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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

Certainly transformerless designs like this diagram are at least being prototyped, and mentioned in patents and R & D publications, if not in production machines yet. During charging the battery is disconnected from the motors, and its wiring is then good enough to qualify as basic insulation. Rather like the old live chassis TVs of yore, without product standards, the techniques used are driven by price alone. I'm not that keen on the idea from an EMC perspective either, as the whole car now flaps up and down with the PWM fast edge rate, creating a whole RF comb of interference. It would of course be possible to add multi stage L-C filtering to the DC battery bus, but I can see it being value engineered away to a minimum if at all possible.

The transistors switch at about 40-100KHz, but the duty cycle of that near square wave is modulated to give an average value that tracks the rise and fall of the mains cycles - with a mean voltage below it it to charge, and above it to generate AC from the battery, much like a VFD.
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0 mapj1 over 5 years ago

Certainly transformerless designs like this diagram are at least being prototyped, and mentioned in patents and R & D publications, if not in production machines yet. During charging the battery is disconnected from the motors, and its wiring is then good enough to qualify as basic insulation. Rather like the old live chassis TVs of yore, without product standards, the techniques used are driven by price alone. I'm not that keen on the idea from an EMC perspective either, as the whole car now flaps up and down with the PWM fast edge rate, creating a whole RF comb of interference. It would of course be possible to add multi stage L-C filtering to the DC battery bus, but I can see it being value engineered away to a minimum if at all possible.

The transistors switch at about 40-100KHz, but the duty cycle of that near square wave is modulated to give an average value that tracks the rise and fall of the mains cycles - with a mean voltage below it it to charge, and above it to generate AC from the battery, much like a VFD.
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Double wound safety transformer for EV supply.

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