Let's say I have a 12v tire inflator hooked up to a in car power outlet. Ten feet from the inflator is a fused plug in the outlet. Three feet from the outlet, between it and the battery, is another in line fuse. Both fuses are 15 amps, if the inflator suddenly draws more than 15 amps do both fuses blow at the same time or one before the other? Thanks.
A fuse question
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I would guess the fuse in the outlet would blow first, as it probably under the dash, and closest to the battery.
The resistance out to the inflator would probably reduce the amount of current that fuse gets compared to the outlet fuse.
So, if both fuses are IDENTICAL, I would say the outlet fuse would blow first.
But this is just a guess on my part.
The resistance out to the inflator would probably reduce the amount of current that fuse gets compared to the outlet fuse.
So, if both fuses are IDENTICAL, I would say the outlet fuse would blow first.
But this is just a guess on my part.
Originally Posted By: Falken
I would guess the fuse in the outlet would blow first, as it probably under the dash, and closest to the battery.
The resistance out to the inflator would probably reduce the amount of current that fuse gets compared to the outlet fuse.
So, if both fuses are IDENTICAL, I would say the outlet fuse would blow first.
But this is just a guess on my part.
Nope, current would be constant throughout the circuit, but voltage would drop as you got closer to the load due to resistance in the wire. (So I don't know which fuse would blow first. Probably the one with the lower actual, not nominal, ampacity - although they're rated the same, there are likely manufacturing variations.)
I would guess the fuse in the outlet would blow first, as it probably under the dash, and closest to the battery.
The resistance out to the inflator would probably reduce the amount of current that fuse gets compared to the outlet fuse.
So, if both fuses are IDENTICAL, I would say the outlet fuse would blow first.
But this is just a guess on my part.
Nope, current would be constant throughout the circuit, but voltage would drop as you got closer to the load due to resistance in the wire. (So I don't know which fuse would blow first. Probably the one with the lower actual, not nominal, ampacity - although they're rated the same, there are likely manufacturing variations.)
One will blow first.
Keep in mind that a 15 amp fuse will not always blow at exactly 15 amps. A continous 13 amp load may cause a 15 amp fuse to blow while an start up load of 17 amps may not. It isn't the current that causes a fuse to blow but rather the build up of heat.
Keep in mind that a 15 amp fuse will not always blow at exactly 15 amps. A continous 13 amp load may cause a 15 amp fuse to blow while an start up load of 17 amps may not. It isn't the current that causes a fuse to blow but rather the build up of heat.
Originally Posted By: Falken
I would guess the fuse in the outlet would blow first, as it probably under the dash, and closest to the battery.
The resistance out to the inflator would probably reduce the amount of current that fuse gets compared to the outlet fuse.
So, if both fuses are IDENTICAL, I would say the outlet fuse would blow first.
But this is just a guess on my part.
NO!
The fuses are in series, so the current through them will be the same.
This is what engineers call balancing on the apex of a comb. In other words the results are unpredictable. It would be a race to see which fuse blows first, and it is possible that both could blow, but more likely one of the fuses will be faster than the other.
I would guess the fuse in the outlet would blow first, as it probably under the dash, and closest to the battery.
The resistance out to the inflator would probably reduce the amount of current that fuse gets compared to the outlet fuse.
So, if both fuses are IDENTICAL, I would say the outlet fuse would blow first.
But this is just a guess on my part.
NO!
The fuses are in series, so the current through them will be the same.
This is what engineers call balancing on the apex of a comb. In other words the results are unpredictable. It would be a race to see which fuse blows first, and it is possible that both could blow, but more likely one of the fuses will be faster than the other.
Its a race and cannot be predicted. One will blow and the other partially melted or damaged. If the current is high enough they will both blow.
Originally Posted By: turtlevette
Its a race and cannot be predicted. One will blow and the other partially melted or damaged. If the current is high enough they will both blow.
Yup, it's a "[censored] shoot". Fuses aren't precision electronics. They respond to time at current. If you run a fuse near or at it it's rating, it may take a little time for it to fail. Go over the rating and it fails more quickly. Go way over the rating (a short circuit) and it fails almost instantaneously. So there's some variability in every fuse.
Edit: they censored that word??? It's the expression used for playing a game with dice.
Its a race and cannot be predicted. One will blow and the other partially melted or damaged. If the current is high enough they will both blow.
Yup, it's a "[censored] shoot". Fuses aren't precision electronics. They respond to time at current. If you run a fuse near or at it it's rating, it may take a little time for it to fail. Go over the rating and it fails more quickly. Go way over the rating (a short circuit) and it fails almost instantaneously. So there's some variability in every fuse.
Edit: they censored that word??? It's the expression used for playing a game with dice.
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You have no reliable way to determine at what load any fuse will blow; what you do know for sure is it won't be instantaneous, and it won't be at the exact current it's rated for.
Note as well that no fuse or circuit breaker is capable of measuring current. What they do measure is heat, corresponding that to a room-temperature current.
Use them, but know that it's all just a guess, and that it takes time to build up heat.
Virtually every fuse or breaker will pass potentially damaging current levels if the length of time the overload occurs is brief enough.
RE: the OP's question: one of the two fuses will eventually blow, but there is no way to predict which one.
Note as well that no fuse or circuit breaker is capable of measuring current. What they do measure is heat, corresponding that to a room-temperature current.
Use them, but know that it's all just a guess, and that it takes time to build up heat.
Virtually every fuse or breaker will pass potentially damaging current levels if the length of time the overload occurs is brief enough.
RE: the OP's question: one of the two fuses will eventually blow, but there is no way to predict which one.
I had exactly this happen on my '91 Integra.
The Integra had an old-fashioned cigarette-lighter socket that could not handle the current-draw of the inflator that I tried to use.
There were TWO fuses in the circuit for the cigarette-lighter outlet, and BOTH of them blew.
The Integra had an old-fashioned cigarette-lighter socket that could not handle the current-draw of the inflator that I tried to use.
There were TWO fuses in the circuit for the cigarette-lighter outlet, and BOTH of them blew.
Thanks for all he replies. According to the manufacturer, the inflator draws a maximum of 12 amps.
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