Convert generator output to 120vac

[dave313]

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?

Dave

 

[TugboatEng]

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

 

[dave313]

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

 

[TugboatEng]

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.

 

[petronila]

dave,

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

Petronila

 

[dave313]

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.

 

[petronila]

Dave,

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 generator´s manual and nameplate parameters said?

Petronila