Allgemeine Informationen zum Laden von Elektroautos an der heimischen Wallbox

Here’s a collection of loose information that I’ve encountered like this in conversations with customers:

Can the wallbox overcharge the car?

No. The car is responsible for its battery.

The theory behind this:

The car reports its maximum current to the wallbox (via PP, the “proximity contact”).

The wallbox now specifies via CP (“pilot contact”) the maximum current (between 6 and 32 A) at which the car is allowed to charge – the actual charging current used by the car must not exceed this value.

Just before the battery is full, the car’s charging system reduces the charging current by itself (my Leaf at 95% SoC) to conserve the battery. This information can be used by my app to end the charge “slightly” early, so that the battery is not charged all the way to 100%.

It’s not clear if this really matters, because the battery has some reserve up and down from its battery management system (BMS) anyway, so 0% SoC and 100% SoC are not the correct battery states, but are a bit more conservative at “not quite empty” and “not quite full”. This protects the battery and extends its life.

Can a wallbox charge “up to the battery level of so-and-so percent”

There are wallboxes (OpenWB for example), they usually use more or less secret/hacked information, how to get the data via a car manufacturer specific interface over the internet. But “directly” this is not possible with current cars. There is a protocol defined that digitally overlays the signal, but that’s not really widespread yet.

My wallbox app can be connected to my Leaf app, so that works for the Nissan Leaf and Evalia.

Can any car charge on 3 phases?

No. Many more modern cars can, but older cars tend not to.

Would it be bad if it can’t do 3-phase charging?

Normally not, if the driving profile fits: if you don’t even need to charge “fast”, one phase (yes, even sometimes the Schuko charging brick) is often enough to charge overnight. Or if you use PV surplus charging and the PV system is not one of the larger ones…

What are the benefits of 1- and 3-phase charges?

First of all, of course: triple the charging speed with 3p charging.

Sounds good, is good, but has more than one catch with PV assisted charging. The minimum current is generally defined at 6 A per phase in the protocol between wallbox and car. Some cars like it a bit higher (e.g. Zoe, Peugeot – there it is better to set at least 8 A, otherwise they may not even start charging, or not wake up when you want to continue charging after a charging pause).

The problem number 1, the biggest: with three-phase charging, a charge thus starts only from 18 A (3 phases with 6 A each), so around 4 kW power! For smaller PV systems, that’s only the power around noon, if at all…

Conclusion 1: so if the PV system is not one of the larger ones (which can already deliver in the early morning so from 4 kW), then you should charge single-phase. Otherwise you give away a lot.

The problem number 2: with 11 kW wall boxes, you can only charge up to 16 A per phase. Now if you’ve been paying attention, you’ll notice the problem: if you then want to switch to 3 phases, you’re “missing” 2 A.

Conclusion 2: if you can’t start “right away” at 3 phases, you should stick with one phase.

What do I need to consider if the wallbox is connected three-phase (almost always), my car can charge three-phase (often), but I don’t want that for PV charging?

Speak how do you reduce the number of phases for charging when the car can charge 3-phase?

This is harder: either you get a single-phase charging cable, or – a bit more error-prone – you have individual fuses installed in the phases. What’s dangerous about this is that you can’t switch them on or off during charging, the charging electronics in the car can resent that. Also goes, if the box is connected by CEE, 2 CEE sockets to have with appropriate phase numbers.

Newer wallboxes (go-eCharger from June 2021, OpenWB soon, …) that also allow switching by itself and save you the emergency solutions from the previous paragraph. Because the switching takes some time (up to 2 minutes!) and because of the 2A gap (hook number 2) it makes no sense to switch this during PV charging. So you have to make the setting before starting the charge.

“My car won’t continue charging if I cancel a charge and then restart the charge”

Yes, a few car manufacturers have (un?)intentionally caused this problem. Peugeot (and by extension Opel), make Zoe versions and Mitsubishi iMiEV, Citroen CZero, Kia Soul.

Here the wallbox manufacturers now have to try to iron this out and so are gradually implementing workarounds: the new go-eCharger, OpenWB and others will solve the problem for now.

Someone with such a car can’t do PV charging if he doesn’t have any of the wallboxes mentioned (that is, without the wallbox solving the problem). Unless he grabs a beer, sits next to the car, and unplugs and re-plugs the charging cable when a cloud passes.

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