×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

240 v genset, 208 v motor

240 v genset, 208 v motor

240 v genset, 208 v motor

(OP)
I have a 240 volt, 8 kw portable genset that needs to power a 208 v hoist motor.  Both are single phase.  The genset is putting out 246 v at no load and is burning up the motor.

Would you expect this to occur?  The motor has to start with full load applied (it's a hoist).  Do portable gensets typically have an adjustable voltage regulator?

Or am I barking up the wrong tree?

Sorry, I'm an ME.

RE: 240 v genset, 208 v motor

Portable could mean anything from "big box store special" to a Stamford/Newage, Kohler or Onan etc.  What brand and model number is it.  On the other hand, getting that much adjustment out of one isn't very likely unless it is designed to be reconnected for multiple voltages. You might be able to drop it enough to help since a hoist isn't usually a continuous duty motor.   

Are you sure the hoist is single phase not 3 phase?

 

RE: 240 v genset, 208 v motor

Somewhere the field current is controlled by 'something'. You can almost certainly find a way of reducing the field current a little, which will reduce the terminal voltage. A few more details would certainly help.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: 240 v genset, 208 v motor

What doees the motor nameplate have for voltage rating?  208 V isn't usually a standard rating...  I would expect to see 230 V, for use on a 240 V supply, or 200 V for use on a 208 V supply.  (Some have a 208 - 230 V rating indicating that it will work on a 208 V supply as well as a 240 V supply.) The generator voltage will pull down when the motor runs; I doubt that genset voltage is in itself an issue.  What do you mean by 'burning up the motor'?  Is it failing, or simply running hot?

RE: 240 v genset, 208 v motor

(OP)
Both are single phase.

A typical genset is a Generac XP8000E.  Details are at:

http://www.generac.com/Portables/XP/Products/XP8000E/

The motor is a proprietary design and more attention was paid to the under-voltage performance than over-voltage, since the power cords tend to be quite long.

The current plan is to use a buck transformer.  Seems easier than having field personnel monkeying with the wiring or regulator.

RE: 240 v genset, 208 v motor

I had the opposite issue with my 6kW diesel light tower. Low voltage. (short story).
Many of those small sets use capacitor excitation.
The voltage is pretty linear with respect the the amount of capacity in the usable voltage range.
You may replace the original capacitor with one of 120/146 of the value of the original cap. The voltage should be right on 120 Volts (plus or minus any tolerance errors in the capacitors.)
Use a cap of the same voltage rating.
DO NOT USE A MOTOR STARTING CAPACITOR.
Many motor starting capacitors are not suitable for continuous use.
If the unit has an AVR (doubtful) it is just a matter of tweeking an adjustment with either an insulated screwdriver or a non insulated screwdriver and extreme caution.
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 240 v genset, 208 v motor

Did you check the Hz? If it's a bit high, maybe you could slow the motor to reduce the voltage.

RE: 240 v genset, 208 v motor

If you can find an old electric clock driven by a synchronous motor, or a newer digital clock that uses grid frequency rather than a crystal for a frequency reference you can use that to check the frequency.

Bill
--------------------
"Why not the best?"
Jimmy Carter

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources