Need Help!- Power Supply Repair/Replacement

[2Bits]

Not sure what I should do. Have the typical HobbyCNC linear power supply that was built with the 'alternative' transformer that fried the secondary. I have very low confidence now in the rectifier and caps. Last spring I was checking the voltages and I had 24vac coming off the transformer, but only ended up with 27v rectified, expected to see roughly 32v. Not sure why that was, or maybe the transformer under load was going back then.

The Triad transformer to replace it is about $60.00 plus shipping, about the same cost as a Meanwell 350 series switching supply. Should I go that route and if so, which one? Not sure which voltage module to pick. They (Keling for example) has 24, 36 and 48v supplies. The 36v I was looking at has 2 versions, 8.8 and 9.7 amp versions, would this be the right one? Are these adjustable to crank them down to 32v dc?

Or should I just replace my transformer, but if I did, I'm thinking I should switch to a Toroidal type, but again, not sure which one.

Would like some thoughts on this.

Mark

[Al_The_Man]

Originally Posted by 2Bits Or should I just replace my transformer, but if I did, I'm thinking I should switch to a Toroidal type, but again, not sure which one. Would like some thoughts on this. Mark

Contact Antek see what he has to offer, he sells on ebay all the time, even if you get something like this ebay 250720244597 you could easily modify for the correct voltage.
The secret to the burn out problem is to fuse the primary correctly, if this is done using the right size fuse you should never burn a transformer out.
Al.

[2Bits]

Another question would be why after 12+ months did the transformer even fry?

The machine has been working beautifully. Is a stepper starting to draw more current because of wear etc? If that were the case would have expected driver chip to fry before transformer. My gut thinks, it's just a cheap transformer that couldn't hack it anymore.

[eldata]

Originally Posted by 2Bits They (Keling for example) has 24, 36 and 48v supplies. The 36v I was looking at has 2 versions, 8.8 and 9.7 amp versions, would this be the right one? Are these adjustable to crank them down to 32v dc? Mark

The 36V 9.7A Keling SPS I have here is adjustable between 29.9V and 43.4V via an easily accessible trimmer pot. It's ideal for servo or stepper use where drive electronics or motors are limited to voltages in that range. You can also get a suitable SPS direct from China (via Ebay) here;

36V DC 9.7A 350W Regulated Switching Power Supply New - eBay (item 160459989405 end time Nov-21-10 03:45:13 PST)

It won't look exactly like the photo and the voltage trimmer pot works in "reverse"....Clockwise rotation decreases the voltage and vice versa. The last one I bougth was shipped (free shipping) in 10 days. Works fine.

[2Bits]

Thanks, not sure how, but I was lucky enough to find replacement parts locally today, not many local stores left these days. The rectifier had taken a dump as well. I replaced both and added a heat sink to the rectifier to help dump some heat from it and with the new parts, I now have 35 volts going to the board where I only had 27v before. So something was amiss with these. Seems to be working well so far.

It would have been cheaper to have gotten the regulated supply, but rather than have wait 5 days or more for it, I have it up and running. I hope before it fails again, or when it does, I will be upgrading my steppers and moving to Gecko drivers. I'm impressed with what I've seen and read about these. The HobbyCNC Pro board has done well, but I'd like to move to the next level.

[Al_The_Man]

If the rectifier shorted and took the transformer out, it was most likely that either the primary was not fused or fused with incorrect rating.
It would be worth checking anyway.
Al.

[allrounder]

Hi, 2bits. You DEFINITELY need a primary fuse, a THERMAL fuse attached to the transformer would be better still. Make sure your secondary connections are good, preferably soldered, as at anything near to 9 amps, bad connections will get hot and add to the heat in the transformer. Any filter electrolytics should be checked and if you can get someone with an Oscilloscope to see what ripple is coming out of your supply - you CAN use an AC multimeter with a polyester capacitor in series to check ripple. Say 0.47uF cap - not critical in value, but definitely not an electrolytic - that way you can see if your filter caps are OK and if they are big enough to supply steady DC to your power transistors or chips. Chips won't work properly with AC ripple superimposed on the DC supply. They will get hot, may fail and won't control correctly. If you originally had a SMPS power supply, they operate at a much higher frequency than your 60 cycle mains and would have filter caps built in. With just a tranny-bridge rectifier supply your ripple will be 60 or 120 cycles per second and larger filter caps would be needed.