VFD seems too good to be true

It seems VFDs are going down the same marketing slope as air compressors and vacuum cleaners, all claiming big power.

As was said, hp is hp. One horsepower is 746 watts no matter how it's delivered. The OP says the VFD is running on 110V, so that means a perfectly efficient product would consume an average of 746 / 110 = 6.8 amps for every hp delivered. But nothing is 100% efficient; it's maybe 90% (for a really efficient unit), so that 6.8 amps ends up being 6.8 / 0.90 = 7.5 amps per hp. Since the mfg is claiming 3 hp output, it means that at least 3 * 7.5 = 22.5 amps is being drawn from the 110V outlet. AFAIK, no homes are wired to handle that.

MKSJ is right, a real 3hp VFD uses a 30 amp breaker when run on 220V. The problem is that the OP is trolling at the shallow end of the market for the cheapest price, and this is what you get, mfgs playing fast and loose with nonsense ratings. Physics doesn't care and will solve the bogus claims by popping your breaker before any real power is delivered.
 
I have a similar drive that is 1.5Kw 110 to 220 3 phase. It pulls 14A @125v . I run it on a 20A 125v single phase circuit

the 3 hp model must require double that
 
I suspect the seller either doesn't have a clue what he/she is selling and is mixing up specs from a variety of different models or is purposely trying to decieve. Either way I would avoid this one.
 
To go over 20A on a 110v circuit you'll need 10 gauge wire (25A per leg or better). You won't be using a 110v outlet receptacle beyond 20A. Efficiencies aren't as good when stepping voltage up (it works better the other way around) so it would be better overall to run a 220v circuit from your panel to your 3hp machine.
 
Okay, thanks everyone. Seems like it's pretty much what I expected. I do have the ability to get 220, but it's going to mean spending $5K or so-- no electrician is willing to touch our panel; it's old and failing and wasn't wired well in the first place, so it needs to be replaced. Then wiring will need to be run to the part of the garage that I'm putting the machines in. So we're going to do that, but obviously that's a chunk of money that could have gone towards machinery, had this VFD turned out to be a magic box.

I appreciate everyone's help, and the time people spent explaining this to me.
 
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kb58 said:
MKSJ is right, a real 3hp VFD uses a 30 amp breaker when run on 220V. The problem is that the OP is trolling at the shallow end of the market for the cheapest price, and this is what you get, mfgs playing fast and loose with nonsense ratings. Physics doesn't care and will solve the bogus claims by popping your breaker before any real power is delivered.
Click to expand...

That's not true at all. I'm not looking at the low end, I just did a Google search, and this is what came up. I don't know which brands are the best-- I did a Google search for "VFD Best Brands", and all I got are those stupid web pages where people put up generic marketing information and an affiliate link to Amazon, so they make money when you make a purchase. If there are high quality brands that I should know about, please tell me. Even better, if there's a high end brand that does what this one claimed to do, I'd really appreciate learning about it. But although there's a person in this thread saying he's using this model to do what it says it does, the consensus is that this is a kludge that's not likely to work out the way I want in the long run, so barring further information, I'll just need to wait until I can get the new panel installed and wiring done.
 
Be_Zero_Be said:
Beware of HUANYANG VFD's
Practical Machinist Forum has banned discussion of them because they are so problematic.
I have different Chinese VFD from eBay that works fine.
220 1Phase input to 220 3 Phase output.
it is 10 HP rated to run a 5 HP lathe.

https://www.practicalmachinist.com/...d-vfd/huanyang-vfds-banned-discussion-338416/
Click to expand...

A fellow in Calgary took delivery of one of those VFDs and it was DOA.
Well unless you tapped on the side of it with a screwdriver handle.
I just bought a Teco 110v VFD for my grinder and it was $250 CDN.
I’m sure it would be less in the US.


Sent from my iPhone using Tapatalk
 
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