Charge rate reduced - unexpected voltage drop error

[watersrog]

Hello,

I have a Tesla wall connector installed at home (small apartment building), on the same circuit as my apartment (I just have single phase). The length of the electrical cable from box to Wall connector is around 15 meters and the cable is 6x5 mm (nor sure how to translate to AWG, I am in Europe)

I can set it to a max of 32A, however, doing so i get the error message in the title and it drops to 24 or even 18A sometimes. Charging speed drops proportionally, from 6.7 kwh to 5 or 3 kwh. The error is not consistent and seems to be somewhat related with what appliances I have on in the house. The voltage is also quite low, hovers between 200 (even a bit lower) and 210V even if it should be around 230V.

I have an electrical protection device for my heating unit in the house and it usually shows 220-230V but I hear voltage dropping noises from it often enough too. The electrician who installed my Wall connector can't be bothered to come to check, he said I probably have low voltage in my neighbourhood but since the heater unit protection shows over 220V, not sure this is the case.

If i keep the current at 24A and the rate at 5 kwh it happens way less frequently.

Now, this might be normal considering I am sharing the same circuit as my home and I don't mind leaving the current at 20-24A and reducing charging speed to 4-5 kwh since I am almost never in a hurry to charge but I wanted to make sure there's no potential harm to the car battery. If I stop and restart charging from phone app, it goes to 32A and then drops again after a while.

Any advice or opinions on this would be appreciated. I can definitely live with slow charging speeds as long as I am sure there's no harm done to the battery.

 

[Sophias_dad]

6x5mm is probably the outer dimensions of the cable(including two conductors, ground, and insulation between them. It can't really be the conductor size because 5mm round would be about 4awg and would have very little loss at 32A over 15 meters. On the other hand, to try to cram two conductors plus insulation in 6mm would be almost silly in the other direction. 2mm diameter(assuming two conductors with 1mm of insulation) is 12A, and 32A would cause severe voltage drop.

I would encourage you to recheck the conductor size. If it really is 4 or 5mm in diameter you must have either serious amounts of load you don't know about or bad connections on one or the other end.

AWG to mm2 | Gauge to mm conversion might help.

 

[watersrog]

Could it be because the electricity is shared with my home, having single-phase. Also, the higher the amperage, the lower the voltage, ie: if I set the current to 32A, there will be around 200V (little higher at night). If I drop it to 18-24A, it goes to 208-210V.

 

[watersrog]

The cable is this, but the link is from the Romanian store where I bought it. It was recommended that I get this to future proof it in case I could install a tri-phase at home.

Dedeman Cablu electric MYYM / H05VV-F 5 x 6 mmp, cupru - Dedicat planurilor tale

Cablu electric MYYM / H05VV-F 5 x 6 mmp, cupru la Dedeman.ro. Aflati informatii despre pret si disponibilitate pentru Cabluri joasa tensiune pe site.

www.dedeman.ro

 

[Eric33432]

Could it be because the electricity is shared with my home, having single-phase. Also, the higher the amperage, the lower the voltage, ie: if I set the current to 32A, there will be around 200V (little higher at night). If I drop it to 18-24A, it goes to 208-210V.

That sounds like voltage drop on the circuit feeding the wall connector. Watch the volt meter on your "electrical protection device" when you start charging. Any decrease on that indicates the voltage being pulled down on your electrical service. Watch the voltage on the car when it first starts charging to when it is charging at 32 amps. That will be a combination of the voltage drop on your electrical service PLUS the voltage drop on the circuit feeding the wall connector. Subtract the voltage drop on the electrical protection drop from the voltage drop on the circuit feeding your wall connector. In the US engineers aim to design electrical services where the total voltage drop is 5% or less and the voltage drop on the electrical service is not more than 3% and the voltage drop on a branch circuit is not more than 3%. If it is the wire being used is usually too small.

Let us know what you discover.

 

[Eric33432]

The cable is this, but the link is from the Romanian store where I bought it. It was recommended that I get this to future proof it in case I could install a tri-phase at home.

Dedeman Cablu electric MYYM / H05VV-F 5 x 6 mmp, cupru - Dedicat planurilor tale

Cablu electric MYYM / H05VV-F 5 x 6 mmp, cupru la Dedeman.ro. Aflati informatii despre pret si disponibilitate pentru Cabluri joasa tensiune pe site.

www.dedeman.ro

View attachment 1070273

Is it diameter ~3 AWG or mm2 ~9 AWG?

In the US 10 AWG is good for a 30 amp circuit, running at 24 amps continuous, so 9 AWG should be good for a bit more than 24 amps if you interpolate.

How large is the service to your house? I've seen some pretty small services, on some very long 400/230 volt distribution lines that go on for way more than a km, in Eastern Europe that are not really designed for these kinds of loads. Some photos would be cool of the service drop, meter, load center, etc.

 

[watersrog]

On the cable specs it says a max of 45A so I gues 100s should be ok?

There's an electrical transformer few hundred of meters from here but, on the other hand, there's a new neightbourhood of couple dozens really big appartment building nearby so there could be a low voltage issue due to that.

Also, the electrician who installed my connector told me the total power installed for my appartment is 9 kw or so this could also explained.

However, I can live with the low charging speed and I can mostly charge at night when usually doesn't drop under 5 kwh. But could the low voltage or the drops have a negative effect on the car or car battery? Voltage stays between 200 and 210 usually.

 

[Eric33432]

On the cable specs it says a max of 45A so I gues 100s should be ok?

There's an electrical transformer few hundred of meters from here but, on the other hand, there's a new neightbourhood of couple dozens really big appartment building nearby so there could be a low voltage issue due to that.

Also, the electrician who installed my connector told me the total power installed for my appartment is 9 kw or so this could also explained.

However, I can live with the low charging speed and I can mostly charge at night when usually doesn't drop under 5 kwh. But could the low voltage or the drops have a negative effect on the car or car battery? Voltage stays between 200 and 210 usually.

A few hundred meters? If that is 2, 3, 4 hundred meters, that is a very long distribution circuit, could be 400 to 800 feet which in the US is very long. That is likely your problem. These systems were not designed for large continuous loads like EV charging.

Voltage in the 210 to 200 volt range is not a problem. In the US the most standard three phase service is 208/120 volt service, which the Tessies are perfectly happy with. (In commercial installations like at hotels and office buildings, a single phase 2 wire 208 volt circuit is most often used for a Tesla Wall Connector.)

For curiosity sake I'd still like to see a few photos if you can post some.

 

[Sophias_dad]

So yeah, the wire you have is 5 conductors of 6 square mm each. In the US, that would be 10awg and not allowed to carry 32 amps(even intermittently)

That said, a quick look at southwire's calculator suggests it shouldn't have all that much voltage loss.

A look at Cable Size & Current Rating Chart suggests 6sqmm conductors should be usable at 41 amps. Its not clear if there's a derating for continuous use in europe like there is in the US, but even if so it should still be good for 32 amps.

 

[watersrog]

A few hundred meters? If that is 2, 3, 4 hundred meters, that is a very long distribution circuit, could be 400 to 800 feet which in the US is very long. That is likely your problem. These systems were not designed for large continuous loads like EV charging.

Voltage in the 210 to 200 volt range is not a problem. In the US the most standard three phase service is 208/120 volt service, which the Tessies are perfectly happy with. (In commercial installations like at hotels and office buildings, a single phase 2 wire 208 volt circuit is most often used for a Tesla Wall Connector.)

For curiosity sake I'd still like to see a few photos if you can post some.

Thanks for the answers! Photos of my instalation? Not sure if I can post photos of local transformer or?

 

[Eric33432]

Thanks for the answers! Photos of my instalation? Not sure if I can post photos of local transformer or?

Photos of service lateral, drop, meter, breaker panel showing the main breaker, etc. Take a photo of the transformer too if you want. You should be able to attach photos. Perhaps if you are a new user you cannot do that???

If your service is rated for 9kW that is only ~40 amps at 230 volts. I would expect the service drop, breaker panel, etc., to be very small.

I would suggest limiting charging to 15 or 20 amps. Maybe less depending on any other heavy loads like electric heat.