12 amps down to 5, and a question

[Stimyg]

Same guy here who posted the thread about the car lowering its charging rate to 32 amps on my 240v outlet upstate. Now here's a new and more problematic one:

During the week I charge at a parking garage in the city. They installed a 120v/12amp plug for me. All week it worked fine, charging at the full 12. Then yesterday it slowed down to 5amps. And what its showing is 5/5, meaning its only trying to charge at 5 amps. I took a trip today and the valet plugged it back in, and again it is charging at 5/5 amps. So it has "memorized" the lower setting and is not trying to charge at a higher rate.

I assume it lowered the rate because of some kind of power surge or brownout something?

If this continues to happen, it is an unworkable situation for me. I can't be continually visiting the garage to reset the charger back to the full 12/12. (Which itself is very slow but ok for me because I mainly use the car on the weekends and can charge all week.). So a couple questions:

First, any idea what might be wrong? Am I right that it probably happened due to a brownout or something?

And secondly, is there a way to reset it to a higher attempted amperage without having to visit the car every time? Ie, with the App?

Any other thoughts for me?

This whole "memorizing" of the charging rate at a given location isn't doing me any favors at the moment.

 

[Doug_G]

This is caused by not inserting the charge connector fully. The pilot signal didn't connect so it defaults to minimum current for safety.

 

[Stimyg]

I will check that out tomorrow. But I doubt that's what happened yesterday, since it lowered the attempted amperage charge rate in the middle of a multiday charging session without anyone touching the car. At least not as far as I know.

 

[montgom626]

This is caused by not inserting the charge connector fully. The pilot signal didn't connect so it defaults to minimum current for safety.

You are correct

 

[XrstalLens]

It will also remember the most recent charge rate at that location. So, once it's plugged in, make sure you check the charge current setting and put it on the maximum.

 

[GaryD]

What voltage does it show on the Model S screen? Take note of the voltage at 5 Amps and adjust it back to 12 and see if the voltage drops more than a few volts. If it does, I'm guessing that the Model S senses a bad connection or a loaded circuit and drops it back to the 5 Amps. Perhaps there is another load on that circuit that gets switched on later that causes a voltage drop.

 

[cinergi]

If it's saying 5/5 it's not a location/memory issue and it can't be adjusted back to 12. Either the connection bad or the cable is bad (or, hopefully not, the car has a problem).

 

[Stimyg]

It will also remember the most recent charge rate at that location. So, once it's plugged in, make sure you check the charge current setting and put it on the maximum.

Is there a way to turn off that function? That's the part that's not doing me any favors.

 

[scaesare]

I will check that out tomorrow. But I doubt that's what happened yesterday, since it lowered the attempted amperage charge rate in the middle of a multiday charging session without anyone touching the car. At least not as far as I know.

To expand on the point made about a potentially faulty cable/port//car-charger, the behavior you describe (amperage scaling back mid-charge) could be explained by the pilot signal being interrupted.

Can you use the same cable at another location successfully?

 

[Stimyg]

Well, I've had a similar issue at another location... But I think that might have been because of it was very hot and in the sun. I'm walking over to the garage to check the cable now.

- - - Updated - - -

Can you explain how the pilot signal works?

 

[scaesare]

Well, I've had a similar issue at another location... But I think that might have been because of it was very hot and in the sun. I'm walking over to the garage to check the cable now.

- - - Updated - - -

Can you explain how the pilot signal works?

There's smarts in the charging station (or in the "head" in the case of the UMC) that can communicate to the charger(s) in the car to specifiy what the capabilities of the station are. The car-charger(s) can then make decisions as to what to do, such as attempt to draw 40 amps form a NEMA 14-50, or 80 amps from a HPWC properly configured. This is the pilot signal. It has it's own small-gauge electrical pin in the cable connector.

If for some reason the pilot signal is not present, such as not inserting the connector all the way in to the charge port or if there's a faulty cable/connector somewhere along the way, the car charger(s) will revert to "safe" defaults in order to avoid any safety concerns. This typically means lower current draws at each given voltage.

I believe the pilot signal is a square wave with specific duty cycle for each capability, as opposed to an actual digital communication, but that's based on a quick glance at the OpenEVSE stuff a while back... so don't quote me on that.

 

[FlasherZ]

I believe the pilot signal is a square wave with specific duty cycle for each capability, as opposed to an actual digital communication, but that's based on a quick glance at the OpenEVSE stuff a while back... so don't quote me on that.

You're correct. Here are the details.

The J1772 Pilot is a 1khz +12V to -12V square wave, the voltage defines the state and the duty cycle defines the current available to the EV. The EVSE sets the duty cycle and the EV adds resistance from the pilot the Ground to vary the voltage. The EVSE reads the voltage and changes state accordingly.

 

[scaesare]

You're correct. Here are the details.

Cool.. thanks FlasherZ.

 

[Stimyg]

That's mostly Greek to me. But to answer an earlier question: I reset the charger tonight. At 12 amps the voltage went down a bit, to about 115 to 119, varying. Is that a big enough voltage drop to indicate anything? For what its worth its 12 hours later now and its still charging at 12 amps 116v.

 

[FlasherZ]

That's mostly Greek to me. But to answer an earlier question: I reset the charger tonight. At 12 amps the voltage went down a bit, to about 115 to 119, varying. Is that a big enough voltage drop to indicate anything? For what its worth its 12 hours later now and its still charging at 12 amps 116v.

No, that's pretty normal. Anything under 6% is normal, and depending on your circuit (especially if it's 14-gauge) you might see up to 10%.