Crank generator or other solution for death 12V

Yes battery output current changes a lot with temperature but Prius really needs very little battery output current from 12V battery. Only enough to start computer. At around -18c or 0F battery takes at least double time to charge.

 

In the case of our original 12V battery, it lost a cell . . . and kept working until the cold weather arrived.

Bob Wilson

 

I linked to only one as an example ... a moment with mr google reveals that it's an active product area. I do think it was a bit goofy of them to build in an LED to tell you it's on.

The thingy I built for accessory loads in my trunk was on the same idea, only I designed its threshold voltage to be above normal battery voltage so it's only on with the higher converter voltage when the car is READY. In that design I went for low drain when it's off ... nothing there then except a reverse-biased transistor and an underbiased zener.

It turns out that was totally a thing too, which was even already available, had I known about it, when I was building mine.

What I like about their product version, that's not in the thing I built, is a settable time delay before turning off. So, for example, if I was powering a thermoelectric cooler as an accessory, I could turn the car off and spend an hour in a restaurant or something without interrupting power to the cooler. And it turns out the product does have a second, lower voltage threshold for battery protection, independent of the timer, where it will shut completely off just like a normal dead-battery protector.

-Chap

 

Chap, ok, I like this answer to the problem.
Which of the 2 disconnects listed do you reccomend, I'm looking for protection from parasitic draw when parked for months while travelling, I would want to put it in line on the positive terminal of the 12v battery...and then when it trips, what do I do, use a short jumper across it's terminals to start the car? Thanks, Robert

 

Well, the ones I've just described are two examples from a larger product category - you might need to hunt around a bit. The one I have in my car I only put there for auxiliary loads - I did not wire it in series with any of the original car circuits, only some extra ones that I added. You can either choose a voltage threshold that is below normal voltage for the battery (so it's always on and only cuts out to keep the battery from dying), or you can choose a threshold above normal battery voltage but below the converter output, which effectively just gives you a switched circuit controlled by the car being in READY, but without having to tease out some key-controlled wire in the harness and drive a relay with it.

That switchable aux function was more what I was looking for personally. It sounds as if you are more interested in the simpler, low-threshold, drop-all-the-loads kind. (In answer to your question about what to do after it trips, I've never used one so I don't know. Maybe some have a reset button?)

The one I listed as an example is probably not heavy enough. The battery terminal fuse is sized at 120 amps, so that could guide you in shopping for a suitable relay. That won't be as small as the one I showed.

-Chap

 

This is where a solar powered, tickle charger makes a lot of sense. It just needs to be one that won't over charge the 12V battery.

Bob Wilson

 

Agreed, and that's what I'll do.

 

I've jumped my dead Prius with a DeWalt 12V battery several times before. The brake pump pulled more current than the computer booting up. Also, I recommend Michelin Smart Jumper Cable instead of regular jumper cable.

 

...then pulling the fuse for the brake pump might allow a severely discharged battery to boot the computers

 

But then your dash lights up like xmas tree.