On 05/09/2011 12:13 PM, Tim Wescott wrote:
On 05/09/2011 12:55 AM, Gunner Asch wrote:
On Mon, 09 May 2011 00:06:29 -0700, Gunner
wrote:
On Mon, 09 May 2011 01:19:57 -0400, "Michael A. Terrell"
wrote:
Gunner Asch wrote:
Ive got a 5hp PC3 vfd running my Gorton MasterMill.
The top end voltage it is supposed to run on..is 230vts + about 5
volts
It will run down to 200 volts.
Im running it on single phase, been doing it for years.
Now the power company has increased my 220 single phase to about 249
volts and when I try to start it..I keep getting OverVoltage Alarm.
I cant get the power company to change the tap down to a normal
voltage,
let alone 220 volts
How do I (cheaply) transform high voltage down 14-29 volts ac?
Id hate to loose the VFD on this mill and have to run it off a RPC
(which also puts out higher voltages)
How much current do you need? A simple buck transformer will do the
job, as long as it's secondary can handle the current.
I believe its 5.7kva
Gunner
Ok...Im going to look REALLY stupid here. Sigh..blame it on the stroke.
Or not..shrug
Ive got a BUNCH of 120/240 transformers..all marked 120/240 12/24
So if I wire one up to 240..does it mean that it will REDUCE the voltage
-24 volts?
Or is the output 24 volts?
Put 240 in, and the output will be 24VAC, in phase with the input. Wire
it up right (in 'buck'), and it'll reduce the output by 24V. Wire it up
wrong ('boost'), and it'll increase the output by 24V.
So wire it up, primary in parallel with your 240V line, and secondary in
series. Then check the voltage with a VOM. If it's 270 some-odd volts,
then just reverse the wires on _either_ the primary or secondary (not
both!) and check again -- your voltage should drop down to 225 or so. If
it's right the first time -- don't change anything!!
5.7KVA / 220V = 25A, so you need a fairly big transformer. _If_ the
transformers are all identical, and _if_ you want to go to the trouble
to get them hooked up right, you can parallel those 240V to 24V
transformers -- but you need to get it right, or you'll have a short
circuit across 48V, instead of two 24V windings helping each other. In
general if you put all the like-colored primary leads to the same
terminals and all the like-colored secondary leads terminals then you
should be safe -- I wouldn't trust that comment for a second. Instead,
you should connect up the primaries, then one by one connect up the
secondaries. Connect a pair of secondaries together _on one side_, then
check the AC voltage between the remaining wires with the transformer
powered up. If it's less than a volt, connect 'em together. If it's 48V,
then swap the direction of one of the secondaries and recheck. If you
have a clamp-on current meter it's probably a good idea to make sure
there's little or no standing current in any of the secondary wires.
Keep adding transformers until the sum of the current ratings is 30A or
so, put the wad of stuff in a fireproof cabinet, don't show it to your
local fire warden, and if your place burns down don't come crying to me.
Sorry -- 5700VA / 220V is around 25.9A. I'd aim for a buck transformer
with a 30A rating, unless you know that the VFD is lightly used. I'd
probably _still_ aim for the 30A rating.
And don't burn your place down.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at
http://www.wescottdesign.com/actfes/actfes.html