camelot-forum.co.uk

I noticed during my cheap charging period I was getting an occasional shutdown of charging of the batteries and think this was due to high grid voltages. I've been monitoring and it quite surprising how this varies.





Found this article which is interesting.

https://yorksandhumberclimate.org.uk/op ... cross-grid

I'm surprised by how your mains voltage increases during the charging period, mine is the total opposite.

Fintray wrote: ↑Fri Oct 18, 2024 3:16 pm I'm surprised by how your mains voltage increases during the charging period, mine is the total opposite.

My 240 -242v that is flat is my off grid voltage.

Ah that explains it.

I thought UK nominal voltage was 240, not 230? Where did that assumption come from?!

At least it's not that rubbish 110v they have over in the US - no use to anyone!

I think 230 came in to equalise us with Europe.

My voltage drops overnight too.

Are you near a very high overnight energy user?

The reason to increase the voltage during this period could be to ensure the voltage does not drop too low for anyone connected near the high load, but you must be upstream of it.

The document says reducing the voltage will save consumers money. Reducing the voltage will surely increase transmission losses as the current increases to produce the same power?

For the consumer, I don't get the saving - a resistive load will draw less power, yes, but if that resistive load is a heater with a thermostat, then the overall power will remain the same - it will just take longer to heat the water in the washing machine/dishwasher/hot water cylinder. Arguably, longer heating means longer time for heat losses - so theoretically less efficient. Maybe your fridge compressor will produce a little less heat, but them it wil be running for longer as its power has reduced.

For non-resistive loads - like a car charger - the power is controlled and so the voltage change will have no effect. Same goes for a switch-mode power supply in an LED light/TV/phone charger/any modern appliance.

What am I missing?

jonc_uk wrote: ↑Fri Oct 18, 2024 3:30 pm What am I missing?

I'm missing it as well. It's a bit like those chocolate teapot voltage optimisers sold for domestic use.

jonc_uk wrote: ↑Fri Oct 18, 2024 3:30 pm Are you near a very high overnight energy user?
The reason to increase the voltage during this period could be to ensure the voltage does not drop too low for anyone connected near the high load, but you must be upstream of it.

(Voltage 240v - 242v is because that is our off grid voltage).
We have our own 100kVA transformer straight off the 11kV network and I don't know of any really high users. Their is a farm near us that makes dog biscuits that has boilers to render the meat but I'm not sure how they are powered. I should monitor the voltage during the off cheap rate as well really. Their is also another farm that has an anaerobic set up.

There was a trial over a decade ago showing about an average of 5% energy saving running at 220V vs 240V for users with non electrical heating. I read somewhere that most modern stuff with switched mode power supplies are designed for max efficiency at 220V which might explain some of the savings.
https://www.ofgem.gov.uk/sites/default/ ... -vx1_0.pdf

And another bit of info here from the IET,
https://electrical.theiet.org/media/149 ... sation.pdf

I can't think of an explanation for your voltage spiking overnight. I'm curious as to whether the voltage rise synchronises with your charger going on and off (can't see why it would go up though)? or just happens without you doing anything?

Yes the UK was 240 +-6% then went to 230 +10 -6% to harmonise with europe - hence most of the existing transformers were in tolerance anyway.

As to lower voltage saving power overnight, when demand tends to be lower ( at peak demand a lower voltage would result in higher amps to provide the same power):-

Well old fashioned transformer power supplies will run cooler on a lower voltage: Any transformers running at low load (substation transformer) would benefit from lower voltage as at low load the magnetization current is the dominant loss, and rises with volts squared. Cheap transformer power supplies are often designed to run near the saturation point of the iron core (cheaper to make) so any overvoltage of the supply can start driving them into saturation and then the magnetization losses rise exponentially.

As for induction motors (fridge / freezer) it's a bit less simple: like transformers, the magnetization current rises with voltage squared so it will tend to run hotter, and again, if they're made too cheap they could be close to saturation voltage, and run much hotter on overvoltage. But conversely if you run the too far below nominal voltage they will have to draw more current, and then resistance heating may start to pull efficiency down.

Switchmode power supplies do tend to run hotter on higher voltages in practice; i can think of a few reasons, though i don't actually know how significant they are:-
there are bleed resistors on any large capacitors so that when they're turned off they lose any dangerous voltage within a few minutes - this seems to be the case even when the supply is not designed to be servicable.
The magnetic component will run closer to saturation when running on higher voltage similar to a regular transformer- again, the cheaper the design the closer to saturation it will operate.
The capacitor ripple current is higher with higher voltage so the caps tend to run hotter.

I do know my laptop power supply (100 - 260v) runs noticeably cooler if i plug it direct into the hydro generator at 135v vs 230v from the inverter.