Featured Automagically destroy wiring in as many as eight places

You know something.
I'm going to look at these type of systems from the perspective of rescuers and first responders, the idea is to keep them safe and make them confident in saving occupants as quickly as possible.

Plus I'm going to bank on the idea that if I'm in an accident that triggers the system and requires me to be rescued from the vehicle, it's highly unlikely the vehicle isn't going to be totaled, so the likelihood that I have to worry about the extra expense of repairing or replacing wiring won't be an issue.

 

From the article, "...as many as eight, if the car has a motor at each wheel..."
So most cars will have 2 to 4.

 

we live in a complicated world with many different priorities for many different types of people.
safety is a big issue for most, especially those with little or none understanding of possible issues they might face.

with more possible issues facing us daily, it's inevitable that some will think of ever increasing complex solutions to even the simplest of problems.

I read in the article the the new Porsche Taycan is using 800 volts. it must be a complex system to optimally be able to charge it's pack in 15 minutes. "charging from 5 to 80 percent capacity in just 22.5 minutes with a peak power input of 270 kW'
2020 Porsche Taycan: EV Range, Power, and Charging Specs | Automobile Magazine - Automobile
quote is close to the very bottom of the page and more restrictions apply covered in the article.

Still, 8 points of access also provides 8 points of failure further complicating an all ready complex system. ymmv

 

Any car with an engine has a system to shut off and depressurize the fuel system in the event of a collision. In the case of electricity, reducing the risks from the 'fuel system' after an accident isn't as simple as turning of a pump. The connection needs to be physically broken in order to de-energize the system. Actually cutting them is drastic, but has less points of failing than some type of mechanical switch.

Like other cars aren't loaded with potential failure points.
Loose ground connections in the 12 volt can cause weird behavior in engines, and shorts in that system have regularly started car fires. Maybe they should have such kill switches at the battery and alternator to reduce sparks igniting fuel and fluids after a crash.

 

Perhaps the concern is with voltage from a motor operating as a generator if a wheel is still turning, say in a rollover collision. In some designs, I suppose there could also be a risk from charged capacitors.

I imagine these would both be more of a risk to occupants or bystanders than to first responders, but it’s one explanation for opening the traction power circuits at multiple points.

 

The hypothetical 8 points of cutting was for a AWD car with a motor for each wheel. I imagine one of these permanent magnet motors can pushing a sizable jolt if a wheel gets spun in some manner.

When hybrids first arrived, first responders were concerned with accidentally cutting into a power cable during an extraction.

 

The goal is to divide the DC source into small enough pieces that all of them are below the 50V OSHA threshold for safety.

Now, divide 400V into 50V pieces and what do you get?

 

That's true, they seem to want to separated the battery from the power electronics. I don't know why you'd do that anywhere but right inside the battery at the point you mentioned (the fuse location).

 

The concern isn't just the battery, but also the motor/generators. Wrecked cars will have to be moved at some point, and wreckers hook metal cables and chains up to them.

 

Like you, ChapmanF, I owned a 2010 Prius. At the same time, I was on the board of the local Volunteer Fire Department, and for the first time in my life started reading fire-control magazines. Yes they do exist. Making sure first responders and occupants were safe in crashes of hybrids was a hot new issue--and one I hadn't thought about at all. I asked the fire chief about what the articles were saying and he told me that they were exactly right.
You are right about cutting things off in or near the battery, but I think the reasons other folks have given for also having fuses at the wheels are also right.
So I agree with the new fuses, even though you and vvillovv are also right about additional failure points.

 

It isn't like a replaceable fuse or circuit breaker wouldn't also be an added failure point.
While they could be reversible for less cost, they could be less reliable at doing the required job. I don't think these companies decided on a blade cutting the cable as the solution before entering the lab.

 

This sounds like a good way to assure that any crash will always total the car. Your insurance company will be sure to take this into consideration when they set their prices. If we were talking about the F-35 Lightning I might shrug and say yeh, sure, but for a car??? Because we can do a thing doesn't mean that we should do a thing. What we have here is a cool solution looking for a problem. Cars ain't it.

 

Do you have any idea what 400V DC will do to you?

Kill you instantly, then boil you, then set you on fire, that's what.

 

The old man used to say "it's not the volts that'll kill you, it's the AMPS" ymmv watt

 

Yeah, well, we have a thing called "Ohms law" that relates the two.

100mA through your heart will stop it. But getting that 100mA there depends on your body's resistance (mostly the surface resistance of your skin since on the inside you're basically highly-conductive sea-water) and the applied voltage.

What makes batteries so dangerous is that they are DC so they don't let go of you like AC does (current causes muscle contractions and AC goes through zero every 1/120th of a second) and they have nearly unlimited current capability so the current doesn't drop when you get across one.

We have UPS' here at work that run on 700V worth of lead-acid batteries. To replace the batteries, you suit up in heavy PPE, and break the battery into pieces until all the pieces are 4-battery strings (48V). Then you pull those out one-by-one and replace them, and then hook them back up into 48V strings. Then suit up and connect the strings. It's very dangerous.

 

One easy way to describe the diff between AC and DC is to describe the ON/OFF switch.
got spark? arc? plasma?
Ohm Ohm Ohm Ohm

all kidding aside, The stuff can be and is VERY dangerous in the most unexpected places as well as the VERY well know places. First time DIYers should take extra precautions while learning about how the systems are designed and worked on while waiting to be surprised by the next unknown behavior that shows up and boggles the mind.

 

A crash that sets off these cutters will set off the airbags, and the cost of replacing those is already totaling cars.

 

Another current thread with much in common:

Is a car "greener" if it isn't durable? | PriusChat

Seems like currently safety is a strong regulatory concern, and durability not so much. Front ends that are VERY pricey crumple-zones, for example.