naive VFD motor control q

I currently have a Toshiba VF-SXS transitor inverter, but it is only
rated for 3/4HP 3phase motor.
I am using 220v AC single phase residential service, and the above unit
is configurred for either single or 3phase input (seems to be a
So, I go onto eBay looking for a larger capacity unit to drive a
different 2HP 3phase motor I want to use.
Almost every listing is for units which specifcally state "3phase
Now , with my limited knowledge of the workings of a VFD, I have
gleened from other threads, that the input stage simply rectifies the
input through a single or 3phase diode bridge, then takes the DC and
does it's magic and produces a variable frequency three phase output at
the same voltage as the input, which in my case is 220v.
I realize that just feeding from one phase would derate the ultimate
capacity, but how can you determine if a 3phase unit will or will not
function when only a single phase supply is used???
BTW, the above Toshiba unit works quite well on a single phase 220v
motor, with the other two legs not connected, even tho there is no
stipulation that this configuration is acceptable.
Any insight would be greatly appreciated
Stew Corman from sunny Endicott
Reply to
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Almost all mid-size (1 to 20 Hp) VFDs will run from single-phase power without complaint. Generally, if you keep them cool, they can handle this in home-shop type use for years without damage. 25 - 50% derating is a sensible caution, but you can even run them at 100% rating in most cases. There have been a few reports of the newest drives having a phase-loss sensing circuit in them.
Reply to
Jon Elson
Jon, Thanks for the fast response
what is the significance of your above comment ?..will this prevent the unit from functioning entirely?
Reply to
You can program many of the units to ignore the error condition.
scorman wrote:
Reply to
M Berger
I ran into one small unit that had a 3 phase sensor circuit and I couldn't bypass it, the Hitachi SJ300. Both the Hitachi SJ100 and SJ200 will run on single phase. Very nice units, easy to program. Get it at or
I'd suggest you skip Ebay as you're a newbie. You'll need the manual and may need to call for tech service.
Reply to
Karl Townsend
I bought one to drive my 1.5hp mill from my single phase house power. By carefully going through the wiring section of the manuals, you will usually find directions about where to hook up the two wires. Mine had me hook up to a specific pair of terminals, and not to use any other configuration if using single phase. I got mine from ebay for a great price, but had to pick out a few I liked and find the manuals on the web, download them, then study them carefully before bidding. Most will take single phase, but it helps to find that useful tidbit that confirms it. Some state the obvious single phase input, but the number of users using single phase is limited, so the manuals aren't written for that market specifically. You'll pay too much for ones marketed for single phase. I derated by a third, since it was short one leg. I got a 3hp unit, so I felt very comfortable with my choice.
Reply to
Carl McIver
Most of the drives I've seen will blissfully continue running on single-phase power without any indication. Most drives over about 40 Hp will indicate a phase fault and shut down. At least one person recently reported a 1 or 2 Hp drive had a phase fault detector and would not operate off single phase power. It would just show an error code in the LED display.
Reply to
Jon Elson
According to Karl Townsend :
Did you try connecting the third power-input terminal to one of the other two? Often that is sufficient to convince it that all three phases are present. If you still have it -- why not try it and report back on what happens there.
A good point. If the eBay auction *specifies* that it provides the manual -- and if necessary a programmer's panel as well -- you should be fine. Otherwise, you might hit problems. The programmer's panel is a keypad and display combination needed if you have to change some of the parameters -- such as spin up or spin-down ramp times or minimum and maximum speeds.
Examples of ones which need the programmer's panel are the two Mitsubishi units (2HP and 3HP) which I have -- from the previous model batch. (I presume that the current ones are similar.p
Enjoy, DoN.
Reply to
DoN. Nichols

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