Will the hybrid battery charge the 12V battery when car is turned off?

Reading through this and similar threads, I sometimes wonder about existing safety regulations and standards governing the batteries found in HV/PHEV/EVs.

I believe it’s easy to think about us as the only end user of these kind of vehicles and how systems and processes are inconvenient or don’t make sense to us. And in a lot of ways, that’s the most common case to be considered.

But I reckon there’s a lot of other stakeholders that are considered in existing regulations and standards, be it the at home wrencher, non-certified technicians, certified technicians, and emergency response personnel that may all have access to these types of vehicles in ordinary and extradinary circumstances.

Thinking about this, and considering how generally conservative engineers/regulators are when dealing with elements of safety, I think it makes a lot of sense to completely isolate the traction battery when the vehicle is off. Introducing other things to sense and regulate that potentially introduces additionally complexity to a system and therefor, additional points of failure.

That said, I admit I might be completely wrong about all of this. I just find threads like this interesting, and I really like my 2024 Prius Prime, so I just wanted to add my thoughts.

 

I'm having difficulty believing that hybrid battery isolation is mandated in safety regulations.

 

I doubt any of us knows whether it was external safety regulations, or requirements Toyota's internal teams thought up, or some combination of both. @Elektroingenieur might know, who doesn't seem to have been around much lately. Clearly since the very first generation, the engineers have been instructed "make sure it's this way when it's off" and that has kept them from pursuing some features that might otherwise be cool and that they've probably thought of, so it would seem the instruction didn't have "if you feel like it" attached.

 

Well, it doesn't seem like much of a design challenge for the system to detect a low 12V battery when the start button is pressed, and instead of a shut-down with an error, a sensor could decide if there's enough juice in the massive main hybrid battery to boost the 12 V battery.

If this issue ever makes it to Toyota, consider this an easy challenge.

 

I don't believe it's a mandate; just a common sense safety approach. Lithium fires are a REAL thing! Isolating and containing it gives the occupants time to escape.
Boeing had an issue with their battery backup system that ground their planes for a couple of months. The only reason the plane didn't catch fire was because of the casing enclosing those batteries.
Greater power density; higher chances of fire or explosion - especially in an accident.

 

I'm no engineer, but it seems simple to protect the hybrid battery from over discharge. Besides, I don't think the Prius uses batteries that catch fire like that.

 

Nobody intends to use batteries that catches fire; again common sense engineering.
You think Boeing intentionally placed those batteries in the plane knowing that it would catch fire??????

 

It's my understanding that Prius uses lithium iron phosphate batteries that do not catch fire.

 

Please do more homework. As you stated, your not an engineer - consumer products must be rendered as safe as humanly and economically possible to operate - even when abused and mishandled by it's operator. Companies that don't do this, don't stay in business for very long..........

Can LiFePO4 Batteries Catch Fire? Unveiling the Science Behind the Flame

 

So the "system" that's going to "detect" that, when the start button is pressed, and the "sensor" that's going to "decide", are powered by some source that isn't the 12V battery (it's dead) or the traction battery (it's isolated). Sort of like having a reserve source of 12 volts to power the basics of making the car READY.

I think there are some retrofit 12V batteries today that contain a reserve that isn't used until you activate it. Might be not too much different.

 

The high voltage battery of the Prius Prime 2023 2024 are NCM 622.
This means lithium nickel cobalt manganese oxide 622 (NCM622) Material cathode.
Chemical Formula: lini0.6co0.2mn0.2o2
And according to the Internet, if their box is damaged, they can set fire.

 

I have installed a 100Ah auxiliary battery, through a smart isolator and bypassable with a switch to boost the regular battery, but I don't consider this to be any sort of remedy for an obvious design flaw.

 

Well, I wasn't too petrified to drive my gasoline powered car due to fear of fire either.
I don't worry about my Prius hybrid battery suddenly catching fire.

 

I recently had an idea about this.
Old cars had low-speed engines and their starter could be spun manually with a "crooked starter". I ordered the parts.

 

If Toyota is serious about improving the customer experience, they will fix this design flaw.

 

To understand why insulation is needed in high-voltage systems, you can hold a bare wire. In fact, of course, you shouldn't do this, it is fraught with damage to the human body and a fatal outcome.

 

I love how freely we on PriusChat toss around terms like "design flaw" as we talk about things designed to meet specifications we didn't see and where the engineers made choices we wouldn't have haven't tried but think we wouldn't have made if facing the same constraints.

 

I think it was clear that I consider it a design flaw.

 

I honestly wouldn’t be surprised if it wasn’t a regulation, but a safety standard used throughout the industry. Just based on how long it’s been around with Prius, past and present. And perhaps other similar vehicles.

 

Correct, I don’t believe this is a design flaw at all, but an intentional decision made to meet specific standards for specific safety goals.