EVSE questions

Hi Dave, It seems a namesake of yours was the first, in 1856.
https://www.climatechangenews.com/2016/09/02/the-woman-who-identified-the-greenhouse-effect-years-before-tyndall/

Hi Harry

Yes, she may have suggested a Greenhouse effect, but Tindall and others following didn't realise that Greenhouses don't actually work that way, and the effect is not real! Polythene greenhouses cannot work that way and are just as effective as glass ones. The real greenhouse effect is to prevent convection of hot air upwards and to lessen the effect of wind. it is nothing to do with the wavelength of heat, it is simply heat loss control. Anyone would think that radiators in a house worked by radiation, they don't it is air convection over the surface. The LW IR electric heaters that make most use of heat radiation to warm us, not the surroundings, but the wavelength of them is very different from greenhouse glass transparency or not as you can see and feel.

I have been looking at your graph carefully, as well as the error band figure. Presumably, the line shown is a least-squares regression, this should show the statistical significance as well, which is low. In other words, one cannot make any predictions about any future temperature. NASA talks about the actual ice cover each year and it varies hugely, again it is not possible to predict what will happen. Generally, this is called weather.

We seem to have drifted away from the OP!


The problem with global warming is political: politicians have swallowed the argument that we cannot afford to do nothing.

I am not talking about that kind of management.

Ah, but we were - and more to the point I suspect the EVSE manufacturers were as well. For the likes office carparks or even domestics with a limited supply and a heavy existing peak demand, I see a market for such things (in the same way that load shedding relays sell in France/Spain, where supplies tend to be small).

 

There is no point whatever in running an electric car unless it is solely charged from "renewables"

Certainly the more renewables the better, but I don't think it's has to be 100% to 'break even' as it were. Conventional internal combustion engines in vehicles are notoriously inefficient - the need to match engine output to road conditions means it runs very poorly much of the time (certainly in urban areas). Burning fuel in large scale plant running at peak efficiency almost all the time claws back a lot of efficiency that can compensate for the distribution and charging/discharging losses. So something like 50% renewables and 50% fossil generated electricity may well be more efficient that say a 100% petrol engine. Don't forget the advantages in local air quality too (a growing issues in many of our cities now).

 

All of this assumes that EV drivers would be happy that they had no control of the charge in their car

I see it more as co-operation rather than totally relinquishing all control. A couple of buttons on the charge point - press one for 'have it fully charged by a certain time in the cheapest way possible' another for 'charge as fast as possible (even if that incurs a higher cost)' sort of thing.


 

Detecting that a CNE connection has failed is very difficult because there is no reference potential available, and using a TT type connection as reference has many problems which we have discussed many times. IF the supply is 3 phase, we may use the 3 phase/neutral voltages to recognise a break under some fairly ideal conditions, but load power factors and powers may seriously sway the results so as to make them unreliable. With a single phase supply there is no isolated Earth reference available, and thus it is probably impossible to detect a CNE break. If someone comes up with a non-TT method I would be interested to analyse it fully and the Patent application would be unlikely to succeed if it could not be shown to work under any possible conditions, by demonstration.

As I understand it, the idea is to use the line voltage as the reference - as that remains reliably referenced to Earth at the source even during a broken CNE event - albeit offset by Uo.


So on a simple entirely single phase system any voltage rise on the CNE due to a broken CNE could be deteected as a corresponding voltage drop in the L-N (or L-PE) voltages.


On a completely 3-phase system (having checked that the L-L-L voltages are normal) you can create an artificial N point that should replicate the voltage at the source's star point (i.e. Earth potential) - and use that as a reference.


The tricky one is where the distribution is polyphase but the installation is single phase - where the single phase L-N voltage measurement approach will work most of the time, but can under some conditions be fooled into thinking all is well when it really isn't. I guess you're into probabilities there - if it works 99.99% of the times the rest is probably an acceptable risk, if it was only 50% of the time it's probably not going to be acceptable. If it's presumed that the severed CNE voltage is going to swing about significantly during the fault as single phase loads switch on and off (or fry) and if having once detected the break EVSE will remain latched in the disconnected state, then the risks are likely to be reduced further. I gather that some manufacturers are adding current monitoring to the EV c.p.c. to disconnect should it reach 30mA or similar - rather like using an RCD to provide direct shock protection - to mitigate any remaining risk.


  - Andy.

Andy,

Electric traction (using batteries or hydrogen as the transfer medium or direct connection to overhead conductors) offers benefits in urban areas where there is significant slow and stop/start movement. Energy can be recovered by regenerative breaking and engine idling losses are removed. There is also an air quality improvement, although with modern engines the emmisions are really very low. If fossil fuels are burnt in a large power station it is easire to contol the combustion and emisions. For long haul where transmission losses are more significant diesel can be a good option as more optimal loading of the engine is possible.

Chris,

The problem is global warming is not the real issue. We should be looking at conserving the planets finite resources and reducing harmful pollution (which does not include the plant food CO2).

The current 'Green' plans are incredibly resource hungry and highly polluting due to the production of the raw materials. Unfortunately wind turbines and solar panels are not made from unicorn poo.

These are interesting points Gentlemen.


Ok Andy, you seem to think that total disconnection if the mains goes 20V down on normal indicates a broken CNE. It may, but may not. You can disconnect everything but disconnecting the Earth connection requires all manner of saftey systems to be safe, a single contactor doesn't do it at all. Remember that Earth connection needs to be disconnected in <40ms, just like an RCD. Any fault will disconnect and reconection cannot be automatic, can it? The fail would be all the time, not even occasionally with a real mains supply. A half-cycle at nearly zero volts is remarkably common and causes no trouble to anything except you mains disconnection idea. The problem is you do not have the time to wait, as waiting could kill someone!


As far as cars go, I currently have a Ford thing with a stop-start engine and extra-low emission on loan. OK it works, but a new battery every couple of years is likely and the cost of one is £££. If I stop and the battery packs up I cannot move, again looney. On an older car, as long as I can do one start I can go as far as I like and the miles per gallon are very nearly as good as my much bigger diesel. Electric cars are good in jams as found in Bristol where I have ther misfortune to live. They are designed into the road system at every opportunity, because of "climate change" and the Council wishes to drive vehicles off the road and everyone to use public transport (including building a tube network at an incredible cost in a hard rock, hilly area). B**** brilliant. I wish I could think of ideas like that, on some immense salary, but unfortunately, I can understand why they are stupid and impossible, which is because I am an Engineer not a politician with an agenda.