Thread: VFD for 3 Phase Mini 30

Stupidly I didn't recheck resistances. Emailed Dave and was pretty up front with him about what happened. Just have to see what happens. If Dave won't warranty it, could I get fixed somewhere here you think.
Graham

Originally Posted by gorriss

If Dave won't warranty it, could I get fixed somewhere here you think.

That would depend on what Dave has put in there, I have no idea. It could be something pretty simple, I think it can be done with a couple of caps and a couple of diodes........but I have no idea how complex they can get. Also it would depend if he has removed part numbers or encapsulate pcd boards etc to make your life hard. And of course its only a guess that its his mod that has failed. If its the VSD you might be able to find someone to fix it.

Stuart

No warranty so I opened it up after asking Dave. Sent him a pic but to me it looks like its just blown a couple of tracks on the circuit board. I can't see any damaged components, but I guess one might not be able to tell just by looking at it, but I will wait to see what Dave says tonight. I might be able to repair the tracks and be back in business.

Interestingly I mentioned to Dave thet the VFD blew up as soon as I powered it up. I didn't get to try running the motor. He reckons the damage was done before I tried to fix the motor - on the previous test, and then it blew next time I turned it on. To quote his reply when I asked if it was normal to blow up when I hadn't pressed run...

"YES it is normal as its likely the damage was done before the last test and shorted an output transistor"

Anyway, I have a little hope that I can repair it, otherwise he will replace it at cost for me.

Graham

Missed this becuase I was using my tablet.

Got any pictures of the damage?(besides I've not seen inside one of these)

Stuart

Hi Stuart

Sorry for the late reply. Been working and got family visiting.

I only have one picture of the damaged track section which I have attached. (It looks quite small after I uploaded it so I hope you can see it?) Soldered up the tracks that were damaged and plugged it all back in now. No more "bangs" but still getting the LV error when I start it up. Incidentally, Dave said there is no problem starting it up without the load wires attached, and I could even run it like that without damage.

Looks like I am up for a new unit, so if I get one I will show you the innards of the old one at some later point. Probably need a new motor as well, but I just remembered an old friend who does rewinds. I will talk to him to see if it is feasible for me to fix the faulty wiring on the old motor. The worry is that if the windings themselves have any problems I could blow another VFD! I reckon the 4 hour drive when I bought the machine must have caused the old internal motor wires to break up the brittle insulation.damaged track.jpg

Cheers
Graham

Hi Graham,
The picture is fine once opened in another window.
As I understand it a megger test will tell you if the insulation in the windings is any good. The cracked insulation you've seen doesnt go very far into the motor and would be easly replaced by someone with the right gear.
Once you replace one motor (and this is the tricky one correct?) it might just be easier to replace both and go with cheaper VSDs?

Can't tell from the picture if its Daves or a factory board(I'd guess factory). I'd say this cap is toast also, but replacing the parts that look blown likely wont get you anywhere... how would you know what value C240 was? and that may just be the start of it. Still you never know your luck.
Thing is sending it to someone that knows what they are doing would likely cost more than a new one.

Stuart

Hi Stuart

Yes I thought about replacing both motors. The problem is that the good motor is a 4 pole (2 speed) for the spindle moulder and I want to keep that speed option. Yes I could do it with a cheap VFD I spose. Also the current good motor is a 100L frame with a bigger shaft than most 3hp (90L frame) motors. So I have the problem with my belt pulley not fitting. Also, that motor has been rewound already. I think I might phone the guy I bought the machine off and get a bit more info about the rewind. Plus I can mention the problem with the other motor (not that I expect much redress). Two motors would be around $600, plus a cheap VFD maybe $200 - $800 total? Dave said he will do me OEM price for VFD which I am hoping will be under $500 including the 75 for freight. One new motor at $300 and I should be up and running (also about $800), and no dramas with pulleys. So those 2 options are both around $800 anyway. What do you think? Are there worries if I go the cheap VFD route. All the suppliers I talked to reckon around $500 for their VFDs. I know there are cheaper on ebay, but what if they blow my new motors?

I am open to your thoughts. If it wasn't for the 2 speed motor I would just buy single phase motors and be done with it.
Cheers
Graham

Got a price for a replacement VFD from Dave. Still not that cheap, so considering the option of 2 new motors and cheaper 240V VFD. Can you tell me are there disadvantages to running the motors in star config (240V) rather than delta (415V). Presumably there would be a higher current draw. My original VFD drew 20 Amps. Will a 240 - 240 model draw more?

Also I still have the problem that my good motor (2/4 pole 440/760V) is a 100L frame with 28mm shaft diameter. A 2 pole motor (with VFD for speed control) would be fine but they only come in 90L frame and my belt pulley won't fit the 24mm shaft. I am waiting on a price for 2/4 pole motor. Probably cheaper to keep that motor and go with Dave's VFD, but dead scared of blowing up another one. That other motor did run without fault though, so I am obviously a bit paranoid!

Cheers
Graham

Hi Graham,
I'm a little confused
I'm thinking you have it backwards(but maybe you mean something else?).

Should

"Can you tell me are there disadvantages to running the motors in star config (240V) rather than delta (415V)."

read

"Can you tell me are there disadvantages to running the motors in Delta config (240V) rather than Star (415V). Presumably there would be a higher current draw."?

As I dont think you arent likely to find a 240V star motor, thats not to say they arent out there. Though you might find 415 Delta pently of those from 3hp and up.

Assuming its the later and you are talking about running a motor either in Delta on a 240V VSD or in Star on a 415V VSD. The input current would be about the same. Both are outputing 3hp so the output current of the 240V VSD would be double the 415V VSD, but the input would be the same.(or there about............I think)


I think the first thing I would to is get the bad motor checked out and find out if its a cheap fix or a rewind/replacement.

You could price getting the good motor rewound for 240V at the same time.

Then just do the maths


Stuart

p.s. The rewound motor was wired in Delta when you got the machine correct?

Sorry Stuart, yes I got that backwards. 240V Delta or 415 Star. Both original motors are/were wired in 440V delta (the option is 760V Star). I have been researching, and my conclusion is the motor will run the same in either configuration (obviously the voltage supply must suit the wiring config).

I pulled apart the bad motor. Basically the lead wires are the problem. The end of the windings are laced and covered in lacquer. Possibly the lead wires could be replaced, but it might end up close to the cost of a new motor. Also since the other motor was rewound and this one is the same vintage, it could be past it's use by date? My thinking is for that motor a replacement at around $300 is the best option.

My other question is another $500 for 415V VFD plus $300 for one new motor OR get cheaper ($143 Huanyang) VFD and 2 new motors. Only prob with option 2 is pulley shaft size on good motor. (Might have to go 2/4 pole for 100L frame with 28mm shaft)

EDIT: One other thing I would like your opinion on. Page 10 of the manual that I got with my VFD says under the "Protection Function" heading that "Output Short-circuit" has "Electronic circuitry protection". The reason my VFD blew was because of a short in the motor. Dave said it didn't blow because I tried to insulate the wires (I never got to press Run). He said the damage was done already and had shorted an output transistor, that's why it blew. Doesn't the manual indicate that is protected against?

Graham

Do not let the shaft size deter you from using a different motor. It is quite likely that there are standard sleeves available to take the pulley to the size you want. Even if there isn't, how hard is it to get a bit of 2mm wall tube and cut a slot out for the keyway, then use a bearing mount glue to fix it (semi) permanantly to the pulley?

You need to talk to a motor rewinder about the insulation on the windings. There are some very old motors out there.
I've heard figures of $50 for digging out the star point, replacing the wires to the windings should be easier than that. But I've never had it done so couldnt say more than that.

You bring up a good point about page 10, If Dave has said that shorting the output wouldnt blow the VSD then what did and why isnt it under warranty?

Other than that the route to go is just a matter of maths.
It may turn out to be cheaper to replace the bad motor but still go with the 415V vsd, all depends that a 2/4 pole 3hp motor +vsd is going to cost you.

Stuart

If I stick with the same type 415 volt VFD and get a new motor I will configure the wiring on new motor in star mode for 415 volts. From what I figured before, I will still get the same performance as if it was 240v in Delta running from a 240 volt source. Is that correct? Do they perform the same in either configuration with the appropriate three phase voltage?

Is there a difference in current draw?

Graham

Originally Posted by gorriss

I will still get the same performance as if it was 240v in Delta running from a 240 volt source. Is that correct? Do they perform the same in either configuration with the appropriate three phase voltage?

Yes at their rated Hz they well be pretty much the same(not sure if they are EXACTLY the same)

Now if one V is better than another above and below the rated Hz I dont know. I'd like to test it but I dont have the gear.

Originally Posted by gorriss

Is there a difference in current draw?

Well I would assume that the current at 240V would be about double that at 415V, would have to be for the kW to be the same.

Or do you mean input current on the VSD?

Stuart