VFD question

It's important to understand that only a relatively small portion of the actual connected load current passes through the buck/boost "primary" winding.

I wonder what the voltage drop would be across a couple electric range elements?

Wes

NOOOO !!

Never put a transformer in the Output of a VFD! It is variable frequency... Those transformers are NOT going to be amused with 20 HZ !!

Keep the Buck transformers in the Line side, where they get 60 hz. just the way they like it..

What? How's that work?

Bob

A buck transformer.

Get a 240v/24v transformer, that has a 24v secondary current rating that's at least as much as whatever you need from the 250v line. Connect the primary of the buck transformer to the line, and put the 24v secondary in series with the 250v supply, in reverse polarity. That will subtract the

Hope This Helps! Rich

Except we're talking about an RPC, not a VFD.

Well, someone else already suggested the buck transformer, but here's a thought - does the VFD have input taps that can select the higher voltage input?

Good Luck! Rich

The only stupid question is the one you don't ask. :-)

I've seen transformers with two 120V primaries that you wire in series for 240V input, or parallel for 120V. This one might also have two secondaries, that would be used the same way; I'd have to see the tranny.

(it seems I'm about the third one so far to suggest the buck transformer.)

Cheers! Rich

It's irrelevant, because that is a Very Bad Idea.

Hope This Helps! Rich

Find a transformer with 240 VAC primary, and about 24 VAC secondary and with a secondary current rating at last as high as the current your VFD/Machine draw. Looks like about 15 A for 3 HP and 240 VAC input, so that will be a healthy sized transformer. Bought *new* it would be far from cheap, but you might have something of the sort around in your collection of whatevers which could be used.

Wire it up as follows (view with a fixed pitch font like Courier to avoid distortion making it difficult to understand);

L1)--------------------+---------+ +------------(L2A) | | | 0 +-3 || | | 3 || 0 | | 240 V 3 || E--+ | Pri. 3 || E 24V | 3 || E Sec. | 3 || E--------+ 3 || 3 || 3 || +-3 || | L2)--------------------+----------------------------(L2A)

The '3's are the primary winding, the 'E's are the secondary winding (thanks to the limits of ASCII graphics). The '0' near one end of each winding indicates the start. If you connect them as shown, the secondary should subtract about 24V from the primary. If you have one of the two windings backwards, it will *add* that voltage instead, so measure the output before you hook it up to the VFD.

Of course -- it *might* be possible that the VFD has a parameter which can be adjusted to change the overvoltage setting. Dig through the manual.

Good Luck, DoN.

The input has two windings, which if connected in parallel are

The output side is similar, but with two windings which are each

If you have a very heavy duty Variac or Powerstat which can handle 240 VAC -- they typically have multiple taps so you can get overvoltage out of them. Wire the input voltage to the full ends of the winding, and the output one tap down from the end. (You can even use the wiper to provide variable voltage to something else (not when your machine is running) if you need that. Again -- *you* are likely to have a Variac or Powerstat which you can barely lift sitting around, and that would be what you need for this.

Good Luck, DoN.

A TRIAC light dimmer is *not* going to produce a reasonable waveform for the input to a VVD -- sorry.

A big enough Variac or Powerstat could do it -- often without even needing to use the adjustable wiper if the taps are right.

Enjoy, DoN.

Maybe YOU are talking about an RPC, but the subject of the OP is " VFD question "

" Ive got a 5hp PC3 vfd running my Gorton MasterMill. The top end voltage it is supposed to run on..is 230vts + about 5 volts It will run down to 200 volts. Im running it on single phase, been doing it for years. "

NO!!! Light dimmers are phase controllers and play hell with other equipment.

It doesn't matter, since the transformer goes before anything else. It operates at line voltage, and in Gunner's case at a constant 60 Hz.

Or a 24V buck/boost in buck mode, for about 10% of the cost.

Cheers! Rich

It does matter, a set of transformers can most certainly come after a RPC, if you only have buck transformers large enough to handle the three phase current, not the single phase current.

Why? Gunner is likely looking for an inexpensive solution.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Why would you put three after the RPC when one at the input ddoes it right? Are you that stupid?