Lathe wiring gone wrong?

[madmatt41]

I got a new to me lathe, a National 14 x 40 gap bed lathe. I had to disassemble part of it to get it into my little shop, but I just got it done, the problem is, I can't get it to power on.


I wired up the VFD and tripped the white switch (red arrow) and the four little lights (red circle) lit up, but any time I would try to engage the lever (double red arrows), the VFD would throw an error code. I did here some noises coming from the wiring in the back, but I never heard the motor even try to do anything. I tried reversing the direction on the VFD in case I got it wired wrong, but it didn't help. I then bumped up the frequency to 120 hz, and it stopped throwing the error code, but I still could get the motor to engage. I put it back to 60 hz, and now the little lights won't even light up. I did try the coolant pump while the lights were lit, and it did activate. No wires were messed with except for the switch (red box above). It had to be disconnected to get the gearbox off when we were moving it. I labeled everything and put all the wires back where they went.

I've wired up 2 other VFD's, one for a mill and one for a surface grinder. There were the same brand, only smaller, and I had zero issues out of either. The only thing I noticed with the new VFD was the display for the Hz keeps flashing(red arrow below), and it didn't do that on either of the smaller ones. It also shows almost no draw being placed on it.


I did open the back panel and check what I could. The red arrow to the main switch is reading 120v into each wire. I did check the fuses(red circle), and they were all good. I also checked the voltages in the yellow circle, and none of them match up to what was marked on it.


I'm sorry if I sound like an idiot, but with electricity, I am. The picture of the back panel is literally what my nightmares look like. Can anyone give me some suggestions of things to try, or if not, who can I call to come and work on this type of thing?

 

[Reddinr]

Could you tell us more about the wiring you did to tie the VFD to the lathe? Are the forward/reverse contactors taken out of the circuit? Is the forward/reverse switch wired to the control inputs of the VFD? Any other details you can provide?

If you are supplying the control transformer from the output of the VFD, the control transformer may not like that at all. It may overheat or just not work well.

 

[markba633csi]

The fundamental truth here is that you can't treat a VFD like utility power- The motor needs to be connected directly to the output of the VFD bypassing all the contactors and switches. Opening the motor connections under power can damage the VFD output stage.
It is possible to use some of the original lathe switches to control the VFD for functions like start/stop/forward and reverse by rewiring them to the
low voltage control inputs of the VFD- you would need a schematic diagram for the lathe and the VFD manual

Some people find that installing a rotary phase converter (RPC) is an easier solution- you can retain the original controls since this is a passive
way of generating 3-phase power from a single phase input; no solid state electronics to blow.
Of course you don't have the advantage of variable speed, electronic braking, etc. but for many folks this isn't a big deal

 

[madmatt41]

I did wire it like it was mains power. I had no idea there were other ways. I had looked at rotary phase converters, but the were extremely expensive, more than the mill or the surface grinder. Do you think I hurt something in the lathe, or just in the vfd?

 

[Reddinr]

You may or may not have damaged something, but quite possible. However, it will not work as you have it wired as mentioned above. There are two ways to go with a VFD.

1. Use the VFD to run the motor directly, NO contactors between the VFD output and the motor. Wire the forward/reverse lever/switch to the control inputs of the VFD and set up the VFD to respond to those inputs.

2. Add a 3-phase sine-wave filter on the VFD output and run the VFD full on (constant 230VAC/60 Hz output) and control the power using the normal wiring (contactors) of the lathe. This is the setup I use but plan to change to method 1 someday.

Next step is to troubleshoot.
Turn off the lathe.
Remove the fuses from the input of the control transformer for now.

Maybe break out the instruction manual for the VFD and figure out what the flashing lights are telling you. If the VFD is not dead then next steps can be taken.

 

[markba633csi]

Hopefully you haven't damaged anything yet. Connect the motor direct to the VFD and try to get it to run. You may have to experiment with settings

 

[mksj]

You might look into a 5Hp Phase Perfect as a alternative to an RPC and would be a direct 3 phase power source for your machines, otherwise with the VFD you pretty much eliminate the stock control board in the lathe and it is also possible that you damaged the VFD you have whne operting it as you have.

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www.phaseperfect.com

 

[Chipper5783]

As per mksj - a Phase Perfect works very well. Matt, you are correct that a good phase converter will be expensive. My PP (had it about 5 years) is the most expensive piece of equipment in my shop. This machining hobby is not a cheap game. Rotary phase converters do work well (I used one for my first 35 years of machining). The PP seems to work better (the machines are more responsive, it is quieter and supposedly more efficient). One big benefit RPC or PP over a VFD is you get a whole shop solution - I keep picking up more machines, usually they have two (or more) motors - in all 20+ motors. The ability to just plug’em in and go is great.

Most of my machines are old style gear change machines (one variable pulley mill, the CNC has a variable electronic drive), and I have never really felt I was missing out by not having dial variable speed. It is on my “some day” project list to convert one of the lathes over - a VFD seems like it would be cool, but probably not a game changer.

Back to the RPC, there are many threads on building your own - they do not have to be expensive. I encourage you to put time/money (more time & less money, or less time & more money - your choice) into setting up a solid, electrical code compliant, 3 phase source and distribution system - it will pay dividends in the end.

 

[madmatt41]

I was going to try and connect the VFD directly to the motor, but there are 6 wires coming from the motor, 5 black and 1 green/yellow that looks like it is a ground. I have no idea what to do with that. I tried googling it, but they only show six wires with no ground, and I can't get to the box on the motor to see how the wires are connected.

 

[mksj]

It looks like you have a 2 speed motor as there is a switch on the front panel for Low and High speed. Would need to see the motor name plate, but usually one would would select the high speed connections unless it is a constant Hp motor. one would need to trace the wires back to see the connections.