Keep it DC for EV charging

[The-J-Man]

Greetings,

As the plan for my powerwall is to only store electricity from a 6KW solar array during the day and then put that electricity into an EV at night im wondering if its possible to simply keep it all DC. It will not be sending electricity to my house at all!
Having an inverter switch it to AC and then the internal car charger switching it back to DC would cause a healthy25% in looses from what I can gather.

So here is the question, can I just keep it DC and charge the car from it directly?
Hardware wise I would probably need a DC wallbox im guessing and they seem to be VERY expensive. Any alternatives?
Would I need astep up transformer? (is that what they are called?) to getthe voltage to 400V like the EVbattery is?
What about the charging rate? Im happy with like 3KW to be honest, even less, 2 would be fine aswell,as it will have all night anyway.


This is just a thought at the moment but technically it would be ideal right?

cheers

 

[Korishan]

Sure, you can leave it as DC. That would save you lots headache and money in the end.

You can't use a transformer, that can only be used with AC. You need to use a buck-converter. Or, build your packs for the 400V output. I recommend the buck as it's a lot safer.
But for those voltages, you would need to build a pretty stout one and several/large capacitors to build the energy up.

 

[1958 greyhound]

I want to warn you about 400v dc if you have never been around it.

120v dc will jump a light switch and never shut off if you move it slow.

 

[jesusangel]

Maybe you must change something at the ev, not for bikes or similar that must use a charger that converts from AC to DC but with electric cars you connect directly to the main so the converter is inside the car.

So you will have to "hack" your car, check the voltage of your car's battery an add some connector between charger and possible BMS so you can bypass the AC charger and connect directly to the battery then you use a big DC-DC converter.

 

[The-J-Man]

Sure, you can leave it as DC. That would save you lots headache and money in the end.

You can't use a transformer, that can only be used with AC. You need to use a buck-converter. Or, build your packs for the 400V output. I recommend the buck as it's a lot safer.
But for those voltages, you would need to build a pretty stout one and several/large capacitors to build the energy up.

Ah ok thanks.

I want to warn you about 400v dc if you have never been around it.

120v dc will jump a light switch and never shut off if you move it slow.

advice taken into account

Maybe you must change something at the ev, not for bikes or similar that must use a charger that converts from AC to DC but with electric cars you connect directly to the main so the converter is inside the car.

So you will have to "hack" your car, check the voltage of your car's battery an add some connector between charger and possible BMS so you can bypass the AC charger and connect directly to the battery then you use a big DC-DC converter.

Most EVs can charge DC now. Im looking at a used Tesla S85 or 85D and they can charge over CHADEMO, this skips the internal 11/22kW charger/s.
I would need a DC charging box of some sort for monitoring etc, like you mentioned.
I found these:http://www.setec-power.com/product/278603-3069417.html
Small and compact and plenty of power for me but you feed them with AC, so no use for me.
I would need the exact same thing, electronics etc, but with a DC input...
Maybe these are questions for the TMC forum and for wk057

 

[The-J-Man]

That got me thinking, would it be possible to rewire one of those units from the link and skip the AC to DC converter thats inside?

 

[egam]

Yep D.C. Contactors are very expensive. It's much easier and cheaper to switch ac voltage.
The only good thing here is that you are not dealing with breaking D.C. Motor loads. The inductance of the motor will create a huge spark across the contactor contacts. To get around that, the contactors employ a spark arrester or spark chutesimilar in concept to a Jacobs ladder that walks the spark away from the contacts with increasing separation.

I would stick to the recommended charger for your ev and supply it that voltage in whatever form it needs it.

 

[The-J-Man]

Yep D.C. Contactors are very expensive. It's much easier and cheaper to switch ac voltage.
The only good thing here is that you are not dealing with breaking D.C. Motor loads. The inductance of the motor will create a huge spark across the contactor contacts. To get around that, the contactors employ a spark arrester or spark chutesimilar in concept to a Jacobs ladder that walks the spark away from the contacts with increasing separation.

I would stick to the recommended charger for your ev and supply it that voltage in whatever form it needs it.

Fair enough, but a CHAdeMO is a recommended standard.
What would be the problem in just supplying a CHAdeMO box with a DC powersource instead of AC?