Pete C. wrote:

john wrote:

Pete C. wrote:


Ignoramus12852 wrote:


I am thinking about something. 480 VAC drives can be bought for next
to nothing. What they have is an inverter circuit and control
circuit.

They probably would not run on 240v because the internal transformer
that would supply voltage to the control circuit would supply only 1/2
voltage. They also might have an indervoltage sensor. I cannot think
of more things that depend on 480 volts being there.

So, if a hack could be done and a 1:2 transformer inserted between
480v inputs and the control circuit, then the drive would become a
240v drive with the same amp rating (and half HP).

What am I missing?

i


It might be an interesting experiment, but since new drives up to a
couple HP are in the $200-300 range and have a warrantee it would seem
to not be worthwhile if you put some reasonable value on your time to
make the modifications and on having a drive with a warrantee operating
within it's design parameters.

If you have enough machines that could use VFDs, you're likely better
off strapping their motors for 480V, buying the super cheap used 480V
VFDs, and finding a single good sized transformer to setup up the shop
240V to 480V to feed the drives.

I get flyers from automation direct that list single phase drives on
sale for less than 200 bucks new for a 1 hp drive. Unless you are
picking up the used drives for almost nothing, its not worth screwing
around with transfomrers and introducing more electrical losses and
potential problems in your system.

John


That's my point. Unless you have say a half dozen 3ph machines in the 5
HP range, new individual 240V drives are a better idea. With those big
machines you could go the step-up and use 480V drives and save some
money potentially. Either way trying to modify the drives is almost
certainly not worth the effort.




Most of the bigger drives use a transformer in front of them to switch
the input voltage.

Just as a side note, with vfds the motors don't always come with the
smoke alarm. It seems that the vfd limits the current and the smoke
doesn't release. I had one fail friday nite that didn't smoke. 25 hp
dc Reliance motor that just wanted to rotate to one position and stop.
The drive limits the current so the coils don't get too much of an
overload. On this motor there was a dead short to ground on the rotor.
The operator said that it had been rumbling for a while.

John