EV Charging Approach - Difficult Choice

[retirede]

Continuous charging at over 32 Amps may not be good for modern lithium car batteries, which are the most expensive component of electric vehicles, and degrade prematurely with heat stress.

Level 4 DC fast charging stations in summer ambient may be the worst way to heat stress lithium vehicle batteries.

Modern EVs have sophisticated thermal management systems to monitor and control battery temperatures. The same heating and AC system used to maintain cabin temperature is redirected to the battery as required. Level 2 charging at 48A will not result in any meaningful battery degradation.
When using a DCFC, it’s not uncommon to see peak charging currents of 400A. If the car cannot maintain a safe battery temperature, it throttles back the current.
It is true that DCFC will cause faster battery degradation, but in most cases, the car will be worn out before the battery capacity becomes a significant issue.

 

[ramsy]

..in most cases, the car will be worn out before the battery capacity becomes a significant issue.

The most reliable information comes from manufacturer's listed instructions.

Apparantly during certain conditions, perhaps ambient extremes, Tesla's wall connector uses a specific fault code that instructs users to reduce charging current.

--------
Seven (7) red blinks

Vehicle overcurrent detected

Reduce the vehicle's charge current setting. If the issue persists and the attached vehicle is manufactured by Tesla, record the vehicle's VIN and approximate time of the fault and contact Tesla. If the vehicle is not manufactured by Tesla, contact the vehicle's manufacturer.
---------

Failure to do this voids the warranty, and Tesla uses telemetry to report all charging events to the manufacture.

 

[wwhitney]

Apparantly during certain conditions, perhaps ambient extremes, Tesla's wall connector uses a specific fault code that instructs users to reduce charging current.

--------
Seven (7) red blinks

Vehicle overcurrent detected

Reduce the vehicle's charge current setting. If the issue persists and the attached vehicle is manufactured by Tesla, record the vehicle's VIN and approximate time of the fault and contact Tesla. If the vehicle is not manufactured by Tesla, contact the vehicle's manufacturer.
---------

I take the above to mean that the Wall Connector has observed that the vehicle is drawing charging current in excess of the allowed amount advertised by the Wall Connector's pilot signal, and therefore the vehicle is not complying with the J1772 charging standard.

An EVSE is just a simple communications protocol for the EVSE to tell the EV the maximum available current, and the EV to tell the EVSE to close its contactor. There are no active measures within the EVSE to limit or control the charging current, the standard relies on the EV to do the right thing.

Cheers, Wayne

 

[retirede]

The most reliable information comes from manufacturer's listed instructions.

Apparantly during certain conditions, perhaps ambient extremes, Tesla's wall connector uses a specific fault code that instructs users to reduce charging current.

--------
Seven (7) red blinks

Vehicle overcurrent detected

Reduce the vehicle's charge current setting. If the issue persists and the attached vehicle is manufactured by Tesla, record the vehicle's VIN and approximate time of the fault and contact Tesla. If the vehicle is not manufactured by Tesla, contact the vehicle's manufacturer.
---------

Failure to do this voids the warranty, and Tesla uses telemetry to report all charging events to the manufacture.

I don’t know a lot about how Tesla manages charging and I’m not saying you’re wrong, but it seems nonsense that the car wouldn’t simply reduce the charge current in these cases. There shouldn’t be any need for user intervention (the user is normally not present in the middle of a multi-hour charge) or to have a nanny function.

 

[ramsy]

..There are no active measures within the EVSE to limit or control the charging current, the standard relies on the EV to do the right thing.

Cheers, Wayne

Tesla's charging current is user adjustable from the vehicle.

 

[wwhitney]

Tesla's charging current is user adjustable from the vehicle.

Correct, that is a measure taken by the EV, nothing is changing within the EVSE when you do that. There are no active measures within the EVSE to limit or control the charging current.

Cheers, Wayne

 

[ramsy]

>The Tesla Wall charger is designed to draw a maximum of 48 amps from a 60 amp circuit. You can set it to draw less.

Perhaps that resets Max current for EVSE ?

 

[jaggedben]

Pretty much all of the plug in chargers are 32 amp max (40 amp circuit). Even the plug in Tesla charger is 32 amps. I'm wondering if they can't get a listing for more than 32 amps since the NEC permits 50 amp receptacles to be fed by 40 amp circuits?

This one seems to offer 40A on a plug.

Enel X JuiceBox 40A 9.6kW Plug-In 14-50 WiFi Enable 25ft Cable EV Charger

Enel X JuiceBox 40A Plug-In NEMA 14-50 9.6kW Wifi Enable 25ft Cable Electric Vehicle Charger 240V.

www.bulbs.com

 

[retirede]

This one seems to offer 40A on a plug.

Enel X JuiceBox 40A 9.6kW Plug-In 14-50 WiFi Enable 25ft Cable EV Charger

Enel X JuiceBox 40A Plug-In NEMA 14-50 9.6kW Wifi Enable 25ft Cable Electric Vehicle Charger 240V.

www.bulbs.com

Yes, there are several manufacturers of 40A EVSEs with a 14-50P.

 

[curt swartz]

Tesla's charging current is user adjustable from the vehicle.

The Maximum charge current is set by the cord adapter or the wall charger.

 

[ramsy]

The Maximum charge current is set by the cord adapter or the wall charger.

Be carefull you don't ignore Wall charger instruction manual bottom of page 27, which requires users "Reduce the vehicle's charge current setting" if "Vehicle overcurrent detected".

Anyone on this forum telling users otherwise violates instructions for this listed equipment, and 30+ years of adopted code from NFPA-70 110.3(B)

 

[retirede]

Be carefull you don't ignore Wall charger instruction manual bottom of page 27, which requires users "Reduce the vehicle's charge current setting" if "Vehicle overcurrent detected".

Anyone on this forum telling users otherwise violates instructions for this listed equipment, and 30+ years of adopted code from NFPA-70 110.3(B)

They way I read that, it means that this can only happen if the vehicle requests more current than the EVSE allows. When this happens, the EVSE faults and shuts off. If you ignore it, the car won’t charge. It does not create a hazardous situation.

 

[Electrical Geek]

I am not sure about California, but in Mass the receptacle in the garage would have to be ground fault protected, no exceptions.

 

[petersonra]

I am not sure about California, but in Mass the receptacle in the garage would have to be ground fault protected, no exceptions.

OP said this earlier.

The 40 amp run from the 70 amp subpanel is only down 4 feet and into ceiling cavity, then 5 feet to exterior wall adjacent to garage door (exterior mount in that location).

It is apparently outside the garage. Don't know if that makes a difference in MA or not.

 

[ramsy]

They way I read that, it means that this can only happen if the vehicle requests more current than the EVSE allows. When this happens, the EVSE faults and shuts off. If you ignore it, the car won’t charge. It does not create a hazardous situation.

That is brilliant possibility.

"Vehicle overcurrent detected" is a fault that punts to vehicle manufacturer, if it persists after we "Reduce the vehicle's charge current setting".

I expected this fault to halt thermal runaway or overheating in the lithium battery, but I can learn to like your idea as well.

 

[jaggedben]

That is brilliant possibility.

"Vehicle overcurrent detected" is a fault that punts to vehicle manufacturer, if it persists after we "Reduce the vehicle's charge current setting".

My wager is that this would pretty much never happen with an OEM vehicle. (Well, unless maybe something was failing, in which case I would park it outside and call someone to tow it to a shop, because battery overcharge or failure could be very dangerous as you know.) But user modified vehicles are a real thing in this world, including some where the charging current might be set manually, and charger listing requirements would appropriately take the possibility of that into account. The point is from the charger's point of view, it's dependent on the car to charge at the appropriate current, so they have to fail safe and explain what to do if it happens. Imo they probably should have appended 'or contact the vehicle manufacturer or a qualified service provider' to that language you quote. So the lay person better understands.

 

[Rick 0920]

If the car required 32A or less, is it still ok to wire it with 6-3 w/ground Romex and protect with a 50 amp breaker?

 

[wwhitney]

If the car required 32A or less, is it still ok to wire it with 6-3 w/ground Romex and protect with a 50 amp breaker?

The EVSE install details don't depend on anything about any EV that may be plugged into it. The EVSE has a (fixed or settable) maximum advertised (to the car) charging current, which is continuous; the circuit and breaker have to be sized to 125% of that.

Cheers, Wayne

 

[tortuga]

I almost never install a receptacle for an EV charger if I dont have to. Saves a GFCI breaker, since most chargers already have a GFCI in them.
I would go with option #3 nice dedicated EMT run to main panel.

 

[retirede]

I almost never install a receptacle for an EV charger if I dont have to. Saves a GFCI breaker, since most chargers already have a GFCI in them.
I would go with option #3 nice dedicated EMT run to main panel.

2020 requires GFCI for “outlets”, not just “receptacle outlets.”