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Old 09-08-2013, 08:45 AM   #1
Kevin in NJ
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Default So you think the fuse on the starter will protect you?

Think again!!

My brother an I were discussing this and it was brought up late in another thread so I am bringing out as a new thread.

Here is what we believe:

The fuse that is placed at the starter is a fuse between the battery and the body does not protect the car when the engine is running.

When the engine is running the generator is providing the electricity and is on the body side of the fuse.

So if you have a short circuit in the body wiring the fuse will only take the battery out of the circuit. The generator will continue suppling electricity.

SO,
The fuse that is placed at the starter is just providing a false peace of mind.

There are other fundamental problems with this single fuse.
Usually it is way too big for the wires it is supposed to protect and it is still possible to get a fire with something less then a short circuit. Keep in mind your toaster can start a fire without blowing the breaker. A thin wire with too large a fuse can get red hot.

To top it off, the fuse is a common fail point that will strand you or cause subtle run issues as it gets a high resistance. The fuse holders sometimes fail or get corrosion as they are really not intended to be in the elements.

If you really wish to protect your car then you need to consider a fuse at the battery and at the cut out for the main power feeds and then a separate set of fuses for each circuit in the terminal box.
Maybe one of the venders will be reading this and come up with a custom solution that can look original till you take the terminal box cover off.

The fuses are to sized for the type of wire they are to protect, not the expected amount of current needed by the devices.

The best protection is a well inspected good set of wiring. The Model A does not have much to catch fire and is not really prone to fires.

Anyway, I hope this is something to chew on (in a positive way) for the group.
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Old 09-08-2013, 09:36 AM   #2
Mike V. Florida
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Default Re: So you think the fuse on the starter will protect you?

Without voltage going out the battery (the battery acts like a regulator), the generator will burn out, stopping the car.
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Old 09-08-2013, 10:04 AM   #3
H. L. Chauvin
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Default Re: So you think the fuse on the starter will protect you?

Many differences of opinion on this subject of providing fuses & other protective wire devices; however, appears many are concerned with adding a fuse near the starter for being somewhat of a safety device for vehicle protection when the vehicle is left unattended & is parked as opposed to when one is driving & someone is constantly present to possibly use a fire extinguisher or other extinguishing devices and/or methods.

Each to his own as to what makes one happy & feel secure -- a nearby phone for dialing 911, two (2) Tylenol PM's, a bottle of wine before bedtime, etc., etc., also works for some in order to attain one's Model A peace of mind.
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Old 09-08-2013, 10:05 AM   #4
steve s
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Default Re: So you think the fuse on the starter will protect you?

Kevin,
I agree with all you say except the implication that the starter mounted fuse is totally without value. In my experience, the danger zone is when I'm fiddling with the wiring while the car is NOT running. I've popped the fuse (actually, I use a breaker) a few times, and suspect it has saved me a world of hurt.

I like your idea of a reasonably authentic looking fuse block in place of the terminal box. I doubtful it could be the same size, and accommodating the original wiring harness would be a challenge. Here's a photo of my inelegant fuse block solution--I wouldn't want to have fewer fuses. I also have a 30 amp inline on the wire coming out of the alternator to the horn/light wiring harness feed. I vacillate on whether my starter mount is too much redundancy, partly for various reasons you mention.

Mike,
Can we be confident that the generator "fuse" would burn out before other wiring was smoked?

Steve


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Old 09-08-2013, 10:52 AM   #5
Mike V. Florida
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Default Re: So you think the fuse on the starter will protect you?

Quote:
Originally Posted by steve s View Post
Mike,
Can we be confident that the generator "fuse" would burn out before other wiring was smoked?

Steve

NO! wires can burn even with fuses/CB's look at house fires all the branches are "protected" but fires do occur due to wiring. Another point is there are problems with fuses and fuse holders whether you have one or 10. There is no absoulte prevention for wiring fires.
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Old 09-08-2013, 11:45 AM   #6
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Default Re: So you think the fuse on the starter will protect you?

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Re-Think Again....

Ok, let's continue this line of thinking. Say a short occurs anywhere after the fuse and the fuse blows. There was obviously a very short duration of high (>30 amp) current causing the fuse to blow, which it did. No damage done so far. Now the generator is trying to supply the fault current, but it can only put out maybe 20 amps maximum. So the wiring is NOT subjected to gross overload, and the fault quickly drags down the voltage so the motor quits due to no ignition and the generator no longer puts out anything. Excitement over.

Now let's see what happens without the fuse. A short now can draw massive amounts of current out of the battery (like the 100 amps starting current). Now is when your wiring harness becomes the next "fuse" and real fire and damage occur. Note that this occurs whether the motor is running or not.

I'm leaving my fuse in place, thank you.
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Old 09-08-2013, 12:07 PM   #7
Ron in Quincy
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Default Re: So you think the fuse on the starter will protect you?

As previously said, I only open the fuse when parking the A for a extended time so the battery is removed from the wiring. When the A is running I am present so if a problem occurs I can take care of it.

Just peace of mind when stored !!!!!!

Using a Diode Cutout will also help to save your generator.


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Old 09-08-2013, 12:29 PM   #8
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Default Re: So you think the fuse on the starter will protect you?

It is your car do what you want, for me I use fuses. More than one fuse is best, you need to understand the current load and the wire sizing to do it right, as well as the proper way to install a fuse holder and no any cheap parts store holder is not the answer as it will fail. If you are not trained in electrical circuits engeneering do not just assume any old fuse and wire will work. Seek the help of someone who has the training to really do it right. Or just leave it stock and hope everything is ok (no pinched wires, no cracked insulation, no oil soaked wires, all connections tight and not correded.... Etc.)

The use of fuses on an A is almost as controversial as what type of oil to use!
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Old 09-08-2013, 06:12 PM   #9
Chuck Sea/Tac
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Default Re: So you think the fuse on the starter will protect you?

I'm no "engineer" but the fuse works for me(real life experience). I have an electronic regulator by the guy in Coos Bay Oregon, and maybe that's why. In a parade blowing my fog horn, in the 25 amp circuit as described. It shorted out, blew the fuse, and the engine died. Since I'm a slow learner, I jumped out changed the fuse and did it again. About the 3rd time I figured out I should stop blowing that horn. When I got home, I found the short in the horn causing the fuse to blow.
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