Electric boiler confusion, and EV charging.

[MrMagic]

A standard domestic wall socket charger (aka 'granny charger) can only deliver 10A max continuous. Even then it still gets a bit toasty.

 

Next is a proper hardwired EVSE (charger) (I'm sure theres a better term) which can do the full 6A -> 32A range continuous.

[SteamyTea]

34 minutes ago, MrMagic said:

A standard domestic wall socket charger (aka 'granny charger) can only deliver 10A max continuous. Even then it still gets a bit toasty.

Yes, why I was wondering what the max is they deliver.

[Jeremy Harris]

34 minutes ago, SteamyTea said:

Yes, why I was wondering what the max is they deliver.

 

 

The max current is typically 32 A in the UK.  The standard allows for more, but I don't know of any AC charge points that can be set to deliver more than 32 A here in the UK.  The maximum current that's available from any AC charge point is advertised to the car by using a pulse width modulated 1 kHz signal on a control pilot wire within the charge cable.  This is a low voltage signalling wire that allows bidirectional analogue communication between the car and the charge point (usually - Tesla do things differently. . . ).  For AC charge control,the relationship^[1] between the PWM duty cycle and the advertised maximum current that's available is that the current (in A) is equal to 0.6 x the duty cycle %.  So a 10% duty cycle = 6 A, a 50% duty cycle = 30 A and a 80% duty cycle = 48 A^[2].

 

The practical limit is set by both the supply capacity and the car onboard charger rating.  I don't know of any UK EVs that have a maximum single phase rating of higher than 32 A, and generally 32 A is about as much as can be realistically added to a UK single phase supply, anyway, given that this current will be drawn continuously for several hours.

 

For charging from a 13 A outlet, then the charge current limit is determined by the continuous rating of a BS1363 plug.  Because the fuse inside a 13 A plug generates a fair bit of heat, the maximum continuous rating of a plug with a 13 A fuse is 10 A, rather than 13 A.  For this reason, the portable charge points that are often supplied with EVs (often called a granny charger, because it's so slow) is limited to 10 A maximum.

 

Because of the high continuous current, it's normal practice to over size the supply cable for a fixed charge point, primarily to limit the temperature rise at the terminations and to reduce the voltage drop and associated power loss.  For runs up to maybe 20m or so 6mm² cable is used, longer runs may need 10mm² cable.  Only 2 core SWA cable is needed normally, as the regs require that a charge point be protected such that any exposed metalwork cannot exceed a touch voltage of 70 V above the local ground reference under fault conditions (such as a lifted PEN conductor).  The safest way to ensure this is to just connect the charge point installation as a TT installation, with an earth electrode and suitable DC tolerant RCD/RCBO (either a Type B or a Type EV).  There are one or two manufacturers who claim to have ways around the need to install an earth electrode, but every one I've looked at fails to comply with the provisions in section 722 of BS7671:2018.  How they can make such claims is beyond me.

 

 

^[1]  This relationship only holds for an advertised charge current from 6 A to 51 A.  From 51 A to 80 A the relationship is current (A) =  (duty cycle% - 24) x 2.5

 

^[2]  48 A/80% is higher than any UK EV or single phase AC charge point can deliver.

[ProDave]

A while back I got a call from out tenants in the B&B.  they had a foreign guest staying with an EV who produced it's Granny charger wanting to plug it in.  Only trouble was it had a Schuko plug on it. So I had to make a hasty adaptor.

 

What puzzled me was this charger, with a moulded on Schuko plug which has a rating of 16A, claimed to be a 7kW charger.  I guess that will be "hifi watts" then?

[Jeremy Harris]

1 hour ago, ProDave said:

A while back I got a call from out tenants in the B&B.  they had a foreign guest staying with an EV who produced it's Granny charger wanting to plug it in.  Only trouble was it had a Schuko plug on it. So I had to make a hasty adaptor.

 

What puzzled me was this charger, with a moulded on Schuko plug which has a rating of 16A, claimed to be a 7kW charger.  I guess that will be "hifi watts" then?

 

 

It may have been like the Tesla granny charger.  That can charge at up to 32 A, and has a 5 pin waterproof connector at the mains in side, that takes a variety of different short adapter leads.  The car comes as standard with a 13 A plug lead and a 16 A commando lead, and sets the charge current to 10 A when the 13 A lead is used and 16 A when the commando is used.  Tesla sell an optional 32 A commando adapter lead for ~£40 and when this is fitted the granny lead will charge at 32 A. 

 

 

[newhome]

A more local news story with a bit more detail. I feel for these guys. Scottish Power saying that they’ll investigate means feck all. None of these folk should be on 15p heating rates when I’m paying 8p for the same meter set up! That said I only manage to keep my bills to an acceptable level as I keep on top of Scottish Power constantly (due to their many mistakes) and I have worked out how to use the system in the most efficient way, and my heating is zoned in every room so I turn it off in the rooms that I don’t use. There is definitely an art to it but I have UFH and I assume these folk have storage heaters so it may be different for them. 

 

https://www.falkirkherald.co.uk/news/people/falkirk-villagers-turn-up-the-heat-as-scottishpower-says-it-will-investigate-high-bills-1-5053785

 

 

 

[ProDave]

ScottishPower’s tariff increases are also causing concern – in 2010 the standing charge cost 11.78p per unit and this increased to 22.47p per unit in 2019. The off peak charge has also gone up from 5.54p per unit to 15.73p.

 

When you visit ScottishPower online and search FK postcodes the first standard tariff that comes up for domestic and economy 2000 on a monthly direct debit for an online account gives 23.70p per day for standing charge, a day unit rate of 17.605p per kWh and a cheap night unit rate of 15.738p per kWh.

 

There is something VERY wrong when they are on a tariff that gives the off peak rate as 15.72p or more with the peak rate even higher.

 

I pay 14.183p per unit 24/7 with Octopus.  they would all be better off ditching the off peak and just going for a single rate.

 

The "solution" to this must surely be dump the economy 2000 and go to a normal E10 or E7 so they can switch suppliers  Is this somethging the tenants could do on their own or would they need permission from the landlord?

[newhome]

1 hour ago, ProDave said:

The "solution" to this must surely be dump the economy 2000 and go to a normal E10 or E7 so they can switch suppliers  Is this somethging the tenants could do on their own or would they need permission from the landlord?

 

I imagine that they would need permission in anywhere rented because it means altering the meters. I think the other issue is what do you have to actually do to remove one of the meters. I was told by Scottish Power that I should pay an electrician to rewire the 2 consumer units into the standard meter, and then Scottish Power would change the meters (in their own time). In the meantime I would be stuck with all of my heating at the standard rate, so in my case almost 16p instead of 8p. For these guys it would be even higher than that. At the time I also couldn't find a tariff that bettered the 8p I am paying for heating but now that I've looked at Octopus Agile I think that could well be the answer for me. I could take great advantage of the very cheap overnight rates, and when I'm working in the office I'm not here until 6.30pm anyway and could easily avoid running anything costly during the high charging period of 4pm to 7pm. 

 

 

[AliG]

Really these people should have ASHPs and not electric combis. They would pay for themselves in 3 or 4 years. It shows up one of the problems of being in a rented place. The landlord (Council) will want to install the cheapest option possible which might cost the tenant money. The tenant won't know until it is too late.

 

Although in this case it seems like the Council actually spent quite a bit putting these systems in, it probably wouldn't have cost much more to put in an ASHP. I think it may be that these boilers have been specifically designed to be an easy replacement for existing systems which may have been the attraction.

[DamonHD]

Only if the tenants (and landlords) understand how to use a heat-pump properly*.  Close to here a heat-pump installation left at least one household with at £4k bill which required intervention of the local MP to defang.

 

Rgds

 

Damon

 

*Was just at a Radbot install in a 3yo house where the tenant had asked for help getting her gas combi system set up properly and the landlord offered essentially no help at all, so HP would have been much worse.

[AliG]

@DamonHDFair point, an ASHP probably would struggle assuming that these houses are badly insulated. They should really have insulated them at the same time.

[ProDave]

How can a HP be set up so wrong to make such a high bill?

 

There is no day to day user input to mine.  It works on a conventional boiler time clock and room thermostats.  It puts just enough heat into the house to maintain it at 20 degrees.

 

Or are you meaning it was set up wrong by the installer?  No doubt if I set mine to something silly to run at 50 degrees all the time it would cost more.  Or if it was set up to work with high temperature radiators then it would not work very well.  But that is not a case of "not knowing how to use it" rather a case of the installer making an error.

[DamonHD]

I don't know the details, but given that many people don't know how to make flat-rate gas work well, and many many people don't understand how to make anything with storage and ToU tariffs work well (eg electric storage heaters), I imagine that they ended up running everything on electric resistance heating at a punative day-time / peak rate.

 

Rgds

 

Damon

[newhome]

I did look up some posts about this tariff on a few forums (mostly complaining about Scottish Power) and people were saying that they were led to believe that their storage heaters would provide heating for about 7 hours or more but in reality they were cold after 3, so they had to run the heating for more than twice as long as they had expected. On the Economy 2000 tariff you can't actually run the heating at peak rate as the second 'control' (heating) meter only has a single rate. During the peak times the supply is cut via teleswitch. The issue appears to be how long these folk are having to run their systems for and Scottish Power trebling the cost within 10 years. I only run my heating once a day and it generally takes 2 hours to heat the slab and provide hot water. I have a 24kw boiler so that's still 48kw at full whack, but it tends to ramp down and uses about 36kw per day. If I was paying 15p that would double the cost of my heating. 

 

[joth]

59 minutes ago, newhome said:

I have a 24kw boiler

Good grief, that's 100A on a single appliance. What sort of grid connection do you have?

 

1 hour ago, newhome said:

so that's still 48kw at full whack,

Nit: 48 kWh

 

[newhome]

3 minutes ago, joth said:

Good grief, that's 100A on a single appliance. What sort of grid connection do you have?

 

 

3 Phase

[ProDave]

2 hours ago, newhome said:

I did look up some posts about this tariff on a few forums (mostly complaining about Scottish Power) and people were saying that they were led to believe that their storage heaters would provide heating for about 7 hours or more but in reality they were cold after 3, so they had to run the heating for more than twice as long as they had expected. On the Economy 2000 tariff you can't actually run the heating at peak rate as the second 'control' (heating) meter only has a single rate. During the peak times the supply is cut via teleswitch. The issue appears to be how long these folk are having to run their systems for and Scottish Power trebling the cost within 10 years. I only run my heating once a day and it generally takes 2 hours to heat the slab and provide hot water. I have a 24kw boiler so that's still 48kw at full whack, but it tends to ramp down and uses about 36kw per day. If I was paying 15p that would double the cost of my heating. 

 

Storage heaters should work with 7 hours charge, but they will be running out of stored heat by the end of the day.  They were pretty rubbish in my 1930's house as that leaked heat like it was going out of fashion and most evenings in winter I needed to top up the heat somehow in the evening.

 

You can't turn a storage heater on outside it's night charge. so you top the heat up with a convection heater, or something else.

 

[SteamyTea]

8 hours ago, ProDave said:

They were pretty rubbish in my 1930's house as that leaked heat like it was going out of fashion and most evenings in winter I needed to top up the heat somehow in the evening.

That would have been because they were too small for the property.

9 hours ago, ProDave said:

Storage heaters should work with 7 hours charge, but they will be running out of stored heat by the end of the day.

I limit the charge period of mine to 4 hours.  Works well.

But that is because they are sized correctly for the house and climate.

[newhome]

Well it looks like Octopus Agile is a no go for me at present as they don't accept 3 phase.

[Jeremy Harris]

12 minutes ago, newhome said:

Well it looks like Octopus Agile is a no go for me at present as they don't accept 3 phase.

 

The reason for this is that there are no smart 3 phase meters available at the moment, I believe.  This means that you're probably out of luck for any tariff that needs a smart meter.

 

Not sure what the Bulb Varifair E7 tariff is in your neck of the woods, but we've been on it for a year now and it's still best value for us.  If it looks OK for you then you could use my code and we both get £50 out of it. . .

[AdamSee]

32 minutes ago, Jeremy Harris said:

 

The reason for this is that there are no smart 3 phase meters available at the moment, I believe.  This means that you're probably out of luck for any tariff that needs a smart meter.

 

Not sure what the Bulb Varifair E7 tariff is in your neck of the woods, but we've been on it for a year now and it's still best value for us.  If it looks OK for you then you could use my code and we both get £50 out of it. . .

 

I assume that must be different for commercial supply's then. My new industrial unit had a 3 phase smart meter and I think emlite produce one to. Well....it was smart with the previous supplier. Apparently not compatible with the edf tho.

[Jeremy Harris]

14 minutes ago, AdamSee said:

 

I assume that must be different for commercial supply's then. My new industrial unit had a 3 phase smart meter and I think emlite produce one to. Well....it was smart with the previous supplier. Apparently not compatible with the edf tho.

 

Not sure what the problem is with domestic 3 phase smart metering, TBH.  Might be something to do with the meter specs, perhaps a bit like the SMETS1/SMETS2 fiasco.  Could also be that the data network system for commercial metering is different to that for domestic metering.  It does seem to be a consistent issue, though, as the inability for suppliers to provide smart metering to 3 phase domestic consumers seems to be a long standing one.

[joth]

13 minutes ago, AdamSee said:

 

I assume that must be different for commercial supply's then. My new industrial unit had a 3 phase smart meter and I think emlite produce one to. Well....it was smart with the previous supplier. Apparently not compatible with the edf tho.

I guess this was put in by a big 6 supplier?

 

The small suppliers don't have much (if anything) in the way of national infrastructure to support meter installs, so most rely on https://www.sms-plc.com/ for installing meters (it seems SMS generally own the meter and the supplier rents it from them) so are at the mercy of whatever SMS choice to supply (or fail to supply) in a given area.  AFAICT,  SMS don't do any 3ph smart meters yet yet. The rarity of them (and inability to supply them) means it's probably in Octopus's own self interest to deny supplying their service on an untested  meter even if you've managed to snag one from another supplier. 

[AdamSee]

No idea who installed it. Previous energy supplier was called "energie" don't think they installed it either though.

[Temp]

On 07/02/2020 at 22:04, ProDave said:

Storage heaters should work with 7 hours charge, but they will be running out of stored heat by the end of the day. 

 

I think the systems in the original news article are electric boilers heating a water thermal store used for both heating and DHW. I suspect the whole system is too small and the store is running out, particular after a shower or two.