SMPSU

T i m · 2021-05-13T15:31:15+00:00

Mate rang last night asking for something to be designed and 3Dprinted and this morning sent me a diagram with vernier calipermeasured dimensions for me to work from.I designed and started the printing but when I checked a bit later,expecting to see it all done (as usual), the printer was off and thehead not parked etc? ;-(Long short, it looks like the 20A x 12V 'open frame' SMPSU has goneweak?eg, After some faultfinding it seemed it could power most of theprinter, just not the heated bed and so I have that now running frommy old 13.5V 12A bench PSU that was last used powering my 70 cmspacket radio and TNC. The heated bed is pulling a good 11.5A (at 13.5V) from the linear PSUand the SMPSU is 'still' running the extruder, Arduino Mega, RAMPSdisplay / interface board and 5 stepper motors?The guy I was helping with the print job is the guy who originallybought the printer kit on the grounds I built it with him ... and thePSU was what was supplied in the kit. It's made in China of course andI'm guessing they may have been reasonably optimistic with it'sratings? That said, it's done a fair bit of work over a good few yearsso owes me nothing.When (if) this job actually finishes, I'll take the PSU out and have alook inside and a measure up then find a replacement that's about thesame size, as it fits under the printers bed and there isn't muchroom for anything taller or wider.I still have one of the game console PSUs that I bought after a 'headsup' from someone here, and a stripped out PC PSU but on that the 12Vis only 16A, and neither will fit under the printer and whilst Ithought it being there wasn't 'a good idea', it actually helps keepall the power cables short and the PSU within the constrains of theprinter itself without getting in the way.Maybe two PSU's would be better than one, (similar to how I'm runningit now as the bed heater role can be completely independent of any ofthe printer electronics as it's powered though a relay) especially ifthey might not like...

SMPSU

May 13, 2021 Last reply: 5 years ago 22 Replies

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T i m 5 years ago

<snip>

Good (simple) check / suggestion and nothing to lose. ;-)

I believe that pot is just a trimmer allowing you to tweak the voltage around the nominal 12V so I don't even have to mark it and would re-set it under load.

I'm not particularly hopeful it will do anything as even if it was 'noisy' and was allowing the voltage to fluctuate around it's entire range, I would have thought it should still have been able to drive the 5A load, even if also whilst fluctuating? I wonder though if that only depends on if the PSU still works at all with (worst case), no voltage on the wiper of the trimmer?

I'll let you know how I get on. ;-)

Cheers, T i m

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Peter Able 5 years ago

We all like the intellectual challenge of a difficult fault - and yet it often ends up being a simple mechanical contact failure !

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T i m 5 years ago

<snip>

On that then, I did give the pot a good working up and down and it didn't make any difference, but as it was simple enough to do, worth a try (so thanks).

I have the question open elsewhere and am being guided by folk who seem to to be fairly intimate with SMPSU's and I'm following a logical path.

I've since measured the voltage across the two large input caps (both showing 166V DC) and checked that there is little ripple. The next is a couple of small electrolytic caps and an opto coupler and then what may be a rectifier in a TOxxx package.

I think I'm understanding the working principles a bit better as well so that's a good thing. ;-)

I also have a couple of new / better PSU's on their way so I can get my 3D printer up and running and if I get this working I can either keep it as a spare, put it back into use on the printer heated bed (very basic role) or as a low voltage / high current adjustable bench PSU with one of the eBay PSU front ends. ;-)

Cheers, T i m

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