Emcoturn 120 lathe retrofit

I think what killed it was they had me set it for braking using the internal resistors to stop a 5hp motor and Xlb spindle going 4500RPM in 2 seconds. It stopped it, but it never worked again. The diagram on the advert showed connections for an external resistor, but there were no terminals on the unit I received, when I challenged them on this they said the internal resistors were enough

LutzTD wrote: The diagram on the advert showed connections for an external resistor, but there were no terminals on the unit I received, when I challenged them on this they said the internal resistors were enough

The internal resistors ought to be enough, and in the event of not being the VFD should fault-out with an overvolt and allow the spindle to coast to a halt.

That was an "ought" and a "should" that do not necessarily apply to some items on eBay.

I have an Eurotherm drive that i paid over 800 euro several years ago, it is a single phase to 3 phase good for 240Hz.
I used it most of the time on a vertical mill with a 1.5KW motor with geared reduction, and it worked flawlessly.
I had cables made and connected with sockets so i can detach and attach to whatever i need it to, mostly for testing faulty motors, or running 3 phase motors on a single phase, as it is a time saver.
I did test a lot of things with it, including known broken motors, motors rated at 3KW ( VFD rated at 1.5 i think), pushed motors to way over their speed limit, and it never broke!! It will display what went wrong (over voltage, under voltage, over current etc), and move on. It has settings for active breaking and coasting and i did try to stop the mill within a single second, it did complain of over voltage and moved on.
Never had a single problem with it.
This is to confirm that Andy is right, it should not go up in smoke, even with a shorted motor windings ( i did test it, shows over current ).
It is a small little bugger, but tough to the extremes.
Regards,
Tom

Any decent VFD should have protections built in. (Calling a super cheap Chinese drive decent may be a stretch.)

I've only ever had 3 VFDs fail, all 3 were quite old with a lot of hours. One I was able to repair with a simple rectifier replacement. and I think all were killed by power surges from the power grid. I've never had a motor failure or wiring problem (including phase to phase direct shorts) kill a drive, they always have just faulted out and shut down.

I've often ran larger motors on smaller drives. Running a 7hp motor, with a 5hp drive will run perfectly well, you just don't get 7hp out of it.

The brake worked once, then a zzzzzzzzz and smoke and that's all folks. Looks like the brake resistors arced. They agreed to refund me half, which was about the same as sending it back and forth to get it fixed. I pulled it apart and maybe I will replace the 2 resistors with something slightly better quality and see if it fixes it. They look like they are both 10W75Ohm, I found some 25W75Ohm replacements for about $15 Either way I ordered a new drive from automation direct. If this one works after the fix Ill save it for a less demanding application.

Might be wrong but they actually look to me like the soft start (precharge) resistors, next to the main diode bridge and soft start(?) relay. Also, "internal braking resistors" don't sound right to me. If there is no external braking resistor, any deceleration is generally absorbed by the internal (switching) losses. Perhaps I'm wrong.

Could you post a slightly more zoomed out photo? If I'm right, the repairs will require more than just a couple of resistors and you are looking at a piece of scrap.

Dunno what VFD you have there but has anyone got a schematic diagram?