Contact US

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!

*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

Convert generator output to 120vac

Convert generator output to 120vac

Convert generator output to 120vac

Hello, I have a Stamford S0 series alternator head controlled by an AS540 avr that is currently set for 120/240vac. I would like to change the winding outputs to 120vac. I know how to change the wiring and set the jumper on the avr but I have a question about the maximum output power.

The field coil is 17.5 ohms and the avr's maximum output power is 82 volts at 200vac. The avr wants a minimum of 15 ohms on the field at 240vac but states a minimum of 10 ohms below 175vac which is where my conversion will be operating. My calculations say that at 4 amps (avr max), the field voltage is 70 volts.

My concern is that the avr won't be able to generate the voltage on the field needed to get maximum power out on the gen set. Will I have to make other changes or will this work just fine?


RE: Convert generator output to 120vac

You can add a control transformer to boost voltage from 120 to 240 for the AVR.

RE: Convert generator output to 120vac

How much current should the transformer be rated at for this avr?

RE: Convert generator output to 120vac

The transformer simply needs to exceed the AVR draw. You listed 4 amps at 70 volts. So 280VA would be the minimum size transformer. In these cases it's simplest to select the first larger size of commercially available transformer.

RE: Convert generator output to 120vac


If this is a single-phase generator the line-line voltage is 240 V and line-neutral voltage is 120 V so you have dual voltage available at full kVA but if you wants only 120 V and full kVA available you must check the winding connections, if actually, the winding is connected in series then you can reconnect the windings in parallel for getting 120 V and full kVA. Just note the current will be the double 240 V current so you will need leads with at least the double size of the originals.

Best Regards


RE: Convert generator output to 120vac

Yes, the gen set is in series and paralleling the output will give me 120vac at 2x the current. My concern is the 240vac avr, that can be set for 120vac, won't be able to supply the field voltage to get full output when set to 120vac. I guess I could measure the field voltage at full load to see what the voltage is but how do I predict the avr output voltage when running at 120vac? The avr says max output @ 200vac is 82 volts, so does that mean @ 100vac the output would be 41 volts? I would rather not have to add a transformer as TugboatEng suggested but I am keeping that in mind.

RE: Convert generator output to 120vac


I believe there might be a way to connect the actual AVR to 120 V only, as you said changing the jumper. Try!!

You can also buy a dgeneriuc AVR that will works for arange of 120-240 V, there are a lot of them in the market.

What the generatorĀ“s manual and nameplate parameters said?


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! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close