Jump Start Tip for Gen 3

that is an incredible dealer.

 

I've found from experience that some jumper cables (re: cheaper), don't have enough gauge to adequately deliver enough power charge. Years ago (not a Prius), I had small gauge jumpers that wouldn't work, but as soon as I put on large gauge cables, the starter turned over.

 

Are you saying that some jumper cables have circuits that restrict the flow of current to one direction. This must be designed to protect electronic components in the host car if the cables are inadvertently connected with the wrong polarity. That's a great idea, if it works. Perhaps I should get a new set of jumper cables. Am I understanding this correctly?

 

You can also use multiple power sources to jump a hard to start car. I learned this back in my tow truck driving days in a former life. Last week I had to jump start my MIL's car and one jumper pack wasn't doing it. I hooked up a second power pack along with the first and it took off like it had a new battery. Someone can correct me if I am wrong but I believe this increases the amperage, not the voltage.

 

I think that's correct. So will thickness of wire. The light weight (8 to 12 Gauge) thin cables are no good for ANY vehicle. They MAY do the job if the 'dead' battery is nearly charged enough to do the job, but they won't handle enough current to actually start a car. A set of 12-ft 4 gauge cables will start a full size SUV as soon as they are connected.

 

If in parallel, yes. Series would double the voltage.

 

That is correct. 2 batteries (power packs or chargers) in parallel will increase the amperage (cranking power) but not the voltage.

Another trick is to plug in a battery or battery charger to to the cigar lighter / accessory power outlet.
I am not sure if that works on the Prius, but I used to plug in a "trickle charger" to the cigar lighter outlet and let it sit for 1 or 2 hours - then there would be enough of a charge back in the battery to start the car.

 

Umm... Putting two batteries in parallel personally gives me the willies. It's one thing if they're in parallel and get charged together and stay together for all time; it's another if one has more or less charge than the other. While battery voltage is roughly constant, it does go up with increasing charge. Hence, paralleling two of the things implies that the higher charged one of the pair is going to discharge into the less charged battery.

On top of that battery voltage is one of those wonderful Gaussian-curve type parameters: A given battery, depending upon construction, chemistry, history, and the phase of the moon will have more or less voltage across it, with the same charge, as a similar battery built on a different day.

I agree that two batteries in parallel will have more current capacity under load. But I sure wouldn't do it often, and I'd be sure to disconnect those two paralleled ones immediately after use.

I do parallel electronic power modules for a living, sometimes - but those things have features that guarantee load sharing and the like.

KBeck

 

Running two (or more) batteries of similar chemistry and voltage in parallel has no issues whatsoever - and never has.
They do not even have to be similar capacity either.
Either charging or using.

Lead acid batteries are used in all cars today (including the Prius - the starter, radios, computers, pumps - etc). It uses a different charger & power buss for it's LiPo batteries.

Lead acid batteries use "constant current" charging to get to a "float voltage" - in automotive batteries, that is 14.5v.
As a battery nears it's float voltage, it uses less & less current to charge.
It doesn't matter how many batteries are in parallel - as long as they have the same float voltage they will all consume less current as they reach their float voltage.

Using multiple batteries in parallel has been done for as long as there have been requirements for high capacity long term electrical storage (emergency backup systems and starting your uncle's farm tractor).
You would be surprised upon walking into a Telco central office or a computer co-location data center and see the huge pile of lead acid batteries they use for emergency backup.

I wouldn't mix chemistries though. Using a mix of lead acid & NiCad or LiPo batteries could be trouble. I'm not sure about the "Gaussian-curve type parameters" aspect of batteries.

 

Thank you for the clarification, although I am a bit disappointed. I was hoping you had discovered a new gadget.

 

Yup. You're all right, as long as batteries are connected in parrarel.

In our fleet we had Alfa Romeo 159 with diesel engine. For some reason it was left on the parking (open air) for near one month, winter, about -20 Celsius (yes... minus twenty degrees). With Diesel engine under the hood and dead battery (not even able to open without key) it was really hard to start it.

First off - tried using jumpstart cables from other Alfa. No success... ECU even did not tried to crank the engine. All controls disappeared in the moment. Then Assistance came with special jump start device. It tried to crank but... failed the same.

Finally connecting jumpstart device with Accu in another Alfa did the job... very hard job.

So yes - it is possible in very hard conditions to do it. But I don't think it is necessary with so small accu and small power consuming device as Prius is.

And back to the topic of 50/50 chance of using wrong combination of cables sides and depleting AUX battery - in Europe every Toyota is covered with 3 year assistance that helps you free of charge with funny situations like locking keys inside, running out of fuel (you are charged only for fuel), starting up with depleted AUX Acu and so on.

I haven't tried in on my Auris but it is good to know that it is

 

Remember that in the Prius, the 12V battery doesnt need enough Amps to crank its starter (there is none). Just enough to start and maintain the ECU and its accessories. So having heavy gauge jumper wires to charge a Prius 12v is not necessary. Although I don't recommend it, even thin 20ga speaker wire can easily carry a couple of amps of current to do this job.
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But when jumping a conventional engine, the thicker the wire, the better. Also remember to do this while the Prius is already started.
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The issue with having a fancy circuit to restrict the flow if incorrectly connected is limited by two things. The circuit would basicly be a Rectifier (or a bunch in parallel). Standard silicon rectifiers have a fixed voltage drop of 0.7V. Those rectifiers must also pass enough Amps to be effective. So for example, if I need 200 cranking amps; I need at least a rectifier rated alot more than 200 amps, and the resulting heat dissapatted by the rectifier would be 0.7v x 200a = 140W of heat for the gadget to safely dissapate. The cost for all of the safety for this safety gadget would be prohibitive. Not to mention the cost of this anti-Darwin-ish device to all of humanity. Sometimes thinning of the herd is a good thing ;-). (Just kidding of course).
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Finally, having a voltmeter around when you mess around with this stuff is always handy.

rich

 

If someone could confirm or refute that would be great, but as far as I know the cigarette lighter (or lighters) are all disconnected when the Prius is off, so plugging a small AC or solar trickle charger into a parked Prius wouldn't do anything for you. It'd be great if I were wrong...

 

Thanks that's clears it up for me, good to know.

BTW all you need to jump start a Prius is a couple of good quality 6V lantern batteries in series (smaller batteries would probably work) and some "jumper cables" made of 16ga wire with alligator clips. I keep those things in the tray above the spare tire. Fortunately I haven't needed them yet.

 

Here is another tip:
When you connect a good battery to a dead one, it will start charging that battery. This means there will be sparks! You should (a) see them, (b) hear them, and (c) maybe even feel them. Not big ones, but enough to tell. If you don't observe any of this, then you did not make the connection! And you need to remedy that somehow.

As an aside, you can also see why we connect the last wire to a point away from the battery, for safety reasons. Of course, in a Prius, this is a non-issue since the battery is at the other end of the car.

 

There is a relay that turns off the lighter socket power until the system power is turned on. However you can trickle charge the battery by connecting to it directly.

The 12v battery is pretty small (compared to standard cars) So I'm not sure if you will benefit or even damage the battery by overcharging it. Personally I would not bother.

-Howard

 

This is one of the advantages of some/most of the jumper packs in that they have a switch so you connect the cables with no juice in them (no sparks) and then flip the switch to electrify the cables. On of my two packs also has a polarity checker on it so you can check the polarity before flipping the switch.