Tesla DC DC when OFF / 12V charging

[jsimonkeller]

Hi guys. I am not sure if this has been addressed elsewhere, but wondering if there is a way for my EV to be able to keep my 12V battery topped off while the car is off. I know that while it is on, I am getting 13.6V steady, but I have a good deal of parasitic drain on the car when off (close to 600mA) and if I leave it for a few days, I am concerned about running down the battery. I know I can use a tender if need be, but wondered if there was a hack to get 12V charge out of the DC DC. I assume the answer is NO because the contactors are closed when the car is off and not charging.

If anyone has addressed this before, let me know.

Thanks!

1978 Porsche Targa
Model S LDU
Tesla Gen 2 Charger
Tesla DC DC

[jrbe]

Can you fix the parasitic drains instead?

[tom91]

I assume the answer is NO because the contactors are closed when the car is off and not charging.

Correct, there is no "quick fix".

As mentioned you need to identify what is drawing that much current. Almost nothing in your system should be drawing power except the charging socket monitoring. So your Tesla Gen2 charger.

[johu]

Also it may be worthwhile to set your DC/DC converter to 14 or 14.2V in case you use a lead acid 12V battery. Otherwise it will never be full thus draining and degrading even faster.

[tom91]

t may be worthwhile to set your DC/DC converter to 14 or 14.2V in case you use a lead acid 12V battery. Otherwise it will never be full thus draining and degrading even faster.

Yes that would require wiring it into the CAN network and setting for example, the Orion2 to send out the correct CAN messages. https://openinverter.org/wiki/Tesla_Mod ... _Converter

[jsimonkeller]

Thanks guys. I figured. I originally had about 1A of drain and took the time to pull back all of the wiring to the basics and added one section at a time. I identified some large numbers in certain areas and put them onto relays that activated when the car started. Unfortunately, a large draw comes from the Infinitybox system that manages all of the car's 12V systems. That makes up 300mA or so.

https://www.infinitybox.com/wiring/system-current-draw/

I have a cut off switch in the back that I use most nights just to turn off 12V when I am done for the day, but might add a battery tender remote terminal since the 12V battery is hidden in the real wheel well.

I had considered adding a small 12V battery in reserve for the starter only, since the car only needs to engage the starter, open contactors and the DC DC floods the system immediately with enough juice.

I also am considering adding this to my Infinitybox system to cut off the battery before it drops too low to start the car. https://www.infinitybox.com/product/inreserve/

I will look into the CAN wiring and settings since I have the ORION BMS and Johan and I are finally getting my CAN connections in order . . .

[nubster]

Couple ideas:

0) Fix the parasitic drain issue.

1) Use a solar panel-powered "tender".

2) Use an Arduino/MCU in "Deep Sleep" mode to wake up every n hours and check the 12V battery level. If it's below a certain threshold, wake the car up to top off the 12V. Be sure to handle low HV battery scenario as well.

[jrbe]

The unfortunate part of using the traction battery to top off the 12v battery is eventually you have 2 dead batteries to deal with along with a large cost.

I wonder if infinity box has a firmware update to fix their large drain issue. I can't imagine anyone is really happy with that.

[johu]

I also prefer cars that consume near to no 12V power at all when "off".

Recent EVs are way to sophisticated to achieve that (preheating via app and all that). So they do as nubster suggests but I reckon they will leave like 20% in the traction battery and have the 12V system die if in doubt. Would take quite long to deplete a 60 kWh battery that way even if only half charged.