No takers so far

The idea Toyota watches forums for engineering change suggestions is very unrealistic.

 

This just isn’t a place where people are brilliant enough to do sophisticated electronic mods.
It’s like the people who want to add an extra battery for more range.
Anything can be done, but at what cost, risk and benefit?
The few people who have claimed to do really sophisticated mods never offer proof, or reveal sources .
Priuschat is more about advice for keeping your car running smoothly. In some cases, the answers are elusive

 

Ecomodder is more likely to cover such big changes.

 

Modifications, especially those not easily reversible, can detract from resale value. Potential buyers are maybe unimpressed to start with, and could be thinking, what else, undisclosed, may have been done.

 

The real issue is not engineering expertise, it's the fact Toyota successfully locks down its software which is where a "no parts required" solution could be created.

The lithium aftermarket battery fiasco is a relevant case in point. While the logic and hardware needed for a power lithium vehicle power source is almost in the public domain, the ability to replace existing Toyota code with anything else is not there unless Toyota wanted to do it. In the lithium case they already sold an integrated lithium solution for gen3 and newer.

Toyota prioritizes safety and reliability over "nice to have" vehicle modifications. They did provide a solution for excessive parasitic draw in their new hybrid, a fix that does not put a bloody bandaid on an open wound.

 

The 12-V-battery issue has nothing to do with the hardware. It is a standard hardware setup like in any other car.

The problem is being caused by the buggy BMS app that interfaces with the hardware. Toyota has little incentive to correct the app, as currently over-the-air (OTA) updates are not possible (except for the multimedia head unit) and very few owners are affected.

This will all be resolved when Arene is fully implemented in the future Toyota cars. The entire car will become an app at that point. Gen 6 Prius should be built mostly on Arene. Current Toyotas will become primitive cars when the Arene-equipped Toyotas arrive.

Arene debuts in Toyota’s all-new RAV4 | PriusChat

 

I am an electrical engineer and I have done modifications to some of the things I have purchased but I would never consider doing anything like this:

1) High voltage scares me.
2) It would void my new cars warranty.
3) It seems like the better solution would be to go after the source of the original problem rather than creating an exotic modification to fix the result of the problem when it happens.

 

I don't think it's a stupid idea, but I do not know if it is practical.

There are some practical solutions: Use a battery tender. Regularly test the 12v battery and replace when needed, and keep a jump pack in your car, particularly since you live in the Great North. I do all. of these things.

I think the main problem with your proposal is this: If the 12V battery has failed, it means it can draw current "forever," and if you try to charge it by transforming the voltage down to 12V, the hybrid battery will eventually drain, and now you'll have two dead batteries. That's besides the expense and safety concern of what you're proposing. The Prius voltage inverter is one of its most expensive components.

 

STOP FEEDING THE TROLL

 

Electrical Engineer #2 responding out of curiosity for the issue. Yes, this can be solved as most anything is possible. The solution will require the HV battery to have a connection to the 12V battery (galvanically isolated buck charger), so this will likely void the warranty. It would also require access to the CAN bus to monitor for the "start" signal which is probably the easiest part of the project. A safety feature could be added that monitors the 12V battery and charge current to alert the user via phone app that their 12V battery is dying and needs replacing. As I say, most anything could be done...for a price.

Or, you could just buy a booster pack which is what I plan to do for mine.

 

toyota marketing used to have a presence here, but i think we wore them down

 

With every engineering problem, there are tradeoffs. From my point of view, the traction battery is much more expensive, and it doesn't handle upsets well. There's a lot of regulation, measurement, and programming in the car to maintain this battery well within limits so it lasts. The 12 Volt accessory battery - not so much. It's cheaper, easier to replace. There's also the optics. If traction batteries started failing, the Prius would not have the reputation for reliability that it does. There's also if the traction battery is discharged, there's no starting the engine, and it's a specialty deal to even try to charge it. If the 12V battery fails, you can jump-start the car. I believe the Toyota engineers didn't allow the traction battery to be used to maintain the 12V battery for these reasons (and probably others). They've done it for the previous generations, too, so it's a fairly well-proven design.

I can see where you'd want to, though. The Gen 5 definitely seems to have an excess current draw on the auxiliary battery. As far as I know, nobody has isolated the system that seems to be draining everybody's battery, which would be the real solution to the problem. Compounding this is the fact that the auxiliary battery in the Prius just doesn't have the capacity that other cars do.

It's your car, so if you want such a charging system, go for it. I don't have a Gen 5, so I'm not as affected by the problem. I'd be more likely to try to diagnose what systems pull down the battery so quickly, and take it back to Toyota to get those systems replaced. I've tried designing some simple circuits over the years, but there's no way I'd want to put something like this in any of my cars - but that's my cars. You can, and should do what you want to your own.

Here's a video of the type of thing I'd be trying.

 

If Toyota thought they needed some random old guys to offer engineering solutions to a nonexistent problem they would hire consultants. If the consultants happened to research opinions and stumbled onto this thread, the trolling and old school thinking exhibited by some would turn them away instantly.

 

If I was faced with a problem described by the OP, a simple and economical solution would immediately come to mind: REPLACE THE 12 VOLT BATTERY with a new one. Voila! Issue solved! No need for engineers. No need for jumper packs, No need for "clever" solutions.

Just saying!