# Weird stuff happened when I plugged in a new inverter.



## Inferno (Apr 29, 2020)

I almost posted this in the CNC forum. 

Long story short, I'm building a CNC machine. 
I'm putting together the structure some days, working on electric/electronic components other days and then working on other stuff other days and so on.

I bought a Chinese inverter. Model #VL620-A. I bought a 110V model for the 2.2KW spindle. It was all part of a package. 
I looked at the book but I'm too freakin old to read 3 point type. I ended up looking at a couple youtube videos. 
They all showed the wiring the same way. Neutral to the far left. Earth ground to the far right. Second from the left is line voltage. 

I took a computer cord and stripped off the end and cleared the insulation on the three wires. I soldered connectors to the wire and then insulated them with shrink tube. 

Green is obviously earth ground. 
White is usually common/neutral
Black is traditionally line

That's how I hooked everything up. 

This is where stuff got weird. 

I plugged it in in my living room. It POPPED. Then my TV and all my other components went off. But the inverter stayed on, with the display blinking in an error state. I didn't think to check the error. 
The weird thing is that the breaker for my TV popped but the outlet I plugged the inverter into was still live. 

This shouldn't be possible, I don't think. 
Is it possible I have the inverter wired backwards and I, somehow, fed enough voltage back through the neutral to overload the TV breaker?

I do plan on using a continuity tester to make sure the power cord white is, indeed, the neutral. If the black and white are swapped in there then that would probably cause issues. 

I also detected magic smoke from the pop. I sniffed inside the inverter and it doesn't smell like magic smoke. I can't imagine I did any damage inside it. 

Any ideas?


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## JimDawson (Apr 30, 2020)

I think we're going to need a picture of the way you wired it.  That ain't normal.

2.2 KW (3HP) is a lot to be running on a 120V circuit, full load current on that is going to be in the range of 30 some amps.


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## Inferno (Apr 30, 2020)

I had my cat hold the unit so I could take pictures.


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## JimDawson (Apr 30, 2020)

I think the ground is the screw below where you have it connected.  Looks like you have the ground connected to the brake - terminal.


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## Inferno (Apr 30, 2020)

JimDawson said:


> I think the ground is is the screw below where you have it connected.  Looks like you have the ground connected to the brake - terminal.


Ah, I can see that now. Frain Bart.

Thanks.


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## JimDawson (Apr 30, 2020)

And I have a question.  How did you get your cat to hold still long enough to take that picture?


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## Inferno (Apr 30, 2020)

JimDawson said:


> And I have a question.  How did you get your cat to hold still long enough to take that picture?


When she sleeps, she REALLY sleeps. That's when I trim her claws.


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## mksj (Apr 30, 2020)

As Jim indicated, you have connected the braking terminal to the ground wire, but most likely you popped the breaker due to the high current draw when charging up the capacitors. VFDs will stay on for around 5 minutes after the power is turned off due to the charged capacitors. If there is a lot of momentum in the system when power loss occurs, the VFD will use the regenerative power to keep everything running until everything stops. The display is the last to shut down because it takes very little power.

If the output is 240VAC 20A 3 phase the input converting to single phase at 120VAC would be 20Ax1.73x2 or around 70A. A 2.2 kW motor is 3 Hp, so around 38A at 120 VAC and that is with conservative overload parameters,  the typical breaker would be sized at 125%. There are other factors such as using a DC choke which will tame the current pulses, but there is no provision for that on this VFD. Minimum breaker size at 240VAC for a 3 Hp VFD is typically 30A. Not really practical to use 120VAC.

Fortunately my cat purrs when she gets her claws cut.


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## Inferno (Apr 30, 2020)

Interesting. So, e en with no spindle connected it will draw that much power? 
When it's all said and done, I can give it a dedicated circuit. Or I could get a different inverter when I'm ready to start making things.


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## macardoso (Apr 30, 2020)

So you ended up connecting your ground wire to the braking resistor to the "-" end of the braking resistor which is most likely directly connected to the lower rail of the DC bus. Effectively you shorted your AC line (hot) to ground through the diode front end of the drive.

If you had a GFCI outlet, it likely would have tripped before the main breaker blew when it detected a spike in fault current through the ground wire.

It will *probably* be OK, but I'd be worried about damage to the AC->DC converter (diode front end) inside the drive with a dead short through the rectifier.

I really don't want to come across as demeaning so please don't take my comments as such. I work in the automation industry and want to see everyone be safe when working with power. I would encourage you to slow down, read the manual, and ask questions when you are unsure. This is a small VFD but it still carries 180VDC on the bus and holds that in capacitors. You could really hurt yourself from a shock if exposed to that. Likewise, you are hooking up a lot of power there and that cable does not look like wire rated to carry 30A. You'd want 10 gauge wire or larger for that power cord or you could risk a fire. 

You guys are very lucky. Wife and I have 3 cats and have to wrap them in blankets to have any chance at trimming their nails. Usually ends up with 3 very ticked off kitties by the end of the night!


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## ttabbal (Apr 30, 2020)

One thing to watch on at least some of these VFDs.. On at least one of my Chinese units, there is no provision for preventing reverse power feeding from the capacitors to the input terminals. I have it wired to a plug for easy disconnect while working on the machine, and got a good shock from the plug. This happened after the LEDs turned off on the VFD. I have been more careful with them since, so it could be one bad unit, or just how they are made. They seem to self discharge after a few minutes, but it's something to be aware of.


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## Inferno (Apr 30, 2020)

Good advice. 
I'm not a novice with electricity but a total noob with the inverters. 
If it's carrying 30A as stated then I need at the very least a 12ga power cord. 

I can't imagine design g a unit without some sort of safeguard inside to protect against backward transmission but then I didn't design these. 
If it's toast, it's probably my fault. Expensive lessons are the ones you remember.


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## Inferno (Apr 30, 2020)

So, a quick noob question. 
What is the braking and is that an input or an output connection? I haven't ever run across a situation where grounding something marked as a negative was an issue.


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## stupoty (Apr 30, 2020)

Inferno said:


> So, a quick noob question.
> What is the braking and is that an input or an output connection? I haven't ever run across a situation where grounding something marked as a negative was an issue.



some vfd's alow you to use an external resistor to dump energy into to stop the motor quicker.


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## markba633csi (Apr 30, 2020)

I think it was a 50/50 chance you would have got it right- inside the unit the ground symbol is over to the right.  Then the outside sticker shows it three positions over.  What are you supposed to do?  Freakin' Chi products
In cases like this you really need to go above and beyond and use a meter or continuity tester or even partially disassemble the unit to know for sure.
-Mark


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## macardoso (Apr 30, 2020)

Inferno said:


> Good advice.
> I'm not a novice with electricity but a total noob with the inverters.
> If it's carrying 30A as stated then I need at the very least a 12ga power cord.
> 
> ...



Some much larger drives that we work with at work might have an active power section to the drive with input fusing and contactors. That usually isn't seen on small drives like these.

Drives like this get blown up all the time in industry. They are considered disposable by most until you get into larger modular models. Fingers crossed that it is all good!


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## matthewsx (Apr 30, 2020)

So now we need pictures of the machine....

Agree if you need that much power to drive the spindle a 220v input would be best. Maybe breaking the unit you have will be a blessing in disguise....

john


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## Inferno (Apr 30, 2020)

matthewsx said:


> So now we need pictures of the machine....
> 
> Agree if you need that much power to drive the spindle a 220v input would be best. Maybe breaking the unit you have will be a blessing in disguise....
> 
> john


The machine isn't nearly close enough to debut. It's still very much in the middle stages. 
I have to balance time, finances, workload, other projects, space to be able to show it off. 

Since I'm a cheap bastard, I also wait for opportunity when buying building materials. 

This month, my disposable cash allowance took a hit due to a blown water pump and 60 mile tow truck ride.


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## matthewsx (Apr 30, 2020)

Okay, whatever you're comfortable with. 

I started my build thread when I got my first part.









						Homemade vertical mill drill
					

Well, I guess I'm gonna try to make myself a mill for cheap.  I found this column on Craigslist for $80.    And I ordered this spindle I can power with a VFD I already have.    And I'm going to get one of these cheap x-y milling tables.    And probably look for a really flat piece of C channel...




					www.hobby-machinist.com
				




And continued it here when I knew it was going to be CNC.









						Homemade vertical mill/drill CNC project
					

I'm sure some of you have seen my posts in the general section about this project.  https://www.hobby-machinist.com/threads/homemade-vertical-mill-drill.77611/page-3#post-664686  But now that I'm ready to start on the controls I figured it would fit better here (mods please let me know if...




					www.hobby-machinist.com
				




I've found the input from folks on this forum to be super valuable throughout the whole process. When they told me something wasn't going to work they were almost always right and I've been saved several times from going in a direction that could have been a waste of time and money. I've also ignored their input and ended up going down some dead ends.

If your machine is from a kit maybe you're confident in the instructions that came with it. But, the great thing about guys like Jim and macardoso is they actually work with this stuff all the time and are willing to share what they have learned. Even if you're sure about the build process I'll bet they can provide tips that will make your machine better and save you money. 

John


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## Inferno (Apr 30, 2020)

matthewsx said:


> Okay, whatever you're comfortable with.
> 
> I started my build thread when I got my first part.
> 
> ...


OH, no doubt that knowledge is useful. 
I'm trying to reinvent the wheel (not really). 
My CNC build is more about the journey than the destination. That doesn't mean I won't ask for a little tourist advice along the way. 

I've been to Jim's place. I know the guy has mad knowledge. I give credit where it's due on that. 

I hope to have a few things I can show along the way. 

And, suffice to say, the closest I'm going to have a kit machine is I bought my steppers and drivers from the same company.


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## epanzella (Apr 30, 2020)

Inverters are diode heavy and they have zero tolerance for reversed polarity.  I have a 3000w inverter that I use to runs saws and whatnot on the jobsite. It connects to my truck batts via a pair of cables with giant alligator clamps like boosting cables.  I hooked it up backwards one rainy night and POOF. Blew every diode in it. After the manufacturer told me it was not field servicable I opened it up and replaced the diodes for about $ 50. You know it was easy because I could do it!


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## ddickey (Apr 30, 2020)

Frequeency? Doesn't instill much confidence.


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## Inferno (Apr 30, 2020)

Well, if it wasn't popped before, it's popped now.

I read the wiring part of the manual again.
I used an ohmmeter to verify that the cord was wired properly. 
I used the ohmmeter to verify that the cord connections were getting to the terminals properly.
I moved the ground from the brake negative to the third lug from the right. 
I plugged in to a dedicated 30A plug and POP! 

This time it popped inside the unit and the display didn't do a thing.
I smell magic smoke when I sniff it.

I might do some forensics and see what popped. I might even redo whatever popped. I've been doing that stuff for 40 years.


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## ddickey (Apr 30, 2020)

I just re read the tag under frequeency converter.
High voltage inside. Mainrained by thr weil-trained peronnnel.
WTH.


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## Inferno (Apr 30, 2020)

ddickey said:


> I just re read the tag under frequeency converter.
> High voltage inside. Mainrained by thr weil-trained peronnnel.
> WTH.


HA!, I thought you were just drunk typing. I didn't even catch the really bad speeling

For the warning: Once you've discharged a flyback transformer, through your body, nothing but lightning is scary.


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## brino (Apr 30, 2020)

markba633csi said:


> I think it was a 50/50 chance you would have got it right- inside the unit the ground symbol is over to the right. Then the outside sticker shows it three positions over. What are you supposed to do?



Gotta watch it though......I think there are two grounds!

The way I read it is that terminal #6 is "FG" (frame ground or chassis) and the screw down to the right is also a ground (with the traditional ground symbol on the plastic).

-brino


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## matthewsx (Apr 30, 2020)

BTW, it doesn't need the ground to work. I'm not using one on the VFD for my spindle. You can just ground the whole machine if you're concerned but  for what we're building....

John


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## Inferno (Apr 30, 2020)

brino said:


> Gotta watch it though......I think there are two grounds!
> 
> The way I read it is that terminal #6 is "FG" (frame ground or chassis) and the screw down to the right is also a ground (with the traditional ground symbol on the plastic).
> 
> -brino


I forgot to mention that there's zero continuity between the screw to the right, or it's twin on the left, or #6.
The three are completely isolated from one another.


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## Inferno (May 1, 2020)

It's dead. 

The autopsy complete. 
First I checked to make sure I was getting proper voltage to the pins. 120v confirmed





I don't know what happened to the first few photos I took but I exposed the top board and inspected all the components for damage. They all appeared fine, at first. 

Next I took apart the unit and removed the top board. It was pretty obvious where the pop was. The weird thing is that this is where the burn was most prominent but there'd no actual connection here, or is there?




This spot is opposite of where the burn is above. It looks like something popped here but with the 10X loop I couldn't really see any bad connections. Maybe a tiny bit of trace delamination but it still looked like it was connected. 





I'm not entirely sure this was designed or assembled right. That solder spot o the board where it's close to the aluminum heat sink just doesn't seem right. Since I don't know if it was designed this way or not, I kept looking. 






Looking at the board below it's hard to see. The yellow relay is directly on top of where the soot blast was in the picture above. With a closer inspection I can see why I won't bother fixing it. 





It's difficult to see but there's definite trace delamination there. The trace blew like a fuse. I could solder jumpers to clear the bad trace but at this point I think I'll cut my losses and just buy another inverter. It kind of pisses me off because I think I may have gotten a faulty unit but I also know I hooked it up wrong.  




All in all, I'm not a happy camper about this. 

Looking at the ground symbol in the plastic leads me to believe there's a ground in that area. There's the brake - symbol and the ground symbol. THe #6 lug supposedly a ground. 
The screw by the plastic ground symbol wouldn't have grounded it. The #6 ground is what I had hooked up when the unit blew. And I blew my house circuit when I had the - on the brake hooked up. 

Maybe the next one will go better. 

I am concerned, however, that the 220v version says "line" and neutral also. 220v in the states doesn't have a neutral. How's that supposed to work?


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## mksj (May 1, 2020)

Most VFD's  are marked for 240VAC in the rest of the world which is N and L1 = 240VAC. In the US we have split phase so L1 and L2. VFD will instruct you as to the connections, typically for US use L1 is one phase and N is connected to the other phase (L2). Do not connect the neutral on a 240VAC VFD. You might consider a better VFD, but then people who buy these brands consider them disposable.


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## Inferno (May 1, 2020)

Well, this last one sure was disposable. 
I'd rather blow up a $100 VFD than a $400 VFD.. Just sayin'.


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## brino (May 1, 2020)

@Inferno,

Sorry, but you're right that one looks pooched!

If you have a strong electronics background it might be worth:
-cleaning up all those marks, and having another look
-for sure the one copper track on the "N" feed into the bridge rectifier did fuse
-on the top (component side) it is hard to tell between components if a track is fused-open, or just started to delaminate due to heat
-that bridge rectifier should be removed from circuit and tested with the "diode" function of the DMM

Other wise, here's the HUANYANG VFD I bought more than a year ago now:
https://www.ebay.ca/itm/7-5KW-5-5KW...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

I got the 240V input 1.5kW model.
I bought it based on a friends recommendation.
It has been working great, although not many hours on it......

Again, the manual was not fantastic, but it got me there.

-brino


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## markba633csi (May 1, 2020)

Agree with Brino- blown trace or traces and blown rectifier bridge at least- I would try fixing it myself, but then I've got spare time
-Mark


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## Inferno (May 1, 2020)

I'm not good with acronyms. 
What's DMM.


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## matthewsx (May 1, 2020)

Inferno said:


> I'm not good with acronyms.
> What's DMM.



Digital Multi-Meter


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## Inferno (May 1, 2020)

matthewsx said:


> Digital Multi-Meter



Thanks. Now I feel stupid. LOL


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## matthewsx (May 1, 2020)

There really are no stupid questions, only questions that can be answered with a google search  

John


Still want pictures of your project BTW (by the way)


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## Inferno (May 1, 2020)

All I gotta say is I'm careful what I search at work. 
Google is NOT always your friend.


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