I own a Ford Fusion Hybrid and it can be jump-started just like any other conventional car.
(A great car by the way!)
This is a nitpick, but wouldn’t a transformer work on pulsed DC current?
In a very simplistic form you have just described how a DC-DC converter works. However be aware that the output from a transformer that is fed with pulsed DC is still AC. So you need to rectify it back to DC. The actual manner in which DC-DC converters work is a bit more hairy - to gain efficiency and allow the use of very small transformers they operate at quite high frequencies, and the circuit is tuned, so considering things as simple chopped DC is an oversimplification. But the idea is there.
In general they are evil circuits, and not designed by the faint of heart. There is a lot of energy moving through them, and typically a large fraction of the circuit complexity is all about protecting things when something goes wrong.
Maastricht’s annecdote pretty much contradicts this. There is no reason why the car should not be OK with the big battery dead. It should work fine just runing from the conventional engine, and it will then charge up the big battery as you drive. The user’s manual suggests that taking it to the shop is an option, probably for those owners whose brain starts to fuse about the point in the manual where it says to open the hood.
hi guys,
you need to drop in over at the yahoo group “prius technical stuff” or google for “hobbit prius” for loads and loads of technical information.
the short answer is that if the traction battery (the “big” battery) is dead, the car can not be jump-started in the traditional fashion. there is a special charger that toyota has produced for the traction battery, and supposedly very few dealers in the united states have one.
the 12V battery is little more than a motorcycle battery, as others have pointed out. its function is to boot the computer, after which the traction battery and inverter can be brought online. the 12V rail in the prius is then driven by a DC-DC converter while the car is in READY mode.
its very easy to deplete the 12V battery, say by leaving a dome light on. i’ve had to jump-start (maybe jump-boot is a better term) my prius a couple of times because of this. another culprit is going on vacation for 2+ weeks while leaving the smart key entry system running. this can deplete the 12V battery as well. Maastricht is almost certainly referring to the 12V battery in his post - you do have to drive around for about 20min to trickle-charge the 12V battery after it’s run flat - but one does not have to take the car to a mechanic to jump-start the car.
the engine can not be started unless the traction battery has enough juice to spin MG1. the 12V battery does not power any part of the drivetrain on a prius.
here’s a good link dealing with the prius “transmission”, which is really a power-split device/CVT.
oh, here’s another good link describing the the power split device, the ICE and the two electric motors, and what they are doing while you are driving:
http://www.ecrostech.com/prius/original/Understanding/WhatsGoingOnAsIDrive.htm
couldn’t let this one go. this just is not true. if there is a total failure of the high voltage electrical system the prius will not revert to being a conventional car. the transaxle is fully dependent on the high voltage system.
This is precisely why I thought they might be able to build a simple device that jump starts the little battery with the big one. Since the traction battery must necessarily be charged, there should be plenty of energy to start the car without the 12V battery.
as others have pointed out the 12V rail in the car is a matter of backward compatibility with common automotive parts, plus regulating 12V down to 5V and 3.3V and maybe 1.5V for different parts of the computer is much more straightforward than regulating 200+V down to these levels. you can use a linear regulator if need be, which will keep costs down. for 200V to 12V and below you need switching regulators, which are more expensive.
anyway, such a device already exists inside the prius, because after the computer is booted the HV battery is supplying the 12V rail via a DC-DC converter. they probably don’t want the HV battery driving any electronics in the car until the computer is up and running and can sense different fault conditions related to the electrical system. so there’s kind of a chicken and egg problem here.
here’s an interesting article about current draw from the 12V battery as the gen 2 prius starts up. the implication is that you could probably jumpstart the car with some lantern batteries in series, provided that the 12V battery is not completely dead.