Is there switched 12V anywhere in the cargo area?

What relay or solid state switch are you going tomse in this project ?

 

Another option is to use a low-voltage disconnect with an adjustable trigger point.

Some LVDs are designed to just cut something off before the battery is fully discharged (say, 11 volts or so).

But if you can adjust the trigger point to somewhere around 13.5 volts, it will be on when the car is READY and the DC/DC converter is supplying power, and off otherwise. No need to find switched 12 V back there, and accomplishes the same thing.

 

I got a two-pack of those from Amazon for about $13, they work great. No enclosure but a ham should be able to sort that out.

 

Can you post a link to such an item, low-voltage disconnect ?

 

In theory, this link will introduce you to Toyota's tech info system which will let you access their electronic wiring diagrams.

I found it well worth the rent when I wired in some bonus goodies.

Good luck!

 

That's the beauty of using a low-voltage disconnect that has an adjustable cutoff point. You set it for around 13.5 volts, and now it's an automatic switch that knows the difference between the car being READY and the car being off.

 

^ That.

If you set the cutoff low, it serves as a battery reserve protector. While useful, it's not exactly what you want.

However if you use Chap's suggestion and you set the cutoff above the battery's theoretical resting maximum voltage (12.86v) but below the READY-state charging voltage (14.1v) then it is a de facto relay that only closes when the car is in READY mode.

That's even better than simple ignition-switched 12v, because it requires you to get the hybrid system into READY and not merely into "ig-on" mode.

@RandyPete search Amazon for B07QNXM4LS and you'll see what I got, or an updated cousin of it anyway.

 

Watching voltages in READY, I see that the car sometimes backs off the charge voltage to closer to 13.5, when it thinks the aux battery is decently charged. So I wouldn't set the trigger point much above that.

Somebody graphing a datalog of the voltage I think produced a picture that showed the voltage dropping significantly every now and then, for a brief instant, which I suspect (but don't know for sure) is the car's way of judging when the aux battery is decently charged (drop the charging voltage for an instant and look at the battery voltage).

I never notice that causing any problem with the low-voltage disconnect I chose, which also has an off-delay that I set for about an hour. (Sometimes I like to be able to stop and get gas or a bite to eat without powering down the stuff I've plugged in.) A disconnect that responds instantly might be another matter.

 

consumes 1.5 watt. Any similar solid state devices that consume less power ?

 

Probably, but those are the first and only such I've bought.

 

Interestingly, the module I'm using also draws some power when off, about an eleventh of a watt.

I'd have thought they could've built it to just draw nothing below the trigger voltage ... at least after its off-delay when it really turns off. The homebrew some-zeners-and-a-transistor version I was using before drew effectively nothing when off. But my homebrew one only worked for about six and a half years, and when it conked out I didn't bother investigating why, I just bought the off-the-shelf one.

 

I hadn't noticed the off-draw mostly because I use mine to prevent deep discharge when I'm using my leaf blower batteries to power bespoke things that don't have their own deep-discharge protection.

So when it shuts down I'm disconnecting and heading back to the charger stand anyway.

 

Hey, I see you're in Denver.
I'm selling my 19" wheels w/Toyo tires if you're interested in another set for winter

 

Could you tap into the luggage light or the charging door light as the 12V trigger? I'm not sure where the switched is positioned for these but might be able to poke around with a multimeter until you find one that is on.

 

You appear to be the pioneer!