Why did my Tesla throttle charge to 24/32 Amps

[Astrape]

Last night Astrape charged fine for the first hour and a half, then the charging limited to 24Amps and in the morning the charge was 25% short of target. The period when the drop changed looks like this in TeslaFi:

Dont worry about the weird at 12am thats when my night storage heaters kick in with 15kW of load. The Zappi charger has limited the house load to 100A because there was a water heater on at the same time. Thats all as it should be. The voltage spike is because the 7kW causes about 12V of voltage drop from network to house to car. So when the Zappi reduces the load the voltage seen by the car goes up. But at 12:36am the voltage dips to 211Volts and the amps clamps down to 24A. I presume this is the Tesla reacting to a low voltage point.
There is about 5V drop from the Zappi to the car, is that normal?
and about 4V drop from the grid incoming to the Zappi which is fine - 60 metres 16mm SWA. So the house incomer was about 220, which is within limits. The incomer drops about 0.5V per kW so without the 10V dropp caused by 20kW the unloaded grid voltage would be 230V. It was 237V at about 8pm this evening. Night time loads are heavy here as we have no local gas and 22 houses come off one small pole transformer. All of that seems perfectly normal for a UK supply. Is the car really supposed to restrict the amps at this fairly normal voltage? or is something else going on?
The Zappi was in FAST mode so no restriction there. I stopped the charge at the Zappi at 6:30 when I noticed this, and restarted it, and the car reverted to charging at 32 Amps.
Its super annoying to get up to a partly charged car when going out on a long work trip the next day. Any insights?

 

[Astrape]

The car app looked like this (24/32A - forum seems to be struggling with pic upload) when the charge was restricted.



Since the Tesla shows the upper charge limit as 32 I suspect it is not intentionally limiting. In other threads when the car limits due to connector temperature for example the upper number reduces. Maybe the cars charging circuit glitched?

 

[GRiLLA]

Is there a message in the notifications under service on the car, it could be something else like a poorly connected cable.

 

[pdk42]

Mine does this about 80% of the time. If you are in the car when it throttles back you’ll see a brief complaint about low voltage. In my case we have a very unreliable supply to the house with a lot of voltage variations. I’m pretty sure that’s the problem. On the few occasions when I use AC chargers away from home, the car works fine.

Our local supply is getting worse in fact. I’ve even seen a voltage of under 200V on one occasion. The local network is pretty useless with lots of properties on some weedy looking PMTs. Usual crap British infrastructure.

 

[Astrape]

Mine does this about 80% of the time. If you are in the car when it throttles back you’ll see a brief complaint about low voltage. In my case we have a very unreliable supply to the house with a lot of voltage variations. I’m pretty sure that’s the problem. On the few occasions when I use AC chargers away from home, the car works fine.

Our local supply is getting worse in fact. I’ve even seen a voltage of under 200V on one occasion. The local network is pretty useless with lots of properties on some weedy looking PMTs. Usual crap British infrastructure.

When it throttles does it revert to the high current once the voltage rises? Considering the incoming is allowed to fall to 230-6% = 216 its not unexpected for the car to only get 211. But as soon as the voltage rises 216 it must be able to recover to normal charge rate as that is a normal allowable supply voltage.

 

[Astrape]

Is there a message in the notifications under service on the car, it could be something else like a poorly connected cable.

Oooh notification list, didnt know about that. Many thanks for that clue. Unfortunately the notifications from that charge have dropped off the list due to many camera blocked messages yesterday . Is there a log somewhere? However last night charging stopped at one point and I found this:

12:51am|HVP_w015 and PCS_a023
Unable to charge.
Service is required.

The charge restarted manually and ran the rest of the night without problems
12:51 coincides with me playing around with the houseload to bring it to the 100A limit / lowest supply voltage to stress test the car charge.
Apparently one of the low voltage points caused a car glitch.
However after I restarted it I saw voltages down to 208 at the car without any current reduction.

Anyway I will raise a service request, maybe there is a hardware problem in the car AC/DC conversion.

 

[WannabeOwner]

the charging limited to 24Amps and in the morning the charge was 25% short of target
...
in TeslaFi

In case it happens again, and if you think it would help, I suggest scheduling "Change AMPs to 32" at various points during the night

Its super annoying to get up to a partly charged car when going out on a long work trip the next day. Any insights?

You can schedule an Alert if car is "Less than XX%" at various times ... no idea if that would be able to wake you or if you would want that to happen! but you could get alerts at various points during the night once there was not enough night left! to complete a charge - e.g. power cut, trip, low AMPs

I have that for my work charge 'coz it trips periodically, but I am a bit of a geek like that ... so might not be a solution for regular mortals.

 

[Astrape]

You can schedule an Alert if car is "Less than XX%" at various times

How do you set that one up? Ah maybe the plug in reminder? Would that work if its already charging just as a level sensor?

>I have that for my work charge 'coz it trips periodically, but I am a bit of a geek like that ... so might not be a solution for regular mortals.<

I'm not a regular mortal either I work for Siemens Automation Tech Support

 

[yessuz]

so...
you have 100 AMP limit.
then you charge at 32 AMP (charger)
and then you have 15 KW heaters kicking in (62.5 AMPS)

don't you think that with almost 100 AMP load you might reach the limit and voltage variations?

 

[WannabeOwner]

How do you set that one up? Ah maybe the plug in reminder? Would that work if its already charging just as a level sensor?

Good point ... I've been using it (at work) for "Charger has tripped" which would, of course, then mean it was NOT charging ... so possibly "Charging slowly at low AMPs" and thus below the level that is needed at that time, to finish by end of Off Peak, might not work ... drat!

 

[Astrape]

so...
you have 100 AMP limit.
then you charge at 32 AMP (charger)
and then you have 15 KW heaters kicking in (62.5 AMPS)

don't you think that with almost 100 AMP load you might reach the limit and voltage variations?

Yes. Zappi is set up to back off the current to keep to the 100 amp limit in that situation, and as I described in OP you see that happen very briefly at the start of the heating period at 12. But that is not what caused it to make a shift to exactly 24A and stay there. At any rate when I stress tested it last night it successfully went to and fro across the 100A limit (Well meeting it and then backing off the Zappi) with voltages down to 208. That didnt trip it and you wouldnt expect it to, since thats a normal scenario. It has worked successfully like this since November so I suspect the car has a problem. Or the car to charger interaction.

From other threads I know the Tesla will stop the charge on undervoltage at 200V.

 

[Big Earl]

How did you arrive at the conclusion that you have a 100 amp limit? What size is your main breaker? What size is the transformer feeding your unit/house? Is that transformer shared with other units/houses?

I ask because if you have a 100 amp breaker/fuse, your maximum limit should be 80 amps.

If you’re on a 15 kVA transformer, your limit is actually ~65 amps. If you’re on a 25 kVA transformer that’s shared with your neighbor, your limit is ~110 amps minus whatever they’re using.

 

[pdk42]

When it throttles does it revert to the high current once the voltage rises? Considering the incoming is allowed to fall to 230-6% = 216 its not unexpected for the car to only get 211. But as soon as the voltage rises 216 it must be able to recover to normal charge rate as that is a normal allowable supply voltage.

No. Once it throttles it stays there. Stopping and restarting the charger will get it back to 32A, and sometimes setting the charge to 5A for a minute and then back to 32A will also fix it.

 

[Astrape]

How did you arrive at the conclusion that you have a 100 amp limit? What size is your main breaker? What size is the transformer feeding your unit/house? Is that transformer shared with other units/houses?

I ask because if you have a 100 amp breaker/fuse, your maximum limit should be 80 amps.

If you’re on a 15 kVA transformer, your limit is actually ~65 amps. If you’re on a 25 kVA transformer that’s shared with your neighbor, your limit is ~110 amps minus whatever they’re using.

The conclusion comes from the 100A fuse, In the UK in general 100% of the fuse rating is your capacity. Also adding a car charger has to be notified to the network operator, They were told 7kW would be added to the max house baseload of 15kW so it then becomes their responsibility to ensure 100A is available ie the full fuse capacity without any diversity factor at my connection, The purpose of notification is to avoid all the problems you mention.

 

[Astrape]

No. Once it throttles it stays there. Stopping and restarting the charger will get it back to 32A, and sometimes setting the charge to 5A for a minute and then back to 32A will also fix it.

Ah so thats another case of poor Tesla coding. Yhe car should be able to monitor the current and revert to a higher charge rate if the voltage stays at a higher level for a period, especially a level within normal limits. AS WannabeOwner says this will need some external automation to ensure it doesnt get stuck at a low charge level. It’s a bit pants if I have to set up a 24/7 box and run some code to supervise the car and correct for Teslas poor coding.

I wonder if the voltage rules are available anywhere on the web. I bet thats gonna be a long search........

 

[WannabeOwner]

It’s a bit pants if I have to set up a 24/7 box and run some code to supervise the car and correct for Teslas poor coding.

I agree, but its the sort of thing where OTA can fix it once the problem is know ... and having 3rd party Elastoplast solution does at least allow working around the problem. Back in the dark ages a problem like this would have required "upgrading to latest model" ... bringing with it a new set of bugs/compromises!

Not heard of it before on the airwaves, so might be a physical problem that needs fixing?

 

[pdk42]

Ah so thats another case of poor Tesla coding. Yhe car should be able to monitor the current and revert to a higher charge rate if the voltage stays at a higher level for a period, especially a level within normal limits. AS WannabeOwner says this will need some external automation to ensure it doesnt get stuck at a low charge level. It’s a bit pants if I have to set up a 24/7 box and run some code to supervise the car and correct for Teslas poor coding.

I wonder if the voltage rules are available anywhere on the web. I bet thats gonna be a long search........

I suspect it’s by design. The logic is probably that there’s a supply issue so the safest is to leave it at the lower rate.

 

[Adopado]

Ah so thats another case of poor Tesla coding. Yhe car should be able to monitor the current and revert to a higher charge rate if the voltage stays at a higher level for a period, especially a level within normal limits. AS WannabeOwner says this will need some external automation to ensure it doesnt get stuck at a low charge level. It’s a bit pants if I have to set up a 24/7 box and run some code to supervise the car and correct for Teslas poor coding.

We have patchy quality mains supply and I've certainly had instances in the past where the charge has needed to back off but then returns to 32A later in the charge. I've also had occasional instances where the amps have been lowered and then doesn't return later in the charging session. Whether this is "another case of poor Tesla coding" is impossible to know unless you have access to the Tesla coding!

 

[Big Earl]

The conclusion comes from the 100A fuse, In the UK in general 100% of the fuse rating is your capacity. Also adding a car charger has to be notified to the network operator, They were told 7kW would be added to the max house baseload of 15kW so it then becomes their responsibility to ensure 100A is available ie the full fuse capacity without any diversity factor at my connection, The purpose of notification is to avoid all the problems you mention.

In that case, you should contact your utility, as the significant voltage drop indicates that your circuit is overloaded.

 

[Astrape]

In that case, you should contact your utility, as the significant voltage drop indicates that your circuit is overloaded.

If you follow through the actual values you will find that I have explained that it is a normal voltage drop.