[Mobile-Portable] Automotive Circuit Breakers VS Fuses ?

[WD8ARZ]

It isnt just about the response timing of circuit breakers to fuses (where 
fuses win hands downs), it is also about failures of breakers to function a 
all. Circuit breakers have been known to fail, not function period. I have 
never heard of a fuse doing that .... hi

For the topic of a circuit breakers to protect small gauge feed wire through 
a firewall to a fuse system in a Rigblaster ..... the higher the current and 
the longer the wire run, the more I would trust fuses over circuit breakers.

Fuses can not only be chosen for the amp rating, but also for the timing 
required to open the circuit. Circuit breakers are slower, period. A lot of 
electronics can be damaged in a fuse breaker system. A fuse will blow on 
voltage / current transients that will protect electronics, that a circuit 
breaker will not respond to.

Look at automotive, industrial and home systems. Note how many of the 
systems uses fuses, and when / where breakers are used. Even where there are 
breakers, there are fuses up line of those. Home breakers are for AC 
systems. Look at the solid state electronics in your home on those AC 
systems. Bet the electronics is fused.

In the case of the Ten Tec that used a magnetic circuit breaker.... that was 
a special application to protect the finals. It was easy during tune up to 
overload the finals, and that happen so easily, fuses would have been an 
aggravation. The magnetic circuit breaker was a special design that would 
trip when current got to high to the finals, but prior to the finals 
blowing.  Bottom line was the poor transmitter design that needed that 
special breaker design.

Power interruptions create voltage spikes and current surges. Inductive 
components have magnetic fields that get large during a spike / surge. When 
the circuit flow is stopped during a blowing fuse / breaker situation, the 
counter emf creates a spike / surge in the opposite direction in the circuit 
creating flows through diodes and other solid state components that may not 
tolerate those events. Fuses blow sooner keeping the spikes / surges to a 
minimum .... circuit breakers that trip during the same event will take 
longer to respond, thus the likely hood of higher voltage spikes, larger 
current surges, and a longer dwell exposure time of sensitive electronics to 
the abnormal power condition during that even.

MOV suppressors are a god send to help control that, BUT too many hits on a 
MOV and they fail to function and need to be replaced. When do you know that 
a MOV fails? If it didnt fail shorted, you dont until electronics is damage 
it was meant to protect. Because of the fast propagation of these voltage 
spikes / current surges followed by counter electromotive voltages / 
currents, fuses are need to protect electronics. Still use the metal oxide 
varisters and other protective devices where you can, just expect to have to 
replace them over time / multiple events that trigger them (such as in your 
power strips).

73 from Bill - WD8ARZ
http://hflink.net/qso/

----- Original Message ----- 
From: "N5WV" <n5wv at comcast.net>
To: <mobile-portable at mailman.qth.net>
Sent: Thursday, November 26, 2009 4:02 AM
Subject: [Mobile-Portable] Automotive Circuit Breakers VS Fuses ?