Backup generator

[Protagoras]

For the water supply, is it possible to get something that works during power outages without electrical complexity?

Is the bore hole pump the submersible lift pump? If so, is this actually a low voltage pump that could be battery powered? Or is this some other pump in the system? And could this be battery powered or a supplementary battery powered pump added?

Is it feasible to convert the water system to solar / battery with supplemental mains charging?

[woody1]

It's a submersible pump, 50m or so underground. It is a pressurised closed system (no header tank), so the pump not only has to lift the water but also charge the expansion vessel (60L) to several bar. Hence it's pretty beefy - 240V ~1kW.

There's a pressure switch which is set to turn the pump on when the pressure in the system drops to 2 bar, and turn it off once it reaches 3.5 bar. I timed it yesterday, and it takes 30 seconds. If we use water sparingly, the charge in the expansion vessel can last several hours. However, a single loo flush is enough to drain it.

[WTFH]

On the car thing, here is a useful website:
https://ev-database.org/uk/#group=ve...030&s=3&p=0-10

[Dorkeaux]

It's a submersible pump, 50m or so underground. It is a pressurised closed system (no header tank), so the pump not only has to lift the water but also charge the expansion vessel (60L) to several bar. Hence it's pretty beefy - 240V ~1kW.

There's a pressure switch which is set to turn the pump on when the pressure in the system drops to 2 bar, and turn it off once it reaches 3.5 bar. I timed it yesterday, and it takes 30 seconds. If we use water sparingly, the charge in the expansion vessel can last several hours. However, a single loo flush is enough to drain it.

Well, then I guess it's:
1) Big generator sized to deal with your demand
2) Buy and install a more efficient soft-start pumping system, with a relatively small generator
3) A cistern (I have an open system with a cistern in my loft. Works great for flushing toilets and such.)
4) Big batteries (lead-acid deep cycle or lithium ion) charged from mains, solar, generator as required with an invertor
5) The electric car thing

Probably too deep for a hand pump..

[woody1]

I'm writing this down as much for my own benefit.

Backup power requirement

1.5kW (6A) for 30 secs (equates to 120A @ 12V)
Estimated start-up 6kW (24A) (equates to 480A* @ 12V)
Twice per hour for 3 days (72 hours)
Total power consumption = 72*2*30/3600*1.5 = 1.8kWh (or 7.5Ah which equates to 150Ah @ 12V)

* which I believe is comparable to the cranking amps of a car starter motor

[Protagoras]

I'd be looking at the feasibility of updating the water system to make it as independent of mains supply as possible.

My thoughts would be
- capture rain water for loo flushing in a header tank, top up the header tank from the bore hole water where necessary
- consider a battery-inverter system that could run the submersible pump 'as is' (probably with a soft-start pump motor)
- consider a replacement lower voltage pump could be used, e.g. 48V
- with any battery system add a mains charger, some solar and maybe even a wind turbine (if the location allows)

[woody1]

Will definitely look into replacing the existing control box (which I think just contains a capacitor) with a soft-start controller. The pump itself is nearly 20 years old, and may not have much much life left in it, so I might get this replaced at the same time.

[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?

[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.

[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).