OT Another Generator Question

I have a 7.5 kW generator mounted on a box truck to run some lights and a 230V, 3HP single phase pump motor. When we try to start the pump with a load, the voltage between the phases drops by half and the current shoots high. When we start it with no load , the voltage stays good, but the current is still up around 16A.

For giggles, we plugged the motor into our shop power (208V), and the motor starts and runs fine at 11A.

Any ideas?

The lights are only drawing 1.5A at 120V.

3HP Pump

I tried the exact same thing with a 3HP pump and a 6.5kW generator. The generator does not have the ability to maintain the voltage during startup because the inrush amps to start the pump are too high. It problably has a start winding and capacitor that needs the additional current.

Is it a real alternator type generator?
Many of the smaller ones are DC then use an inverter to create 60hz.
Even though they are rated enough they will not start an RV AC unit (cap start)whereas a smaller real generator will start the same unit. The real generator does struggle but it starts it.

Thanks for your input guys, we got it running when someone realized that the pulley they had put on was for a 5 hp motor that had been originally spec'ed for the project. We downsized the pulley accordingly and away she went.

Thanks again.

A 3 HP pump is nearly half of generator capacity. That can be a challenge for any alternator (mostly the voltage regulator) and for the prime mover ie engine and governor.

To ease starting
1. Unload the alternator as much as possible
2. Shut the discharge on the pump (I assume centrifugal). After pump starts running open teh discharge to keep pump cool.
3. Put the smaller loads back on alternator

Dan Bentler