12V battery low-voltage auto-disconnect

this is a great idea for people who keep there pri for more than 4 or 5 years, or tend to have senior moments with their doors and light switches. thanks for the hard work and well thought out write up srivenkat!

 

I feel that I must respectfully disagree. I think of the traction battery as living in a castle surrounded by a moat. The only way across the moat is a drawbridge which is raised and lowered from the outside. The reason why it is surrounded by all this is because it is dangerous, potentially a man killer, and they had to have serious protections if they wanted to bring something new into the American market. They had to get past all the American Safety Nazis, and this setup is what did the trick.

It *is* a nuisance when your 12 volt dies and you can't get in there, but they had to weigh that against the needs of emergency personnel, and service techs, and the Detroit disinformation campaigns, and they went with a product that mostly wouldn't kill people, and that they could sell in our market.

 

Everything you say is reasonable, and I'm sure Toyota had it's share of trouble getting this system approved, but I don't see how it serves the interests of safety to have the aux battery go completely dead. Without being an engineer, I can think of several ways it could be avoided without endangering the main traction battery in any way. I've seen low-voltage cut-outs, which isolate a battery from any current drain when the voltage falls too low. I believe most lithium batteries have such built-in protection as well.

In my scenario, when the aux battery falls to say, 10.5 volts, it shuts off any further current drain, and waits for the user to return to the car. There's still enough power in the aux battery to engage the computer, start up the system, and start charging the aux battery. This way the aux battery isn't damaged or destroyed, the user doesn't need a boost, and he/she are on their way.

The only advantage to the current design that I can imagine is to the dealer; to be able to justify charging the customer for service and possibly a new battery.

 

Nice idea, nice thread. Thanks for taking the time to post it. It would also be great if you would update it down the road as to how it is working out. We go for 3 week vacations, about every 3 years, where our car is parked in some garage for that amount of time. I might try this out myself.

 

I haven't designed anything. I am proposing a design change, which has been the subject of controversy on this forum in the past. Currently, I carry a booster-pack in case it happens to me again.

 

Srievenkat
I have been looking around, and surly can not find a low voltage disconnect for $25. Best I have found is on Amazon, for a "Battery Prog Brain T-1" for $54.13 + free shipping. I also found "Priority Start 12 volt" units, but they seem to be less reliable, (in reading reviews) and even more expensive, yet they do not require any button pushing to disengage the disconnect.

Is your Battery Brain a T-1 model??

 

The OP ebay price was a bargain and the opportunity was at his door.
I was not as lucky and paid for a couple of the T1 about $47 a piece.