EV charger ratings & questions

[kylegordon]

Hi all,

I'm being asked to supply location data and overviews for an Zaptec Go EV charger install that the car dealer is providing. Before I point them at the desired location, I just want to ask if it's even worthwhile. I don't want to lead them on a wild goose chase.

All of this kit has been fitted within the last 5 years, and I'd like the charger to be installed on and fed from the garage consumer unit - but I have my doubts.

The house has a 100A main fuse, and a 40A RCBO supplies the garage, via 3x 6mm buried/ducted SWA. My understanding is that cable is good for 44A when buried, so the 40A RCBO makes sense.

The garage has a 1.5kW HVAC heater and a 2.2kW compressor (sockets circuit, 32A RCBO), plus the usual idle usage of ~200W when all the lights are on (lights, 6A). There's a car lift as well, hanging off a 2.2kW VFD inverter (20A RCBO - used to be lower, but startup current often tripped it).

By my maths, a 7kW EV charger would far exceed what the garage can supply, and am I right in thinking diversity doesn't count here because it's a workshop?

Are my options then a Zaptec Go with a sensing kit in order to dial it back when the garage is in use, or to find another location? Are these Sense features compliant enough to permit that idea?

Thanks for reading this far

 

[ericmark]

A complex question, to charge an EV is not a problem, to charge an EV within the time one can get off-peak supply is something else. Much is down to why you want to charge, next door to me, it is down to being handy to charge at home rather than take it to a charging station. My son however is more concerned with cost.

He tells me there is a mileage sweet point, two low, and it does not pay, and too high and one can't charge it enough in 5 hours. So reducing how much it can charge in 5 hours may tip the balance. However, it depends on when you get the 5 hours. Which in turn depends on the tariff you get.

 

[Murdochcat]

The RCBO / RCD protecting the EV has to be dedicated to this circuit only

Could you post a photo of your garage CU?

 

[kylegordon]

@ericmark fair point. We have batteries, solar and an ashp, and are on Octopus Flex already. We also mostly work from home so the car will have plenty of opportunities to charge at 5p/Kw or when there is or has been surplus solar. Quick edit addendum... this install and charger is also free from the dealer

@Murdochcat as below. The labels are offset by one... Feed to this CU is from the 40A CU in the house.

 

[ericmark]

The RCBO / RCD protecting the EV has to be dedicated to this circuit only

The house has a 100A main fuse, and a 40A RCBO supplies the garage

Yes, that would need to change. And there are questions as to where the CT coil will go, whole house or garage supply, also if being charged inside the garage, then no need for loss of PEN as being charged within the equipotential zone.

But my next door neighbour tests and reviews cars, he does not own an EV, but does have them at home when under review, he has an EV charging point for convenience, but does not need an EV tariff, and is not worried about it charging within a set time. My son has an EV as it is cheap to run, he has the car supplied by the same people as his energy, and has a very cheap rate of 6p/kWh and the energy provider decides when it charges, with a maximum of 5 hours. My supply the 5 hours is fixed, more expensive at 8.5p/kWh, but I know this is 00:30 to 05:30 every day. At this time of day, only items selected to use off-peak are running, so not worried about other items in the house. But my son could be using power at midday, he does not set the time, his supplier sets that.

Also, it will depend on who fits the charge point, firms like Octopus have very strict rules, these are beyond what regulations require.

In theory, you can have all sorts of controls, which for example look at solar production etc. In practice, one is looking for basic plug and play. i.e. what the manufacture of the charge point has included in the unit as options. I can fantasize as to what I could program into a PLC, but in real life that is not going to happen, you will use something off the shelf. And what is on the shelf seems to change month by month.

I note the CU in picture has two old type A RCBO's and one type AC RCBO yet you said there was a RCD in the house, so seems a bit odd, the C20 raises questions as to the loop impedance, needs to be down to 1.09Ω in fact, to keep within volt drop, 0.52Ω, so garage SWA run less than 20 meters, or looking at the charger tripping out with under voltage. Since you clearly have lighting in the garage, the volt drop permitted is 3%, I do agree you can likely get away with more, but my point is it is a complex question, and unlikely to find answers over the internet.

 

[robinbanks]

Why would diversity not apply? These garage appliances don't run all the time, so the concept that you're not loading the circuit to the max/your loads click on and off is still relevant. Breakers don't trip the instant you go over 40A by a few milliamps; they're thermal based and there's a curve to how long they take to break depending on how far over current they are

You can usually dial down chargers too btw, and even a ~32A single phase 7kW charger doesn't necessarily draw it all the time (cars charge more slowly above ~80% full) nor does it necessarily need to; you may find that having the charger set to 5kW in the daytime and 7 at night still meets your charging needs while freeing up capacity for the garage

 

[kylegordon]

@ericmark cool, thank you for the info. This is an external charger. The garage is more of a workshop for my classic stuff

Fitters would be Qvanta, who I've never heard of until now. House CU picture attached if you wish. I was wrong about the feed being an RCBO, it's just a MCB. Cable run from house to garage is 40 meters.

The garage C20 was a swap a couple of years ago by the electrician who installed it all, as the original (RTA061630B B16) occasionally tripped itself when the ramp was being started up under load.

I will stand back and let them decide methinks. I have a preferred place for the charger on the wall of the garage, and will order it with the offered Zaptec Sense kit in case that helps their decision making.

The 'easy' location for the charger, with direct access to the house CU, would involve limiting access to the drive and front path whilst the car is being charged, which we're not terribly keen on!

 

[robinbanks]

let them decide

Better for you to say what you want and they make that happen; your house, your money, your constraints- you have to live with the results, not them..

 

[kylegordon]

@robinbanks Not a clue. I know that diversity may be a involved but I'll leave that one to the experts. Is it permissible for garages? It's residential, but at 68sqm the council had to fall back to commercial rules for it.

I agree though, the compressor, lift, etc, aren't going to be operating for long periods, although the heating does.

Good point about just saying what I want. I am overthinking this. Zaptec Go and Zaptec Sense it is, and they can figure out the install within the free install constraints

 

[robinbanks]

Note that the heating likely also cycles its compressor on and off, and if 1.5kW is the heat output rather than the electrical input it could be a lot less in terms of consumption thanks to the way hvac systems employ the Carnot cycle so all in I wouldn't have significant concerns that a 40A supply would have unavoidable nuisance over current trips from adding a car charger

It is also practically possible to monitor power flow on a circuit and dynamically balance out the power draw from the charger so that on overall upper limit for all attached appliances is adhered to. It needs extra monitoring hardware but is an existing, proven solution in the EV space

 

[kylegordon]

@robinbanks yep, the heating is 1.5kW electrical input. One of these beasties - https://www.appliancesdirect.co.uk/p/eiq-18wminv/electriq-eiq18wminv-wall-split-air-conditioner Best investment ever for a garage!

I think the Zaptec Sense kit does that power monitoring you speak of, so fingers crossed this all works out.