I fried my spindle motor, and would like to understand why

[knipknap]

Hi!

Up until an hour ago, I had an Isel ISA 750 spindle (https://www.isel.com/en/spindle-motor-isa-750-manual-tool-exchange.html). I tried to run this using an Omron JX (3G3JX-AB002-EF) (https://de.rs-online.com/web/p/frequenzumrichter/7051844) VFD.

I mostly followed the "test run" instructions from the Omron JX inverter handbook:

Configured the spindle power to 0.75 kW
Configured the output current to 220V
Configured number of poles of the motor to 2


In addition, I also configured the frequency settings, but here I was unsure, because the spindle doesn't specify them in the same way as they need to be entered in the VFD. It only lists the "cut-off frequency", which the specs explain as "frequency to which the motor effect is designed". So I thought I would be safe by staying close to those values and made the following settings in the VFD:


"Base frequency" I set to 295 Hz
"maximum frequency" I set to 305 Hz


And then I tried to run it. The spindle went up in smoke after approx. 3 seconds, and now has a short between phases.

Now before I try to buy a new spindle and try again, I would like to understand what I did wrong.

Any hints?

[JohnHaine]

I suspect nothing and the spindle was faulty. However I think the max Freq should be set to 400 Hz if you want 24000 rpm ie 60x400 and the base to whatever the min speed is.

[dazp1976]

Hi!

Up until an hour ago, I had an Isel ISA 750 spindle (https://www.isel.com/en/spindle-motor-isa-750-manual-tool-exchange.html). I tried to run this using an Omron JX (3G3JX-AB002-EF) (https://de.rs-online.com/web/p/frequenzumrichter/7051844) VFD.

I mostly followed the "test run" instructions from the Omron JX inverter handbook:

Configured the spindle power to 0.75 kW
Configured the output current to 220V
Configured number of poles of the motor to 2


In addition, I also configured the frequency settings, but here I was unsure, because the spindle doesn't specify them in the same way as they need to be entered in the VFD. It only lists the "cut-off frequency", which the specs explain as "frequency to which the motor effect is designed". So I thought I would be safe by staying close to those values and made the following settings in the VFD:


"Base frequency" I set to 295 Hz
"maximum frequency" I set to 305 Hz


And then I tried to run it. The spindle went up in smoke after approx. 3 seconds, and now has a short between phases.

Now before I try to buy a new spindle and try again, I would like to understand what I did wrong.

Any hints?


I suspect nothing and the spindle was faulty. However I think the max Freq should be set to 400 Hz if you want 24000 rpm ie 60x400 and the base to whatever the min speed is.

The motor states 300hz max.
This kind of thing happens when you mix and match.
Should have got a matching vfd from isel.

May have broke both.

[JAZZCNC]

The motor states 300hz max.
This kind of thing happens when you mix and match.
Should have got a matching vfd from isel.

May have broke both.

No, it doesn't, Isel doesn't make VFD's they just supply another manufacturer VFD that is set up to match their spindle. Any suitably sized VFD with the correct setting will work fine, with any spindle from any manufacturer.

The problem could be a number of things and like John says most probably faulty spindle in the first place or incorrectly wired because just entering the wrong frequency wouldn't burn it out within 3s, it would squeal and complain but wouldn't kill it dead.

The base Frequency should have probably been 50hz or 60hz to suit your country's grid power. The Motor rating of 300Hz is the Rated HZ which will provide the rated power and going higher would just make it spin faster but with lower power, but go too high and you would get overheating, etc.

My suggestion is to contact Isel and ask which VFD they use and what settings they use.

[m_c]

The motor states 300hz max.
This kind of thing happens when you mix and match.
Should have got a matching vfd from isel.

May have broke both.

But 300Hz would only give 18'000rpm (ignoring rotor slip), not the indicated 23'000rpm in the torque curve.
Going by the same torque curve, I'm guessing what they mean by the cut-off frequency is the frequency at which the spindle enters constant power output, in which case Base Frequency should be set to 300Hz, with Max frequency being 400Hz.

The only way the spindle could be damaged that quickly, is if the VFD was driving too much current through it.
To do that would take the power/current being set far too high (would need to be using a well oversized VFD), the initial test speed being quite slow (or the spindle being locked/stalled), and the base frequency being set too low (even if the power was set too high, the back emf from an undersized motor would automatically limit current, unless the base current was set too low, which would mean the VFD would output a higher voltage than needed and drive excess current through the spindle).

There is also the possibility DC injection could cause the same result, but again would involve wrong power settings and an oversized VFD.

[knipknap]

The base Frequency should have probably been 50hz or 60hz to suit your country's grid power.

Oh, this makes complete sense to me and explains why the base frequency isn't called min frequency... I think this is a very likely explanation.

Thank you everyone.

[Muzzer]

I'm not convinced about that. For 2 pole motor at 50Hz, the speed would be 3000rpm. It doesn't look like a machine that is ever intended to run directly off 240V / 50Hz.

The normal definition of base speed is where the back emf equals the dc bus voltage, beyond which the torque starts to fall off and you are in a constant power region. From the max torque curves given that looks more like 18000 rpm. That seems to be what these Germans call the "cut off frequency" and would be 300Hz for this machine. https://www.isel.com/en/mwdownloads/download/link/id/4093/

If you were running with base speed set at 18000rpm / 300Hz / 240V / 3.4Arms phase current, you shouldn't be able to go wrong / toast your motor. Did the motor ever work in your possession? Is it possible you bought a duff, used machine? Did the insulation break down between the windings and the chassis?

[JohnHaine]

As I said, I suspect the motor was duff