The earthing system isn't my concern. What worries me is that if the vehicle body is carrying the filter current and it becomes disconnected from earth at any point, then the vehicle body will be at supply potential, which could be 400V AC. Admittedly the filter will limit the current, but it will certainly be enough to cause a startle reaction, and it is vital that the correct kind of RCD is fitted in the installation, since the current will have a significant HF content as well as a DC bias.
Electric Vehicle charger installation
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That's all very true, but it's equally true of any 'Class I' equipment with exposed-conductive parts which has earth-referenced EMC filters on its power feed - and, indeed, of any Class I equipment which loses its connection to earth and also develops an L-E fault. ... in all cases, of course, asuming that the victim provides some path to true earth.
The earthing system may not be your concern, but it's what the discussion was about - i.e. why these chargers must not be used with TN-C-S supplies, but are apparently OK with TN-S (or TT)!
Kind Regards, John
Why can't a car be a Class II appliance, as far as the charging system goes?
Of its own nature it is pretty well insulated from the mas of the earth (yes, I know that tyres contain graphite, but I believe they're in the 100kΩ range....)
Of its own nature it is pretty well insulated from the mas of the earth (yes, I know that tyres contain graphite, but I believe they're in the 100kΩ range....)
That's what I was wondering, too - which is why I asked whether the car body was connected to the supply earth. At first sight, I really can't see any reason why everything to do with the car couldn't be isolated from the supply (including earth) - but maybe I'm missing something.
Kind Regards, John
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Well, if it can't then bang goes any possibility of EVs made from polymers and carbon fibre.
Maybe hybrid vehicles are the future:
Maybe hybrid vehicles are the future:
I don't know, but I imagine that Nissan, Mitsubishi, BMW, GM, etc have thought of that. Perhaps they feel they need to use the body as an EMI shield, given that an EV contains sensitive electronics as well as HF generators.
If that's their reason, they are going to have a bit of a problem with the 'plastic'-bodied cars to which BAN referred. Of course, if the charger were external to the car, then the issue wouldn't exist (at least, as far as the car was concerned).
Kind Regards, John
Most of the charging points I've seen have 2 outlets, so 2 EVs could be charged in adjacent parking bays. The worst case would be that one loses its protective conductor, thus becoming "live", while the other doesn't, so the full supply voltage would appear between 2 large metal objects about 18" apart, and accessible to members of the public, including the more vulnerable children and the elderly, and perhaps in rainy weather.
Well, yes, I agree with all that - and it sounds like a very good argument for not connecting the car bodies to earth - or, at least, keeping the cars well apart (hence no 2-outlet charging points). However, again, what you talk about would be no more likely with a TN-C-S supply than any other.
Kind Regards, John
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At 380vdc can't see how the issue wouldn't exist. The voltages may vary but they are on the high side. The electro-haul of years ago was 10,000 volt OK wagon not a car and used pantograph not batteries and inboard generator but the idea that electric cars are extra low voltage is flawed.
As I understand it, the 'issue' that stillp was talking about was of the car body rising to high (AC) potential relative to ground, due to the EMC filter components on the AC side of charger unit, in the event that the CPC connection to the supply were lost. If the charger were external to the car (with no exposed-conductive parts) and the only connection to the car was an isolated DC supply (no CPC), the risk of the car body becoming live (with AC) by that process obviously 'would not exist'
...or have I misunderstood you?
Kind Regards, John
The problem is that EVs use different batteries, so I can't imagine the charger being external to the EV until the far-off day when a single design of charger can charge all manufacturers' EV batteries. Even then, I can't imagine the EV manufacturers wanting to trust an external charger on their delicate and expensive batteries.
Fair enough - but there would seem to be the option of having a Class II 'charging unit' with an isolated output. What would be the problem with that?
Kind Regards, John
I would think the problem would be the need to have an earth connection to achieve the EMC requirements.
Maybe what I'm talking about is not strictly Class II - I'll have to look up the definition. Anyway, what I'm talking about is essentially a unit with no exposed-conductive parts, provided with an earth for the purpose of the EMC filtering (assuming that is all on the supply side - or, at least, on the supply side of isolation), with the output totally isolated from the AC power feed (and the associated earth). I think that could be achieved without a 50Hz transformer (which might be impractically large), but I need to think a little more about that.
Kind Regards, John
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