Reply to: Backup generator

[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.

[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]

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.

[woody1]

I want to test if it's possible to power the water pump (1.5kW) with an inverter.

I'm thinking a 3kW (6kW peak) inverter might suffice. I'll probably go for a more expensive pure sine wave one, so I've always got the fallback option to use it with electronic devices (TV, laptops etc).

My plan is to power this from my car's battery (with the engine running?) just as a test. If this works then I'll get a big leisure deep cycle battery.

Does this sound reasonable?

Any recommendations on makes of inverter?

[DoctorStrangelove]

The chinesium replacement capacitor is some ridiculous prince like £28 or so.

A similarly rated 12uF polypropylene capacitor is about £3.

£25 seems a lot to pay for a funny shape.

As a bodger of long standing I really couldn't justify it. .

[Dorkeaux]

The 12uF capacitor wasn't an electrolytic being 450V AC or something. Replaced it with a fine bodge job using 4uF 800V paper in oil capacitors out of an ancient scope and it worked ok.

I still don't understand how the field gets energised but there you go.

Whew.. well, if it works, it works.
I use electrolytic caps around those values and voltages all the time in power supplies and valve audio amplifiers. They cost little, but are polarised.
Maybe for your application the poly film caps would be a better choice. If you google it, you can buy those exact can capacitors all day long for about a fiver.

[DoctorStrangelove]

The 12uF capacitor wasn't an electrolytic being 450V AC or something. Replaced it with a fine bodge job using 4uF 800V paper in oil capacitors out of an ancient scope and it worked ok.

I still don't understand how the field gets energised but there you go.

[Dorkeaux]

I think both my generators (defence in depth ) have 12V charging.

The other thing I found was that the thing won't start generating on load, so you have to start it, get it running, then turn the load on.

The alternators fitted to the el cheapo chinesium generators are weird.

I had to replace a 12uF capacitor on one because it had dropped to 2uF and the resonance was wrong. Truly weird.

No idea what the output waveform is like but I wouldn't run anything electronic off mine.

I've got a 300W 12V to 240W inverter for running sensitive stuff.

Pure sinewave inverter generators are available.

Yes, all true.

Tulipy electrolytic caps are the bane of my life.
I keep a stockpile around to recap things that fail, but of course they age even if they aren't installed, soo..

My modest generator has an inverter, and all my computer gear runs off a UPS which hopefully provides some protection.

The OP's pump probably doesn't give a stuff though.

[DoctorStrangelove]

Sure, if your car isn't over-sophisticated.

For charging a battery I would think even the cheapest, nastiest generator would do a better job, though.

I think both my generators (defence in depth ) have 12V charging.

The other thing I found was that the thing won't start generating on load, so you have to start it, get it running, then turn the load on.

The alternators fitted to the el cheapo chinesium generators are weird.

I had to replace a 12uF capacitor on one because it had dropped to 2uF and the resonance was wrong. Truly weird.

No idea what the output waveform is like but I wouldn't run anything electronic off mine.

I've got a 300W 12V to 240W inverter for running sensitive stuff.

Pure sinewave inverter generators are available.

[Protagoras]

Just in case perhaps you've not seen them, so-called 'portable power station' products are available. I've not used one myself, but a bloke I know has one on his boat (not sure what make it is).

e.g. https://www.ankersolix.com/uk/products/c1000

This could be a good option for running some portable LED lighting etc during power cuts rather than connecting to the car.

[woody1]

On reflection, maybe the easiest thing to do, if the power looks like it's going to be down for longer than a day, would be to just do what one of our neighbours did and check into a hotel.

[woody1]

Sure, if your car isn't over-sophisticated.

It's 19 years old so I doubt it, and the battery is readily accessible. When the electricity goes down, I hook a 12V 10W LED to it so we at least have some lighting in the house.

[Protagoras]

Just thinking...

If I get a deep cycle 12V battery and it runs down before the power comes back, could I recharge it using the car with the engine running?

Note that for lead acid batteries you don't want to be discharging below 50% capacity to avoid shortening battery life.

Also, lead acid battery capacity depends on discharge rate. The battery Ah specification will be at a given discharge rate, commonly c/20. i.e. a battery may be specified as 100Ah capacity at a 5A discharge. At higher discharge, the Ah available is reduced. But lead acid batteries are reasonably cheap so it's easy enough to put several in parallel (with a separate fuse on the output of each).

[Dorkeaux]

Just thinking...

If I get a deep cycle 12V battery and it runs down before the power comes back, could I recharge it using the car with the engine running?

Sure, if your car isn't over-sophisticated.

For charging a battery I would think even the cheapest, nastiest generator would do a better job, though.

[woody1]

Just thinking...

If I get a deep cycle 12V battery and it runs down before the power comes back, could I recharge it using the car with the engine running?