AC charging tip

[RobinH]

Finally had occasion to use the MG supplied AC charge cable at the weekend - parking in Windsor for 6 hours so decided to use the BLink charge point.

Downloaded the app, gave it all the details, could not get the charger to connect to the car.
Phoned the helpline, they reset the charger, talked me through the process, I tried the next charger along, still no connection.

Then it twigged....
The cable was still coiled up & wrapped (as supplied). I have noticed a couple of times at home when the wife gets her Leaf's cable all twisted up the charge can fail.
Unwrapped & uncoiled it, the car connected first time and we went on our merry way.

My electronics engineering days are a dim & distant memory but I assume a twisted or coiled cable can create an inductive loop that interferes with the signal - although I stand to be corrected by someone who knows what they are talking about!

 

[Coulomb]

I assume a twisted or coiled cable can create an inductive loop that interferes with the signal

I highly doubt that this is the reason. Its certainly recommended that you uncoil the cable so that the heat doesn't concentrate, but it should have no electrical effect.

All I can think of is the plug not making a good connection, and uncoiling the cable reduced the weight on the plug and that allowed a good connection for the control pilot signal.

 

[Tim Green]

Well there is a pin in the plug that enables or disables the charging system according to some handshaking system. I have no idea of the input impedance at the car of that pin, but it is just conceivable that a spurious signal could act to inhibit the charge. That may supposition may require that the car end was plugged in first, and the ac supply pins connect first at the other end? Pure speculation....

 

[Roldorf]

I have found the main problem to be the order in which you connect to the car. Most chargers require you to initialise the charger with your card/app then connect the cable to the charger then connect to the car. If you do it the other way round often the charger will not connect and start the charge.

 

[Coulomb]

Well there is a pin in the plug that enables or disables the charging system according to some handshaking system. I have no idea of the input impedance at the car of that pin, but it is just conceivable that a spurious signal could act to inhibit the charge.

I believe that you're thinking of the Control Pilot signal. Its impedance is pretty low, less than 10k ohms. With the EVSE plugged in, that has 1k impedance, so lower again. I highly doubt that spurious signals would affect that.

More likely IMO is poor contact due to oxidation or corrosion, moisture, worn plug and/or socket, weight of the cable on the plug.

 

[Tim Green]

I don't know where you got 10k ohms from, did you measure it?
I would expect the output impedance of the wallbox to be lower, as you say, but my conjecture is that the ac pins connect first, so if the car end is plugged in first, a short time of the coiled cable conducting ac is possible, which could induce spurious noise on the control pin.

 

[Coulomb]

I don't know where you got 10k ohms from, did you measure it?

It's from Wikipedia J1772 / signalling, basically R3, 2.74 kΩ. Type 2 signalling is similar to J1772, and identical for the Control Pilot (here called Pilot):

Once connection is established, relay K1/S2 connects, putting 1.3 kΩ (R2) in parallel with the 2.74 kΩ, resulting in 881 Ω, less than 1 kΩ. But before the control pin makes contact with the EVSE, the impedance is 2.74 kΩ.

my conjecture is that the ac pins connect first,

The control pin does indeed connect last, so the AC pins do connect before the control pin. However, the On Board Charger should not be drawing significant current from the AC pins at this stage, except for some low value EMI suppressing capacitors. So your theory is possible; I still think it's unlikely.