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.
“Why does a car like the Tesla still have old-style fuses?”
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Re: “Why does a car like the Tesla still have old-style fuses?”
#12Well, 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?
Re: “Why does a car like the Tesla still have old-style fuses?”
#13This 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…
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,…
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)
Re: “Why does a car like the Tesla still have old-style fuses?”
#14Well, 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)
Re: “Why does a car like the Tesla still have old-style fuses?”
#15The 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. 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 th…
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.
Re: “Why does a car like the Tesla still have old-style fuses?”
#16This 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…
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,…
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.
Re: “Why does a car like the Tesla still have old-style fuses?”
#17Having 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.
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 sy…
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.
Re: “Why does a car like the Tesla still have old-style fuses?”
#18So if the computer fails the car doesn't burn to the ground?
Re: “Why does a car like the Tesla still have old-style fuses?”
#19Even 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.
Re: “Why does a car like the Tesla still have old-style fuses?”
#20The 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. 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 th…
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...