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P Jones

VFD Input Question

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So I ran into an issue in my shop the other day. Went in to get some work done just to discover the VFD I have for the grinder is having issues. Now, I could go through the trouble of getting it sent in and repaired, but then I thought about an opportunity here. I just put in a 230v outlet for my welder and figured if I had the outlet and the money, I might as well get a setup for some more power behind my grinder.

So I started shopping around and doing my research and while I know what I want, I'm just not sure on the details. My last setup was a 115v input setup, so the wiring was a little easier for me to understand. This hasn't been bad, but from what I've read the outlets you use for a welder generally aren't the type that are typically used for a grinder. Most recommend a 20 amp connection, where mine is 50. To be more specific, its a 230v single phase 50 amp outlet. Now the question is that while most VFDs specify the input and phase of the power, they don't mention the amps.

So I don't know exactly what I'm missing here. How can I tell whether the amperage will work for a VFD? I feel like the answer is something really simple but I can't place my finger on it.

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Posted (edited)

There's a max HP rating for VFDs. This will correlate to a max amperage rating at 230V, but as long as it's rated for that input voltage and HP, it should be fine. Remember, P = V * I (and then convert from Watts to HP) B)

All that being said, the grinder motor determines power. Doubling the input voltage halves the current draw, but won't change anything else.

Edited by AJ Chalifoux

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230V single phase at 50A is 11500 VA: There will be a power factor to consider, so probably not enough to run a 15 HP (11,250 W) motor via a VFD, but more than adequate for any motor/VFD you might fit to a 2" wide belt grinder.

 

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The main thing amperage does is make sure you're not pulling more power than the wiring can handle.  Note I am far from an expert on this stuff, I defer to Tim Gunn on all things power-related (be that gas or electric).  Basically, the 50 amp circuit for the welder is because if you tried to run it on a 20 amp circuit you'd trip the breaker.  If you don't have the breaker, you'll melt the wiring.  You can run anything with a lower amperage draw on a 50 amp circuit, but not the other way around.  This is also why you need to make sure all the wiring is up to snuff.  I got lucky with my house because the previous owner had the garage wired to be able to handle a welder and a range of other high-amperage tools.  Of course, he half-assed most things, which is why the house itself was wired with 100-amp fused mains.  We had that redone with 250-amp service and replaced the old fabric-insulated and knob-and-tube wiring (house built 1927) with modern stuff that can handle modern power requirements.   The sub-panel in the garage was done right, though.  I've added a few more 220V breakers to run the power hammer and grinder, and ran a few more 115V outlets since there were only four to start with.  

The short version is that amperage requirements are to protect you, not the equipment.  you'll be fine.

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I'm a little slow in getting to a response with work and all, but thanks to everyone for the input.

The most I'm looking into for my grinder is a 3 HP motor + the vfd to go with it. Anything over that'll probably be overkill. 

But yeah that all helps make a little more sense out of it. I'll have to decide now which components to get before I leave before my next rotation.

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