EVSE source current

[garygid]

The EVSE probably needs "-12" as well as the "+12" DC supply.

[EVDRIVER]

The EVSE appears to use a separate power supply of a bit over 12VDC. We might want to check that before connecting to 240V. We may have to provide our own separate 12V source.

Are you surmising ... in the guts of the (simplified) emergency EVSE they assume 120V AC input, and use that to create 12VDC (and possibly 5VDC) to power the micro-controller ? Hmmm ... yes that could present a problem. (I was hoping for zero mods of the guts.) So, unless they design the US, Euro and Japanese versions input voltage tolerant and with PSU components that auto-adjust ...

Most 12v supplies are universal, if there is GFI then it will have more to do with that component.

[AndyH]

The EVSE appears to use a separate power supply of a bit over 12VDC. We might want to check that before connecting to 240V. We may have to provide our own separate 12V source.

Are you surmising ... in the guts of the (simplified) emergency EVSE they assume 120V AC input, and use that to create 12VDC (and possibly 5VDC) to power the micro-controller ? Hmmm ... yes that could present a problem. (I was hoping for zero mods of the guts.) So, unless they design the US, Euro and Japanese versions input voltage tolerant and with PSU components that auto-adjust ...

Something to verify before releasing the magic smoke.

[camasleaf]

Resurrecting this old tread because I could not fine a title that better matches my question:

What is the EVSE going to do if the car goes over the set current limit? For example the EVSE says 24A but the car keeps/jumps charging current to 32A. Does the J1772 standard include any required action on the EVSE part like gradually remove the pilot signal and then open the relays? Is there any overload allowed? For how long?

Thank you.

[GerryAZ]

I don't have the standard handy, but I think it will just wait until the supply breaker trips.

[camasleaf]

Looking at Dousida on Amazon:

Control Box
Leakage protection(Restart recover)
Over-voltage under-voltage protection (self-checking recover)
Overload protection (self-checking recover)
Lightning protection

It seems that it has its own overload protection. I am not sure if is required by J1772 standard and how it works. I will look for the manual.

[nlspace]

...
What is the EVSE going to do if the car goes over the set current limit? For example the EVSE says 24A but the car keeps/jumps charging current to 32A.

For that to happen would require an error or fault on the car side. The OBC uses a current sense resistor for feedback and does closed-loop current control based on CAN buss commands from the VCM and the duty cycle of the PWM pilot signal from the EVSE.

The Panasonic and the Blink EVSE units also have current sensing internally, but i haven't studied other brands. No idea what the response would be if somehow an overcurrent occurred, but i would think it would drop the pilot and open the internal relays to stop the session.

What are you modifying to create such a condition?

[camasleaf]

I did not experience this condition. I am trying to see if the EVSEs performs a similar overload protection as a motor starter. If they do then electrical code could be updated where the breaker in the panel only provides short-circuit protection and thev overload (overtemp) protection is provided by the EVSE. I belive that in certain conditions this could reduce de wire/conduit size resulting in savings without compromising safety. For thousands and thousandsof installations this could add up.

[camasleaf]

Here is an example: 80A EV charging load that should never go over 80A since that is the limit of the chargers. Current code requirements dictate #3 line wires, #8 ground, 1" conduit with 100A breaker.

Since the load "never" goes over the 80A a #4 wire with the proper insulation material, that has an ampacity of 85A, should be sufficient if we look at the wire operation. Ampacity is defined as maximum continuous current at the specific temperature. So #4 will not even reach 75C regardless of how long the car is charging. But since the breaker does not like 75C at its terminals we cannot use an 80A breaker and need to use 125% breaker.

The 100A breaker will protect the #4 wire and the EVSE and the car charger from any short-circuit and ground-faults. But if the car decides to draw 100A then the 100A breaker will not trip and the #4 wire will overheat, destroy the insulation and cause a fire/fault.

If the EVSE will act as a motor overload set at 100% and additionally asked the car to reduce current if it reaches 80A then the EVSE is protecting the #4 wire from overheating or overloading.

If all EVSEs would be designed to act this way, for me this is a perfectly safe solution: #4 wire, 100A breaker, and 3/4" for a 80A EVSE.

Disclaimer: No, I do not plan to do this installation and I do not plan to burn the house down. This discussion is just theoretical since the EVSE behavior at 81A is not known nor standardized.

Any thoughts?

[nlspace]

Can a higher ampacity be used if only 2 of the 3 wires is a current-carrying conductor?

a single #4 with the same insulation rating can carry 125 A in open air. How does that get de-rated for 2 current carriers in a conduit?

Can 3 #4 plus a #8 fit in the diameter of a 3/4" conduit?