Charger reading battery percentage from the car

[JodyS21]

I noticed when DC charging recently (on first proper long journey), that the charger knows (it displays it) what percentage the battery is.
Clearly it is something that is and can be communicated via the type 2 cable.

So, why don't our installed home "chargers" read it and are able to manage the charge percentage?
- I have the Ohme charger which has no idea what percentage the battery is at, I am assuming from what I've read that none of the others do either?

Obviously, a DC charger, is kinda managing the charge to a certain extent as it is doing the actual AC-DC conversion. But in terms of the plug/connection it has to the car, it uses the same connector/pins as when charging AC - yes it has the 2 additional pins but they're purely for putting the DC power through not for communication.

Am I missing something obvious here.
I cannot think of any reason why when charging using our home AC devices, they too should not be able to read the cars battery percentage and therefore should have the facility to be allow the user to specify charging schedules/logic based on the actual battery percentage.

 

[Cocijo]

Good point. Is It connected to DC charging only and uses the 2 DC connections to transmit the info to the charger? Perhaps when using the inverter on AC this info is not avaiable?

 

[JodyS21]

Just done some reading and there are 2 types of communication allowed, the basic uses PWM pulse width modulation, then there is also an advanced protocol - it would appear that DC must use/needs the advanced data communication.
AC can get by just using the basic PWM to indicate the maximum current that is available.
I cannot find anything that says AC cannot use the advanced comms protocol too, so it can get the SOC & SOH data etc.

 

[EWD]

Surely because the DC charger connects DC voltage straight to the battery it can detect the voltage drop between the voltage supplied and the voltage in the battery. From this it can work out the state of charge.

 

[Coulomb]

I cannot find anything that says AC cannot use the advanced comms protocol too, so it can get the SOC & SOH data etc.

I'm pretty sure that the protocol says that the advanced protocol is only invoked if the PWM signal is an extreme value, i.e. one that represents less than 5A or more than 80A. So the computer in the car (possibly EVCC) doesn't turn on the advanced protocol for ordinary AC charging.

However, I think that you may be right that it may be possible at least in theory for a specially designed AC "charger" to use the special PWM signal, triggering the advanced protocol, and yet starting an AC charge, not DC. Then the EVSE could presumably do extra things, such as displaying SOC. I doubt that it could display SOH, but it might. Most cars would not be set up to expect this, unless it's buried in the specifications somewhere. It's hard to know, as I believe that the specifications are pay walled.

The advantages will likely not outweigh the cost, especially the development cost, unless someone pioneers it and makes the information generally available. Then perhaps market forces would ensure that all but the cheapest, most basic EVSEs would offer these features, including perhaps a "charge to X%" feature.

 

[Coulomb]

Surely because the DC charger connects DC voltage straight to the battery it can detect the voltage drop between the voltage supplied and the voltage in the battery. From this it can work out the state of charge.

No. You can't reliably determine SOC from battery voltage, especially in some random car turning up at a public charger, and especially not when pushing power into the battery.

 

[Chrispydoc]

I've never worried abut the %.

My GOM range is all I need. It's 178 miles when full, in eco with everything switched off. It has proved very very accurate over the last 18months.