Double wound safety transformer for EV supply.

Just throwing this idea out there, it has some clear limitations but it seems it could be a useful approach in some situations especially when the models of cars to be used are known.


If we accept the load current argument from G12/4, and decide to make the charger no less safe then a bus shelter then it is not the load that is really of interest but the neutral current. There is the option of providing a 3-phase charge point and omitting the neutral entirely. The result is a charge point that will charge some, likely many models of cars, but (probably) doesn't comply fully with the charging point standards and there are some vehicles that will refuse to charge. It should however be safe and because no load current can flow in the neutral under any circumstances it is safe to connect to a PME earth without needing an unreasonably low electrode resistance.


In terms of supported models I am pretty confident the Zoe (the only model I am really familiar with) will charge from such a supply. It initially does a L1-E loop test, which would pass. The three phases are hardwired to a 3-phase bridge rectifier in the charger and its normal behaviour is that if it sees appropriate L1-E volts but nothing on the rectifier output it closes a contactor shorting L3 to Neutral which allows single-phase charging (I would hope it also checks for L3-N volts first!). It is essentially a 3 phase charger by default with a link to make single phase charging work. This sort of behaviour is likely true across many models, most cars for the EU market support an 11 kW charging mode which is rare here; 16 A 3-phase (which they use where we would install a 7 kW single phase charger). Cars designed for the US market often only support AC charging at 240 V and below but where these are fitted with or adapted to type 2 connectors these are always connected L1 to N so wouldn't charge but would be safe.


Limited in that a three phase supply is needed and not all models will charge, but no transformers are required and the earthing considerations are essentially the same as for a lamppost. It seems like it might be useful for workplace charging a fleet of Zoes or similar.

Just throwing this idea out there, it has some clear limitations but it seems it could be a useful approach in some situations especially when the models of cars to be used are known.


If we accept the load current argument from G12/4, and decide to make the charger no less safe then a bus shelter then it is not the load that is really of interest but the neutral current. There is the option of providing a 3-phase charge point and omitting the neutral entirely. The result is a charge point that will charge some, likely many models of cars, but (probably) doesn't comply fully with the charging point standards and there are some vehicles that will refuse to charge. It should however be safe and because no load current can flow in the neutral under any circumstances it is safe to connect to a PME earth without needing an unreasonably low electrode resistance.


In terms of supported models I am pretty confident the Zoe (the only model I am really familiar with) will charge from such a supply. It initially does a L1-E loop test, which would pass. The three phases are hardwired to a 3-phase bridge rectifier in the charger and its normal behaviour is that if it sees appropriate L1-E volts but nothing on the rectifier output it closes a contactor shorting L3 to Neutral which allows single-phase charging (I would hope it also checks for L3-N volts first!). It is essentially a 3 phase charger by default with a link to make single phase charging work. This sort of behaviour is likely true across many models, most cars for the EU market support an 11 kW charging mode which is rare here; 16 A 3-phase (which they use where we would install a 7 kW single phase charger). Cars designed for the US market often only support AC charging at 240 V and below but where these are fitted with or adapted to type 2 connectors these are always connected L1 to N so wouldn't charge but would be safe.


Limited in that a three phase supply is needed and not all models will charge, but no transformers are required and the earthing considerations are essentially the same as for a lamppost. It seems like it might be useful for workplace charging a fleet of Zoes or similar.