, when you say isolated can you be more specific ? It's isolated between AC in and DC out for sure as it's a switched mode design with meaty high freq. transformers. Does that help ?

Cheers
Robin

Jonathan
07-07-2014, 11:02 PM
Sorry, that wasn't very clear. I meant, is there any electrical connection between either of the DC output terminals and the AC input or earth?

Wobbin
08-07-2014, 05:37 PM
Hi Jonathan,

Fluke says no... > 60 Meg all ways.

Cheers
Robin

Jonathan
09-07-2014, 09:01 PM
That's promising ... I bought a second one. Thank you for checking.