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

https://www.facebook.com/stevewoz/posts/10153145090701282

by primigenus • 12 years ago

114 70 12 years ago

sfeng• 12 years ago

Having fuses as a last-ditch safety measure can be a really good idea, as often the alternative to a fuse blowing is a fire. That said, they should probably be using self-resetting circuit breakers rated to trip before the fuses blow. It's possible they do and his car has a legitimate short.

Dylan16807• 12 years ago

I don't understand; is there a benefit to having a fuse on top of a circuit breaker?

mixmastamyk• 12 years ago

CB doesn't need to be replaced.

sliverstorm• 12 years ago

I imagine your parent was thinking about the fact that fuses are dirt simple and thus pretty reliable. Breakers are reliable too, but certainly more complex

danjayh2• 12 years ago

Having a fail-safe functionality (vs ... fail-deadly, I guess, with no fuse) is critically important (far more than just being a good idea), but there's no reason it can't be a circuit breaker with feedback to the computer system. Self-resetting would probably be a bad idea (if there's a short, you really do want it to stay off), and even having computer control of it would be questionable (although if the control system met DO-178 standards, it'd probably be fine), but even a simple feedback mechanism would be a huge win. For that matter, there's no reason that the computer can't tell you what fuse is blown, what it affects, and show you where to replace it.

Here's the real deal: a fuse costs cents, and a breaker costs dollars. Fuses rarely blow, so increasing cost two orders of magnitude for an extremely minor benefit doesn't make a lot of cents (har har har). Even Tesla cares about cost control - imagine if the whole car were two orders of magnitude more expensive. I expect that a feedback mechanism would probably actually be cheaper than breakers, since it could be a single, cheap chip rather than expensive mechanical devices.

rdw• 12 years ago

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 inexpensive.

teovall• 12 years ago

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 expensive, and almost certainly be less reliable. For what? Very little benefit for a very small subset of customers.

KISW! Sometimes a small length of wire in a plastic holder is the best answer to a problem.

danjayh2• 12 years ago

Agreed. However, adding a single CAN bus ADC to the fuse PCB (to sense no voltage on circuits with a blown fuse) would cost almost nothing, and would allow the computer to provide information on the blown fuse and instructions on how to replace it. IMHO, breakers = expensive needless feature creep, but user feedback = welcome to 2015.

EDIT: I was thinking of the 12V accessory fuses. In light of the reply from Tesla, I can imagine where if the drivetrain fuse blew you might not want an average user replacing it ... and I imagine that for something like that, it probably already throws a code that gives you an idea of what's wrong.

vxNsr2• 12 years ago

Blown fuses are one of the rarer issues that car owners face, so it likely is a cost/benefit thing - putting an engineer on that project just isn't worth the time and cost of implementing the idea vs say working on improving battery efficiency. (especially from a marketing perspective)

agoetz• 12 years ago

Adding a new sensor to monitor the fuses would not be cheap:first off, you have to have signal conditioners for the a/ds that can handle esd transients, and >60 v load shed events. In addition, the existing design probably just has fuse holders physically mounted to the holder packaging, which means now your paying for microcontroller, can transceiver, and pcb. This doesn't include NRE costs including development and testing.

Suddenly your "inexpensive" adc had become a $200 ecu that merely tells the driver wheat part of the car isn't functioning, right before they check the most common cause of the problem.

walshemj2• 12 years ago

yep getting a shock from the battery pack from a tesla is going to be bad news if not fatal.

That is one of the downsides of ev's whist an electric shock from mains is unpleasant its unlikely to be fatal higher voltage and amperage shocks are very nasty.

spb• 12 years ago

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"

percept• 12 years ago

I like your way better.

vxNsr2• 12 years ago

Someone at tesla answered the question:

Marc Rogers[0] Woz - Kristin[1] cant post to your thread but here is her answer:

So there’s a few things at play here. For context, I run the Product Security team at Tesla and I’m safety-trained on the HV systems - I’m also working hands-on with a small drive inverter on a hobby project right now.

First and foremost, our large drive unit pulls about 1000A at full load, and switching that with silicon is tough. We use a bank of custom IGBTs on each of the high/low sides of each of the 3 rotor phases in order to handle the power, and that’s with active fluid cooling. You can switch that much current with silicon but it ain’t cheap, and you’ll need either active cooling or a bunch of thermal mass if you want the thing to switch more than once. http://www.teslamotorsclub.com/attachment.php... is a decent pic, the object on the left is a single-phase switch, you can see 6x transistors laying flat at the front for one side of the phase (the other bank is behind).

Secondly, Model S is an AC induction motor so the current through the winding ramps up more-or-less linearly over time until the phase switches off (or changes direction). You’re at high power but you’re not switching the load at zero-crossing as you would in a resonant load such as a Tesla coil, instead you have to switch at an increasing current depending on how much power you want to the wheels. You now don’t just have to switch a lot of power, you have to switch it FAST so that the resistive losses in the FETs don’t blow out the power channel due to ohmic losses. Your switch is now not just big and bulky, it’s complicated (since you need an additional HV supply) and pretty sensitive to things like stray capacitances. On the previous pic the big black brick on top of the PCB is the capacitor that dumps into the IGBT gates to make them switch fast enough.

Finally, I believe there’s a regulatory issue. I think I’m right in saying that automotive standards around the world require that all electrical systems are fused, and considering that there’s multiple separate power rails it’s not inconceivable that an event could take place that leaves the HV drive rail powered on but kills the 12V accessory rail that powers a lot of the CAN systems. You could end up disabling your active fuse while the HV system is still energized, and considering the amperage our lithium packs can deliver (P85D draws up to 1.5kA) that’s not going to end well.

Woz: I would LOVE to put you under a Tesla NDA and then give you a _real_ tour of the vehicle - ping me at kpaget@teslamotors.com if you’re interested. I’m curious, do you still have one of my RFID cloners on your shelf somewhere? [2]

[0]https://www.facebook.com/marcrogers?fref=ufi

[1] https://www.facebook.com/kristin.paget

[2]https://www.facebook.com/stevewoz/posts/10153145090701282?co...

lylebarrere• 12 years ago

The response from Kristin Paget at Tesla:

"So there’s a few things at play here. For context, I run the Product Security team at Tesla and I’m safety-trained on the HV systems - I’m also working hands-on with a small drive inverter on a hobby project right now.

csirac23• 12 years ago

I think woz is perhaps staring at a big bank of 3, 5, 10 and 20A fuses though. As mentioned in my other comment, experimental aircraft have a few different instrumented electronic circuit breaker solutions such as http://verticalpower.com/ which can integrate with the cockpit EFIS.

mts_• 12 years ago

The referenced link from the reply: http://www.teslamotorsclub.com/attachment.php?attachmentid=5...

And link to the comment: https://www.facebook.com/stevewoz/posts/10153145090701282?co...

mrfusion• 12 years ago

Why the NDA? Isn't their goal electric vehicle adoption?

Too• 12 years ago

In a way what he is proposing is already used for some systems of a car, although far from everything and mostly for lower currents. Some ecus are capable of delivering enough power from their own I/O pins to drive other components, if any of these outputs are shorted the ecu can detect this, power off the output and enter appropriate failure mode(diagnostics code + disable other functions). When the short is gone it will automatically activate again if considered safe.

csirac23• 12 years ago

Well, amateur experimental aircraft have something like this available: http://verticalpower.com/ - but there's a lot of negative reactions to this kind of technology, because it introduces new failure modes where none previously existed before.

But I think something that people forget is that generally, fuses are there to protect wiring and fixtures (switches, connectors, etc) from fire. Preventing the device on the circuit that you, the user, cares about from completely melting down is just a nice bonus.

That's why building wiring codes generally spec fuses to cope with the capacity handled by wiring and switches, rather than the loads attached to it.

EDIT: In any case you NEVER want the car to silently and automatically try to "re-set" a tripped breaker, surely. You want this kind of fault to present itself noisily and obviously; it's a precursor to a potentially dangerous condition.

Any automatic re-set will have to factor in some cool-down time for the wiring in between attempts... what is the temperature of an overheating pair of conductors in the wiring loom when the breaker tripped? What rate of heat dissipation is there allowing them to cool down again? A wire which has experienced overheating will have a different (higher) resistance after the short-circuit event. Even if the wire isn't permenantly damaged, the temporary increase in temperature will still guarantee a momentarily higher resistance. Will the wire still have low enough resistance to trip the breaker again when the short is applied again?

arethuza2• 12 years ago

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.

lmm• 12 years ago

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 got right.

raverbashing2• 12 years ago

Well, even planes use CB today instead of fuses (and remote CBs on top of that, meaning they can be turned on/off electronically)

I think WOZ is suggesting an active current control that, while doable, is probably too risky (and you really don't want to blow the expensive parts)

tzs2• 12 years ago

Well, even planes use CB today instead of fuses (and remote CBs on top of that, meaning they can be turned on/off electronically)

If you have something drawing too much current in a plane, and so it is a fire risk, it still might be overall safer to continue to use it. For instance, if it is something involved in lowering the landing gear you might decide it is safer to risk a small fire in order to get the gear down than to do a gear up landing. Something resettable, like a circuit breaker, therefore makes a lot of sense in a plane.

With a car you are almost never in that kind of situation.

raverbashing2• 12 years ago

You may also want/need to turn some things off, not necessarily because of a short-circuit.

Vespasian• 12 years ago

Also you have trained personal and emergency plans on board of a plan in contrast to your average street car

sokoloff3• 12 years ago

Pilot (of smallish airplanes) here. Landing gear failures are almost never fatal unless they make the crew mismanage the airplane into a crash. (Eastern 401 or the one in the Bahamas last month (C6-REV) where the press is hailing the pilot a hero for only killing 1 pax, when the reality is no one should have gotten hurt or even wet if properly handled.)

For an important item, I'll reset a breaker once in flight. Nothing electrical is that critical, and I carry portable AHRS, GPS, and handheld VHF radio.

Few things are worse than fire, so if I have any concern about the electricals, they can all stay off and I'll extend the gear manually with the crank system. Other planes have gear that free falls or has an N2 bottle to blow the gear down.

I don't think any civilian aircraft have had fatalities from a simple gear-up landing.

ck2• 12 years ago

So if the computer fails the car doesn't burn to the ground?

venomsnake• 12 years ago

Even before seeing it was Woz that posted - the answer in my head was "because they work". And he made no compelling argument to have something else.

I don't believe in smartness for smartness' sake. For a fuse to fail you need 1) wrong fuse 2) physical damage to the fuse (not sure if there is a case in which this would cause it to not break the circuit), different set of laws of physics.

davidbanham• 12 years ago

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.

sillysaurus3• 12 years ago

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.

rkangel• 12 years ago

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

spiritplumber• 12 years ago

I've replaced most of the easily blown fuses in my car (accessories, etc.) with PTCs. Now I joke that turning the car off and then on again fixes the problem. However, I wouldn't do that with a vital system (starter motor, etc.) because a blown fuse generally informs you of a deeper problem, rather than being the problem itself.

http://en.wikipedia.org/wiki/Resettable_fuse They make these in automotive format, or you can go to Digikey, get a PTC of the current you like, and solder it onto a blown fuse.

PTCs have the advantage of being straight replacement, and if you want, you can add a Hall sensor to see if current is flowing without creating paths to ground or other problems.

Anyone knows how to add this answer to Woz's thread? The "awesome power of social networks" isn't that awesome, since I can't answer on the thread linked...

x0054• 12 years ago

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 device is drawing too much power. You learn from your mistake, unplug the device, and reset the circuit. If a car blows a circuit, then there is something seriously wrong with some component of the car or the wiring. You don't want the user to be able to reset the circuit, you want someone who knows what they are doing to figure our what went wrong.

I fix all of my own cars, and never once have I ever had a blow fuse "just because." There always was an underlining cause which needed to be addressed. Except once, when a 10A fuse was used in a circuit that required a 25A fuse, on a window motor.

So, basically, in a well functioning and well designed car a fuse will not fail just because. So why bother replacing a part that costs less then a cent with a part that costs several dollars. I hate this attitude, just because something CAN be complex, does NOT mean it has to be complex.

Take car modules for instance. It used to be that back in the day (the 90s) your headlights were operated by a mechanical relay. This relay was expected to fail at some point (though they very rarely actually did fail) and as a result this relay was installed in an easily accessible place. If it did fail, it would cost $10-15 to replace it plus 5 minutes of labor.

New cars nowadays have solid state switching modules to operate headlights, and everything else in your car. These components are not expected to fail, even though they often do. Don't believe me, talk to any mechanic. However, because they are not expected to fail, they are often installed deep inside the car. So, now, if your headlight module fails, it costs $400 in parts, and several hours of labor to fix the same problem. Progress?

Stop making things needlessly complicated. Blade fuses are a fine solution to a problem.

moe• 12 years ago

Progress?

Yes. For the companies selling the parts and the repair services.

brudgers• 12 years ago

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.

Spooky23• 12 years ago

You got it.

I looked at a fixer upper house where the mains still had an ancient fuse box. Most of the high draw fuses had old pennies wedged in with a blown fuse. How the place was standing, I don't know!

chrisfarms• 12 years ago

When I first moved into my flat I discovered that the previous owner had wedged some kind of brass plate across the contacts for the cooker circuit. Terrifying.

tzs2• 12 years ago

These components are not expected to fail, even though they often do. Don't believe me, talk to any mechanic. However, because they are not expected to fail, they are often installed deep inside the car. So, now, if your headlight module fails, it costs $400 in parts, and several hours of labor to fix the same problem. Progress?

Hell, when the HEADLIGHT BULB fails, which is something that IS expected to happen, it can be a pain in the ass to deal with on some cars. Some have sealed headlight units that have to be replaced when a bulb dies, costing hundreds of dollars.

Even ones where the bulb can be replaced sometimes make it ridiculously annoying. A low beam went out on my 2006 Honda CR-V. In theory it is easy to replace. Reach in, disconnect a cable, pull off a rubber seal, release a metal retaining clip, and the bulb can be pulled out. Reverse those steps with the new bulb, and you are done.

In reality, there is a bunch of stuff in the way, making it very hard to actually reach the damn thing. On one side, I was only able to do it by wedging my arm in, leaving it bruised and very sore for days. At least I could actually reach the low beams. While there, I tried to reach the high beams and could not get anywhere near them--I think when they go out I'm just going to give up on them.

Once you are in, it goes well, with the possible exception of the retaining clip. This is not unique to Honda, BTW. A lot of cars use the same kind of retaining clamp. Here's a drawing of how it works [1]. It is hinged at one end (the red circled part in that image), and it hooks under a piece of metal at the other end. It takes a fairly large force to make it hook there.

Here's the problem. You can't see this damn thing when you are trying to unlatch or latch it. The headlight housing is in the way. You can maybe see the end of it that is toward the bottom, but that is not helpful because they orient it so the hinge is on the bottom, and it is not the hinge end that people have trouble with.

Looking at YouTube videos of people explaining how to change headlight bulbs, and reading forums, it looks like it either latches easily, or it just won't latch and you are in for 30 minutes of flailing.

All the car maker would have to do is flip the orientation 180 degrees, so that the hinge is on top and the latching part on the bottom. Then you could see the latching part, and it least know what you are trying to do. The way they are now, you are going in blind.

I can understand that when they lay out components in the engine compartment, they have many constraints, so I can believe that all those things that made it hard for me to reach the bulb had to be there. I can believe that making an opening big enough for easy bulb changing might have made them have to make the car longer or something, that would have added a noticeable cost, and they could reasonably decide that it wasn't worth it.

The retaining clip orientation, though, is almost certainly completely arbitrary, and they just did not consider the effect on the ease of bulb changing (or deliberately picked the worst orientation to encourage people to visit a dealer instead of changing their own bulb).

[1] http://www.suzuki-forums.com/attachments/2g-2006-grand-vitar...

electromagnetic• 12 years ago

The issue is the engine compartments for a lot of vehicles are arranged by subcontracted firms. I know a guy who works for a company that does this for Ford, GM and Dodge, and there's not a mechanically inclined person in the bunch.

They're playing jigsaw with an engine compartment trying to get all the parts in in the most compact, but still workable, way possible.

It's sad when you think about it, because not only does it squeeze a lot of at-home maintenance out, which used to keep vehicles affordable, but now almost everyone discussing new vehicles discusses the maintenance costs.

Honestly, I'm not surprised the domestic car market essentially failed, because they're $40,000 printers. No one gives a crap about the up front price anymore, because they know they're getting screwed on the after-expenses so everyone's looking up how much their yearly maintenance expenses are going to be to make sure they don't end up paying more than the vehicle in a decade.

marincounty• 12 years ago

Yea, I like progress, but I don't like progress that hasen't been thought through to the point of, "What will happen when the component fails? Will the Technician be able to fix the failed component--in a reasonable amount of time?". I see too many items being throw away because it makes no financial sense to fix. I feel, as consumers, we need to ask for, and buy products that are able to be repaired. I know most people don't care, but some of us like to fix our cars, appliances, electronics, etc.. I don't blame it all on manufactures though. I remember when I went to automotive school in the ninties. Saturn made a conscious effort to make a vehicle that mechanics could easily work on, but no one seemed to care. Yes, Saturn was plaged by other problems, but I did appreciate the fact that the engineers at least tried to build something--knowing that components will need to be replaced, or fixed. For years, I see this trend towards more gadgets(components that will fail) added to every consumer product, and every year these products become harder to fix? I cringe when I see an automobile loaded with extra stuff that can break. I don't think there's a mechanic out there that doesn't breath a little sigh of relief when a customer comes in with an older simple automobile? The average person out there asks me why I keep that older Toyota p.o.s. as a spare car. Mechanics never question why I keep my p.o.s..

sokoloff3• 12 years ago

This is an odd place to give car repair advice, but since I just did this job today on my wife's 2005 (same car), I have to say its one of the easiest headlamps I've done. 5 mins total for a low-beam. If the latch were reversed, it wouldn't hold itself out of the way when inserting the new bulb. You'd be trading one problem for a worse one, IMO.

Should you need to do a high-beam, you may need to pull the battery on the (US) driver side, or the power steering reservoir on the other side. The PS bottle comes right off (no tools, IIRC), so it's only the one high beam on left side that's particularly tough.

walshemj2• 12 years ago

Yes I suspect that woz hasn't ever seen any serious electrical kit the fuses for those look just like the normal cartridge fuses but way scaled up.

it was only 20 years ago that a local company stopped making knife edge switches (the sort used as props in Frankenstein movies )

grkvlt• 12 years ago

This relay was expected to fail at some point (though they very rarely actually did fail)
These components are not expected to fail, even though they often do.

I think this is wrong. If you look at QA statistics, you will find that parts are getting _more_ reliable. The old relays were expected to fail becuase they _did_ fail. The new modules are not expected to fail, and this is indeed the case. They fail much less often, and of course this means that in the occasional cases where failure occurs, it will be difficult to replace or repair.

Overall reliability is increasing and to say otherwise would seem to be a glib misstatement or misunderstanding.

antidaily• 12 years ago

"What's the problem?" "Car won't start." "Did you try restarting it?"

rcxdude• 12 years ago

No joke, I have seen a car which would occasionally refuse to start (with no indication of an error: the dash was basically blank) until you disconnected the battery, waited a few minutes, and then reconnected it.

wiredfool• 12 years ago

Disconnecting the battery and waiting is how to clear the fault flag on ODB-1 era GM cars/trucks (at least, probably others as well.) And if you short two pins on the ODB connector, then power on, it will flash trouble codes on the check engine light.

And apparently some of them have 160 or 8192 baud serial on that connector, with really expensive cables, unless you're handy with an arduino or similar. Now that the truck is working, I'm not sure I need to do this... yet.

upofadown• 12 years ago

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.

sokoloff3• 12 years ago

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.

ArkyBeagle• 12 years ago

When a panel fuse on a car has actually gone out, it's an indication that Something's Gone Terribly Wrong and simply pushing a button on a popup isn't the right move. Tow it to the shop.

I say "actually" because I presume it's possible to have a false failure now and again - there may be a nonzero number of times in which the fuse just pops, that fuses just wear out.

lnanek2• 12 years ago

Can't say I've ever seen a fuse in a car blow that didn't come from a short that had to be fixed anyway. Having a circuit breaker or software solution some end user would just flip again would damage the system even more and risk fires. Maybe Woz is smart about computers, but doesn't know anything about cars?

korzun• 12 years ago

Have fun trying to troubleshoot something that uses a controller of some sort .vs fuse system without thousands of dollars of equipment.

Really... have fun. I rather check the fuses and trace the wiring for that part using a meter.

g8gggu89• 12 years ago

I'd worry about this if I had a fuse blow in my car in the last 10 years.

Animats• 12 years ago

He's talking about fuses for the low-current auxiliary circuits. From the title, I thought he was talking about fuses in the battery and propulsion system. Fuses very rarely blow for random reasons today. There's been some progress since the "Lucas, Prince of Darkness" era.

The high-power system uses fuses because, if things overload there, you want power disconnected reliably and you want it to stay off. Lithium batteries do not handle overloads well. Not at all.

al2o3cr• 12 years ago

Short answer (pun only somewhat intended): interrupting high-current DC is not as straightforward as it looks. For instance, deactivating a set of relay contacts tends to cause an arc if any amount of current is being interrupted (inductive loads make this worse). For AC, this is manageable since the waveform will hit a zero-crossing in a a handful of milliseconds worst-case, terminating the arc. For DC, no such luck. In extreme cases, the arc can actually WELD the contacts together.

Fuses will, barring ludicrous overload (putting a 12V fuse in a 10kV DC circuit), fail open - a definite positive for a safety measure.

Using fuses makes sense in a lot of applications because they are (as noted above) safer, cheaper, and more reliable. It probably doesn't hurt that a fuse is easier to diagnose; control circuits can intermittently fail but an "intermittently blown" fuse would be an odd thing indeed.

stretchwithme• 12 years ago

I think its because fuses don't blow in a car because you plugged in one too many things. They tend to blow because there is something that needs to be fixed. Maybe circuit breakers make it too easy to ignore serious problems.

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

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