Reply to: Backup generator

[woody1]

OFCH uses a bit more electricity than you might expect.

I haven't actually measured it but according to the boiler installation manual, it uses max 140W (burner 90W; circulating pump 50W).

Apart from the borehole pump, the only other big item we'd want to keep running in an extended power cut is the fridge/freezer. I put a plug-in power monitor on it, and was quite surprised it was only 125W. I knew the LCD TV didn't use much but measured it anyway - 45W.

[woody1]

I've been looking into soft start controllers, and apparently they can be problematic with "capacitor start motors" which is what our pump has.

AI seems to give a good summary of the issues:
https://share.google/aimode/6MtSRsCszefE3F7rx

[woody1]

It's a B6, so just a regular lighting one. I remember many years ago, before LEDs, installing a 1000W halogen outside light but had to swap the bulb for a 750W because it kept tripping.

[Protagoras]

What's the letter on that 6A circuit breaker (CB)?

I'd guess that it will be a 'B' or a 'C'.

Most domestic CBs will be 'B' curve (trips at 3 to 5 times rated current) and used where surge currents aren't excessive.

For the motor, quite possibly, the CB is 'C' curve (should trip at 5 to 10 times rated current in under 5s).

[Dorkeaux]

The pump is on its own circuit, and I hadn't noticed before that it's only a 6A circuit breaker. It's never tripped but I guess that's because the inrush current (20-30A) is only momentary?

Circuit breakers generally trip very quickly on straightforward shorts, more slowly on inrush current.

It depends on not just the amperage rating, but the trip curve rating as well.
Trip curve ratings on domestic circuit breakers are printed on the front of the breaker. They are types B, C or D.

I had to Google the following, You can do it too, Woody1!

Type B: For general lighting/sockets; trips at 3-5 times the rated current (e.g., 30-50A for a 10A breaker).
Type C: For higher inrush, like motors; trips at 5-10 times the rated current (e.g., 50-100A for a 10A breaker).
Type D: For large inductive loads (motors, transformers); trips at 10-14 times the rated current.

[woody1]

The pump is on its own circuit, and I hadn't noticed before that it's only a 6A circuit breaker. It's never tripped but I guess that's because the inrush current (20-30A) is only momentary?

[sadkingbilly]

Ah... magic smoke!

my favourite kind

[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.

[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!

[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.

[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. .

[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.

[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.

[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. .

[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.