Not sure what you mean by "ICCB" in this context. All charge points must have an EVSE (Electric Vehicle Supply Equipment) module for bidirectional communication with the car charger, both to switch power on or off and to tell the car charger what the maximum available current is from the supply. The EVSE for a granny lead is contained in the box close to the 13 A plug end of the lead, which has the 1 kHz Control Pilot signal generator, with the right duty cycle for the advertised maximum current that is available, plus the voltage sensing circuitry that detects when the car charger is loading the Control Pilot signal to command the EVSE to turn the power on or off. The unit also contains some safety provisions, including those that form a part of the Control Pilot sensing and also earth leakage sensing on the supply.

 

Hi Jeremy, what I meant by ICCB was what some suppliers use a name for the 'little' black box between the 13amp plus and the type 2 connector. From your very comprehensive answer it would seem that there has to be something between the 13 amp plug and the type 2 connector so it's not possible to build ones own granny charger. Or is it!

 

I have no idea what the abbreviation ICCB stands for, but the box in the lead is an EVSE, almost always with some additional electrical protection in the form of earth leakage detection. The EVSE controls the switching of power to the car charger and also tells the car charger how much current can safely be drawn from the supply (10 A maximum in the case of one fitted with a 13 A plug). You can certainly build one, the signalling interface isn't hard to design and code. The protocol is contained in IEC61851. The Control Pilot signal starts as +12 VDC relative to PE, fed via a 1 k source impedance. When the car is plugged in it is loaded down to +9 VDC, and this drop is detected by the EVSE which then starts the 1 kHz Control Pilot signal, which swings between +12 V and -12 V before the 1 k source impedance (so the swing is between +9V and - 12 V initially at the Control Pilot terminal on the Type 2 connector when plugged in).

The car then measures the duty cycle of this signal, to determine the safe maximum current that can be drawn, and having done that loads the Control Pilot down to +6 V, - 12V. This additional load on the positive going part of the Control Pilot is detected by the EVSE, which then closes the main power contactor to supply power to the car. There are various fault detection features built in, such as measuring whether the -12 V part of the signal is correct, as well as monitoring the positive going signal for changes. If either the car requests that power be turned off (by removing part of the load on the positive going signal) or a fault condition is detected, the EVSE will turn off the power.

The earth leakage detection part works on the supply to the car, and measures the difference in current between line and neutral. If there is no leakage to earth (indicating a fault) then these two currents will be equal. If they differ by more than 30 ma then the EVSE will shut off power as a safety precaution.

There are some EVSE kits available, like the Open EVSE project: OpenEVSE - Electric Vehicle Charging Solutions

 

TL;DR = The box on a granny cable is what tells the car "Hi! I'm a charger and you can draw up to 2.4kW from me."

 

Almost, it really just says "Hi!, I'm a mains outlet and you can draw up to 10 A from me".

These things are just fancy mains outlets with a fairly clever switch.

The power drawn by the charger (in the car) for 10 A can vary a lot, and be anything between 2.162 kW and 2.53 kW, depending on the supply voltage at the car. For the official normal UK mains voltage of 230 VAC it would be 2.3 KW (although most supplies are closer to 240 VAC in reality).

 

Thanks guys for all that info - clearly the idea is back in the cupboard. Thanks Jeremy for the link to OpenEVSE could be a way forward but based in the US could be an issue. Thanks again

 

There is another option, although it isn't one that I really like that much, as it involves having mains powered stuff inside the Type 2 connector, and these do tend to let a bit of water in I've found. The kit is available from a store in the Czech Republic, here: EVSE Kit v3 for EV charging station/cable (2x16A relay) - kit only | shop.GWL.eu

This small EVSE will fit inside a Type 2 connector, but it is a bit fiddly to get it in there and wired up neatly. This provides no form of earth leakage protection, so really needs an RCD plug to be fitted at the end of the cable, like this, perhaps: https://cpc.farnell.com/masterplug/prcdkb/rcd-safety-plug/dp/PL14216?st=rcd plug The mains cable needs to be rated for outdoor use and be OK to carry 10 A for long periods, and the best choice would be to use 1.5mm² H07RN-F : https://cpc.farnell.com/pro-power/h07rnf1-5m/cable-rubber-h07rn-f-3-core-1/dp/CB19619

The result would be a granny lead cable without the brick, that could be made to any reasonable length you need (although I'd suggest not going over about 15 to 20m). The small EVSE module really needs some sort of moisture protection, and I'd be inclined to seal it up with conformal coating after soldering up the wires, something like this: https://cpc.farnell.com/ambersil/6130004030/conformal-coating-acrylic-400ml/dp/SA02317?st=conformal coating .

I can't honestly say that I much like this approach, but I did make up something very similar myself years ago, as a long lead to carry around to charge my old Prius PHEV. In my case, I made my own EVSE using a small home made circuit board with a PIC microcontroller, a miniature 16 A relay, plus some ancillary components, all fitted inside a Type 1 connector. I knew the risks this carried, and always used it with caution, but I did like the fact that I could carry a long cable in the car that didn't take up as much space under the boot floor as the standard granny lead.