Sizing well pump inverter (first post)

[Texas Wellman]

All I can tell you is that some generators are over-rated and some are under-rated. I guess the Honda is "under rated". I do not remember what the start-surge rating is but I know that it will easily start up to a 1.5 HP 3-wire pump with a CSCR (cap start cap run) control box.

LRA is just an estimate. Once the motor starts to spin even a tiny amount the LRA goes down. LRA only lasts for a fraction of a split second.

Do you mean a 5k inverter with 10k surge capacity? I guess I don't understand how the EG3500 can start a 1.5 hp pump. The locked rotor amps would have to be lower than the max AC output of the generator? 29.8A? I would thing the larger motor would be more difficult to start. I got the 3 wire pump and the cap/start cap/run for the lower starting power requirement, although, I'm not sure it matters terribly looking at the start requirements of the pump.

[Mike90250]

The pump starts will be for household usage, so multiple starts to refill pressure tank drawdown. Probably a few starts in the morning, nothing during the daytime and again heavier in the evening. The 4548 is just shy of what we need and with other loads running concurrently it might not work so well. Is there any problem using an inverter that's a bit too large for the rest of the household needs?

So without the solar contributing, it's going to hit the battery bank pretty hard early in the AM, when the batteries are soft from all night

We don't really need a 6k inverter except for the one load. The rest of the time it probably will not exceed 3k or so. I don't think the tare losses between the 4548 and he 6048 are significant.

My normal loads are 200 - 300 watts. Till the toaster or microwave are fired up. The only time I've ever pulled more than 3KW, was when the house was under construction and the floor dude clipped into the power panel to run a 3HP floor sander.
I watched my batteries get lower and lower for 2 days before I saw what he had done, then the contractor tried 2 generators and finally had to rent a 10Kw tow behind generator to run the sander. I was amazed the inverter would run that huge motor. The XW's are really beasts.

Mike, just curious what welder you are using with PV? I had basically written off using a welder without generator support.

30 year old 240VAC, 200A Lincoln MIG with huge tapped transformer in it.

[inetdog]

All I can tell you is that some generators are over-rated and some are under-rated. I guess the Honda is "under rated". I do not remember what the start-surge rating is but I know that it will easily start up to a 1.5 HP 3-wire pump with a CSCR (cap start cap run) control box.

LRA is just an estimate. Once the motor starts to spin even a tiny amount the LRA goes down. LRA only lasts for a fraction of a split second.

With generators, you have a different mechanism behind surge overload tolerance than with inverters (except when talking about inverter-output generators).
1. The current from a generator is limited in a hard sense by the resistance of the generator windings. That limits the short circuit current and to some extent the current which can be delivered without a major voltage drop.
2. The current is limited in a more flexible sense by the heating effect of the current in the output windings. If only one half of a 240 generator or one phase of a three phase generator is loaded, it is possible to hit the thermal limit in a minute, more or less, while staying within the capability of the prime mover (engine).
3. The power delivered by the generator in a steady state is limited by the maximum power that the engine can develop. And as the speed starts to lug down, the power output will decrease even with the throttle full open. The maximum power of the engine may or may not also be limited by the available engine cooling, if it is a weak design. But in the very short term (seconds) the kinetic energy of the rotating mass of the engine and the generator can deliver a very large power surge as it slows down.

The off-grid inverter is limited by the battery and wiring resistance, the thermal protection, and the resistance of the output elements. If the inverter is conservatively designed, there will be a substantial surge possible until the circuit overheat causes the protection to kick in. A less conservatively designed inverter will just shut down in response to the current rather than the built up heat.