Ditching gas, going electric immersion only, a wee project

1961Nick

Solarchaser said:

My colleague running intelligent octopus says they ask for the charge of the car and the limit of charge suggesting they want to select when to charge, I cant really Do that with the heat as I'm running off specific timers.

I suppose if they spoke to smart plugs etc it could be doable. 
But yeah until mid Feb I'm on 4.5p for 3 hours, so I will really start looking in earnest come mid January 

With 6 hours available you could cut the Tesla's charge to 16 amps & still add the same number of kWh?

Solarchaser

I didn't explain that very well.
The intelligent octopus doesn't add charge the whole time, it just goes by a finishing soc of the car and calculates how many hours are needed.
So in theory you plug in for 12 hours but only 6 are charging, and those 6 may not be continuous. 
But I'd need the heating elements to always run when the price was low, and unless octopus activated smart plugs to activate my pir controllers for the heaters, then I wouldn't have the control to add as much heat as I wanted.

Today I know when my off peak period is, and use normal plug in timers to run the pid controllers to heat the tanks, if the times of off peak were variable each night, this wouldn't work.

If I've misunderstood how intelligent works, that would be great, this was taking it from my colleagues explanation, and its possible he has picked it up wrong too.

I just got the impression from what he said about entering figures in the octopus app every night that it really meant octopus were honing in on the EV only part of off peak, whereas I need off peak for battery charging and tank heat as well, not just car charging.

1961Nick

Solarchaser said:

I didn't explain that very well.
The intelligent octopus doesn't add charge the whole time, it just goes by a finishing soc of the car and calculates how many hours are needed.
So in theory you plug in for 12 hours but only 6 are charging, and those 6 may not be continuous. 
But I'd need the heating elements to always run when the price was low, and unless octopus activated smart plugs to activate my pir controllers for the heaters, then I wouldn't have the control to add as much heat as I wanted.

Today I know when my off peak period is, and use normal plug in timers to run the pid controllers to heat the tanks, if the times of off peak were variable each night, this wouldn't work.

If I've misunderstood how intelligent works, that would be great, this was taking it from my colleagues explanation, and its possible he has picked it up wrong too.

I just got the impression from what he said about entering figures in the octopus app every night that it really meant octopus were honing in on the EV only part of off peak, whereas I need off peak for battery charging and tank heat as well, not just car charging.

Good news... the core off peak for IO is 6 hours from 23:30 to 05:30. This period will always be at the lower rate - currently 10p/kWh. I think your colleague is getting confused because Octopus can give you a charging schedule (after plugging in) that includes times outside of the core... this is also @ 10p/kWh.

(I have left the scheduled charging setting at 23:30 to 05:30 on my wall pod so that Octopus think the car has just been plugged in when the charger comes on at 23:30. This stops any car charging occurring when my domestic batteries are set to discharge.) 

Freepost

Solarchaser said:

I have 4 x 3kw elements going through a 50A trip, and it tripped on Wednesday.

Do you know when it tripped? I would have thought, probably at switch on due to a spike, if so you may find staggering the switch on by a few mins for each pair of immersion heaters will resolve the problem!

F.

Solarchaser

1961Nick said:

Solarchaser said:

I didn't explain that very well.
The intelligent octopus doesn't add charge the whole time, it just goes by a finishing soc of the car and calculates how many hours are needed.
So in theory you plug in for 12 hours but only 6 are charging, and those 6 may not be continuous. 
But I'd need the heating elements to always run when the price was low, and unless octopus activated smart plugs to activate my pir controllers for the heaters, then I wouldn't have the control to add as much heat as I wanted.

Today I know when my off peak period is, and use normal plug in timers to run the pid controllers to heat the tanks, if the times of off peak were variable each night, this wouldn't work.

If I've misunderstood how intelligent works, that would be great, this was taking it from my colleagues explanation, and its possible he has picked it up wrong too.

I just got the impression from what he said about entering figures in the octopus app every night that it really meant octopus were honing in on the EV only part of off peak, whereas I need off peak for battery charging and tank heat as well, not just car charging.

Good news... the core off peak for IO is 6 hours from 23:30 to 05:30. This period will always be at the lower rate - currently 10p/kWh. I think your colleague is getting confused because Octopus can give you a charging schedule (after plugging in) that includes times outside of the core... this is also @ 10p/kWh.

(I have left the scheduled charging setting at 23:30 to 05:30 on my wall pod so that Octopus think the car has just been plugged in when the charger comes on at 23:30. This stops any car charging occurring when my domestic batteries are set to discharge.) 

That is great news, and 10p for 6 hours sounds top drawer!

Freepost, yeah it trips after they have been heating about 2.5 hours, so it's the trip heating up rather than surge.

I've found pulling down the front flap of the CU helped a bit as the trip wasn't contained within the plastic, after that the mcb was tripping about 30 mins after all the current draw stopped.
And now I've opened the door to the leccy cupboard for those 3 hours and it hasn't happened since.
But at the end of the 3 hours both the 50a trip and the 63a circuit rcd are pretty darn hot to the touch.

Back in the day, a guy who used to design stuff for the electric board (shows how far back in the day it was) said that an mcb would only trip on a spike of 4 times its rated current... I dunno if its true, but he was a clever guy, that's for sure

70sbudgie

Solarchaser said:

Back in the day, a guy who used to design stuff for the electric board (shows how far back in the day it was) said that an mcb would only trip on a spike of 4 times its rated current... I dunno if its true, but he was a clever guy, that's for sure

MCBs don't generally trip for small overcurrents, as they are usually designed to detect / break on faults - which don't produce only small overcurrents. An MCB that tripped for overcurrents instead of fault currents could give you too many spurious trips. 

However, the thermal aspect of an overcurrent is one of the effects that an MCB is supposed to protect against. So it could be that the heating is "fooling" the MCB. I put it like that because really the MCB is doing its job - its breaking the circuit to prevent further heating before anything catches fire.

Solarchaser

Yeah i really feel its doing its job, I dont feel there is any fault in it.

Infact I recently replaced a faulty mcb in a friend's house, and was interested in its failure so drilled out its rivets to take it apart, the yellow circle shows where it had been arcing inside, (contacts were no longer meeting) however what interested me was the coil round the cylinder, I assume (and be happy to be wrong) it's a coil to heat the cylinder with something like wax to melt inside (this is how thermostats in car engine cooling systems work) and so extended heat in the mcb would melt the wax which would retract the cylinder, pulling down the arm and trip the mcb.

1961Nick

Solarchaser said:

Yeah i really feel its doing its job, I dont feel there is any fault in it.

Infact I recently replaced a faulty mcb in a friend's house, and was interested in its failure so drilled out its rivets to take it apart, the yellow circle shows where it had been arcing inside, (contacts were no longer meeting) however what interested me was the coil round the cylinder, I assume (and be happy to be wrong) it's a coil to heat the cylinder with something like wax to melt inside (this is how thermostats in car engine cooling systems work) and so extended heat in the mcb would melt the wax which would retract the cylinder, pulling down the arm and trip the mcb.

It's being run just over it's load rating for a sustained period so it's just doing it's job. Once all the surrounding metal & plastic has heated up the temperature of the trip mechanism is going to start rising so that's why it's tripping after an hour or so.

Heedtheadvice

I would not like to disagree with your old leccy contact but there are several types of mcb (A to K). Commonly in domestic consumer units type B is used and that does equate to his approximation. The types go from fastest acting to slowest for different protection reasons but trip time nevertheless all follow a non linear curve of current vs time approximating to integral of current.

Also modern mcb working  is to protect a fault current (Rapid switch off) and over heating of cables usually with a combination of bimetallic strip and solenoid. Some goodish info at https://byjus.com/physics/miniature-circuit-breaker/

Wax might seem a good idea and would work for heating effect but not the rapid shut off required for fault current but, as far as I know, not used for reliability reasons.

I would be a bit concerned given your cables are getting warm/hot (perhaps where there is less cooling?) and would be inclined to beef them up a bit!!

Solarchaser

Yeah after my theorising I decided to look for a diagram to see what it was, a solenoid as you said, not a thermostat as I figured


It uses bimetallic for thermal, which is fair enough.

I'm using 10mmT&E for the supply to the consumer unit for the tanks, and it doesn't seem to get warm, just the 50a mcb and the 63a /30ma rcd are hot to the touch.
I will take some 2.5T&E to one of the heaters through an ssr just to reduce the load on the 50a mcb.
I'll take a feed from my 50a trip for ev charging as it has lots of headroom for another 12a since the car can only charge at 28ish amps and its a 50a trip (also supplied with 10mmT&E) that leads to a small CU with a 32a for zappi and spare 16a trip.

Normally not keen on 2 different feeds to one circuit, but I figure as long as I do it through another isolator and through the SSR then there shouldn't be any electrical cross over issues.
(Pid will still be triggered through the original circuit, but current draw will be through the other circuit activated by ssr)