Sag 12 vfd conversion problems

[Jim Moser]

I have a Graziano Sag 12 two speed motor lathe 1725 and 860 rpm windings. Never could figure out the contactor wiring for the low speed and the high speed started chattering so I opted to bypass all the old mag starters and try a vfd direct to the motor. Got a Vevor h100 7.5 hp import vfd. It starts the motor fine on both sets of windings but on the high speed when I engauge the electric clutches it shuts down with an over current error code. The low speed winding behaves better as I can use the first 3 speed clutches but 4th speed shuts it down with OC error code. Is there some kind of OC buffer parameter I can look for? There is hundreds of parameters in these things. Maximum motor amps is 16 and the vfd is rated for 33 amps. Seems like the instantaneous engaugement spikes the unit and shuts it down. Plus the thing has a high pitch whine I don't. Like. I have 4 other vfd's that are quiet and work great. I thought I oversized this enough but it does seem small for a 7.5 kw, all my other ones are 1 to 3 hp.
Any thoughts
Thanks. Jim

 

[rons]

If I'm not looking at my VFD manuals once a week I have to go through a refresher course each time have to look at the manual when something comes up.

Thoughts:
Perhaps a response time number can be changed.
Increase or decrease VFD carrier frequency to reduce any whine. Adjusting up may help your OC.

 

[JST]

The VFD will have some "hard limits". And then there may be several "soft", or time controlled limits.

There are typically several current ratings. There will be continuous motor current limit. There will also typically be a shorter term overload current, often 150% for a minute or so. There may be a 200% rating that is for short surges, which may allow only 2 to 5 seconds.

Motor acceleration obviously draws high current. You can slow the acceleration parameter so the time to accelerate is longer. That works in many cases, and may be all you need to do.

Watch out, though, because in some cases of large inertia loads, too short AND too long can BOTH cause an overload. This is because if there IS an overload, and it goes on too long, it trips on the 150% time limit.

So you need to be slow enough to stay under the heavy overload (200% for instance) rating and it's short time limit (which may not be published), but you may need to push the overload up close to the 150% point so that the motor will speed up in a time short enough not to time-out.

I've seen cases where shortening the accel worked for just that reason. You can tell, because it starts coming up to speed, but shuts down after a fairly long time, but before it gets to speed.

Also, see what the VFD does on an overload. Many have a "cut-back" option instead of a shut-down, so that the VFD will cut back the current to avoid shutting down.

That may be enough current to accelerate the motor and get it started. Or it may not in some cases. But look for that parameter and see if you can set the VFD to do that. Might do the trick.

About that whine.... It may be normal "carrier frequency" noise, and you might be able to set the "carrier" frequency higher and avoid the noise. That's most likely the issue there. Setting the carrier higher also makes the VFD get hotter, so don't do it unless you need to.

But, in some cases, it could mean a problem with wiring on the higher speed setting. Probably not, but worth a look to be sure. "Inverters" that make audible noise may be "unhappy" about something, and you might be hearing a noise related to a protection circuit.

 

[Jim Moser]

Thanks for the responses,
I did play with the carrier frequeny settings, it was on 5 of 1 to 10 ,the whine did seem quieter at 8 or 10 but I noticed some clicking noises in the headstock I assume transmitted from the motor? Put it back on 5 to be safe. This motor starts fine with the VFD set at 60 cycles but it is directly connected to a gearbox with 6 wet clutches 4 speeds and forw and reverse. The OC shutdown accurs when I engauge the high speed run clutches. I see some torque percentage perameter setting but no amp buffer or delay. It wont work on the low speeds if I set the motor amp setiind for 18 amps as shown on the motor, had to increase to 25 amp to get it to not shutdown when the clutches were engauged. So I assume the motor is not protected. Also I measured the amp draw with the motor running the gear box, no clutches engauged and with a Fluke clamp meter I see about 12 amps on each 3 phase leg but on the single phase 220 input leads only 6 amps per lead, this seems backwards to me?