got bit by Power Factor !

[Sunking]

Can you get/borrow a scope and look at V/I curves? That would probably tell you a lot about what's wrong. My guess would be high harmonic content (i.e. gets square-wavey or peaky) when the load gets inductive (i.e. when the pump turns on and gets to speed.) If that's the problem, some additional capacitance between the pump switch and the pump might help.
PS; if either harmonics or voltage sag cause high current that will trip the motor protector even if the overall wattage stays low,
Try the other direction and choke off the pump flow with a valve.

Ditto.

Even though the KVA may be within range of the generator, the pump PF sounds like it falls outside the range of the generator. Do you know the generator spec PF. Something like .8 maybe? If you know the PF of the pump and KVA you can calculate and add a PF correction cap.

[inetdog]

It is true that some generators cannot handle high inductive power factor. If that is the case PF correction caps are the best solution.
A lightly loaded motor will have a worse power factor than one at full load. Are you reducing the motor load by restricting the flow? '
Try adding a resistive load in parallel to see if that improves things.

[jflorey2]

Something about the PF of the pump, and the lightweight rotor of the alternator.

Can you get/borrow a scope and look at V/I curves? That would probably tell you a lot about what's wrong. My guess would be high harmonic content (i.e. gets square-wavey or peaky) when the load gets inductive (i.e. when the pump turns on and gets to speed.) If that's the problem, some additional capacitance between the pump switch and the pump might help.
PS; if either harmonics or voltage sag cause high current that will trip the motor protector even if the overall wattage stays low,
Try the other direction and choke off the pump flow with a valve.

[Bala]

You will have to school me a lot more in how this is a power factor problem.

You essentially have only about 1/3 load on the genset.

I know of power factor but not in detail.

I have had a fair bit to do with a lot of generators running a lot of things. I worked in a hire company as a mechanic and we had an in house electrician.

I would still be thinking a problem with the generator or the pump.

pooring rain hers so have my main genset on right now. 10kva twin cyl lister with stamford.

[Mike90250]

the RPM & voltage is fine. I just can't do anything else but run the pump (the inverter logs it at 1,000watts) but this new lightweight alternator gear apparently has no headroom for PF losses. The inverter qualifies it just fine as a generator and pulls full load from it. Going to have to add this to the generator stickies. Same generator will not run the control circuit of the gas oven. (burners on the same range OK) And the old '30s generator won't run the garage door opener.
Likely related to all the safety gadgets
IMG_20160302_102438817_HDR-c.jpg

[Bala]

I would say there is a problem with the generator or the pump other than power factor.

probably not telling you anything you dont know

But, Check your generator / Hz - Engine RPM and make sure its governing to hold under load.

[Mike90250]

yesterday, my pump would not stay running, the Motor Protector circuit kept shutting it off after 20 seconds. I tried cleaning the filter, and running the outlet into a bucket, minimal backpressure, and it would still shut off. I really did not like the idea of having to repair a bum system in the rain, Rain. Clouds. Generator. Pump always worked on the other 3Kw generator (1930's gear) But the new generator - won't run the pump. Something about the PF of the pump, and the lightweight rotor of the alternator. The Subaru/Hatz diesel genset is rated 3.3Kw peak, 3Kw cont. But it's so lightweight (my old alternator weighs more than the new genset) I seldom run it at more than 2.5Kw charging batteries,
Goes to show that sometimes small is too small. With no other loads or battery charging going on, I can barely run a 1/2 hp pump off a 3Kw genset. What a pain that Power Factor can be. I guess the motor protector circuit did not like something in the power quality and shut the pump down.