Backup generator

[woody1]

I'd really not do that ... !

I think a good approach would be to take the full specification of the pump induction motor and discuss the requirements with some bore hole pump inverter suppliers to obtain a recommendation regarding an inverter capable of dealing reliably with the usage pattern and in particular the motor starting current (which should be stated on the motor / documentation).

The starting current will be multiple of the running current and this really needs to be known to size the inverter. Also, the inverter will have circuit protection, and this needs to be appropriate to the specified load characteristics. No point having an inadequate inverter that trips when the motor starts and fails after a few months.

Once you know the required specification and cost of the inverter this could be compared with the cost of replacement pump options (e.g a low voltage pump), considering also battery storage (at which point lead-acid batteries will probably not be the best answer).

I really would look at this from a system perspective and ensure that the elements are correctly specified and integrated.

Personally, if I had such a need, I'd get in touch with a specialist supplier of off-grid bore hole systems to discuss requirements, options and products.

I don't want to go OTT for the odd power cut, especially when the existing system has worked trouble-free for 20 years.

Not sure a low voltage submersible would be capable of raising water 50m and then pressurising the system to over 3 bar. Even if this was possible, you've got to be talking a high amperage motor, which would require very heavy gauge wire to minimise resistance losses with 50m of cable.

For example, I've got a 12V 5A (60W) submersible that I use for pumping out small floods. Even using quite heavy gauge cable, anything more than a couple of metres or so, and the performance starts to tail off. And to get even close to the pumping power of a 240V 1.5kW pump, you'd need something way, way bigger than this little pump. The copper wire would have to be so thick to carry such low voltage/high amperage for 50M that I can't see it being feasible TBH.

[Protagoras]

Yeah, I think that's the challenge!

Until it's time to change out the pump and modernise the system, maybe it's best left alone.

PS
I've seen 48V pumps that claim to work with a 50m head ... but this is at the expense of larger cabling.
Many of the larger pumps on offer now appear to have variable frequency drives; presumably the tech moves on as more people run these things off battery / solar systems.