Generator Issues

[grsthegreat]

One well company owner told me he loves portable generators. He gets lots of business replacing well pumps every year because of undersized generators.

 

[ponytug]

One well company owner told me he loves portable generators. He gets lots of business replacing well pumps every year because of undersized generators.

So, since I know that you (@grsthegreat) know so much about sizing generators, how does one appropriately size a generator to a well pump? Is it some number of kW/HP? LRA of the pump motor not more than XX% of the generator full load amps? Or?

I have a backup well that is 2HP/240, but our main well pump is 3 phase delta 5HP. I have been thinking of getting a generator and add a VFD large enough to cover the main well, but I haven't managed to size the generator.

All the best,

Peter

 

[Patrick Herd]

Warning: Engineering opinion coming from a 400/230V land dweller

One thing to consider if you have a 220/110 generator and potentially big 110V loads is to use an autotransformer. Victron make them for the purposes of load balancing split phase systems for generator and inverter supply. Autotransformer - Victron Energy

An appropriately sized autotransformer will allow a 3kVA 110V load to be run on a 3kVA 220/110 generator for example (within reason of course)

 

[ponytug]

Warning: Engineering opinion coming from a 400/230V land dweller

One thing to consider if you have a 220/110 generator and potentially big 110V loads is to use an autotransformer. Victron make them for the purposes of load balancing split phase systems for generator and inverter supply. Autotransformer - Victron Energy

An appropriately sized autotransformer will allow a 3kVA 110V load to be run on a 3kVA 220/110 generator for example (within reason of course)

Yes, it is a great product and used more often by sailors than landlubbers for some reason. I would also point out that the autotransformer can help clean up the quality of generator power as well.

All the best,

Peter

 

[Steelauzzy]

We have been using generators for primary power for a couple years now. Loads such as microwaves and welders tend to hit the generator hard and the governors have a hard time catching up under the load. Our solution was to increase the wire size so we had As small a voltage drop as possible aswell as add a decent size transformer and a motor running the largest pulley we would find (as a flywheel)
What I found is the grid has so many rotating masses like tens of thousands of pounds if not a ton more and of such a size that any sudden loss would only equal x% of the capacity so the effect on system rpm is basically none. With a small generator when a load jumps on that’s 10% + of the Gen capacity it has enough kick to lower the rpm. This in turn lowers voltage and frequency and causes a massive amp spike that the Gen now has to compensate for so it goes full Skookum then sometimes that causes over rpm/voltage/frequency and fries the pants off your circuits.
A small flywheel and a transformer act as a buffer for that millisecond drop so the Gen has time to pickup and carry the load. Your other option is to upsize your generator so you never exceed 35% load.
Fuel source is also a key factor. Running on gasoline you should have decent response. Propane alright response but If running on nat gas it doesn’t have the same kick to maintain. You have to de rate max capacity and significantly de rate sudden loads.
As an alt a small solar battery system would act as a ups and if sized properly will cause a dramatic performance boost for small generator systems. This obviously has a better roi benefit than flywheels and transformers.

 

[grsthegreat]

So, since I know that you (@grsthegreat) know so much about sizing generators, how does one appropriately size a generator to a well pump? Is it some number of kW/HP? LRA of the pump motor not more than XX% of the generator full load amps? Or?

I have a backup well that is 2HP/240, but our main well pump is 3 phase delta 5HP. I have been thinking of getting a generator and add a VFD large enough to cover the main well, but I haven't managed to size the generator.

All the best,

Peter

Actually i generally never even take a well pump into consideration when installing a 22KW Generator because there wont be any effect on a well pump, even a deep water pump. Where it matters is when a customer has a 5,000 or 7,500 watt portable unit and wants to power house and well with manually flipping breakers. At this point i place a clamp on meter and log actual start and run amps that the well uses during operation. Then i also use a clamp on meter to check what amperage there wanting to run When power is out. Most of the time i can convience customer to go larger and get a 10 kw portable once they see the actual readings.

on well houses i ALWAYS contact the well company and get their recommendations on generator requirements. They have always been helpful. And i have never had a call back that generator wouldnt work during a long outage.

 

[Walker1]

I did not read all the threads, so not sure if this angle has been covered. If it has done it in the past and can’t do it now, then either the load has changed or the generator has changed. Most likely scenarios is that the fuel in the genny is crap. pull the carb bowl and look at the fuel, most likely you will find water in the bowl. Then run your torch cleaners up the main orifice, spray with some carb cleaner and reassemble.
I can’t tell you how many machines I have fixed over the years doing this.

 

[Larry Caldwell]

One thing people ignore is the power factor of the pump motor. A typical pump motor will have a running power factor of 0.6 to 0.75. The locked rotor (starting power factor) can be as low as 0.2. A generator has to have enough power to make up for inductive losses at startup. A motor typically pulls less than its rated current when running, and only pulls the maximum amps when fully loaded, but starting a pump motor makes heavy demands on the generator. 1 hp is only 746 watts, but divide that by 0.2 and you need 3730 watts to start it. A 2 hp pump needs 7,460 watts to start it, and that's with no other load on the genny and no line losses.

 

[ponytug]

Makes sense to me. All the usual starting forces, plus all of the back pressure from the water in the pipe, would certainly add up to quite a draw. I don't know why I am surprised; my AC has some insanely high LRA, like 114A, which would be an even lower PF as the running amps are more like 18.

I can see that I need to go clamp an ammeter around one of the leads on the pump and check the starting current.

Thanks for all the input.

All the best,

Peter

 

[grsthegreat]

That, and as a motor ages, the amps go up to start and operate. Lumber mills here regularly clamp meters on to check starting loads to determine when to rebuild or replace motors.
i wonder how electric car motors will age out. Time will tell.

also, i& you go into community well houses youll see a chart with history on amperage draws on the pump motors. Also to track replacement.