giving jump starts using my Prius?

From the 2004 Prius FAQ list on Yahoo's Prius-2G group:

The important thing is apparently to disconnect the jumper cables before trying to start the other car on their own battery.

This thread discusses the subject at length, as well.

 

Thank you -- an excellent clarification.

 

Boosting a diesel motor with the Prius? I'm surprised you didn't FUBAR the Prius.

As far as giving somebody a boost, I wouldn't for some very good reasons. I should explain that I won't leave somebody high and dry.

First of all, the Prius doesn't really have a "true" 12 vdc system. If you look in the right rear hatch under the floor, there is a very tiny 12 v battery that is used to run 12 vdc things (Lights, radio, brake booster pump, etc). As far as size, think motorcycle or lawn tractor.

The Prius used the inverter system to convert the +208 vdc from the main NiMH pack to 12 vdc to keep the tiny battery at optimum charge. I doubt it can put out more than 40-50 amps at 12 volts.

The NiMH pack is used to start the ICE, run the electric motors, and also to run the variable speed electric A/C compressor.

Second of all, in a conventional car/truck, giving a boost really puts a lot of demand on the alternator and voltage regulator. You can easily destroy an electronic voltage regulator.

Boosting also can introduce a lot of surges and spikes into both electrical systems. If you happen to leave something like a radio on, you may cook it. If the surge/spike destroys the PCM or another critical engine computer, you're toast.

A lot of the Ford Super Duty tow trucks have from the factory 2 alternators, with one alternator just used for keeping the large auxiliary battery charged to boost cars and to operate the emergency lights. There is no danger of cooking the tow truck system.

With every other car and truck I've owned, I've always hooked up the cables and then had the other car wait for 5 mins. I run mine at 2,000 RPM the entire 5 mins, then I would disconnect the cables. Usually, with a +100 amp alternator, that was enough to get them started.

After reading up on how the Prius HSD works, I firmly decided there was no way I'd use the car itself to give a boost or accept a boost. I went to a local Canadian Tire which happened to be having a sale on emergency boost packs.

I picked up a 700 amp capacity emergency booster for $50. It has polarity protection, surge protection, and spark protection. So far, I've used it twice to boost other motorists and it works very well. Since it has such a large capacity, after 20-30 secs the other car will crank like summer and fire.

All I do is plug it in 4 hours once a month, as the manual recommends, to keep the internal battery at the proper charge.

If you look around at car dealerships, that's all they use to boost cars on the lot. They were FUBAR'ing too many cars using another car for a boost. Even if they have to throw away the boost box ever 6 months, that's cheaper and safer for them.

 

Bob:

As far as the VW TDI, it wouldn't hurt to get the battery load tested. Maybe time for a new battery, as the battery not only has to turn over a high compression diesel, but also has to operate the glow plugs.

Check the battery, engine, and body grounds too. If the car is over 4 years old, it doesn't hurt - with the battery disconnected of course - to remove the bolts to the body and engine grounds, smear them with silicone dielectric, and snug them down again.

On my 1992 Honda Prelude, after 5 years the motor would sometimes crank sluggish and idle rough. The motor ground wire that attached to the rad support was corroded at the bolt. Cleaned everything out, reassembled with gobs of silicone dielectric, and that cured it.

It's also a good idea - again with the battery disconnected - to take the battery cable off the starter motor and make sure that the bolt isn't corroded. Reassemble with silicone dielectric.

As far as the issue of whether you FUBAR'd the Prius, only time will tell. With many semiconductor components, they may tolerate the occasional surge.

However, the junction (Such as N-junction semiconductor) may be slowly damaged. That sort of thing won't show up immediately. Either way, I'd suggest looking around for one of those emergency booster packs.

Size it to anticipate the highest draw you have to worry about, in this case that VW TDI. At least 700 amps for that thing. If just for the Prius, all you have to worry about is getting enough juice to "boot" the car and run the power brake booster, a tiny 100 amp booster pack should be plenty.

Hope this helps.

Jay

 

The DC/DC converter can put out anywhere from 80-100A, and doesn't need ICE to run any more than the A/C compressor needs ICE to run.

Few cars could actually start another car solely from their alternators. The other typical car alternators according to my dad who had been a mechanic for years, put out about 80A, so they too could not start a car, nor could the jumper cable deliver the current one would actually need to start. But it can boost.

The Prius could boost, but with all the electronics, including the 'alternator' being all electronic, I wouldn't want to chance blowing anything. Should be fine to try and charge another car enough to allow their battery to crank on its own.

Better to use a booster pack.

 

Dan:

Good point.

In a conventional car, the capacity of the battery gives the "boost" and the alternator keeps up with running load. In the Prius, due to the small size of the 12 v battery, you're really limited.

In my old Ford truck I have a 1,000 CCA battery. It's a huge thing, like a Group 78 size, and weighs a ton. The old truck only has a 40 amp alternator, but the truck only has to run headlights, heater fan, and windshield wipers.

With that battery, I can easily boost a tractor. So if you pick out an emergency boost pack with a high rating, not only do you easily cover the Prius demand, but most cars and pickup trucks you're likely to encounter out there.

Jay