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silvercbx 08-27-2013 07:32 PM

VFD Question
Does anyone here know about VFDs? I don't want to burden the forum if it is not appropriate here.

GoldenSparky 08-27-2013 09:03 PM

What is your question?

ddawg16 08-28-2013 12:23 AM

Variable Frequency Drive....typically used for 3 phase motors....but there are single phase....and some single phase in to 3 phase (used to power 3ph off a 240Vac line) Golden says....."question?"

mpoulton 08-28-2013 01:06 AM

A bunch of us here know quite a bit about VFDs.

Blondesense 08-28-2013 09:59 AM

Volunteer Fire Departments?


ddawg16 08-28-2013 10:08 AM

Very Fine Diva's?

md2lgyk 08-28-2013 10:18 AM

Some of the military equipment we manufactured where I used to work had VFDs to control the speed of 3-phase, high-pressure pumps in reverse osmosis water purification systems. All I really know about them is that they were large (about the size of a dorm room fridge) very, very expensive, and complicated to program.

ddawg16 08-28-2013 01:30 PM

Vacuum fluorescent display

V.F.D., a secret organization within Lemony Snicket's A Series of Unfortunate Events

Virtual Floppy Driver

Virtual Floppy Disk

Vicarius Filii Dei

TheEplumber 08-28-2013 05:58 PM

Worked with freq drives on hydronic systems before
I set the pump, electrician wired, controls did their part. We all stood and watched during start up- pretty simple really :)

silvercbx 08-28-2013 07:52 PM

What I am contemplating is a test bed to check out Motorcycle Alternators used on the Honda CBX. It is a 360W enclosed unit that is independent of the engine. I plan to mount the Alternator on a frame and a driving motor to spin it, either at the motor rpm or use a step-up pulley system to increase the rpm. From what little I have learned, so far, is that the VFD can be used to vary the speed of the motor. The one I have in mind is a single phase input with a 3-phase output to a 3 phase, 3/4 hp motor. The vfd will also step up the motor from the 120V input to 230V output, which matches the motor input. To avoid overheating at lower speeds, I plan to set up a couple of small cooling fans aimed at the motor. In case you're interested in exact components, the Grainger P/Ns are: VFD - 5WJK2 and MOTOR - 11w351. To me, the components seem to match ok and with some minor engineering, I think I can couple the motor to the Alternator without too much trouble.
I'm in new territory here, never having dealt with VFDs before; any pitfalls? Any comments on the grand plan?
Thanks (and for all the various definitions :jester:

SPS-1 08-28-2013 09:23 PM

What is the speed range that you expect to be running the motor at ?

ddawg16 08-29-2013 12:36 AM

I understand what your wanting to do...VFD is a good application....

But I would suggest keeping your costs down and maybe going with a single phase to single phase setup......

If you have not bought the motor yet....hold soon as I get to work in the morning I'll send you some more exact details.

AB has a power flex VFD that is in the $500 range for the HP your wanting to use.

What is the maximum AC power you have available?

J. V. 08-29-2013 11:19 AM

Keep in mind, many VFD today can out out up to 400 HZ, maybe even more.
So the base speed requirement is very important.

The motor you purchase should be the right RPM. You can exceed the motor rated RPM (base speed), but you loose torque proportional to the increase over base speed.
Same with under speed. Less torque.

So how hard is the alternator to turn over? If its light load better for you.

3 phase motors are cheaper and much more reliable than ac motors. I would stick with your idea.
Single phase input to VFD and three phase output to the motor.

ddawg16 08-29-2013 11:44 AM

Your typical AC motor is going to be either 1200, 1800 or 3600 RPM if running on 60 hz.

Here is a link to the Allen Bradley PowerFlex 4. They have one that is 120Vac in...230Vac 3ph out.....


I can give you the contact info for a local rep...

You need to do 2 things....figure out what motor you want and what VFD will drive it....

silvercbx 08-29-2013 08:09 PM

Well, I'm feeling a little overwhelmed! I read (skimmed) the AllenBradley stuff and just got lost in all the specs; most of which I don't think I'm concerned with. But I did think about it and have some question(s) and further info.
1) Am I correct in believing that the variable speed control is done by varying the FREQUENCY? Prior to discovering VFD, I always thought speed was varied by chopping the VOLTAGE but is than now 'old school'? Just for learning, how does varying the Frequency change the motor speed?
2) The particular motor I am looking at has a shaft speed of 3420. I like that speed as I can double it with a pulley set-up and drive the Alternator to over 6000 rpm, something I want to do (the CBX can hit over 9K rpm and running between 4K and 7K rpm on the open road is normal)(Just as an FYI [in case you 'might' be interested] this is a 6-cylinder bike and has a fantastically rapid acceleration rate, so they put a mechanical clutch between the Drive and the Alternator to protect internal parts.) Anyway, testing the Alternator at 6840 rpm will tell me all I need to know about it. Being able to change the pulley set-up to drive the Alt at very low speeds (500 rpm or more) is very important as it is needed to know when it begins charging into the battery system.
3) I was told that 750 Watts = 1 HP, so the Alternator at 360 Watts will require just a little less than 1/2 HP to drive it (under full 30 amp load). I kind of figure that doubling the speed of the motor (with pulleys) will place extra load on the motor but I think a 3/4 HP motor can handle it (besides, their is a HUGH jump in costs when I move into the 1 HP level - both in the VFD and the Motor). Of course, the factor of reduced torque at higher and lower motor speeds is a factor I have no way of determining.
4) What little contact I had with 3 phase motors during my years with IBM did let me agree that they are better than single phase motors for what I'm trying to do. But I have no technical experience with them. I only picked that motor because it had the right rpm and the price was good. As I am big on reliability, if anyone has a better motor (than doesn't pick my pocket), I'd be obliged.
5) To my uneducated eye (very), this is a simple speed control project; no programming, no remote. All I want to do is mount the Alternator, select the pulley range and turn it on, varying the speed by just turning a knob (pot, rheostat, whatever). I'll rig up a photo tach on the shaft to see a visual of the Alt rpm at any given setting. I'll build an electrical testing setup to measure the amperage and voltage from the 3 stator windings and what the Rotor amperage draw is (I might even scope it but I think meters and selective switches will do the job ok.
I do appreciate all of the input; I hate being ignorant in this area but...........

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