Power Supply Question

[Drools]

Is there a way to determine a ballpark figure for the current of a power supply when it is not printed anywhere? Would looking up the components data sheets and get the current rating of say the bridges give me close idea?

[irving2008]

Not really... designers will use many parts from the same device family depending on price/availability so it could easily be well overrated for the application because the price was right or they were using the same part elsewhere. What sort of power supply is it?

[Drools]

Here are some pictures of the power supply.

[Al_The_Man]

Generally the decider is the size of the Transformer, I would hazard a guess at 500va tops.
Looks to be a regulated linear supply.
Al.

[MyCattMaxx]

Sometimes ''Googling'' the numbers on the transformer will turn up ratings.

[irving2008]

Do you know the output voltages? That looks like it has a high voltage output ~24 - 30v and a low voltage ~5v at a guess. the thing in the TO3 can is a LM323K 5v regulator... on a good heatsink this was rated at 3A but given the age of this unit - 1984 - I'd guess at 1A max in reality. The transformer core, based on its dimensions, is good for ~200VA so assuming 30v output that would suggest 5 - 6A which ties in with the pair of 6800uF smoothing capacitors - they would give acceptable ripple on that sort of current...

[Drools]

the whole unit is out of an old wide (~20") carriage dot matrix printer, googling the number on the transformer gives me a spare part from a Printek forms printer. The output of the board is +5, +12, +42, -12.
http://www.jpcparts.com/02039.html
Would this power supply run 3 x 270oz/3amp steppers?
I have 2 complete units maybe using both of them would work?

[irving2008]

Originally Posted by Drools the whole unit is out of an old wide (~20") carriage dot matrix printer, googling the number on the transformer gives me a spare part from a Printek forms printer. The output of the board is +5, +12, +42, -12. http://www.jpcparts.com/02039.html Would this power supply run 3 x 270oz/3amp steppers? I have 2 complete units maybe using both of them would work?

Were you measuring that 42v off load? I'll guess it'll be 32-35v on-load as its unregulated (the other rails are regulated). Then I'd say you're still looking at 5 - 6A capability.

3 x 3A steppers needs 3 x 3 x 66% ~ 6A so I'd say go for it... the volts will drop a bit on peak load when all three stepper phases are on together but unless you are trying to drive them to their limits it'll work OK, Indeed unlike a switchmode supply that 30/40v rail should hold up quite well in the peak situations. Keep the other as a spare.

You can't really do any damage trying it out unless you short something (there being no short-circuit protection on the PSU) - the worst that will happen under load is the volts will drop too low and the transformer will get warmer. Fuse each motor/driver seperately with a 5A fuse and wire each driver directly back to the power supply (unless you have a 3 in 1 driver board with a single power connection, in which case a 10A fuse would be appropriate). then monitor power supply volts under opearting conditions to check its holding up OK.

[Drools]

Well the reason I ask is because I have been using one of them in my router.
http://www.cnczone.com/forums/showthread.php?t=86166
It has been working ok so far and I just wanted to make sure I was doing the correct thing by using it.

[Drools]

One more question, I'm only able to get a Accel of 10 and a Velocity of about 50 from my setup before the motors stall. I hate it when the system stalls in the middle of drilling holes for a PCB, swiss cheese...
Anyway using the avrstmd.com (1/10 microstepping) drivers, 1/2-10 lead screws, 270oz Tormach steppers and the above power supply. Should I expect more from the system?

[pfred2]

Maybe if I knew 10 or 50 of what I could hazard an opinion as to if you should expect more or not. I feel that maybe you should expect some more though. 270 oz/in. steppers should move a well built router over 100 IPM.

As far as your whole power supply dilemma goes why not simplify your setup somewhat similar to this?

http://www.avrstmd.com/power_supply.html

Apparently it was good enough for them. Maybe the extra nonsense you have going on with your present power supply is interfering with your purpose? Simplifying is a common method of problem solving. Or you could always learn to be happy with what you have.

If it were me I'd gut what I could use out of that supply you have and make what I needed.

[Drools]

Thank you for the help pfred2, I will try that.