Re: VFD's

There are a few items to keep in mind.

First, VSD's are rated for amps. As you know, your 440 motor at 2
amps can be wired for 220 at 4 amps. The limit is the drive amps.

many people get a VSD with reserve. ie: they get a 7.5 hp unit for a
5 hp motor. perfectly alright.

You still need motor protection. disconnect for one. AND fuses, and
heaters/thermal disconnect. The VDS does have lots of neat stuff
inside, and can simulate these functions, but still requires them.
If you already have a motor starter, keep it.

Remember too that although this device offers little danger, most
home owners insurance does not cover electical fires caused by non-UL
motors and non-code wiring. I ran my lathe with wires laying on the
bench, coverd in chips. After I made the adapters I needed it got
into metal conduit fast.

The VSD constantly looks at the motor characteristics, volts, amps,
hz and re-adjusts them continuously. I have seen poorly operating
motors work perfect with just the addtion of the VSD and nothing
else. The key here is VOLTS TO HERZ RATIO. the voltage is converted
into DC and changed (modulated) to keep the motor in it's normal
paramters.

If a 3,400 RPM motor spins at 60 cycles, it would be a 1,700 RPM at
30 cycles. The problem is that the voltage would be too great at 30
cycles, so it must be reduced. Note too that your normal amp probe
will not read correctly. it is designed to operate in a specific hz
range, the minimum being something like 45 hz. It will read as the
flux field still exists, but the meter reading are not calibrated for
the conditons.

Your 25 hp VSD will run your 1 hp motor and your 1 hp VSD will run
your 25 hp motor. No really, but only up to the max amps of the
drive.

Dave

--- In CAD_CAM_EDM_DRO@y..., "johnhe" <johnhe@s...> wrote:
> Ahhhh haaa! The light dawns. I know, it's like talking to a plank
of wood
> but until thirty seconds ago I'd never really understood the
difference
> between star and delta. You learn something new everyday, do you
know it
> takes 3 years to build up the layers of sugar on jaw breakers?
>
> Thanks for all the answers everyone, I'll shut up now,
> John H.
>
> -------------
> Yes, Yes Yes and yes again.
> 440volt at 3 amp is the same as 220v at 6 amp.
> repeated in case you missed it:-
> 440volt at 3 amp is the same as 220v at 6 amp.
> So you put 240 single in and get 240 three out but at a higher
> amperage.
> To get your 440v motor to work on 220v you change the terminal
> connections from star to delta. In star the voltage has to go
> through two coils that are rated at 220v hence 440v supply.
> In Delta only one coil is connected hence 220v.
>
> >I thought the
> > inverter only changed the frequency of the current, not the
> voltage. Boston
> > Ficor said that most 3 phase motors that work on 460v are
> reconfigurable to
> > run on 230v 3 phase. Is this what you mean?
>
> Yes you are getting it. Invertors change the frequency but they are
> also capable of putting out the amps required to run on 220v
>
>
> >I have to do all this wallying
> > because I don't have the money to make any £300 mistakes, I'm also
> > electrically retarded when it comes to VFD's. : )
>
> That's why people who have gone this way are giving you the benifit
> of their advise and mistakes. They are not doing it so they can
smile
> as you fall flat on your face.
> Most modern motors will change over from Star to Delta. You have to
> look for 6 terminals in the box. Older motors have the star point
> buried inside the windings.
> If you decide to get this machine and the motor will not chance over
> I'll GIVE you a bloody motor to stop you whining <bg>
>
> John S
>
>
>
> Addresses:
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