Circuit Breakers, Fuses, and Bears, Oh My!

["content22207" <brobertson@xxxx>]

Hopefully Dave will allow one public tiff (it's for the general
welfare, honest -- see my comment about protecting your computer)...

Of course circuit breakers and fuses are not *IDENTICAL*: they're
shaped differently, install differently, and one of them doesn't have
to be thrown away. But functionally, they are equivalent. In fact, I'd
argue that a fuse is even more sensitive, making it a better protector.

I wasn't in the DMC boardroom when the decision was made either, but
it is likely they decided to use a breaker in the fan circuit because:
1) Has anybody ever seen a 40 amp auto fuse?
2) The fuse box is full already
2) Resetable vs replaceable protection in the fan circuit could be a
perceived advantage (my own fan circuit has yet to give me problem
one, but that's another thread altogether)

BTW: I also drive 4 Lincolns, 2 AMC's, and a truck, all of which have
*FUSES* for headlights and wipers (among other "critical" systems --
isn't the fuel pump critical too?).

Re: "higher than usual current" -- the DeLorean is *basically* a 12
volt car (how common). 12V radio, 12V headlights, 12V cooling fans.
Energizing any of these components actually produces a momentary DROP
in voltage. The amps whizzing past will certainly jump, but that's
what our protection devices are rated for.

Point of clarification: when I said fan fix fuses were redundant, I
meant with the breaker, not with each other. I also used the plural
wire*S* for those of us who did our own bypass -- we have two fuses too!

Circuit breakers AND fuses are both HEAT sensitive devices. If an
electrical abnormality creates heat, they will activate. But not all
abnormalities create heat (que the public safety announcement Dave).
Probably the most misunderstood protection needed is against excess
voltage (amperage draw is pretty well covered). Voltage spikes do not
necessarily produce heat. The "1.21 gigawatts" in a bolt of lightning
for example may fry the TV without tripping the breaker to the den. Or
pass through unscathed 24 gauge telephone cable. If your computer is
plugged only into a circuit breaker equipped power bar, it is not
really protected. I don't think excess voltage is a concern on the
road, but you might want to check with Martin G or John H.

Keeping your D's electrical system stock does allow easy reference to
the printed wiring diagram. But the nice people at the factory
engineered in some weaknesses IMHO worth redoing. We're talking about
more than fan relays here: passing full side & tail light amperage
through the dash switch is a bad idea. Fuse 8 appears to have
inherited everything that wouldn't fit anywhere else. I see nothing
wrong with improving what is already a nice automobile. Of course it's
a good idea to document what you've done, but then don't you just have
a wiring diagram with appendixes?

With our luck some DMLer with an electrical engineering PhD from MIT
is going to respond and prove us both wrong...

Bill Robertson
#5939

>--- In dmcnews@xxxx, "jtrealtywebspannet" <jtrealty@xxxx> wrote:
> Fuses and circuit breakers are completly different devices. The only 
> thing you can say they have in common is that they are protective 
> devices used in electrical circuits. The main reason that there is a 
> circuit breaker in the cooling fan circuit is for the ability for it 
> to take short periods of higher than usual current so you can start 
> the fans,(when motors start they have a very high current draw, much 
> higher than when they are running steady-state). The circuit breaker 
> also gives the automatic resetability which is desirable in critical 
> circuits like headlights and wipers (not that hey are used in 
> Deloreans but are on most cars). Unless you really understand what you 
> are doing in the electrical system it is best to keep it as stock as 
> possible with the exception of the recomended relay and circuit 
> breaker upgrades. Make sure all connections are clean and tight and 
> you actually have the correct size fuses in the correct locations. 
> Carry an assortment of fuses for emergencies so you can always replace 
> a blown fuse with the correct size. FYI the fuses in the Fanzilla are 
> not redundent, each fan has it's own fuse so if 1 fan dies it won't 
> take the whole circuit with it, now you REALLY know what the Fan Fail 
> Light is supposed to do, tell you when you have a bad fan! 
> David Teitelbaum
> vin 10757
>