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Double wound safety transformer for EV supply.

Hi everyone, I have only posted once before so thanks to anyone who replies!

I am following on from the earlier "70 volt PEN conductor not allowed to exceed post", and looking into supplying a client with an electric vehicle power supply from a three phase isolating transformer BS 7671 722.413 (1.2): " The circuit shall be supplied through a fixed isolating transformer.."

The general consensus seems to be that an external IP box with an RCD (Type B) and a tethered lead is the standard to follow, and this may be the only option with a 230 volt domestic supply, but why not use a 3 phase 400 volt step down or tapped, safety double wound isolation transformer in a standard 100 -200 ampere or above industrial units/sheds?

( Subject to load and diversity).

The answer often stated when I have asked sparks/engineers is that in-rush current are too high but a type D CB BS 60898 will 'let through' the in-rush ( the transformer manufacturer agrees), and will still give at 5 seconds- (final circuit exceeding 32 A) 0.44 ohm EL ( 10oC) , so is achievable in many situations local to Birmingham.

I was then going to run a fused cable out to an external isolated IP 65 box with a Type 2 socket to IP44 or above ( 722.55.101).

Isn't it better to engineer a solution to the upcoming electric charger deluge, rather than buying (insert well known manufacturer name here), and lots of single phase loads usually dumped onto L1?

I would be interested in any thoughts or problems you may consider....

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0 mapj1 over 5 years ago

Firstly understand that the charger, which may or may not involve a transformer and diodes, is in the car, and as such is different for each model.

Generally mains is rectified and then sliced with power transistors to provide the waveforms required to charge the batteries on that vehicle, whose number and charge characteristics are again similar but different for each model

e.g the Zoe has a 400V battery made up of 2 paralell strings each of 96 cells in series.

The Tesla 3 has contains 7,104 cells arranged as in 16 parallel banks each containing further parallel strings of about 350V each.

There is no 50Hz isolation transformer as such, the switching frequency is supersonic. These block diagrams of what is in a typical car may help

All the current generation of charging points do is to close a contactor to provide a connection to the mains when certain interlock conditions are met.

If you understand circuit diagrams, this here is a delightfully simple but fully standard compliant example of the sort of thing you may have in the wall box, and is in the public domain.

Better still there is a full description of how it meets that standard also on the web here
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0 mapj1 over 5 years ago

Firstly understand that the charger, which may or may not involve a transformer and diodes, is in the car, and as such is different for each model.

Generally mains is rectified and then sliced with power transistors to provide the waveforms required to charge the batteries on that vehicle, whose number and charge characteristics are again similar but different for each model

e.g the Zoe has a 400V battery made up of 2 paralell strings each of 96 cells in series.

The Tesla 3 has contains 7,104 cells arranged as in 16 parallel banks each containing further parallel strings of about 350V each.

There is no 50Hz isolation transformer as such, the switching frequency is supersonic. These block diagrams of what is in a typical car may help

All the current generation of charging points do is to close a contactor to provide a connection to the mains when certain interlock conditions are met.

If you understand circuit diagrams, this here is a delightfully simple but fully standard compliant example of the sort of thing you may have in the wall box, and is in the public domain.

Better still there is a full description of how it meets that standard also on the web here
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Double wound safety transformer for EV supply.

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