VFD Carrier Frequency?

Ken226

Ken226

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I'm in the process of switching my lathe over to 3phase / VFD power. I got a 2hp Seimens motor on ebay for 99$ with free shipping, and a Teco Westinghouse L510 VFD.

I've got the new motor mount fabricated and the motor installed. I've drawn up a circuit diagram, based largely on the info posted by @mksj in an old thread, using the factory controls and contactors to operate the VFD.

I'm just waiting on a few more switches to show up in the mail, before I can finished building the wiring harness.




Regarding the carrier frequency. I've been setting up the VFD parameters with it sitting on a workbench, temporarily wired directly to the motor, which is installed in the lathe.

So far, everything runs great. It's smooth, powerful and quiet. 10x better than the chinese single phase motor it's replacing. The odd helical surface finish I get on some steels has even disappeared!

But, on carrier frequency settings from 10k hz and below, there's a low volume whine from the motor that just almost matches the tinnitus I got from my time in the military. Even though it's not loud, the tone is like an icepick in my left eardrum.

If I set it to 11 or above, the whine completely disappears! Is there any reason I can't leave it set to 11khz?

The default setting was 5khz. I've read that the higher settings can be harder on the motor and VFD, but I'm really really liking the way it runs @ settings >10. From 11 on up to 16 (max), sounds fantastic.

Is there any reason I can't leave it on 11?

I'm just waiting on a couple more switches from eBay to complete my panel and installation.

 
Higher carrier frequencies are usually better at providing power to the motor, but they tend to be harder on the windings, ie it might fail sooner, especially with non-inverter rated motors. Since you have a bonafide reason to use a higher frequency, go ahead and use it, just know that you might need to replace the motor windings sooner. I have constant tinnitus from my years working around machinery, do what’s best for your ears. I would replace a dozen motors before I would take a risk with what is left of my hearing.
 
Ulma Doctor said:
i routinely set high carrier frequencies. 11KHz is just fine
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That info makes my week! I'm gonna have a shot of scotch now

Though that noise wasn't loud at all, the pitch just somehow meshed perfectly enough with my tinnitus that it was giving me a weird headache, kinda behind the eyes. Funny, that whine was a fraction the volume on my single phase motor, but still almost painful.
 
Ischgl99 said:
Higher carrier frequencies are usually better at providing power to the motor, but they tend to be harder on the windings, ie it might fail sooner, especially with non-inverter rated motors. Since you have a bonafide reason to use a higher frequency, go ahead and use it, just know that you might need to replace the motor windings sooner. I have constant tinnitus from my years working around machinery, do what’s best for your ears. I would replace a dozen motors before I would take a risk with what is left of my hearing.
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Yea, that's a great point.. At only 99$ for the motor, I'd much rather replace it every few years than get a headache every time I use the lathe.

The motor (Seimens 1LA7096), has F rated insulation, but I didn't see anything on the tag about being inverter rated. I swapped in a new set of FAG bearings as soon as I got it for 20$. I noticed when I had it apart for the bearing swap, that the quality seems immensely better than the chinese motor it's replacing. Smooth castings, the endcap screw holes actually line up with the threaded holes in the body. It was kinda pretty on the inside, vastly different than the stock motor.

I wonder how much the 11khz carrier frequency will effect it's lifespan.
 
Well don't feel too bad, because if you had perfect hearing, it would probably drive you nuts anyway. I had to keep raising the frequency on mine until it no longer felt like someone had a dental drill against my skull.
 
Typically not an issue at this level, just be aware that for some VFD's there maybe be some derating on the output (typically with higher Hp units). Get into bigger VFDs with higher Hp and longer motor cable runs then it becomes a problem. My default is 12kHz. You are good to go.
 
I would think the insulation in the Siemens motor would be top notch- I don't think you will have any problem for many years
-Mark
 
Ken226 said:
Yea, that's a great point.. At only 99$ for the motor, I'd much rather replace it every few years than get a headache every time I use the lathe.

The motor (Seimens 1LA7096), has F rated insulation, but I didn't see anything on the tag about being inverter rated. I swapped in a new set of FAG bearings as soon as I got it for 20$. I noticed when I had it apart for the bearing swap, that the quality seems immensely better than the chinese motor it's replacing. Smooth castings, the endcap screw holes actually line up with the threaded holes in the body. It was kinda pretty on the inside, vastly different than the stock motor.

I wonder how much the 11khz carrier frequency will effect it's lifespan.
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With a good quality motor, and in a hobby environment, you probably will not notice a difference in lifespan by increasing the carrier frequency.

Having worked for FAG in a past life, you will be happy with the performance of the bearings, they make an incredibly good product, and that is coming from someone that was laid off by them. Western quality motors are night and day difference than the Chinese motors. Sometimes it hurts paying the increased cost, but you will be far happier in the long run. Inverter rated motors have at least F class insulation. I’m not sure if Baldor actually markets this, but all their motors are VFD rated and I would expect the other quality manufacturers to be the same.
 
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Awesome! Thanks for all the great info everyone. I'm pretty happy with the motor so far. Enough so that I ordered a second, 3hp one to keep on-hand for the day I decide to put in my PM935.

I noticed alot of little differences between that Seimens motor and the "capacitation induction motor, made in china" that came out.

Like, the Seimens motor has little blue rubber ish seals in the end caps. The stock motor had nothing even resembling seals.

Here's the motor data plate:
 
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