Tesla charger - any known issues with occasional low supply voltage?

[arg]

@arg
So based on what you've said, I guess the problem would be if the voltage is consistently low while the car is charging at 32A as this could drag our entire property's supply voltage down to a point where there could be a danger of overheating cables attached to any high load anywhere in the house or garage especially if this were over a long period.

Does that sound that right?

I think you've slightly misunderstood here. Assuming everything is as you say, the risk is that the car thinks there could be overheating cables in the house when actually there are not. If nearly all of the voltage drop is in the supply wiring, then it's the supply wiring that might possibly overheat (which, so long as it's outside the house, could perversely be a good thing because they will be forced to fix it!)

How low a voltage is actually dangerous in this kind of situation?

Low voltage is in itself very rarely dangerous. (I was going to write "not" rather than "very rarely", but to be pedantically correct there are a few things that can actually overheat as a result of low voltage - primarily old-fashioned types of electric motor - but you are unlikely to have any of those in a modern household, and the degree of voltage drop we are talking about probably isn't enough to cause a real problem if you did).

What we are talking about is low voltage being a symptom of something else being wrong - if the voltage a moment ago was higher and it's now lower, where have those volts gone? If the voltage at the DNO transformer hasn't changed, then those volts have been lost somewhere between there and the car, and are turning into heat: if the voltage has dropped by 10% then 10% of the total power being delivered is now heat - that's a lot of heat! If the volts are being dropped uniformly along a very long cable from the transformer, then it's just a nuisance - that whole cable is getting a little bit warm as the heat is spread out. However, if most of the volts are being dropped across a poor connection between cables somewhere, then that's serious because all the heat is concentrated in one place and it will be getting very hot indeed.

Am I likely to have the same issue with any other electrician being cautious in this way? ie. are the installers being reasonable or are they just trying to walk away from a job that's causing them more hassle than they want?

It appears that your installers are inflexible - they have one fixed design that they want to use, and can't/won't consider any other. This is common in some organizations where they don't have sufficient fully qualified staff: the people doing the work may be good craftsmen capable of doing the actual installation work but are not qualified to do design. So they work to a number of fixed designs under the supervision of a qualified supervisor .

Regardless of this installation, I will be looking to stick an opensource current/voltage monitor and logging as close to the supply feed as possible so that I can go back to the DNO if neccessary, but the fact is that replacing the supply line to our house would seem to involve digging a trench across the neighbour's garden so this isn't really something I want to deal with if possible.

That does assume that the supply cable across the neighbour's garden is the sole source of the problem. That seems slightly unlikely unless it's faulty or you don't in fact have a 100A supply as you believe. (or it's an enormous garden, of course).

 

[arg]

"The car might or might not throttle back - you don't particularly want it to, and this isn't the case which the feature is designed to catch, but it might be fooled into thinking so. Still, the throttling back probably won't stop you getting the charge you need."

I disagree, the whole reason I upgraded from a 16A for a 32A (first car was a hybrid) was to make sure I got an over night charge on off peak electric, If I get home late in the evening at say 20% it takes hours before it gets back to 90% for next morning drive, on 16A even 24A but 32A it is like 6/7 hours which is a good time. It has on numerous occasions throttled back over night and the car no where near charged to 90% in the morning, in my case it pretty well makes no difference as my daily miage generally is a lot lower, it is only a couple days a week I do like 200 mile on a 90% charge.

Fair enough. It's stopping you getting the charge you need at a sensible price.

I assume it's clear from the car's indications that you are in fact suffering from the voltage-triggered throttling problem rather than the "stuck at 16A" problem other people have been reporting on the Model 3?

 

[bangtidy]

@arg, thanks again.

When the DNO guys came to look at the supply, they were very much of the view that it was an issue with the supply line and the fix was basically a new supply line installation. They didn't actually do any testing themselves although they did get another team to check that things were okay at the other end of the supply line and apparently that was all okay.

Am i right in thinking that if, when I turn the oven on (which is connected by 10mm2 cable and it's own 60A fuse directly back to the main supply) and the voltage metered across the L and N of a plug socket drops to 220V in the house, that the problem really has to be in the supply line?

I'll have to just set up some monitoring as close to the supply entry point as possible and see what happens.

In reality the two largest loads in the property are the induction cooker and the EV charger and it's very unlikely that these will ever be running at the same time anyhow.

 

[bangtidy]

Oh and yep, the length of the supply line is long. We're a bit out in the sticks and the length of our supply line is long - the DNO guys basically looked at their supply line map and said, 'yep, the line is long which is why the voltage is dropping.'

But they didn't say, '...and that might mean that it's dangerous if you use it too much'!

 

[arg]

Am i right in thinking that if, when I turn the oven on (which is connected by 10mm2 cable and it's own 60A fuse directly back to the main supply) and the voltage metered across the L and N of a plug socket drops to 220V in the house, that the problem really has to be in the supply line?

It certainly means the problem isn't in the oven circuit. It could be anywhere upstream of there that is common with the socket circuit. "its own 60A fuse" sounds rather odd (60A is enormous for an oven and big even for an induction hob). If you actually mean a separate breaker in the consumer unit, then there's the busbars within the consumer unit and the tails back to the meter (and more significantly, their connections). So there's still a small portion of your installation that you haven't ruled out by that test.

Still, if you've had the DNO out for low voltage you would think they would have spotted something like that.

Oh and yep, the length of the supply line is long. We're a bit out in the sticks and the length of our supply line is long - the DNO guys basically looked at their supply line map and said, 'yep, the line is long which is why the voltage is dropping.'

Well, they are supposed to design their supplies to meet the limits. If it was pre-1996, it should have been designed for 240V +/-6% (so min 225.6V), otherwise for 230V +10%/-6% (216V). Something must have happened since then if you now have supply voltage outside those limits.

One possibility is that it was originally specified as a 40A or 60A supply and got improperly upgraded to a 100A fuse (or you don't in fact have the 100A fuse you think you have): if you are actually drawing more current than the supply was declared to be, then this is your fault and you will have to pay if you want anything done about it.

Another possibility is that your neighbours are using too much power and a big part of the drop is occurring in the portion of the supply cable you share with them.

A final possibility is that the voltage at the transformer is too low. Traditionally, the transformer is set up to give the maximum permitted (253V) when there is no load, so everybody will see a bit less than this due to the drop in their supply cables - people with the longest cables will see the most drop, but it should still be within limits. It is possible that the voltage at the transformer is now lower. It could be because demand has increased (new houses etc) and the transformer is too small (overloaded); though in that case you'd expect to see the voltage much higher at times when none of your neighbours are using power. It could also be because they've deliberately adjusted the transformer tapping to reduce the voltage because other people were seeing too high a voltage - perhaps because lots of people have installed solar generation - the quick fix for those problems has caused the opposite problem for you.

Your long supply cable is undoubtedly part of the problem, but not necessarily all of it. If you are seeing below 216V at the meter other than momentarily, and you can show that you are still using no more than the size of supply that you are paying for (tricky to find out what that actually is), then it's up to them to fix it.

This can sort-of be worked out by reverse calculation: if it really is a 100A supply, then the most that it is allowed to drop is 37V (from 253 down to 216) when going from nothing to full load of 100A; in practice somewhat less than this since there has to be an allowance for neighbours and the HV network. So say 33V. That means that drawing 3A shouldn't cause a drop of more than 1V, or 32A shouldn't cause a drop of more than 10V. So if turning on your car causes a drop of more than 10V then something is wrong: either it wasn't designed as a 100A supply, or it is now worse than designed. However, if turning on the car only causes a drop of (say) 5V but the voltage was already 220V before you started, then it's not a volt drop problem so much as the voltage being low to start with. This is not going to be totally accurate, but a useful sanity check on the numbers.

 

[bangtidy]

It certainly means the problem isn't in the oven circuit. It could be anywhere upstream of there that is common with the socket circuit. "its own 60A fuse" sounds rather odd (60A is enormous for an oven and big even for an induction hob). If you actually mean a separate breaker in the consumer unit, then there's the busbars within the consumer unit and the tails back to the meter (and more significantly, their connections). So there's still a small portion of your installation that you haven't ruled out by that test.

It may be a 40A fuse but it's definitely a big separate fuse so the cooker has it's own circuit that bypasses the consumer unit and connects directly to the 100A fused supply.

One possibility is that it was originally specified as a 40A or 60A supply and got improperly upgraded to a 100A fuse (or you don't in fact have the 100A fuse you think you have): if you are actually drawing more current than the supply was declared to be, then this is your fault and you will have to pay if you want anything done about it.

It has a 100A fuse and the DNO accepted the installation of theh charge on the basis that we have a 100A supply so I can only assume that we're supposed to have a 100A supply.

I really need to get some monitoring on the supply line to see if we really do have a problem that I need to hassle the DNO about. The impression I got from the DNO though was that any fix would simply require me to pay for the installation of a new supply line which wouldn't be a cheap or simple option.

I guess I'll have to prove to them with logging that it's their problem if it turns out that the supply is actually regularly dropping below 216V.

 

[MrBadger]

It may be a 40A fuse but it's definitely a big separate fuse so the cooker has it's own circuit that bypasses the consumer unit and connects directly to the 100A fused supply.

Thats similar to our induction range/hob (Rangemaster) - 63A RCD consumer unit from a Henley (100A supply), with 50A MCB for the range and 16A MCB for a single garage outlet (currently used for 10A car charging). I checked with Rangemaster at the time, and even though its a max 18.3kW load (around 75A), they recommended a 45A fuse due to diversity. The reality is that we have never drawn even close to 1/3rd max load.

 

[bangtidy]

I've actually started encouraging my wife to make more use of our new Instant Pot pressure cooker....

 

[MrBadger]

New I've actually started encouraging my wife to make more use of our new Instant Pot pressure cooker....

Anemic chicken and chips is a particular favourite of ours... the taste more than makes up for its looks.

 

[bangtidy]

Anemic chicken and chips is a particular favourite of ours... the taste more than makes up for its looks.

Fantastic things aren't they - Oxtail stew's a winner. And Coq au Vin in 10 mins!

 

[eddycrim]

Did you ever get a fix on the supply line, or did you just live with it?

I have all the symptoms you describe and I suspect its the same issue.

 

[qwickshot]

Contact your DNO if you have low voltage, they will fix it.

 

[bangtidy]

Did you ever get a fix on the supply line, or did you just live with it?

I have all the symptoms you describe and I suspect its the same issue.

DNO weren't interested in fixing the line. I swapped the Matt-E box for an appropriate RCD and it's been absolutely fine since then.

Got the money I paid the installers back and resold the Matt-E box on ebay.

Hope you get yours sorted!

 

[thewishy]

I swapped the Matt-E box for an appropriate RCD and it's been absolutely fine since then.

This is a little concerning. The Matt-E is intended to protect against PEN faults, an RCD doesn't protect against this. In certain specific conditions, it's possible that a fault on the DNO's cable could result in the PE (earth) becoming live.
PEN faults are a concern for outdoor charging, when somebody could be touching true earth and then your car, in which case they could get a severe shock.

The Matt-E boxes detect the possibility of a PEN fault when the voltage drops, and shuts down. The legitimate alternatives are
- Charger with built in pen fault protection (Not the Tesla charger), although that'll be electronic and may suffer from similar issues. It may recover from a low voltage condition better than the Matt-e. Also it'll cost a fortune, so not a good idea
- Charging indoors, and setting up the charger such that charging outdoors is not possible
- A physical earth rod

 

[bangtidy]

- Charging indoors, and setting up the charger such that charging outdoors is not possible

This. Luckily I have a big garage.

At some point though, I do also plan to get a physical earth rod installed as well.

 

[qwickshot]

To be honest, I’m not sure why so many people go for the pen fault detection devices over an earth rod.

I’d have thought an earth rod is cheaper and not exactly a significant amount of work to install, you just need a bit of clear ground to hammer it into. It’s also just one less point of failure given the complexity of a pen fault detection device.

 

[thewishy]

To be honest, I’m not sure why so many people go for the pen fault detection devices over an earth rod.

I’d have thought an earth rod is cheaper and not exactly a significant amount of work to install, you just need a bit of clear ground to hammer it into. It’s also just one less point of failure given the complexity of a pen fault detection device.

My driveway is tarmac, we'd have to run a cable for some distance to get to a clear spot for an earth spike.

I bought a charger with pen fault built in. Just a shame it didn't have a DP RCD...