I think we are all saying the same thing, just looking at the math from the different denominators.

Ross is right in that amperage is the driving factor in circuit breakers because that is the amount of electricity that you are trying to limit. But it is because at a constant voltage, increases in amperage increase the wattage, wattage is heat and heat is what pops the breakers (or for that matter burns/melts fuses). DCCBs are simply little meat tongues that bend when they get hot. If they get hot enough, they bend enough to disconnect from their contact point. The breakers themselves don't care about voltage - just heat, but the laws of physics in the electrical equation demand that with one factor remaining constant (as voltage does in our systems) the other two must rise (or fall for that matter) proportionally.

IOW the wattage heat is a direct proportion to the amperage and thus amperage can be controlled by calculating/designing and constructing the breaker to separate when it reaches a certain temperature. They are very accurate.

And that is why fuses "burn" (actually melt) when they are over amped (yes amperage sensative) because you are using the mathmatically, emperically, consistant direct ratio of heat produced for a given amperage. Too many amps, it melts the fuse - tis true - but, it's the heat generated from excess watts (that is the side product from excess amps) that is used, and causes the melting.

That's a cool idea using CBs in the fuse holder. Do you happen to have a link to a site that has those?

 

Look at it this way. A 30-amp 12v fuse or CB blows at ~360 Watts, right? If I hooked it up to 1,000 volts DC and put a load of .36 amp on it, do you think either would blow? I don't think it would. Any volunteers to try it???

 

You could stand in a bathtub naked full of salt water and hold on to a 1000 volt wire and take a .36 amp charge and not even feel it. You do the same thing with a 10 volt wire at 50 amps and it'll kill ya. Same diff here.

In your scenario, that's right, you can manipulate any of the factors in the formula to stay below the critical 360 watts and the things not going to pop - even if the rated amperage of the fuse or CB is exceeded.

Like wise, if you manipulate any one of the factors in the formula to a wattage above 360 watts, it's gonna blow - even if the rated amperage is not reached.

And th ereason for that is despite the fact that you are trying to limit amperage, you are doing so by USING a device that is sensative to the WATTAGE that is directly proportional to the amperage. It's kind of like using your tachometer to measure how fast you are going.

The Laws of Mathmatics are not the issue here, nor is the fact that you are trying to limit the amperage in the circuit.

The point that is trying to be made is HOW the device works, and what changes in the mathmatical formula do effect it.

Again, a fuse or a circuit breaker is installed to prevent excess amperage across a circuit. But it does so - the way it actually functions is by reacting to the heat produced from the excess wattage generated by that excess amperage.

It may be a 30 amp breaker, but it's going to pop at any amperage that produces over 360 watts.

 

All I said was I couldn't get my truck to show a charge

 

Yeah----Trouble maker!

 

Great thread Folks! Always interesting to learn new things..and fixing a problem along the way adds to the rewards..
As with any electrical problem, an analysis of the schematic and understanding how the circuit is'supposed' to work necessary..in hindsight I think the main clue was that the problem was intermitant...it works..dosen't work..works..doesn't work..acting just as a circuit breaker should.
I've been around this stuff for some time,but it never ceases to amaze me 'what I forget'.( read overlooked)...resistance and amperage being so closely related in this example reminds me of the simple stuff we sometimes forget..and as Julie states' how the component" actually works as related to the rest of the circuit .I
I especially liked Ewatness's contribution..Watts=Volts times amps..While Ohm's law doesn't even mention watts..as heat.Well done Ewatness..Glad you got it fixed Bob! Thank's to all who contributed to my " learning curve"..

 

here's one:
Wire Terminals, Automotive Wire, Battery Terminals & Electrical Supplies

note: not an endorsement, just the first site I came across.

 

As I mentioned in one of my previous posts I work in the industrial controls field, I run my own industrial panel shop and I really feel stupid about having to ask for help on this. These trucks have such simple systems but there are still some problems that are hard to find if you don't take the time to think them out. I just didn't take enough time to thoroughly think it out. The little time I was able to spend on the truck was spent with a focus on the regulator. I'm glad we have the people on this board who were able to redirect me in the direction. Once the idea of a faulty circuit breaker was mentioned and I took another look at the wire schematic, it all came together. It was fairly simple problem, I just wasn't looking at it right. It always seems we overlook the simple stuff.

Oh well, it's another thing I'll put into the data bank and will be able to pull it out the next time some one has a similar problem.

 

Don't beat yourself up Bob

Its very easy to forget the basics and "overthink" the problem.

One of the best aspects of this site is that there is always someone willing to give you a smack on the forehead and steer you back in the right direction. I'm glad you got the problem fixed

Bobby

 

Hey Bobby, I knew you'd show up if there was an offer of free frosties, virtual or real

I agree, we have a really good group of people here.

 

Thank you CMORTIZ for the compliment. After I posted that simple formula I read the follow ups in the thread and decided I was way out of my league but this thread has been a clinic in auto electrics. Thanks Julie for the great info. I've re-read it several times trying to get it all down and will continue to do so. Remember, there are lot of us out here watching daily the great info and experience that is shared. KEEP IT UP!

 

Hey Bob!

I can't count the number of times I was looking RIGHT at a problem and couldn't see it, or looked at a drawing and the brain just would not make the trace - I call it getting "Scope Locked." It's like when you can't remember that certain Movie Stars name when you are talking about a picture.

I find that just having the "second set of eyes" can pick it out for you - and that's just natural. That's one reason I spend at least an hour here every day.....I learn new stuff, I review what other folks have said, and it really helps clear the mind.

I have read many of YOUR posts on a subject I just couldn't figure out and walked away saying "of course, why couldn't I see that?"

This place is invaluable. I wish they would do something about the search. I save the good threads to favorites to refer folks back, but I fear if we can't get back to retrieve these posts, this good info will be lost!

And that's a real shame. If you think about it from a technical information standpoint what we talk about here the best if sometime not the ONLY record of this stuff and the ONLY source for it.

GO FOR A DRIVE!

PS Hey Mertz...Ohms are camoflauged in the equation. Volts = Amps x Ohms. So resistance (ohms) is assumed (or is that "futile") - voodoo!

 

The other side is that if enough of us throw enough possibilities at the problem, eventually someone's suggestion will be the right answer.
Kinda the old saying "if you put enough monkeys in front of enough typewriters..."

 

But Alas! ..Never 'assume" anything! ..especialy on old ford trucks! LoL!

Luckily Bob had parts 'on-hand',..swapped them out and ..Voila!

I was kinda waiting for some multimeter readings from a couple of spots on the circuit breakers..at the jumper-bar in particular, maybe a voltage reading at both ends,when running ok ,then again at the same points when the lites went out or the engine died, then to narrow things down a little closer,with the ignition 'off'..a resistance # on the 1k scale across the jumper-bar ,or,with everything diconnected from both breakers to see what was happening..to say it in Spock terms..to get some 'knowns'..you now would have an idea 'what-it-ain't'..a re-check at the same points when it fails,when it's running fine,when it fails etc, would have satisfied my curiosity.Great thread though,easy enough for most to follow and humourous to boot Adding multimeter readings might have made things more complicated
I learned,studied,practiced,exercised,..and 'forgot' Ohms Law at least 3 different times so far in my life, but I get as much enjoyment from working around it ,I think,as much as you do..it;s very interesting and rewarding..and at times,fustrating Ha! Ha!
I've always been taught that with any 2 of the 3 Ohms law formulas (to be determined in each individual case), you can find the answer to your problem..most people don't go that far, they don't understand Ohms law, the multimeter (needed to get those #'s),electric power flow through a circuit(how it's supposed to work)..thru swx's,relays,cb's etc, much less how or when to plug those findings in a calculator...complicate that with what I jokingly call" WWII " aircraft electrics..can be quite confusing to alot of people..thanks for adding humor,science and theory to the subject.
BTW, as for Ewatness post..I just thought that was an 'easy way' to remember at least 'one " of the 3 formulas! LoL! W=V times Amps ,
W.V.A that's one I wrote down! learn something everyday!
The world may never know what the 'true' culprit was with Bob's truck with no measurements, and the part changed without them...but I think we can all agree, it was probably high resistance somewhere ,at some point across those cb's. Keep it Fun! Thank's Again!

 

After seeing this thread go on for days, I had to see watts up.

I can't resist saying this:

You guys are ohmnipotent!