Gorfllub
Posts: 75
Joined: Sat Aug 04, 2018 6:08 pm

What will happen if we "force" AC down the charging port?

Tue Aug 28, 2018 9:19 pm

So.....

From what I understand, the EVSE is turned on by the car by a resistance (voltage) . Basically the car tells the EVSE when to open/close the relay contained withing to let the AC flow.


What would happen if the EVSE didn't shut off when the car requested it to do so?

Would the car not really care and stop charging anyway? Would the car stop charging but throw a code? I assume it will stop charging. But will it cause grief?


I'm looking at powering some AC devices (100-240V, so level 1 or 2 is OK) that I may want to turn on while the car is plugged in but not charging.

It's easy enough to trigger the EVSE to turn on, but will it cause problems?

jray3
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Re: What will happen if we "force" AC down the charging port?

Wed Aug 29, 2018 10:21 am

Some of us conversion hobbyists upgraded our charging inlets to J1772 but kept our Manzanita Micro PFC series chargers, which though being the most versatile chargers on the planet (AC or DC input, 12-360V), are non-isolated and rather unreliable on commercial J1772 stations, both with Manzanita internal upgrades and 3rd party spoof boxes such as from Tuscon EV.

As such, we often use J1772 cords with no proximity or pilot signal plugged directly into the wall! :o
I'm 95% sure I've plugged that hot wire into MR BEAN before with no effect. I believe it is because the J1772 pilot signal not only brings in the offboard EVSE contactor, but also the onboard relays that energize the battery charger, so you can't get AC power without having the charger energized.

On a related note, attempting to pull 120V loads from a 240V commercial EVSE (using a spoof box) will trip safeties unless it is multiple 120V loads that are very well balanced between the two hot legs. For the moment, this prevents enterprising RV owners from camping in our charging spaces!!
2012 i-SE "MR BEAN" 94,000 miles
2000 Mazda Miata EV, 78 kW, 17 kWh
1983 Grumman Kurbwatt EV,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

Gorfllub
Posts: 75
Joined: Sat Aug 04, 2018 6:08 pm

Re: What will happen if we "force" AC down the charging port?

Wed Aug 29, 2018 1:08 pm

Awesome.

That's pretty much what I needed to know.

The first device will likely be a marine style on-board 12v charger for the isolated system I plan on installing. I found some "world wide" versions that work on almost anything from sub 100v to 250 AC 50 or 60 hz. So theoretically it should not cause any problems in 240v mode and still operate fine on 120 as well.

I would need to spoof the evse to turn on, but not the charger contactors. That will be simple enough to accomplish.

coulomb
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Location: Brisbane, Australia

Re: What will happen if we "force" AC down the charging port?

Wed Aug 29, 2018 5:21 pm

Gorfllub wrote: What would happen if the EVSE didn't shut off when the car requested it to do so?

I don't think that the car can ask the EVSE to shut off. [ Edit: not correct, see next few posts.] J1772 is about telling the charger not to draw more current than is available at present. Either because the wiring can't take it, or because there is another vehicle plugged into the same source, and this is your share right now that is safe for the wiring. The wiring will be protected by circuit breakers, so this is mainly about nuisance tripping.

So "forcing" AC into the AC input is just like plugging a charger into the wall. It will draw whatever power it needs. The only problem could be that this amount of power could exceed what the wiring can safely provide, or it might trip the breaker and someone's computer could lose data.

If the source is 120 VAC, then you can hardly exceed what is available, unless that 120 V is being provided by a very small generator.
Last edited by coulomb on Wed Aug 29, 2018 8:30 pm, edited 1 time in total.

kiev
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Re: What will happen if we "force" AC down the charging port?

Wed Aug 29, 2018 6:43 pm

The OEM charger has about 10 Ohms of pre-charge impedance on the AC Line that feeds a diode rectifier bridge and charges up 3 parallel 680uF electrolytic caps, for a total of ~ 2mF, so the precharge of the caps takes about 60 to 100 msec.

In addition there is a AC detection circuit that lets the microcontroller know that power has been applied to the charger. Somewhere along the way this information gets sent to the EV-ECU which controls the contactors and relays to allow charging. Without some command from the EV-ECU the charger will not turn on, but there will still be voltage held up on the caps if you "force" AC down the charging port.

i don't know what controls the shut off, but the EVSE turns off the AC to the charger when the pack is full.
kiev = kenny's innovative electric vehicle

Gorfllub
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Re: What will happen if we "force" AC down the charging port?

Wed Aug 29, 2018 7:04 pm

i don't know what controls the shut off, but the EVSE turns off the AC to the charger when the pack is full.


One of the pins changes resistance which tells the evse to disconnect the AC power.

I just want to make sure that if there is voltage on the AC inputs when the car doesn't want it, there will be no issues. When I say "force", that's all I mean.... AC voltage coming in when the car doesn't want it.


Coulomb,

The car indeed tells the charger what it wants. When to turn on and when to turn off. All by set resistances.

The evse tells the car how much current it's allowed to take based on a PWM sine wave signal.

coulomb
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Location: Brisbane, Australia

Re: What will happen if we "force" AC down the charging port?

Wed Aug 29, 2018 8:29 pm

Gorfllub wrote: The car indeed tells the charger what it wants. When to turn on and when to turn off. All by set resistances.

Ah, my bad. It must be that the 1.3kR resistor that pulls the pilot signal to ground (after the diode) gets removed. Connecting it is what signals the start of charging (car asking for AC on), so it makes sense that removing it would tell the EVSE to turn off the AC.

In which case, the consequence of keeping the AC on after charging is complete would be that a little electric energy is wasted. Though possibly the car might detect the "error" and set an error code.

Gorfllub
Posts: 75
Joined: Sat Aug 04, 2018 6:08 pm

Re: What will happen if we "force" AC down the charging port?

Thu Aug 30, 2018 1:26 pm

The potential error code is my concern. Although I guess, not really if it doesn't shut down some systems.

My "check engine" light Is already on from a 12v battery replacement, so at this point I wouldn't even notice.

Using extra power is A-ok as I pretty much only charge at work on their dime.

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