Which is better VFD 120 or 240 input voltage? I have both

title says it all, about to order a VFD, is there any advantage to 240 over 120 input voltage?

thanks!

You really need to state what you want to drive with it.

But, in general, the 120 V input type will be limited by the current capability of the 120V circuit, and the extra losses/lower efficiency due to higher input current for a given power output.

Generally, about 1.5 HP is the maximum, and that is pushing matters.


If you are not forced by some circumstance to choose the 120V (lack of 240V at the site, for instance) you will probably want to use a much more common 240V input unit.

its a very old bridgeport with pancake motor, and an old sb hvy 10 lathe. probably 3/4 hp, maybe 1hp max. both voltages are available on site but obviously using a regular 120v plug in power cord would be easiest...

FlyinChip said:

its a very old bridgeport with pancake motor, and an old sb hvy 10 lathe. probably 3/4 hp, maybe 1hp max. both voltages are available on site but obviously using a regular 120v plug in power cord would be easiest...

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Hi,

I have machines on VFDs (hitachi L200) on both 120v and 240v.

One thing: if the 120v circuits are GFCI,
You may find nuisance tripping which can be hard to eliminate. I thought I would end up with a simpler setup on 120v but ended up dedicating a circuit to get rid of the GFCI, negating the point of using 120v.

So in the future I would just do 240v.

Interesting. I have two VFDs on a GFCI circuit never had a trip in a couple years. Then I moved them to two new circuits also GFCI, no trips.

So if thats the only issue I may suggest my friend go with the 120 (its easier and the units are much cheaper for some reason.)

Update, on delaers electric, I found the L510 TECO VFD is actually cheaper (and smaller) for the 230v version. It's also a little smaller. Ordered that model.

Hi,

It isn’t 100% consistent behavior, and there are drive parameters which reduce the occurrence and also different GFCIs out there. So YMMV, but I found it unreliable.

Phil

Just so that you know (and for the benefit of future readers contemplating the same issue):
The 120V and 230V drives are identical, except for the fact that the 120V version has an ADDITIONAL set of components called a "voltage doubler" on the input side. This is why the MOTOR must be 230V even though the input is 120V; the voltage doubler rectifies the 120VAC into 165VDC, then through electrickery, boosts that to 330VDC (at 1/2 the current), which then goes directly to the DC bus of the VFD to be ready for the transistors to make it look like 3 phase AC again. That adds cost, size (in some cases) and more parts that can fail over time. I would chose 240V every time if both are available.

As to the ability to "using a regular 120v plug in power cord":
One of the reasons why the 120V input option stops at 1.5HP is because that is the maximum limit of a 20A circuit (if you ignore the NEC rules), and although the basic NEMA 5-15 receptacles are technically rated for 15A, you are allowed to put them on 20A circuits. HOWEVER, that means the ENTIRE circuit must be capable of 20A, not just the receptacle and breaker protecting it, so that means it must have 12ga wire minimum. Many (if not most) 15A receptacle circuits are wired with 14ga wire and a 15A breaker. So in reality, the PRACTICAL limit of a 120V input VFD is actually 3/4HP. Add to that the fact that in most cases those receptacles are not dedicated circuits,and you can easily end up with an overloaded circuit when trying to run the VFD fed machine while having other things running at the same time. So in reality you usually end up running a dedicated circuit anyway and if you are going to do that, you might as well use 240V.

Jraef said:

... through electrickery ...

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First time I've seen that word. Love it! Thanks for the great information.

Jraef said:

Many (if not most) 15A receptacle circuits are wired with 14ga wire and a 15A breaker.

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HUH? I built and wired my own house years ago and it was always 14 gauge for lighting circuits and 12 gauge for DCOs..has that changed?

Stuart

Jraef said:

Just so that you know (and for the benefit of future readers contemplating the same issue):
The 120V and 230V drives are identical, except for the fact that the 120V version has an ADDITIONAL set of components called a "voltage doubler" on the input side. T.........

Click to expand...

In many cases, the doubler requires ZERO extra components, in fact, it does not use all that would otherwise be present. Often, moving one wire will convert the regular rectifier to a doubler.

Usually, the capacitors need to be a more robust variety, as the "ripple current" can be higher for a doubler. But the number of components can actually be less than for a regular full-wave rectifier.

Usually you need a second bulk storage capacitor, as they charge one cap on the positive cycle, the other on the negative cycle, and put them in series. But many drives probably use multiple caps anyway.

Old computer power supplies just had a switch that added or removed the link that changed it from a straight bridge rectifier to a voltage doubler.

240 to reduce or eliminate current on the neutral. Better for noise reduction. Run a larger wire size and be absolutely sure the grounding conductor is sized correctly and terminates per code.

And to mention 14 AWG on 15 Amp 120 circuits, when the National Electrical Code is adopted by the Authority having jurisdiction, 14AWG is the minimum size conductor in tables. If you want to go larger that is OK.

SomeoneSomewhere said:

Usually you need a second bulk storage capacitor, as they charge one cap on the positive cycle, the other on the negative cycle, and put them in series. But many drives probably use multiple caps anyway.

Old computer power supplies just had a switch that added or removed the link that changed it from a straight bridge rectifier to a voltage doubler.

Click to expand...

Yep, switched one of the input lines from the bridge rectifier to the junction between series capacitors.

If you are going to do that, the choice of capacitor may need to change, but one suitable for the doubler works fine for the straight rectifier.