“Why does a car like the Tesla still have old-style fuses?” • Hacker News Board

Re: “Why does a car like the Tesla still have old-style fuses?”

#31

Post by upofadown » Sun, Jan 11, 2015, 1:33 PM UTC

The fuse is also protecting the wire. So in a car you have a big fuse (fusible link) protecting the big wire to the fuse box. Then you have a bunch of little fuses protecting the wire on each branch circuit. All these fuses are intended to last for the life of the vehicle. The only time they would blow would be on the type of fault that would require further troubleshooting. It is unlikely that you could produce an electronic current limiter that would be cheaper and more reliable than a single use fuse.

My father the mechanic used to like to tell me about an exception to the rule as an object lesson about the trade off between risk and reliability. Back in the days of breaker ignitions the ignition circuit was almost never fused. A blown fuse in the ignition circuit could strand people out in the middle of nowhere. The extra risk was acceptable to eliminate the situation where the fuse blew when the ignition might of been able to continue to work in some sort of degraded mode. It was OK that that degraded mode might involve smoke and flame.

Re: “Why does a car like the Tesla still have old-style fuses?”

#32

Post by agumonkey » Sun, Jan 11, 2015, 1:51 PM UTC

lmm wrote: post #27

arethuza wrote: post #23

Earlier quoted context omitted.

On the point about building wiring codes, here in the UK we actually do have both central fuses/circuit-breakers and load specific fuses in the plug for each device. After reading your comment it did make me wonder as I plugged our coffee machine this morning how the design substantial chunk of plastic and metal I was holding was influenced by the aftermath of WW2.

The British plug is a marvel of good engineering. Other countries look on it with envy (except possibly Australia, which has a similar design of its own, IIRC). Now of course it was "overengineered" by the standards of the time, to compensate for our ludicrous, dangerous, and still-legally-required "ring main" system, which as you say was due to aftermath-of-WW2 copper shortages. But the plug design is the part we go…

Indeed lots of good sense included in the plug http://www.youtube.com/watch?v=UEfP1OKKz_Q

Re: “Why does a car like the Tesla still have old-style fuses?”

#33

Post by csirac2 » Sun, Jan 11, 2015, 1:55 PM UTC

robin_reala wrote: post #30

lmm wrote: post #27

Earlier quoted context omitted.

The British plug is a marvel of good engineering. Other countries look on it with envy (except possibly Australia, which has a similar design of its own, IIRC). Now of course it was "overengineered" by the standards of the time, to compensate for our ludicrous, dangerous, and still-legally-required "ring main" system, which as you say was due to aftermath-of-WW2 copper shortages. But the plug design is the part we go…

Australian plugs are good, but have the live pins at the top (so for example a dropped coin will balance across them and short when the plug is pulled out), the plug doesn’t have its own fuse and the socket isn’t shuttered with no plug inserted.

A few years ago they mandated the inner-most 5mm or so of the active pins be insulated for that reason, so that by the time you have enough of the plug out to reach exposed conductor with your fingers it's disconnected. At least that's idea... and I can't tell you how much ebay junk is sold with the old "illegal" exposed active pins

Re: “Why does a car like the Tesla still have old-style fuses?”

#34

Post by spb » Sun, Jan 11, 2015, 2:05 PM UTC

teovall wrote: post #7

This is a perfect example of the KISS principle. Since I would never presume to call Woz stupid, let's call it the KISW (Keep It Simple Woz) principle in this case. Woz is proposing that Tesla take well proven, very reliable, simple, inexpensive fuses that are very rarely even seen by customers and replace them with complex integrated circuits and software that will need a lot of testing, almost certainly be more exp…

I've never interpreted the second S to be addressing the listener. I've interpreted it as a two-item list of things you should "keep it": "simple, stupid"

Re: “Why does a car like the Tesla still have old-style fuses?”

#35

Post by arethuza » Sun, Jan 11, 2015, 2:24 PM UTC

robin_reala wrote: post #30

lmm wrote: post #27

Earlier quoted context omitted.

The British plug is a marvel of good engineering. Other countries look on it with envy (except possibly Australia, which has a similar design of its own, IIRC). Now of course it was "overengineered" by the standards of the time, to compensate for our ludicrous, dangerous, and still-legally-required "ring main" system, which as you say was due to aftermath-of-WW2 copper shortages. But the plug design is the part we go…

Australian plugs are good, but have the live pins at the top (so for example a dropped coin will balance across them and short when the plug is pulled out), the plug doesn’t have its own fuse and the socket isn’t shuttered with no plug inserted.

So Australian plugs are a bit like UK ones except upside down? :-)

Re: “Why does a car like the Tesla still have old-style fuses?”

#36

Post by brudgers » Sun, Jan 11, 2015, 2:50 PM UTC

x0054 wrote: post #25

Because cars are not expected, under normal circumstances, to experience abnormal amounts of current on any given circuit. Unlike a house, where you can easily plug in something into the outlet that can overwhelm the circuit, in a car each circuit is designed specifically for a given maximum load. When you blow a circuit in a house, you have most likely massed up and plugged too many things into one outlet, or your d…

The reason fuses are prohibited in distribution panels for homes and many other types of buildings has nothing to do with the magnitude of the potential overcurrents. The prohibitions on fuses and requirements for circuit breakers exist because experience has shown that occupants will frequently short across rather than replacing blown fuses.

The resulting fire and shock hazard endanger not only the occupants but the general public and firefighters responding to calls.

Re: “Why does a car like the Tesla still have old-style fuses?”

#37

Post by percept » Sun, Jan 11, 2015, 3:18 PM UTC

spb wrote: post #34

teovall wrote: post #7

This is a perfect example of the KISS principle. Since I would never presume to call Woz stupid, let's call it the KISW (Keep It Simple Woz) principle in this case. Woz is proposing that Tesla take well proven, very reliable, simple, inexpensive fuses that are very rarely even seen by customers and replace them with complex integrated circuits and software that will need a lot of testing, almost certainly be more exp…

I've never interpreted the second S to be addressing the listener. I've interpreted it as a two-item list of things you should "keep it": "simple, stupid"

I like your way better.

Re: “Why does a car like the Tesla still have old-style fuses?”

#38

Post by jpindar » Sun, Jan 11, 2015, 3:21 PM UTC

nmeofthestate wrote: post #28

rdw wrote: post #17

Earlier quoted context omitted.

On top of this, mechanical circuit breakers would have vibration issues when mounted in a moving vehicle. If it's too vibration-resistant, it might not trigger under overcurrent conditions. If it's not vibration-resistant enough, the car flakily breaks on bumpy roads. Solid-state circuit breakers do exist, and would solve the vibration problem, but some quick Googling didn't turn up anything that looked at all inexpe…

Sounds plausible, but if you Google "automotive circuit breaker" you'll find they exist and are quite cheap.

Mechanical breakers are standard on Harley-Davidson motorcycles. I doubt there's any road vehicle that experiences more vibration than a rigid framed Harley.

They are self-resetting, but make a fairly obvious noise when they reset.

Re: “Why does a car like the Tesla still have old-style fuses?”

#39

Post by rkangel » Sun, Jan 11, 2015, 3:23 PM UTC

sillysaurus3 wrote: post #24

davidbanham wrote: post #21

To me the interesting part of this was how social media is sometimes absolutely amazing. Woz idly poses a question about the fuses in his car and has an engineer from the manufacturer write a detailed response in short order. That is incredible.

That's less social media and more Woz asking a question. Or rather, this is the internet at work, not social media. The only thing social media has done is reduce the time between question and answer. And that's impressive, but it's not the fundamental shift the internet itself was.

Social media does mean that we all see the answer, not just Woz.

Re: “Why does a car like the Tesla still have old-style fuses?”

#40

Post by sokoloff » Sun, Jan 11, 2015, 3:44 PM UTC

The short answer is cost and that fuses are perfectly sufficient.

Blade fuses are 100 for a dollar. PTCs are a handful for a dollar. Infineon ProFETs are a couple dollars per.

When's the last time you blew a fuse on your car? For most of us, it's never. For those of us who have, there was almost certainly an electrical fault that was the root cause.