eli5: How do we control which battery gets charged when you charge one battery from another.

Question

I was reading an article on the prospects of using electric vehicle batteries to help smooth out grid demand, especially in California. That got me thinking.

For this to work, the car charger would have to control somehow if it was providing power to, or asking for power from the battery in the car. How does this happen? I’m not asking how the electronics talk to each other, I mean how do we control which way the electricity goes.

My first thought is the electricity would flow towards the side with lower resistance (or voltage or something like that, I’m no electrical engineer.) But then I thought about my wireless headphones. They are an example of one battery charging another and the charging cradle will happily drain its battery down to a very low state in order to charge up the actual headphones. Perhaps the wireless headphone thing is a bit of smoke and mirrors and the battery in the charging cradle is actually “stronger” even when it says it is nearly depleted…

Anyway, how do we control which way the electricity flows?

In: 0

Answer 1

Many EVSEs (electric vehicle servicing equipment aka car chargers) are connected to the internet or the cars themselves are. Depending on where you live, currently, almost every car or EVSE has an option to delay charging until a certain time when the grid is under less load. Power companies incentivize this by charging higher rates during peak demand and significantly lower rates late at night. So to control when your car is charging you can either set up a timer which automatically starts charging your car if you have it plugged in at a certain time, or have it controlled the same way some grids can control your thermostat, it must hte connected to the internet.

Contrary to popular belief, power companies don’t want you do use as much power as possible. When they design the grid, they have to design it to supply power during the hottest heat wave and during the coldest winter storms, they can’t design for what the average load would be during the year so there is a shit ton of excess capacity late at night. That’s why many electricity intensive industries operate at night and that’s when they want you to charge your car.