[TheForge] Frequency Converters

[Steve Smith]

Chuck Robinson wrote:
> Hey Folks,
> I don't know my ass from my elbow about frequency converters, but the latest
> Surplus Center  flyer has  a Leeson 3 phase 3450 rpm motor advertised for
> $150. Item # 10-2041.
> Is this a good candidate for FC controller?
> If so what is a good source for the FC and approximate price?
> Chuck

Chuck, I'm not finding your motor on the Surplus Center's web page (I 
assume you mean http://www.surplussales.com/ ), so I can't help you 
there. It looks like their web page isn't fully cooperating with 
Mozilla. Note that used three phase motors (scrapyard, auctions) often 
go cheap.

I think you're talking about a Variable Frequency Drive (VFD); a box of 
electronics which produces three phase (variable frequency) out of 
single phase or three phase. A good source is:
http://www.dealerselectric.com/
Note that they sell a package deal on a VFD and a motor. To see their 
VFD's, click on "Browse our Inventory" then "Variable Freq. Drives". 
They are very helpful on the telephone. I bought an FM100 from them for 
my mill (which of course I haven't had time to put in yet...). A couple 
of things to note about VFD's:
1. You can't hook the VFD output up to a bunch of wiring with different 
machines on it. The VFD must drive your machine directly, not even using 
the switch on the machine (there are ways to work this, just not 
directly). Otherwise, the VFD can be damaged by a no-load condition.
2. You can get units up to 3HP that will take single phase input and put 
out three phase output. Above 3HP, you need to derate by one step if you 
have single phase in. For instance, if you want to run a 5HP, 3 phase 
motor off single phase, you need to use a 7.5HP VFD.

If you don't already have a three phase motor, it may make more sense to 
buy a single phase motor. This is probably cheaper than buying both a 
three phase motor and a VFD.

Steve Smith