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.

[DoctorStrangelove]

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.

Ah yes: add electronics to an induction motor to make it "more reliable". .

If it's 50m down a hole then 240V sounds good, otherwise you end up with cable that would fit a 300A arc welder.

Stone me:

https://inverterdrive.com/group/Sing...ent%20is%2055A.

55A. .

[woody1]

Measured the power consumption of the pump yesterday; it's 1kW.
Ordered a 3kW (6kW peak) pure sine wave inverter. A charity had been donated a few new ones, and was selling them on-line. So, if nothing else, £77 goes to a good cause.
https://www.ebay.co.uk/itm/277635379315
Picked up an old car battery for free from the local garage to test it with. It still seems to have enough juice in it.
Anyway, will see if it works.

[Protagoras]

Stone me:

https://inverterdrive.com/group/Sing...ent%20is%2055A.

55A. .

LOL. Hence need to know the factor between starting current (may be called LRC) and full load current in order so know about starting the thing and the rating / timing of circuit protection.

Lenz's Law in action; need the rotor spinning to produce 'back EMF' to limit the current.

[DoctorStrangelove]

Pretty tricky with a single phase motor, no star delta starter for that, though there is such a thing as a soft starter.

'Tis only half a century since I did owt with big motors.

Ah, them were the days, it was all green fields around here then, with the 8080 as The Big New Thing. .


We await further experiments with innerest. .

[woody1]

Pretty tricky with a single phase motor, no star delta starter for that, though there is such a thing as a soft starter.

Assuming the inverter doesn't go up in smoke, if it won't run the pump I can always use it to power the telly, laptop/broadband, LED light.

[ladymuck]

Assuming the inverter doesn't go up in smoke, if it won't run the pump I can always use it to power the telly, laptop/broadband, LED light.

Ah... magic smoke!

[Protagoras]

Ah... magic smoke!

Hopefully the inverter has some suitable protection so that it will trip out and not continue to try to deliver current to the motor in the event that the motor fails to start.

[sadkingbilly]

Ah... magic smoke!

my favourite kind