I have 208V wye 3-phase in my shop. From the recommendation of this group,
I installed a single-phase buck boost transformer to boost the 208V to 230V
(single-phase) for my single-phase compressor. It works great.
I noticed in the McMaster-Carr catalog that they have 3-phase buck boost
transformers that can boost 208V to 240V. The motor face plates on my
3-phase mill and lathe say 230V. Should I bother to install a pair of buck
boost transformers for these machines? Are 3-phase motors less sensitive to
lower than expected voltages?
Maybe. It depends on whether the motor is under-excited at 208 v all the
time, or just at full load. Can you measure the line current draw?
Does the motor seem to deliver full power? Do you expect to load the
motor to full load? (Ie, if it is a 3 Hp mill with R-8 spindle, you may
never need the full 3 Hp from it, and it will likely be fine running at
a bit reduced voltage.) If you expect to need the full power from the
motor in routine work, and the plate says 230 only, not 208/230, and
especially if the motor draws a lot of current or runs hot, then I think
you would do well to deliver 230 V to it.
Jon
Unless you are experiencing motor stalling and/or over-loading, causing
motor overheating or trip-out on a regular basis, there is no reason to
boost the voltage. Theoretically, you get (208²/230²) or 81% of normal
starting and max running torque, and a little slower full load speed, but
most people never more.
Randy
You can consider 240V to be the 'US Standard' nominal voltage, but if
it sags to 230V under load and voltage drop it's still acceptable.
You really shouldn't run 230V or 240V marked equipment hard on a
208V feed unless the motors are double-rated 208/240V, or you check
that it is not running overloaded - check the running full-load
current against the nameplate amps.
If the load is highly variable (like on a lathe) just don't take as
big a cut - they really should put panel ammeters on all machines
(with a marked redline) so you can see at a glance if you have the
feed rate set too high - BEFORE the motor has a "Magic Smoke Escape"
moment...
That said, if you want to be sure not to have a motor-toasting
incident get a set of 16/32V buck-boost transformers and hook them up.
A small transformer can boost the voltage for quite a large load, but
you need to read the instructions.
If you aren't going to use the connected equipment for a while, turn
off the power at the transformer primary breakers - no sense wasting
power exciting the transformers for weeks at a time.
Last time I messed with a buck-boost was for a friend who needed to
service 208V wired automated stage lights, and only had 120/240V 1ph
available at his shop. Rewiring them to 240v before servicing them
and changing them back when done is out (terminal strips break), so he
put in a bucker and a set of permanent 20A 208V receptacles -
twist-lock, straight-blade and stage pin.
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So what about the opposite ???
I have several ventilation fans within a greenhouse rated @ 208 I am running
on ~ 236V......Dayton 24in dia fans to be exact.
They start fine and dont heat up even if run all day long in hot
weather--any cause for major concern in your opinion ???
You can consider 240V to be the 'US Standard' nominal voltage ...
Only for single-phase machinery and data processing equipment.
Standard U.S. voltages include: 120, 120/240 (cooktops and the like), 240
(commercial only), 120Y208, 277Y480.
Motors and the like are usually specified as 208-240.
It depends on the motors.
We used to run on 240V here in UK but other countries ran 220V. The cheap
motors designed for 220V didn't last as long as our domestic ones designed
for 240V even when fitted as OE to machines.
Now we are slowly dropping our voltage to be in line with Europe and will
eventually end up at 220V.
All the above are single phase voltages. For 3 phase, multiply by 1.732
John
The engineers at Dayton are based in the USA and know they're liable
to be run on 240V, I'm surprised they weren't marked as dual rated.
Call them and ask, or if a newer one smokes they may not honor the
warranty.
Other than that (and considering you already own them...) if they
don't draw over nameplate current and don't run hot, I wouldn't worry.
I'll bet they're running well under max current.
But as they die off through normal attrition, see if you can find
dual-rated or 240V rated motors - and if you have a whole bunch (dozen
to hundreds) already bought and installed you might give up and
consider a buck-boost or two.
Some of the stuff in this business falls into big gray areas, and as
long as it works and it's safe, who cares why - leave it alone. ;-)
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