lithium question

BFL13 wrote:
No clue about EVs. Can you use a DC-DC charger instead of the 7-pin like you can with a gasser? The limit with those is the alternator amps vs the DC-DC input so not to over-task the alternator. What happens with an EV?

Well, I'm definitely not an expert in this kind of thing, but I can tell you the way I understand it.

So, EV's still have a 12 volt battery for providing power to things like lights, fans, heat pumps etc etc and of course the charge line on the 7 pin connector. The 12 volt battery gets its power from the 82 kwh 400 volt motive pack via a DC to DC converter. But, at least in a Tesla, you can't just connect a load to the 12 volt battery and this is why. All outputs from the 12 volt battery are monitored. If you hook up a separate DC to DC converter to just charge a separate battery external to the car, (like the trailer battery) it will detect that more current is going out of the battery than coming in and it will throw a code. I'm not sure of the consequences of that.

So the only other choice is to use the accessory 12 volt plug in the dash or the one in the hatch area. These will provide 12 amp continuous or 16 amp peak power so one can power an inverter and in turn power a small battery charger. I'm sure there are DC to DC converters out there that would work but I couldn't find any.

However, there is a catch. The car needs to be in "camp mode" for those to work. Camp mode is a tesla feature that allows you to car camp. Keeps the display on for watching movies, keeps the HVAC on for staying warm or cool and allows access to all the USB and accessory ports for phones, coolers etc. However, this typically drags the main pack down about 18 percent per day depending on the weather. This is why I think it is a super inefficient way of keeping a trailer battery charged.

A little story. We have a 2 KWH UPS in the house for critical loads like the fridge or entertainment centre. (We need to be able to watch zombie movies during power outages). Good for about a day of power outage. Works well. But last year we thought about in an emergency extending that using the Tesla. So we actually went thru the motions of getting a little inverter and 7 amp battery charger, putting the car in camp mode and hooking it up to the batteries of the house UPS. Worked great, Kept up but got pretty warm. We ran it for a day to prove it would work and then called it quits. And yep, sucked the car battery down 18 percent, almost all of which was wasted running the various systems of the car. So yah, definitely NOT the way to go when camping. A 700 dollar super quite propane inverter generator is a much better way to go.

Here is a pic of what we used. Like I say, once we get the trailer we'll figure it out pretty quick. Our first long trip is from the interior, up the island, ferry up the inside passage to Prince Rupert and then a great circle back to the Okanagan. Figure 6 or 8 weeks should do it. Lots of hiking coming up. :)