Can I use traction battery to jump start dead 12v battery?

Seriously. Jump pack is a better way to go.

I was just confirming for you that it was technically possible.

In fact.... since I had a high voltage pack disassembled in a Prius that also had a low 12v battery, I gave it a try for fun. Just to say I actually did it. Good times.

 

Funny you should mention that - my brother flies a plane (a 4-seater Mooney) that has two batteries - one main, one backup. Recently, he was going to come pick me up in it, and discovered that both were dead. He had plugged both of them into battery tenders to keep the batteries topped off - but then forgot to plug in the battery tender. So the airplane batteries sat there, powering the battery tender's LEDs for however long, draining them completely.

Whoops. Nothing's foolproof, I guess.

 

Yes, there is a DC to DC converter in the Inverter. In theory, it could be located in the shell of the HV Battery, safely producing 12 volts. In practice, the Inverter is liquid cooled for a reason - Heat. Cooling the converter is non trivial. (see video) Currently the HV battery is air cooled, adding the converter may require a third liquid cooling system.

 

if it could be pulled off cheaply, 12 volts dc and 120 volts ac would be huge.

 

I just picked this up. 33 bucks, fits anywhere. amazon.com/gp/product/B013UJ2JCE/

 

If it's OK to keep that DBPOWER Jump Starter DJS40 plugged into a USB port all the time, that would be the perfect solution to having a reserve battery available anytime as a jump-starting device. I'm afraid to keep my own jump starter plugged in all the time in case I'd ruin it, so there's always the possibility that I'd have forgotten to charge it just when I needed it the most.

Because I tend to consider things mechanistically, I think the best way to think of the traction battery is as if it was a fire hydrant under very high pressure, and you'd only need a cup of water from it to charge your battery. The equipment needed to pull a cup of water out of a high-pressure hydrant safely would be quite complicated, don't you agree? To continue the analogy, if there was a way to have the fire hydrant drip just a little all the time, and have a way to collect those drips, there'd be a way to get your cup of water without having to tap directly into the dangerous high-pressure system. That's what the back-up jump starter would do for you - collect the 'drips'.

Does my analogy make sense to folks? Things that make perfect sense in my mind don't always come out right on paper.

 

No, not on a Prius.

I don't know enough about the Camry Hybrid to know how it might work there. But it would require a very significantly different electrical architecture than the Prius possesses.

 

Since this is a prius turd gen forum, my answer is no, because this is a turd gen forum. Let’s get some rav 4 12v dead battery engine starts also, cant leave them out.

 

Alright, I'm not afraid of stirring the pot with dumb electrical ideas, so here goes: Yes, this is totally doable, possibly with nothing more than the laptop power brick you already carry. Don't try this at home unless you have serious amounts of clue and high-voltage gloves and a CPR-trained friend standing back. Even then don't. (But if you do, post photos!)

The reason is that your laptop brick is a switch-mode power supply (the "switch" here refers to how the transistors are turned on and off inside, not to any physical power button), which works by first rectifying the incoming AC to a high voltage DC, which it filters and buffers in a capacitor. Then it chops high frequency pulses of that HVDC through a transformer, which achieves isolation between the HV and LV sides. (They do this after the chopper because the transformer can be much smaller -- trafos for 60Hz have to be large to be efficient.) Then the output of that transformer is rectified and filtered, et voilá, LVDC! (See figure 3.0.1 in this article, and note that the first input trafo is usually not present in modern designs.)

So, what happens if you feed HVDC into such a thing? It doesn't care, it works fine! Most wide-input SMPS will run happily on HVDC, some are even specified for it. It means you're only using half the diodes in the input rectifier, but these aren't likely to be a critical limit anyway.

Most laptop bricks these days provide about 20 volts. What happens if you connect the output to a dead VRLA sitting around 10 volts? That's gonna depend on the specific unit, but at least some will happily dump their full current into such a load for at least a moment before declaring a fault and shutting off. And furthermore, many will automatically retry after a moment, and "sneeze" coulombs into the load in hopes that the short may go away sooner or later. This may or may not charge the battery very quickly, but in at least some cases, it should fix ya right up. (Open question: Suppose you add some ballast resistance and thus voltage drop, so the brick doesn't see its output sag so much....)

An older 15-16v brick, like the early Thinkpads and stuff, would be ideal and probably not even see a fault condition.

If I were in the aforementioned A-team situation and had to get my dead car started, you bet I'd be reaching for the sockets and popping open that HV battery to get at the sweet juicy 200-ish VDC inside. But because I'm trying to avoid death (either from the bad guys killing me before the end of the episode, or from the battery), I'd pull the service plug first, make my connections, then replace the plug.

 

If I were in that A-team situation, I would reach into the glove box and pull out the jump pack, which is not a bad thing for the A-team to have around. It wasn't super cheap, but neither are high-voltage gloves. (I've bought both.)