Blown VFD

K

Ken H>

Joined
Dec 31, 2011
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Since I've suggested the cheap Chinese VFDs for hobby use (not full time) I felt I should report todays event - it finally happened. I've been using a NEMA 1 enclosure Chinese VFD for the last 5 or 6 yrs (used several times/wk) and today it finally blew - with a BANG! I pulled apart enough to see metal dust got inside to short across PC board traces and blew a PCB trace and a 50 amp "insulated-gate bipolar transistor" (IGBT) in one leg of circuit. Perhaps I could repair the trace and replace the IGBT, but there's also a small SMD diode that's blown and I'm not sure what it is. I might try it one day - maybe a good winter project?

With the last couple of VFDs I've installed I took time to make a good filter around the air inlets, this one I've never been very careful about dust in this VFD. I've been planning to replace the "slapped on" filter with the type I used on last two VFDs, just never "got around to it" type of thing. It's been working for years so no rush? Well, today it happened. 5 (6?) yrs from a cheap VFD and poor filter installation isn't too bad. I ordered another today and should be here next week. I'll do a better job of inlet filters and maybe it will last 10 yrs? Those things are getting cheaper - I think this one is $60 shipped?

Later
 
I just installed a cheap vfd on my surface grinder. I was amazed when it actually worked. It's pretty impressive that they can last that long. If mine lasts 5 years I will consider it a success. Hardly seems worth repairing for that price...

I may have to look into a filter for mine, seems like a great idea.
 
Derek, I agree totally - in fact the VFD I ordered today was only $34 shipped from USA, and should be here July 29th. We'll see just how well it works. The first Chinese VFD I purchased was a Telco for..... don't remember but well over $100. It's been in use for over 7 yrs on my lathe. The 2nd was the one that blew today for $120 or so and in service for 5 or 6 yrs. The 3rd and 4th were purchased less than a yr ago for $70 or so each. Today ordered one for $34 shipped. Note the price drops?
 
How about insulating the board from shorts with spray insulation? You know something like a spray on lacquer made for it? I've used it with great success on motor windings. In a pinch I've used clear rubberizing spray paint. Like the flex seal crap.

This should protect it even if a small amount of metal dust did build up inside
 
"IF" you could get the full board covered really good that would help. There are 3 different boards inside and they're sorta on the hard to get to for really good full coverage. It could be done, but you'd have to take VFD completely apart to get good coverage.

I think using a good filter on the inlets, and perhaps blowing inside out pretty good each yr or so would work pretty good. Remember, these VFDs cost around $70 shipped these days so it's not like a major expense for one to break. Keep a spare on hand if desired.
 
That may be true but generally any components that will get hot enough to have problems with a thin layer of conformal coating or insulation will likely already have a heatsink or large copper pad or trace it is bonded to and the insulation will unlikely effect it
Cushing H. said:
Heat is one of the enemies of circuit boards. If you insulate this way you might create too much heat build up and cause it to burn out.
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drew1972 said:
Where are you finding vfd's so cheap
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The one I just ordered for $34 shipped is this one: https://www.ebay.com/itm/293157787550?
I'm not sure I'd recommend ordering until we find if I actually get it or not. There are plenty listed for $71 shipped from USA: https://www.ebay.com/itm/302145135626? This one shows the same model number I have and they're really easy to setup.

Here's a 2 hp for $55 shipped from USA: https://www.ebay.com/itm/133096467035 It's not the same as the units I have but should be ok.
 
Depends on the quality and design of the board. Heat can affect the traces too (delams and separations at vias). As the quote goes: “ do you feel lucky?”
Backyard said:
That may be true but generally any components that will get hot enough to have problems with a thin layer of conformal coating or insulation will likely already have a heatsink or large copper pad or trace it is bonded to and the insulation will unlikely effect it
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Backyard said:
How about insulating the board from shorts with spray insulation? You know something like a spray on lacquer made for it? I've used it with great success on motor windings. In a pinch I've used clear rubberizing spray paint. Like the flex seal crap.

This should protect it even if a small amount of metal dust did build up inside
Click to expand...

I've thought about coating the boards in epoxy or silicone before. I know certain electronic components are sometimes cast or coated in resin to protect them. I doubt that a thin layer of epoxy would cause any heat issues. A low to mid temp hot glue might even be an option.
 
Oh, I do agree a good coating of the boards would work pretty good. The problem is getting the boards and components 100% covered. To get a good coverage the VFD would have to be taken apart, removing components from the heatsink to get to back side of board. Can it be done? Yes, I do think so and I do think it would work. Do I think it's worth while at the low cost point of these 2hp Chinese VFDs? Not really. Remember, I got 5 or 6 yrs from the unit without good filters over the inlets. I suspect a good filter over inlets the way I now have on newer VFDs, then perhaps take time to blow out inside with air pressure might extend the life of VFD by a few more years.

Again, with all this said I think the KABC drives are a better choice for a full time 40+ hrs/wk operation. For a hobby operation that makes 30 or so knives/yr (I'll make more like 10/yr)..... compare $50 vs $350 cost. I think I'll go with the lower cost option.
 
Drew Riley said:
I've thought about coating the boards in epoxy or silicone before. I know certain electronic components are sometimes cast or coated in resin to protect them. I doubt that a thin layer of epoxy would cause any heat issues. A low to mid temp hot glue might even be an option.
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Oh ... when you said "spray insulation" the thing in my head is that spray on thermal insulation (expanding foam - like "Great Stuff") :(. If you are able to identify something that sprays on as a thin layer - then certainly agreed, I doubt it will affect heat issues much.
 
3M 1601-C is what you want. I've used both the red and clear version. Red is great to see coverage but clear is better for circuit boards to still be able to see components and traces
 
Backyard said:
How about insulating the board from shorts with spray insulation? You know something like a spray on lacquer made for it? I've used it with great success on motor windings. In a pinch I've used clear rubberizing spray paint. Like the flex seal crap.

This should protect it even if a small amount of metal dust did build up inside
Click to expand...

A lot of electronics come that way now-a-day. It’s called conformal coating. I know my cheep 10hp VFD is coated. It looks like a thick lacker or epoxy that’s over everything. My current thought is to use a VFD that’s at least rated for double what your going to drive. I find the cost of the 10hp vfds to not be so bad and that’s what I use on my mill and lathe. Mill is 1hp and lathe is 7.5hp. I have ran my 10hp press off of it but I did not like it.
 
Ken H> said:
Yep, that 3M 1601-C stuff is pretty good, but costs more (or almost as much) than VFD does at $42/12 oz spray can. https://www.amazon.com/dp/B074T4D93R

I agree with using over rated VFDs, I use 3 hp for my 2 hp motor and the 1.5 hp for 3/4 and 1 hp motors.
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At my work it’s standard to install drives that are 25% over required hp. I think it’s a standard in the industry as well.
 
I've used cheap spray lacquer from home Depot too. Not for anything that cost a lot but it seems to work just as well. Only issue I've seen was with the solvenated type, sometimes the printing on the board would smear or run. Not the components IDs but secondary printings and ink. If you did a light misting first and let it dry it didn't have that problem. If it was mine that is what I would do

I used to purchase a version that was much cheaper than the 3M stuff from graingers. Seems to have been discontinued though. Not sure if they cary an alternative. Also McMaster Carr has some P/N 7437K21 for $7.80
 
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I agree. I heard for the cheap Chinese ones it was double the rating. I would say do at least 50% over for them
JTknives said:
At my work it’s standard to install drives that are 25% over required hp. I think it’s a standard in the industry as well.
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