Flaming Mastech PSU?

So I figured I would share this story with you guys.

For starters, the reason I have not been as active as I used to be is because I have been working on school pretty intently, working at my job pretty intently, and, in my spare time, either hanging out with my girlfriend or working on my 40W 808nm eventually-to-be-handheld laser.

And, who woulda thunk, it was when working on this laser that such a disastrous event occurred!

Up until now, I have been heavily draining three IMR18650s in series as my power supply for the CC driver (the driver can output up to 50A! Whew!). However, while cleaning my workspace (at the request of the lady), I found I had a modded ATX PSU under my bench, complete with an on/off switch, a capacitor draining high-power resistor on the inside, and two banana plugs for the 12V and 0V rails. I figured that, instead of draining my batteries over and over (probably killing their lifespan), I could just hook up my modded ATX PSU to the Vin on my driver, solving any battery life issues. So I did some soldering and got it hooked up. Note that, at this point in the story, the ATX PSU is off.

Then, after some simple rewiring so everything looked nice and tidy (or at least as tidy as it could get!), I attached my Mastech PSU to the other input, set at 2.5V (I am - err, was - using it as a 2.5V reference because I haven't ordered the correct voltage regulator yet - still in the testing mode of the driver). Then, once I assured that everything was hooked up properly, my driver's switch in the off position, the ATX PSU's switch in the off position, and my Mastech in the off position, I flipped on my Mastech PSU first, as has been my protocol whenever I worked on this driver (with batteries, of course).

All of a sudden, I see smoke coming out of the Mastech (thick, black smoke) and I peak inside the gratings and I see a huge flame inside!

Holy hell, that was a shock.

Anyway, I quickly blew out the flame (from the outside through the grating), turned off the Mastech PSU, unplug it, open the windows and start ventilating the area (if the smoke alarm went off because of something in my room, the rooming people would come and confiscate all of my soldering equipment, etc.).

Fortunately, the fire alarm didn't go off and the CC driver and ATX PSU both seem to be intact.

Something interesting to note: my ATX PSU was not even on when it burst into flames. The only thing different between this set-up and my previous set-up is that my Mastech's ground was connected to the ATX 0V rail - no other circuits had been made yet because the other two switches were off.

Anyway, I opened up the Mastech and, obviously, I see large scorch marks on the top of the metal cover, the bottom of the main board is charred (but maybe still functional?) and there is a wire between the main board and something else that literally broke connection - i.e. the connection fried. My guess is that is the problem. It may also be related to the 2N3055 on the back though.

Anyway, I figured I would share this with you guys, in hopes that you guys get a nice laugh. It wasn't a fun experience for me, but it sure as hell is worth a story!

Remember that unless you unplug the PSU or turn off the physical switch on the back of the ATX PSU, the ATX PSU still supplies power for its low-voltage outputs. I think only the 12V outputs are off until the power-on pin is shorted to ground on the power connector.

The fire might have been caused by a voltage differential between some of the other points in the system.

Something you might also check is to see if anything fell into your Mastech. It just seems odd that so much current could've caused an internal fire from just the output of the PSU. Many of those power supplies will cut off power should that happen.

Anyway, good that nothing worse happened.

I did turn off the physical switch on the back of the ATX. I also installed a bleed resistor in the inside of the ATX PSU to prevent cap charge-up. Anyway I was using the 12V output from the ATX.

Another thing - there wouldn't have been any voltage differential besides between the two grounds on the Mastech and the ATX... why would there be? Nothing else was connected to anything else.

Another point - nothing fell into the Mastech - I can assure you of that. I've already taken the thing apart and it seems that just single wire fried. It may have been some insulation burning off due to a short in the Mastech, but the flame was at least 3.5 inches high.

I require photographs

I don't think you're supposed to put switch mode power supplies in series with eachother, due to grounding differences. Usually when this happens they turn off to protect themselves, but in this case it seems that may have failed.

Something to do with grounding I bet caused this. That's the only thing I can think of that would cause it.

Also if you need a voltage reference, use a http://www.fairchildsemi.com/ds/TL/TL431A.pdf for it.

As Cyp says...

Photos, or it didn't happen.

Smash it to pieces with an axe. I think that's what another member did with his 1W Cree 6 445

Smash it to pieces with an axe. I think that's what another member did with his 1W Cree 6 445

I will get pics when I get back home. In the worst state at the moment - Ohio -.-

Anyway, they weren't actually in series. If anything, they would have been in parallel. Anyway, I already ordered a nice voltage reference IC, just didn't have it on hand at the moment.

i killed my Lab power supply



Marx generator discharged through me (ouch) through ground then back up into the power supply. The generator was operating at 54kV at the time.

It ruined the voltage feedback and the voltmeter was showing 54VDC on the front meter at all times!

Well okay, we can all know that 54kV is obviously going to kill a PSU =p

Must be the time of year when PSUs die because mine crapped out on me last week. I have no idea how or why, but when it's on it doesn't read nor send current anymore regardless of the settings.

Wolfman I'm glad your fire wasn't anything worse, like an explosion. Thanks for sharing your story :beer:

Switchmode power supplies shouldn't be put in series unless you know they're ground isolated (- output isn't grounded), and they should not be paralleled at all. They rely on feedback from the secondary side to keep their output voltage consistent, so if one PSU is trying to adjust for the other PSU's slight voltage difference, it'll cause issues.

Well, now I know! XD