Model S charging @ only 16 amps on 40 Amp, 240 Volt Circuit => Why?

[CurrieG]

I plugged my Tesla Model S Performance into my 240 Volt, 40 Amp home charging receptacle , but it only charged at a rate of 16 Amps... Very slow! The incoming voltage on the dash was showing @ 239 Volts. Had the Model S charging rate set to 40 Amps.

Does anyone know what the parameters / algorithm the car uses to determine / set the charging current?

Thanks!

 

[Vger]

This happened to m on one of my first charge stops. Make sure that the plug is inserted all the way into the receptacle on the car. It is really easy to not get it all the way seated. Surprisingly, in if it is not all the way in, it will still charge, but at much reduced current. I guess it measured the resistance across the connection, and limits current accordingly.

 

[dsm363]

Have seen that a few times. As vger said, need to simply put a little more pressure on plug and should latch better and charge at 40A.

 

[CurrieG]

Thanks.... Will try this.

 

[Doug_G]

I think I can see how this might happen. The power pins engage before the pilot signal pin. Without the pilot it will assume minimum amperage.

 

[Vger]

I think I can see how this might happen. The power pins engage before the pilot signal pin. Without the pilot it will assume minimum amperage.

Yes, that fits the symptoms! It is odd that they designed it this way-- very different than the Roadster. In some ways it provides a fall-back to get some charge. But I would actually prefer it demanded the pilot signal and advised you to remove and re-insert the connector.

For those also new to the car, note that there are two levels of resistance while you insert the connector. One hits what feels like significant resistance at first, but you have to push through this to get the connector seated and locked properly.

 

[Billott]

Happened to me, as well.

 

[strider]

Yes, that fits the symptoms! It is odd that they designed it this way-- very different than the Roadster. In some ways it provides a fall-back to get some charge. But I would actually prefer it demanded the pilot signal and advised you to remove and re-insert the connector.

It's for safety. If the car is still charging and you remove the plug, the pilot signal will drop before the charging pins come out. That way charging can stop before the charge pins let go and preventing arcing.

 

[agileone]

Charging begins at 40A for about 10 mins and then it drops to 10A ???

Just got my 60Kwh MS on wednesday, and I noticed this strange behavior last night. I do believe that charging was all done at 40A on the first night, since I was in the car configuring things for most of the time, I would have noticed.

Is this normal, since charge was showing 275km of range, so it only needs to put in about 25km more juice, for a standard charge ?

Is this the charging system protecting the battery when almost at standard ?

This behavior has me worried since I am/was planning a road trip next week...

I will try going to a Sun Country charge station tonight to see how it behaves on 70 amps.

 

[mnx]

Not normal, after ramping up the current mine pulls 10Kw from start to finish of a standard charge.

 

[Doug_G]

This can happen if you don't insert the plug all the way into the charge port. The pilot signal fails to connect and it defaults to the minimum current.

 

[mknox]

This can happen if you don't insert the plug all the way into the charge port. The pilot signal fails to connect and it defaults to the minimum current.

Is the point of the pilot signal to tell the car what adapter is on the UMC? Otherwise I would have thought no pilot signal, no juice at all. If it is just for the adapter, then it makes sense to default to the lowest current so as not to overload the circuit it's plugged in to.

 

[dadaleus]

My understanding is it is tied to whether it fully latches. If not, it limits to 16amp so if someone pulls it out it won't be a hazard. If this happens, stop the charging, remove the cable or J1772 adapter (it may need to be unlocked because it may be partway latched), and then reinsert it more forcefully. If you can't make it work at over 16amp ever, contact Tesla as something's broken or defective.

 

[Vger]

Is the point of the pilot signal to tell the car what adapter is on the UMC? Otherwise I would have thought no pilot signal, no juice at all. If it is just for the adapter, then it makes sense to default to the lowest current so as not to overload the circuit it's plugged in to.

As I understand it, there are two purposes of the pilot signal, implied by a number of the comments above:

1) To inform the car what is the maximum available current for charging (encoded by DC voltage);

2) to prevent arcing that could rapidly damage the contacts, by instructing both the EVSE and car to open contactors until the pilot signal is stable.

 

[mknox]

As I understand it, there are two purposes of the pilot signal, implied by a number of the comments above:

1) To inform the car what is the maximum available current for charging (encoded by DC voltage);

2) to prevent arcing that could rapidly damage the contacts, by instructing both the EVSE and car to open contactors until the pilot signal is stable.

Still curious as to why there would be any current at all if no pilot signal is present.

 

[Doug_G]

Still curious as to why there would be any current at all if no pilot signal is present.

Because without the pilot signal, the car is allowed to draw 16A. There's no requirement for an EVSE at all. The Roadster "Spare Cable" (120V 12A) doesn't have any pilot signal.

At low current there is no risk of significant sparking when you disconnect it.

 

[mknox]

Because without the pilot signal, the car is allowed to draw 16A. There's no requirement for an EVSE at all. The Roadster "Spare Cable" (120V 12A) doesn't have any pilot signal.

At low current there is no risk of significant sparking when you disconnect it.

Fair enough, and admittedly I don't know much about these protocols. I just figured if they're going to have the pilot there at all, it would at least have to be present to allow current to flow. I do see your point about the 120 volt Roadster cable, but the Model S connector, whether it be UMC, HPWC or Supercharger will always have a pilot connection, no?

 

[Doug_G]

Fair enough, and admittedly I don't know much about these protocols. I just figured if they're going to have the pilot there at all, it would at least have to be present to allow current to flow. I do see your point about the 120 volt Roadster cable, but the Model S connector, whether it be UMC, HPWC or Supercharger will always have a pilot connection, no?

Apparently they used the same design as the Roadster. Perhaps they originally planned to have a "spare cable" similar to the Roadster's, then figured it wouldn't be that much cheaper than the UMC and didn't bother offering them. It also helps a lot that the UMC is tiny compared to the Roadster's, which is almost painfully immense.

 

[mknox]

It also helps a lot that the UMC is tiny compared to the Roadster's, which is almost painfully immense.

It still amazes me that they can push 90 kW (Supercharger) through that relatively small connector. I remember seeing the early prototype S when it came to Toronto on the tour, and I think they were still using the Roadster adapter:

 

[Doug_G]

The original prototype had a Roadster drive train in it.

Yes, the connector is pretty amazing. The old "rule of thumb" is that you can put 1000 Amps per square inch through solid copper. So you could put 200A through a connector with an area of 1/5th of a square inch.

Of course once it's got insulation on it then you have to make allowances for reduced heat dissipation, and you have to be concerned with contact surface areas, reliability of the contacts, etc.