Stepper motor drivers LEDs light up only briefly

I just got my v 1.2 stepper motor drivers together, and figured out the secret trick for turning on the power supply (connect green wire with any black wire). However, when I attach the drivers for testing, all the LEDs light up for a moment then go out again. Repeatably. The power supply is an old Mitac X-145C which I haven't tried for any other electronics projects yet (pulled it out of my old server a few weeks ago). Should I be looking for oddities in the power supply, or is it time to debug the driver board (sigh)?

Thanks in advance,
-Lars

Hi Lars.
If there is a short circuit, many power supplies will turn themselves off or trigger internal protection circuits, cutting the power.

Try just one board at a time, see if it does it with all your boards:
Try with two, then three - it might indicate an overload condition

If you've got a camera with a good 'macro' (close-up) lens, take a photo of both sides of each board. Then inspect the photos. The enlarging effect of looking at the hi-res photo is much better than inspection under a magnifying glass, and the lighting is better. Look for any 'shorts' between pins where the solder has bridged.

if you can, try with another power supply - depending on how many old PCs you have lying around :-)



Other tips for stepper boards:
turn all your potentiometers to minimum (counter-clockwise)
Add big heatsinks to the driver chips (they can get very hot)

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Reprapping blog and other rants: [renoirsrants.blogspot.com]
My Reprap: [sites.google.com]

Thank you. I do happen to have a good macro camera, so I'll have to try that, and do some testing of what's connected to what with a multimeter. I didn't know the power supply could shut itself off like that, but it makes sense and is probably a good thing! I already have fairly large heatsinks, but gotta try the potentiometers.

-Lars

:-)
My PSU - if you short any voltage to ground, it will turn itself and the PSU fan off, and will not tun on again until you've unplugged it from the mains.

other PSU's have slightly different protection.

The pots limit the current through the steppers - I think if the steppers are not plugged in, they have no effect - but it's a good idea to stop things getting hot.

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Reprapping blog and other rants: [renoirsrants.blogspot.com]
My Reprap: [sites.google.com]

You may need dummy loads on the 5V and / or 3.3V rails to keep the PSU happy. E.g. 10 ohm 5W, or a car sidelight bulb.

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[www.hydraraptor.blogspot.com]

Tried with some 10ohm 7W resistors, both on 3.3V and 5V and on 3.3V and 12V (with the driver out of the loop). PSU still shuts down. Is very unhappy PSU, and I have had no luck finding a data sheet for it. I have measured many parts of the board and found not signs of a short. Stuck again

does it happen with all the boards plugged in? or just one?

if it happens with any one board plugged in, it sounds like the PSU. you could try not using any boards at all, and instead add an old PC case fan or car bulb as a dummy load to see if it triggers the same behaviour. if it happens with something else too, it's probably a problem with the PSU.

also, if you've photographed the boards, you could post the photos. Sometimes a fresh pair of eyes can see something you've missed. (don't be embarrassed about the soldering - it can't be worse than mine :-) )

Depending on your resources, see if you can borrow/find another PSU to compare.

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Reprapping blog and other rants: [renoirsrants.blogspot.com]
My Reprap: [sites.google.com]

It happens with boths boards simultaneously plugged in, as well as with either of them alone. And with just a car bulb attached (12V 21/5W). In all cases with 10 Ohm 7W resistors on the 5 and 3.3 V lines. By now, I'll either have to buy a new power supply or open up this one and try to figure out what to cut/jumper to override the low load shutdown.

There is also something up with at least one of the boards. I fixed one bad connection, and now one of them lights up both the bi-color LEDs while the other lights up only one. I guess since I have no power to work with, I might as well take proper pictures of them tonight and see if there's anything to see that way.

-Lars

I don't know if it helps but I plugged an old hard drive in, all works fine then!

Plug the HD in with everything else.

Does it work?

If so, leave plugged in for now.

:-)

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Reprapping blog and other rants: [renoirsrants.blogspot.com]
My Reprap: [sites.google.com]

Philwaud2 Wrote:
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> I don't know if it helps but I plugged an old hard
> drive in, all works fine then!

That sounds like your power supply needs a minimum load on it.
The disk will do, for now. But you might want to find a cheaper load resistor, esp. if you have data on the disk, or other use for it.
(One low-cost/easy-to-get load for the 12V rail is an automobile brake-light bulb.
That might also load the +5 enough, but I haven't tried that.) A power resistor on the +5 rail is probably the best long-term solution. Ballpark 10 ohms, 5+ Watts.

HTH,

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Larry Pfeffer,

My blog about building repstrap Cerberus:
[repstrap-cerberus.blogspot.com]

I like the bulb idea, it's one of the things I was going to look at. The hard drive method was just a simple quick solution!

So I swapped my power supply out with one my brother had lying around, and the new one works! Even better, it works without the 3.3V and 5V load resistors on it. One of my boards has a short, though, the other is fine. On a board that hasn't been connected to the Arduino, can one expect anything about how the bicolor LEDs will light up? The good board has only one of the lighting up. I'll connect it to the Arduino soon enough, but wanted to hear if that's a good/bad indicator or just random.

Those load resistors got quite hot, though. Ow

I have macro shots of the bad board (no cookie!) here:

Backside of board:
[farm4.static.flickr.com]
Front of board with heatsink removed:
[farm4.static.flickr.com]
Side view of board:
[farm4.static.flickr.com]

-Lars

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[repstrapdk.blogspot.com]

Counting the two bicolour leds as four discrete lights, one or two should light up at any given time. Try manually strobing the step pin, if all is well the lights will change. As for the dodgy board, is there a dead short across the board? Any change if you take out the DIL chip? Instead of load resistors, I use a spare 12v cabinet light I had, illuminates the build area nicely at the same time.