How much wattage to charge up an EV?

KCross

ELM327 wrote: »

So at 7am while my car is possibly still charging and my neighbours have an electric shower - what happens?


Car drawing 7kW, electric shower probably 8kW, baseline domestic usage of approx 1kW per house too.

Its not a literal thing, its an average. Obviously you can charge at 10kW if you want but if everyone does that it takes the grid around you beyond its design limits... hence upgrades required to stop lights dimming and voltage drops etc.

The big difference here with cars and elecric shower analogies is that the car is charging for hours, the shower is mins. Big difference as far as the transformer is concerned and it overheating.... think of rapidgate for transformers!

zilog_jones

It's not going to be charging constantly at 7 kW or 10 kW or whatever either - we know they ramp down as the SOC gets near full. Still a lot more significant than a shower though.

KCross

zilog_jones wrote: »

It's not going to be charging constantly at 7 kW or 10 kW or whatever either - we know they ramp down as the SOC gets near full. Still a lot more significant than a shower though.

That ramp down only really occurs for rapid charging, not applicable to home.

When charging at <7kW it pretty much charges at full tilt until about 97%(on the Leaf anyway)... its the last few percent where it ramps down and then finally goes into cell balancing mode which is less than a trickle.

As an example... a 24kWh Leaf at 6.6kW charges at full tilt for over 3hrs. Multiples of that for the new 64kWh cars that are coming.

antoinolachtnai

ELM327 wrote: »

So at 7am while my car is possibly still charging and my neighbours have an electric shower - what happens?


Car drawing 7kW, electric shower probably 8kW, baseline domestic usage of approx 1kW per house too.

It depends how many houses are on the transformer.

If the transformer is maxed out or above the rates capacity for half an hour it won’t make a lot of difference. (You might however see some voltage drops for various reasons, not just to do with the transformer).

If you keep running the transformer above the rates capacity it will greatly shorten its life.

Not all kWs are created equal either. A load of 7kW car chargers will effect the transformer differently from an equal number of 7kW heating elements.

This isn’t just about EVs. Heat pumps running long hours are also an issue.

The way to avoid this is to schedule the consumption.

ELM327

antoinolachtnai wrote: »

It depends how many houses are on the transformer.

If the transformer is maxed out or above the rates capacity for half an hour it won’t make a lot of difference. (You might however see some voltage drops for various reasons, not just to do with the transformer).

If you keep running the transformer above the rates capacity it will greatly shorten its life.

Not all kWs are created equal either. A load of 7kW car chargers will effect the transformer differently from an equal number of 7kW heating elements.

This isn’t just about EVs. Heat pumps running long hours are also an issue.

The way to avoid this is to schedule the consumption.

Can you elaborate further on this one? I would have expected that once you draw a kWh it is a kWh of energy and it doesnt matter what you use it for. If you draw 7kW for one hour you've taken 7kWh and surely it doesnt matter if you're using it for heat or for charging or to shower.

antoinolachtnai

ELM327 wrote: »

Can you elaborate further on this one? I would have expected that once you draw a kWh it is a kWh of energy and it doesnt matter what you use it for. If you draw 7kW for one hour you've taken 7kWh and surely it doesnt matter if you're using it for heat or for charging or to shower.

That is mostly true. But different types of load effect the distribution part of the electricity system in different ways.

Here is the best explanation I could find. It does unavoidably head into the electrical engineering technicalities.

https://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=1165&context=ece_fac