DC home charging?

[Martin]

Can any of you cleverer EV drivers help me understand why I can’t charge my DC car directly from an array of solar panels, which generate electricity in DC, without going through an inverter then back again through the granny charger. I read somewhere that it was possible, but I can’t find any instructions on how to do it.

 

[Razergd]

Well, if you do this it will be way more expensive circuit. You need a converter to both manage the solar array power point and manage the comms and current levels going into the battery. I don't think you'll will find an of the shelf solution for this and if you do it will be very expensive.

 

[N2STY]

The dc panels on your house are very low current that's why it goes to a dc to ac converter to step it up even if you have a house battery it will probably be dc to ac to dc to charge as batterys like a steady current

 

[Coulomb]

Two main reasons:

1) You need something to prevent the panels from over-charging the car battery. Usually, that's the On Board Charger, but that expects AC, or one of the computers when charging from a rapid charger, but that requires a bunch of complex protocols.

2) High voltage DC is difficult to switch, as the current never crosses zero. So breakers, relays, etc are expensive and less available than AC equivalents. So it gets expensive switching your panels back to your house energy system when it's not charging the car, for example.

You could probably cobble together something DIY, IF you know what you're doing, but you have to get access to the car's battery safely. That is most likely through the CCS (rapid charging port). The closest project I can think of is Damien McGuire's rapid charging on a converted BMW, where he uses used electric BMW parts to facilitate the CCS comms. The car won't connect the battery to the big DC CCS terminals unless you talk to it just right. It has to be that way of course, for safety.

Damien's YouTube channel: https://www.youtube.com/evbmw

[ Edit: It's sobering that the first video when I noticed in the above page was about a fire in a converted EV. He was very lucky and didn't lose the whole car. But it's a good reminder that safety is important, especially where high voltage DC is concerned. ]

Most people conclude that because marginal solar power is essentially free, a little inefficiency doesn't matter, so they just use the standard DC → AC → DC approach.