Small single-phase VFD for 120V? (2023 Update)

They might signal a fault and shut down if one or more connections are seen open. Like when you only connect one of the output phases to a load.

Just shaded-pole motors, usually.

A problem with the small drives from Automation Direct is the same all the others I looked at have. Aside from transfering 1-phase to 3-phase even the 120V versions put out 230V max. That's a recipe for magic smoke even if you tell everyone never to go past 50% or program in a limit.

Beats me why this is. There are so many applications for variable speed of smaller induction motors. Such as heated water circulation, cooling systems et cetera that only need small motors to overcome a miniscule gravity load. They are single-phase and run on regular mains voltage.

I guess so. It never settles down.

It's a really cool algorithmn. It starts up with the fans barely turning, basically silent, and never does anything acoustically dramatic.

** You on drugs ? Take a f****ng look at one.

..... Phil

Joerg wrote: ==============

** Why post drivel like that?

" not ideal" = what ??? And how do you know?

Being deliberately vague does not make you sound intelligent - it's f****ng stupid.

.... Phil

Joerg wrote: ==========

** That is total BULLSHIT !!!

Domestic and AC equipment fans run silently at low settings on a Variac.

..... Phil

Joerg wrote: =========== re: using a Variac:

** Bullshit !!!!

** Monitor the AC current in the Variac primary.

Bet you see a different story.

..... Phil

How many speeds do you need? I've never seen a weird speed pumping or racing issue with a decent speed controller (not a light dimmer, those are garbage, always) on even crap fan motors. They mighy run loud, or over heat at lowspeeds, or close to stall but that's about it.

The Dart Controls 55AC series is as good as it gets for a triac based speed controller. Built well, handles high currents, easy to fix and sometimes real cheap on ebay-

scratch that bogus URL.

The manufacturer is

Perhaps, but to burn the motor takes a lot of power and surely running the motor from a variac at reduced voltage reduces the liklihood of heat damage?

The load on a fan does not rapidly fluctuate - I'd have thought a variac transformer would work just fine, even if not the "officially approved" method?

piglet

piglet wrote: ===========

** Motor current drops in line with applied AC voltage.

So I squared R losses drop even faster.

** But is is - just a tad expensive for lost cost fans.

..... Phil

No, of course it doesn't; it drops in line with applied AC voltage minus the back-EMF of the motor. That back-EMF is missing if the motor isn't rotating at the intended (circa 1800 RPM in 60 Hz land) rate.

A nominal 1720 RPM induction motor at 1/4 HP is developing that 1/4 HP with a 'slip' of 80 RPM; at higher loads, it goes below 1720 RPM, and burns up.

whit3rd = INSANEa Google Monkey wrote: ============================= piglet wrote: ===========

** FFS is their no end to the vile lunatic Google troll.

Read this:

FOAD you pile of stinking autistic shit.

..... Phil

True, there may be no back EMF. But as Phil Allison showed at 50VAC the fan was consuming less than 2W - that is not going to make any serious heating problem.

I think Phil has done us a big service by making actual measurements!

piglet

** Don't inductors produce " back emf" ? Though the things did. ** Piglet is a fair dinkum genius.

** Far from it - I just broke the cardinal rule of usenet debates.

Which a s in war and politics - the truth is irrelevant .

...... Phil

True. Some VFDs allow one to program to disable that fault.

The main application for 120 Vac single phase in to 220 Vac three phase in small sizes is to allow three-phase industrial machines to be run from US domestic single-phase power. Three-phase 220 Vac industrial equipment is cheap and plentiful on the used market in the US.

One common use is bench grinders and sanders and drill presses, where the variable speed is an added big advantage. One sees a lot of these machines on Craigs List.

One can also get three-phase fans and circulation pumps, which are intended to be driven by a VFD which is commanded by some kind of PID (Proportional Integral Derivative) temperature controller, versus the more common bang-bang controller.

Joe Gwinn

For a test I drove this with an aerospace test setup (frequency- and voltage variable) and after finding the sweet spots there was considerably less hum from the fans at reduced RPM. Hence, I'd like that kind of setup in a tiny box instead of 19" rack size and that's why I started this thread.

Ok, thanks, I can do that.

Four would be fine if I can adjust each one to a target speed.

It's not a dimmer but made for AC fan control. Not sure how hot it is, it came with the fan assembly that was in there previously. The pumping sounds like stall - catch up - stall - catch up. Only in the 40-80% RPM range, outside that it's fine.

Thanks. It a pricey test though :-)

Ah, that may be an option. The other job would be to make 110% sure that it can never go past 120V because most VFDs put out 230V max, even those for 120V input.

Yes, that may be the reaon. Probably not enough market for driving 120V motors.

This situation requires the small muffin-style fans.

hmm, maybe just some relays and a small power transformer in buck mode would be fine. Fan motors are almost the opposite of a synchronous motor, always run at extreme amounts of slip, and voltage control is the easiest way to slow them down. The only catch is you need to sort of trace out the curve of speed to voltage for these fans. Some drop speed with 10% line voltage loss, some do nothing at all until you drop to 80% line voltage. They're all different and you will never get a nice linear "0-10" speed control with these, ever. To go real cheap, try a furnace transfomer. You can buck them to get something like 80% line voltage with one switch or relay. ... I've never seen a weird speed pumping or

Odd. Are the motors themselves OK? High heat is a killer for small bearings and motors. Not sure you can relube them or not. Luckily Papst stuff is top quality to start with though.

Maybe you can call and ask for a loaner. They're surpringly responsive to odd requests. zoro.com is usually the cheapest legit dealer if you buy new.