Expensive reminder to pay attention to that “little voice...”

[luxige]

(Posted in General Discussions since it relates mainly to safety).

I’ve been wiring and setting up a VFD for my new milling machine. (Lots more work than I anticipated).
I had done a little bench testing to dial in some of the settings. But it wasn’t until yesterday that I had the final wiring done from breaker box to motor, so I put the motor on a chair and rolled it over to the eventual site of the mill. The mill will be disassembled for a while, so I wasn’t going to fully check out the system under load, just a quick shakedown. Then disconnect the motor and shelve it again.
So I opened up the little electrical box on the motor that houses the terminal block and connected the power cable. Then because I am extremely clever, I recognized that I could save a ton of time and trouble by not closing up the little electrical box until after I ran my quick check and disconnected the cable. The little voice was there but I could barely hear it because I couldn’t be bothered to pay attention. What could go wrong?
Answer: a screwdriver could fall out of my shop apron as I hit the On switch and short across the motor leads. (Actually, many other things could have gone wrong, and I’m painfully aware that I was lucky. A VFD is expensive, but much cheaper than an ambulance ride or a funeral).
Anyway, loud pop, quick puff of smoke, and a few hundred bucks evaporated. (Unless the motor is also fried...)

So listen to the little voice, it’s on your side. And, what looks like a shortcut, isn’t.

I sent an email to Wolf Automation to see if they think it might be repairable, but I would think it’s a goner. If I opened it up to try to diagnose the damage, which parts would be the likely suspects?

 

[francist]

Oh that little inner voice again! If he only had a big stick to hit us over the head when we don’t listen to him we’d be much better off!

Glad you’re ok and it was only the drive that got fried.

-frank

 

[GL]

Oh yes, the kiss of death (sorta) - this is the stick:

What could possibly go wrong?
All you have to do is...
Hey y'all, watch this...

Assume you have missed something when these are uttered, or thought.

Glad you're ok too.

 

[RJSakowski]

Most likely, you fried the output transistor(s) Most driver transistors a re either MOSFET or IGBT transistors. Either of these transistors use high impedance circuits for driving them so the chances of a short on the output propagating deeper into the circuitry is slight. There may be a short circuit protection circuit as well. In any case, it may be a cheap fix if you are up to doing it yourself.

I have had a number of instances where the output transistors failed , in one case due to transient voltages genreated while under load and in anothere due to reversing the polarity of a high current charger. Both fixes were under $10 each.

 

[Mitch Alsup]

What could go wrong?
<snip>
Anyway, loud pop, quick puff of smoke, and a few hundred bucks evaporated.

Never let out the magic smoke.....

 

[luxige]

Most likely, you fried the output transistor(s) Most driver transistors a re either MOSFET or IGBT transistors. Either of these transistors use high impedance circuits for driving them so the chances of a short on the output propagating deeper into the circuitry is slight. There may be a short circuit protection circuit as well. In any case, it may be a cheap fix if you are up to doing it yourself.

I have had a number of instances where the output transistors failed , in one case due to transient voltages genreated while under load and in anothere due to reversing the polarity of a huigh current charger. Both fixes were under $10 each.

Thanks RJ.
I’m willing to give a repair a try, but I don’t know much about circuitry. I have a cheapo multimeter that I put on the caps and they seem ok, at least they showed conductivity and a resistance change over a few seconds.

The manual references IGBTs. However, I can’t find anything that I’d recognize as a transistor. There is a component that looks like a big transistor, but it has four leads. The position label on the circuit board is “DM2” and it is screwed to the heat sink. It’s next to two huge resistors.
There is another component that looks like a monster IC, also screwed to the sink, with no label on the circuit board, 16 pins on one side and 8 pins on the other side.
There are two white ceramic components, also unlabeled.
There is one component that is obviously bad, unless it survived the hole I blew through it. It looks like an IC and has 16 pins, or rather had them because most of the pins on one side are cooked clean off. Don’t know if the pcb traces are ok. The label for this dead thing is “CT1” while all the ICs are labeled “IC4” (for example). Nothing else is labeled “CT.”

Here are some pictures:

 

[matthewsx]

Oh yes, the kiss of death (sorta) - this is the stick:

What could possibly go wrong?
All you have to do is...
Hey y'all, watch this...

Assume you have missed something when these are uttered, or thought.

Glad you're ok too.

You forgot "hold my beer"

John

 

[luxige]

Ha!

 

[matthewsx]

Thanks RJ.
I’m willing to give a repair a try, but I don’t know much about circuitry. I have a cheapo multimeter that I put on the caps and they seem ok, at least they showed conductivity and a resistance change over a few seconds.

The manual references IGBTs. However, I can’t find anything that I’d recognize as a transistor. There is a component that looks like a big transistor, but it has four leads. The position label on the circuit board is “DM2” and it is screwed to the heat sink. It’s next to two huge resistors.
There is another component that looks like a monster IC, also screwed to the sink, with no label on the circuit board, 16 pins on one side and 8 pins on the other side.
There are two white ceramic components, also unlabeled.
There is one component that is obviously bad, unless it survived the hole I blew through it. It looks like an IC and has 16 pins, or rather had them because most of the pins on one side are cooked clean off. Don’t know if the pcb traces are ok. The label for this dead thing is “CT1” while all the ICs are labeled “IC4” (for example). Nothing else is labeled “CT.”

Here are some pictures:

That's not pretty. Doesn't even look like you can read the component label to get a replacement, and yes the traces, and anything else that got damaged downstream but isn't obvious....

New board at least probably.

John

 

[RJSakowski]

Thanks RJ.
I’m willing to give a repair a try, but I don’t know much about circuitry. I have a cheapo multimeter that I put on the caps and they seem ok, at least they showed conductivity and a resistance change over a few seconds.

The manual references IGBTs. However, I can’t find anything that I’d recognize as a transistor. There is a component that looks like a big transistor, but it has four leads. The position label on the circuit board is “DM2” and it is screwed to the heat sink. It’s next to two huge resistors.
There is another component that looks like a monster IC, also screwed to the sink, with no label on the circuit board, 16 pins on one side and 8 pins on the other side.
There are two white ceramic components, also unlabeled.
There is one component that is obviously bad, unless it survived the hole I blew through it. It looks like an IC and has 16 pins, or rather had them because most of the pins on one side are cooked clean off. Don’t know if the pcb traces are ok. The label for this dead thing is “CT1” while all the ICs are labeled “IC4” (for example). Nothing else is labeled “CT.”

Here are some pictures:

Power transistors usually have some sort of heat sink attached. Looking at your photos, it looks like the damage is more extensive and a board replacement is in order. Sorry!