MacGyver a flat 12v battery from the HV ?

[Jon the Chief]

Is there a way to fool the 12v regulator/converter to give a charge to a flat battery from the HV battery?

It would save a lot of grief if you are stranded far from help with a dead battery.

Jon the Chief

[Skwyre7]

If the 12v battery is dead, how would you boot up the computers for the HV battery to charge the 12v battery?

[Jon the Chief]

My guess is that the computer closes a relay, if you duplicate the signal the computer gives then the charge system should fire up?

Or not, does anyone know.

Jon the Chief

[jayman]

Originally Posted by Jon the Chief

My guess is that the computer closes a relay, if you duplicate the signal the computer gives then the charge system should fire up?

Well, this is chicken-and-egg time. The Prius computers need 12 vdc, and the only way to get that relay in the HV NiMH pack to close is to have the car boot up first.

If the 12 vdc battery is flat, nothing happens. The car is completely dead. You need a boost to get going

[kenmce]

Is there a way to fool the 12v regulator/converter to give a charge to a flat battery from the HV battery?

There is no simple or standard way. If you made a direct connection between the 12-volt and the traction battery the 12-volt would probably go off like a bomb. Wisely, Toyota has made it hard for you to do this.

It would save a lot of grief if you are stranded far from help with a dead battery.

The 12-volt doesn't do all that much work. I've jumped my car with the battery out of an emergency light. You might look into getting a little 12-volt battery, Ni-Cad maybe and setting it up to trickle charge when the car is on, or have a solar panel in the window to keep it topped off. It would be enough for a self jump or two. I'm not sure if you could use the cigarette lighter plug to connect them.

[hobbit]

some 'gator clip leads and a really big resistor?
.
_H*

[fruzzetti]

Originally Posted by hobbit

and a really big resistor?

LOL... You're talking about a BIG resistor, and you're talking about melting it anyway. You really could design a voltage regulator for it, but then you'd need access to the hybrid battery taps which would PISS OFF the computers when you fired the car up; I'd bet every single alarm you can think of would go off, including some none of us have ever heard of. Moreover, you're safer just getting a lantern battery and clipping it onto the 12V battery in parallel with a couple 10ga wires. And it would cost a tenth of that voltage regulator.

~ dan ~

You could also get one of those quick battery chargers that plug into the wall and include a 50A "quick start" option. Then just jump the car from your wall.

[David Beale]

OK, here ya go. Open the HV battery box. Find the relay. Install a plastic rod through the case to the relay contact assy. When you press on the rod, it closes the relay, energizing the charger, with will then allow someone else to press "start" to fire up the computers, which will then take over the job of holding the relays closed.

But don't do it. It's very dangerous, could blow some of the electronics, and is just silly. A simple boost will suffice to do the same. The Prius takes a 45 Amp 1/2 second pulse when you press the brake pedal, then another when you press "start". After that the HV system takes over and charges up the 12V battery with 13.8V.

If you want to be "self sufficient" get a portable car booster. They are inexpensive, fairly small, and work well with the Prius. They will also allow you to boost other cars, something you shouldn't do with your Prius.

[Jon the Chief]

Yep, that was what I reckoned.

I know it is something you would not do for fun. But it is like any engineering problem you know how it can be done, and you know when you might be forced to do it.

On ships you plan for the worst and you operate the vessel to make sure it doesn't happen.

But if your Prius is stuck in a snow drift, knowing all the systems and how they can be operated could save your life.

Jon the Chief

[qbee42]

Originally Posted by Jon the Chief

On ships you plan for the worst and you operate the vessel to make sure it doesn't happen.

Which is of course why ships never sink or are left dead in the water.

I know what you are saying, but just had to poke a little fun. For any backup system you have to do a cost vs benefit analysis, and also look at the problems that could be introduced by using the backup. With the Prius, the control systems are powered by the 12V bus, so you need a source of 12VDC before you can fire off the inverter. It would be relatively simple to provide a backup 12V charging system, but that adds extra cost and weight, and offers the risk of drawing down the HV battery through misuse.

Tom