EV Chargepoint - Wiring Options

ban-all-sheds said:

Not always. Your ambient has been over that for periods of several hours this week, and EV charging can be, I expect, a sustained load for several hours.

Click to expand...

The ambient temperature within my house and garage has not actually exceeded 30°C recently.

In any event, my point was that, as I illustrated, the rough calculations assuming an ambient of 30°C are consistent with temp rise the OP has observed.

ban-all-sheds said:

I hadn't thought about this before, but given the nature of the load and the possibility of rising temperatures, I would consider it prudent to assume a 40°C ambient when doing cable sizing calculations for EV charging.

Click to expand...

I would personally regard that as unnecessary. However, the very simplistic calculations I presented considered only temperature rise (and ignored such things as the heating of the space, changing resistivity etc.) - so, even if ambient were 10°C higher than 30°C, the effect on those calculation would only have been to raise the working temp by 10°C - still well within the cable rating (even if 'pretty warm'!).

Kind Regards, John

If the cable is only going to get to 40-45° with a 30° ambient, then using a Ca 0f 0.87 is not going to produce a need for a larger cable.

But if it's going to get to 70° then IMO a larger cable should be used.

ban-all-sheds said:

If the cable is only going to get to 40-45° with a 30° ambient, then using a Ca 0f 0.87 is not going to produce a need for a larger cable.

Click to expand...

Exactly my point.

ban-all-sheds said:

But if it's going to get to 70° then IMO a larger cable should be used.

Click to expand...

Of course, but that is not the OP's situation.

Kind Regards, John

The OP's situation is irrelevant to the general principle of whether we should start to assume a higher ambient temperature for circuits which could be under full load for several hours. The only instances when doing that would become a "problem" would be when it was the right thing to do.

ban-all-sheds said:

The OP's situation is irrelevant to the general principle of whether we should start to assume a higher ambient temperature for circuits which could be under full load for several hours.

Click to expand...

Well, for a start, it was the OP's situation that I've been talking about.

However, as for the general principle, I totally agree that one should undertake calculations on the basis of the envisaged 'worst case' scenarios. Just as I personally regard it as fairly crazy to undertake calculations on the basis of an essentially arbitrary 230V (or whatever), rather than the actual worst-case possibilities (at least as low as 216.2V and at least as high as 253V), I would equally regard it as inappropriate to calculate on the basis of an ambient temp of 30° if it were envisaged that the actual temp might exceed that value. ... and all that, of course, becomes even more important in fairly 'marginal' situations.

Kind Regards, John

stillp said:

No, external chargers have had that problem.

Click to expand...

I think this may be a case of semantics and I could have worded my post better.

First..... Caveat lector - I make no claim on the correctness of the information in this post. This is my opinion formed through researching manufacturers and suppliers websites; wikis; various fora and playing with my mates Model S Tesla helping work out why it took so long to charge at home.

Some definitions of words I used in my post (rightly or wrongly) -

Charger - aka battery charger, battery management system. This is the device that is responsible for charging the cars batteries and is commonly built into the car much like with laptops and mobile phones. I'm not saying all cars have on board chargers, but this seems to be the case for the currently available EVs on sale today.

Chargepoint - aka charging point. The power supply for connecting to EVs for the purpose of charging. This is commonly external much like a laptop or mobile phone power supply (which we often call phone charger). In its simplest form it could be a 240Vac 32A commando socket through to an intelligent box which communicates with the connected cars on board charger stuff like available phases, ac/dc voltage, max current.

In my post I wrote the chargers were internal to the car and are sensitive to voltage drop and reduce charging current (this was the case with my mates Model S) probably for safety - which makes sense to me as a voltage drop could indicate an overload condition or high resistance path.

I did not intend to suggest the chargepoints were not sensitive to a voltage drop. Again this would make sense from a safety perspective. However, the conversation was about chargers.

If by external charger you did mean a chargepoint, I would be interested to learn which ones are sensitive to voltage drop especially where the sensitivity is excessive or not a safety feature as I had previously assumed, so I know which to avoid.

Thanks.

JohnW2 said:

I would equally regard it as inappropriate to calculate on the basis of an ambient temp of 30° if it were envisaged that the actual temp might exceed that value. ... and all that, of course, becomes even more important in fairly 'marginal' situations.

Click to expand...

That is why I said:

I hadn't thought about this before, but given the nature of the load and the possibility of rising temperatures, I would consider it prudent to assume a 40°C ambient when doing cable sizing calculations for EV charging.

Click to expand...

ban-all-sheds said:

That is why I said said:

I hadn't thought about this before, but given the nature of the load and the possibility of rising temperatures, I would consider it prudent to assume a 40°C ambient when doing cable sizing calculations for EV charging.

Click to expand...

Click to expand...

Yes, I know you did and, as I've said, although I think that is perhaps a bit pessimistic, if one/you believe that ambient could go as high as 40°, then I totally agree that such is the figure one should use for design calculations.

However, in terms of the general principle, if I'm not mistaken you are still a believer in using the arbitrary nominal supply voltage (be it 230V, 240V or whatever), rather than the actual envisaged possible maximum and minimum, for design calculations. Is that not correct?

Kind Regards, John

ChewChew said:

If by external charger you did mean a chargepoint, I would be interested to learn which ones are sensitive to voltage drop especially where the sensitivity is excessive or not a safety feature as I had previously assumed, so I know which to avoid.

Click to expand...

I meant what you are calling a chargepoint. My experience with the ones that shut down due to the transient voltage drop on current spikes is limited to investigation of battery failures due to two manufacturers' products, but was 3 years ago and those designs have now changed, so it would be wrong to mention their names.
However my advice still stands - use the largest CSA cable you can to avoid spurious shutdowns.