Charging an ev via discharge

[mikgle]

Has anybody tried to charge a second ev via the MG4 discharge cable? Is it possible even?
Was wondering if it could provide an emergency small charge if someone ran out of juice. I boiled a 2.7kW kettle with mine so in theory could be done..

 

[siteguru]

As long as your V2L adapter can supply enough power, then there's no reason I can see why you can't plug in a granny charge lead into it.

It won't be very efficient vs power delivered to the other car, but could be enough to allow both cars to then make it to a rapid or fast charge point in an emergency.

 

[Vipar]

Better to call the AA more charge applied at no cost.

 

[mikgle]

Yeah, was just curious.. I actually tried it on my wife's Zoe but it wouldn't charge.
I tried a couple of times but no dice. It came up with a message on the Zoe display "impossible to charge by battery". So it must have known somehow.
Maybe something to do with the earthing? But you would think if it can power a kettle or other earthed appliances it should be OK.. weird.

 

[mikgle]

Both the MG and the Zoe charged up as normal afterwards, and the discharge worked on kettle..

 

[Coulomb]

Both the MG and the Zoe charged up as normal

Do you mean nothing was damaged and they still charged as before from utility power?

Or that after some fiddling, it started working via V2L from one car to the other?

If the latter, what "charger" did you use? An EVSE (AC "charger") is supposed to do some sort of earthing check, and if that test fails, it's supposed to refuse charging (not turn on its internal relay to connect AC to the Type 2 plug). I don't know the complete details of that test, but I can't see how a V2L could pass that earthing test.

I tried using V2L to charge my ZS EV, and it didn't work. After being initially puzzled and disappointed, I decided that both EVSEs that I tried (MG and a Chinese one) were failing the earth test. Sadly, unless I missed something, neither EVSE told me (via LEDs, since neither has a display) what the specific problem was.

My assumption about the EVSE earthing test is that it looks for a consistent low voltage from neutral to earth, possibly after injecting a small current. If as I suspect the V2L neutral is floating with respect to the vehicle chassis, this test would fail.

I wonder how the earthing test is done in North America, where 240V is actually two out-of-phase 120V "hots" with respect to earth. Maybe they check for approximately 120V AC from "neutral" to earth first, and check that pushing it with a small current doesn’t change the voltage significantly.

 

[mikgle]

Do you mean nothing was damaged and they still charged as before from utility power?

Or that after some fiddling, it started working via V2L from one car to the other?

If the latter, what "charger" did you use? An EVSE (AC "charger") is supposed to do some sort of earthing check, and if that test fails, it's supposed to refuse charging (not turn on its internal relay to connect AC to the Type 2 plug). I don't know the complete details of that test, but I can't see how a V2L could pass that earthing test.

I tried using V2L to charge my ZS EV, and it didn't work. After being initially puzzled and disappointed, I decided that both EVSEs that I tried (MG and a Chinese one) were failing the earth test. Sadly, unless I missed something, neither EVSE told me (via LEDs, since neither has a display) what the specific problem was.

My assumption about the EVSE earthing test is that it looks for a consistent low voltage from neutral to earth, possibly after injecting a small current. If as I suspect the V2L neutral is floating with respect to the vehicle chassis, this test would fail.

I wonder how the earthing test is done in North America, where 240V is actually two out-of-phase 120V "hots" with respect to earth. Maybe they check for approximately 120V AC from "neutral" to earth first, and check that pushing it with a small current doesn’t change the voltage significantly.

The former.. couldn't get it to charge the Zoe. I do know the early Zoes are very fussy earthing wide and I used to hear a lot of failed ac charges because of that.
Ho hum..

Either that or maybe the ac output from the MG has a distinctive sine wave shape which other evs recognise, maybe not very pure waveform? Anyway, im sure its nothing to do with the actual power level, my observations are that the mg takes 10A on a granny lead, ie about 2.4kW, about the same or even less than the kettle..

 

[Barrie]

MG to MG works fine and I also charged a Tesla with my MG Marvel.

 

[Everest]

MG to MG works fine and I also charged a Tesla with my MG Marvel.

You say that, but I'd suspect, as @Coulomb suggested, that it is the EVSE/granny charger that is refusing the source, rather than the vehicles themselves.
(edited to add... not so sure now, see my posing #11 below)

Interestingly, Bjorn Nyland often charges EV's from a portable power bank when he does his "how does the EV respond when you run out of charge" tests - from what I recall he has done that with a variety of vehicles - and the issues with charging from a power bank (earthing-wise) I would have thought would be similar to charging from a V2L supply.

Anyway, im sure its nothing to do with the actual power level,

agree, if it was power-limited it would be the MG that dropped out, rather than the Zoe refusing to start charging.

It came up with a message on the Zoe display "impossible to charge by battery". So it must have known somehow.

Hmm... on second reading, I'm going to contradict what I wrote in post #10 above... If the EVSE refused to start providing power due to an earthing issue, then wouldn't the Zoe simply sit there waiting for the EVSE to kick in (like it would with a timed or delayed charge)?

And how does the Zoe know you're trying to charge "by battery"? Could be poor AC waveform - has anyone put an oscilloscope on the output of an MG's V2L?

 

[mg4mc]

Yes, it looks pretty good. See here: V2L discharge specs, 60Hz output on Australian MG MG4 EV

 

[Everest]

Looks very good

 

[siteguru]

It may have been that the granny charge lead that was used didn't like the voltage level from the MG4, which is around 217Vac as I recall. Yes, that's within spec but right at the low end.

 

[mg4mc]

I also wonder if the voltage out of the granny charger is a bit lower again? Or is it just relay switched rather than electronic?

 

[Gadget Geek]

I have 2 portable EVSE's, one will charge from my portable power bank, one will not. I suspect it's an earthing issue with the control electronics

 

[Everest]

I also wonder if the voltage out of the granny charger is a bit lower again? Or is it just relay switched rather than electronic?

Obviously the voltage at the end of a wire will be lower than the start when a current is being drawn, but not if no current is flowing. An EVSE just switches the AC with a relay, not a Triac.

 

[GaryMG4]

Just tried MG4 to Niro, it appeared to work briefly at 0.5 kW then stopped.

 

[Everest]

Any message / indication why it stopped? IIRC 6A (or about 1400W) is the minimum rate for AC charging, so at only 500W rate it shouldn't work anyway.

 

[mikgle]

My feeling is its more to do with the Zoe inverter more than anything else, as I said earlier many instances around of Zoes refusing to charge because of an earthing issue. Or maybe just very fussy.
I shall have to try it on another ev make and see..

 

[mikgle]

It may have been that the granny charge lead that was used didn't like the voltage level from the MG4, which is around 217Vac as I recall. Yes, that's within spec but right at the low end.

I shall test the voltage at the mg4 3 pin socket when I get around to it but it may not be representative unless there's a load on it.

 

[Bam Bam]

The legendary Jerry Pan charged one MG4 from another one