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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

by sfeng 12y 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 12y ago
I don't understand; is there a benefit to having a fuse on top of a circuit breaker?
- mixmastamyk 12y ago
  CB doesn't need to be replaced.
- sliverstorm 12y 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
danjayh 12y 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 12y 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.
  - nmeofthestate 12y ago
    Sounds plausible, but if you Google "automotive circuit breaker" you'll find they exist and are quite cheap.
    - jpindar 12y ago
      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.

by sfeng 12y ago

Dylan16807 12y ago

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

mixmastamyk 12y ago
CB doesn't need to be replaced.
sliverstorm 12y 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

danjayh 12y 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 12y 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.
- nmeofthestate 12y ago
  Sounds plausible, but if you Google "automotive circuit breaker" you'll find they exist and are quite cheap.
  - jpindar 12y ago
    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.