Tesla App reducing charging current by itself?

[MikeHolliday]

The 3's charger can actually deal with around 285 input volts, at least. There's no effort to regulate the total draw to 11.5kw, unless maybe it was added via software in the past year. The Gen2 HPWC was happy with 277V as an input and I've regularly seen 285V at 48 amps, leading to around 13.7kw. It was great, and I still don't know why they stopped supporting it in the Gen3. Technically, they didn't officially support it in later Gen2's either, but it was just a manual change.

Additionally, it'll deal with input voltages around 185V, although not when it starts at a 'normal' ~240V. This was actually on the same charging post as the 277V, but via a different J1772 charger that had to be connected to a 208V supply, and by the time it hit the car it was more like 190V or so.

If your voltage is dropping from 208 volts to 190 volts you have an issue. Tesla recommend no greater than a 3% voltage drop which would be 202 volts. From 208 voltage to a 190 voltage is almost 8%. At 8% you are going to have conductors getting hot. The NEC recommends that the maximum combined voltage drop for both the feeder and branch circuit shouldn't exceed 5%, and the maximum on the feeder or branch circuit shouldn't exceed 3%.

 

[MikeHolliday]

Well the drop in Amperage didn’t start until I updated the Tesla app on my iPhone.

I think that the car is getting smarter and adjusts according to the voltage. But with a continuous charge your voltage drop is recommended to not exceed 3%.

I think when the car sees a voltage drop of greater than a given percentage is is backing of of the current to lower the resistance in the wire.

 

[MikeHolliday]

This most commonly occurs when the seasons change and the connections in the Wall Charger expand and contract. Trip the breaker, open the Wall Charge and torque the wire attachment screws. I would also do this, cautiously, in the breaker box. It could be other issues as noted above, but this is an easy one to do.

Good luck!

Properly torqued with the initial installation with Copper Wire you should never need to re-torque, aluminum is a totally different matter and I would never put aluminum wire in my house.

 

[SilverString]

The 3's charger can actually deal with around 285 input volts, at least. There's no effort to regulate the total draw to 11.5kw, unless maybe it was added via software in the past year. The Gen2 HPWC was happy with 277V as an input and I've regularly seen 285V at 48 amps, leading to around 13.7kw. It was great, and I still don't know why they stopped supporting it in the Gen3. Technically, they didn't officially support it in later Gen2's either, but it was just a manual change.

Additionally, it'll deal with input voltages around 185V, although not when it starts at a 'normal' ~240V. This was actually on the same charging post as the 277V, but via a different J1772 charger that had to be connected to a 208V supply, and by the time it hit the car it was more like 190V or so

My MS limits it to about 11.7 kW not familiar with the 3's or Y's

 

[ATPMSD]

Properly torqued with the initial installation with Copper Wire you should never need to re-torque, aluminum is a totally different matter and I would never put aluminum wire in my house.

Yes, properly! But this is such an easy thing to check.

 

[redmunds]

Does anyone else have an issue where the new Tesla app reduces charging current at night? I'd like to charge at my full 48 amps, but the app keeps reducing it to 18 amps. I adjust it and every night it does the same thing

Is your car charged to the specified amount in the morning? If so, then it doesn't matter what amperage it takes to get there, right?

The Tesla app recently added a way to Schedule a Departure time. Is that set? I haven't tried this yet, but I'm wondering if the amperage is getting throttled because it doesn't need to charge at full 48 amps to reach specified charge limit by the departure time?

 

[Sophias_dad]

At 8% you are going to have conductors getting hot.

No, that's just not right. If that 8% is spread over 300 feet of conductor, its a mediocre but not dangerous installation. OTOH, if its 3% getting lost over 10 feet of conductor, something is gonna melt. The two chargers were around a hundred feet from the nearest building, plus an unknown distance within(but it was probably a 500+ foot building!)

Keep in mind, the feed voltage is allowed to be several percent off before its even considered out-of-spec, and the 277 volt feed line was undoubtedly coming from an entirely different distribution network(480V three phase) than the 208V supply. I didn't do the installation of either, I just took the free power.

 

[MikeHolliday]

I will highly disagree with your thoughts, in the US 5% is considered out of spec, please see NEC 210.19(A)(1) below...

NEC 210.19(A)(1) Informational Note No. 4 limits the voltage drop at the furthest outlet of a load to 3% of the applied voltage. This allows 2% drop in the feeder. Alternatively, the maximum combined voltage drops on the feeder and branch circuits going to the furthest outlet of a load should be limited to 5%.

 

[Sophias_dad]

I will highly disagree with your thoughts, in the US 5% is considered out of spec, please see NEC 210.19(A)(1) below...

NEC 210.19(A)(1) Informational Note No. 4 limits the voltage drop at the furthest outlet of a load to 3% of the applied voltage. This allows 2% drop in the feeder. Alternatively, the maximum combined voltage drops on the feeder and branch circuits going to the furthest outlet of a load should be limited to 5%.

This is irregardless of the length of a cable.

Voltage Tolerance Standard – ANSI C84.1 – Voltage Disturbance

I read that RANGE A as 114V continuous supply being 'okay' on a 120V circuit... conveniently 5%... If you scroll down a bit and click on 208V, you'll see that the at-the-meter range for range a is

218V - 197V​

and losing 3% of that 197V would come out to 191V, close enough to my 190 example.


Further, while it'd be bad to live in the Range B region, apparently it is sometimes done, and the voltage at-the-meter can then be 191V, and taking 3% off that happens to be a very familiar 185V.

I really don't care. I was just trying to convey that 8% losses doesn't mean a HOT cable, it may just mean a LONG cable, or maybe a combination of a long cable and a low meter voltage. I'm guessing the conductors were mildly undersized for the length of the run.

 

[Rocky_H]

Remember that most of the time a Continuous Load requires a wire one gauge larger than would normally be used. Since a 6 gauge wire is rated for only 55 Amps and a 48 Amp draw times 125% (See code below) gives you 60 Amps which means that a 4 gauge wire is required for a 48 Amp draw.

If you're going to try telling people the amp rating of wire, you need to be more specific than this. You can't just say "6 gauge wire" like you did here.

You state that it's 55A, but that's only if it is NM-B, Romex multi-wire cable. If it's individual wires in conduit, then 6 gauge is rated at 65A, not 55A.

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

 

[Ruffles]

Definitely check your connections on the wire block in the charger. I got messages like that and this is what I found:

 

[MikeHolliday]

If you're going to try telling people the amp rating of wire, you need to be more specific than this. You can't just say "6 gauge wire" like you did here.

You state that it's 55A, but that's only if it is NM-B, Romex multi-wire cable. If it's individual wires in conduit, then 6 gauge is rated at 65A, not 55A.

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

Ok, yes, 6 AWG Romex is rated at 55 Amps and 6 AWG THHN in a conduit is Rated at 65 Amps. But I have seen a number of installations of individual using 6 AWG Romex on a 60 AMP breaker. By NEC when using a continuous load (A load that may extend beyond 3 hours, as with charging an electric car) both the Breaker and the wire must be rated at 1.25% of the load. Which means if you are using a wall connector to charge with (regardless of the manufacturer), if it is drawing 48 Amps, then that location needs a 60 Amp Breaker and Conductors rated for equal to or greater than 60 Amps.

 

[Sophias_dad]

But I have seen a number of installations of individual using 6 AWG Romex on a 60 AMP breaker.

Regardless of what you have seen, it isn't allowed and if someone's house burns down because they do what you saw, it would be very bad indeed.

On TMC I've seen all sorts of garbage installations, some by electricians.

On the flipside of this argument(and I've made it myself) is that NEC's rules/regulations are extremely conservative, so pushing a few more percent than is supposed to be allowed through a wire is really unlikely to cause any trouble at all. It may become an issue in some areas, with some conditions(many wires bundled, very high ambient temperature, and so on). I wouldn't want to be(or think myself) responsible for loss of property or lives.

 

[MikeHolliday]

I fully agree and I have even spoke "electricians" that are totally unaware of the the Continuous Load of an EV.

 

[rickybobbee]

I fully agree and I have even spoke "electricians" that are totally unaware of the the Continuous Load of an EV.

yup. I almost had an electrician install my charger, he didn't know what he was doing he was going to use the wrong wire, wrong breaker and who knows what else. I fired him and got someone else to do it right. sad thing is he was a tesla authorized installer and had done other installs on the cheap and probably still is

 

[Dickie_L_J_O]

I’m also experiencing this issue with the UMC - also only since the new app was introduced.

I set 7A and hit charge and it’s fine. However, the next day I check before scheduled start, and it’s dropped to 6A. Rinse and repeat, adjust to 7A, drive around, come back and in the garage it’s already gone to 6A.

To be clear this drop doesn’t happen whilst charging, only before the next session.

 

[andaconda]

I still think it is the APP - I'll set it to charge @48amps only to find later that its charging @47amps. Not a big deal, but a little irritating. Now if I were charging a 12amps - yes that would make a difference.

 

[RandyS]

@NJcarowner

On the car screen, what is the voltage in the very beginning of the charging session before it gets to full power, and what is the voltage on the screen at the full 48 amps? In addition, how long is the wire run from your panel to the NEMA 14-50 or Wall Connector and what size/type of wire is it? We can help you better with this information.

 

[MikeHolliday]

@NJcarowner

On the car screen, what is the voltage in the very beginning of the charging session before it gets to full power, and what is the voltage on the screen at the full 48 amps? In addition, how long is the wire run from your panel to the NEMA 14-50 or Wall Connector and what size/type of wire is it? We can help you better with this information.

Absolutely, I believe that the car will reduce the Amperage if the voltage is low to prevent a current issue. Volts = Wattage divided by Amperage. If you have a Gen3 Wall Connector 240 volts = 11,500 watts/48 Amps or if the voltage drops to 230. 11,500 Watt/230 Volts = 50 Amps draw, But I believe that when the car sees a lower voltage it will lower the wattage. As an example, if it drops the Wattage to 10,500/230 volts = 45.65 Amps,

 

[ATPMSD]

it will lower the wattage

I get what you are trying to explain here, but I suggest some of your points may be confusing, for example, the stated relationship that Volts = Wattage divided by amperage, while mathematically correct, is IMHO a bit misleading.

Basically, and more simply started (as you noted in your first sentence), the car monitors voltage and if the voltage is low it lowers the amperage until the voltage is acceptable. The resulting wattage is then Volts x Amps.