Seems we're arguing over convention than actually what's happening, but that's just an observation.

Bill, I'm confused with your second drawing with the colored arrows: what prevents the green arrow that turns right towards the right battery negative post from turning left and shorting the positive of the left battery to ground? I don't remember my electrical engineering class very well anymore, so I'm probably just missing something.

I'd be very interested in the outcome of this project, whether it will work or it won't, the problem is is puzzling to my mechanical mind.

 

And here is why you are wrong. In an earlier post I mentioned Conventional Current Flow (positive to negative) erroneously. To be correct I should have said Electron Flow (negative to positive). What the heck, it's been 30 years since I have learned this and as I get older little used things like this slip away.

So, I did a google search because I know I am correct.

From: Conventional Current vs. Electron Flow

Your theory is good subford but you have to remember that diodes have been around long before Electron Flow Theory and their schematic symbols were never changed. Read the last 2 paragraphs on the quoted text.

Technically, we are both correct on theory, old versus new, but your diodes are reversed in your diagram.

BTW, my wise old uncle taught me electronics in my youth. In the 70's I took an Electronics course and again I took another in the late 80's. In the 70s there was no discussion on Electron Flow. It was a new thing in the 1980s.

 

I can answer this, there's a diode to the left battery.

His drawing has other problems, first the ground connection between batteries would short the first(left) 12v battery. If the diode closest to ground was turned around it could in theory help charge the second battery if both batteries were completely dead. But in practice this wouldn't do any good, the batteries can't charge fast enough for it to matter.

Second he has the second(right) alternator grounded, this would be correct if it is a 24v alternator, but not for a 12v alternator. With a 12v alternator grounded the second battery(right) would never go over the 12-14v charging voltage that alt puts out.

 

Very True........As we just learned....

 

This is a rather useless argument, but I'll stick my nose in anyway. I'm no elctrical "expert" but my stuff just keeps working. It seams to me that because diode symbols are based on "conventinal theory" ie positive to negative, then the only incorrect diode in his diagram is the one to ground between the two batteries.

But as I said this is silly because NONE of those diodes are needed.
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kcorey, subford, and greenwoodford, is this stuff that I'm suggesting making sence to you guys?

Greenwoodford, any idea how long your out of country?
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Edit, I think it just hit me what he was trying to do with the diodes and ground between the two batteries. It would be correct if the second alt is 24v, but also un-needed, expensive, and more to go wrong.

 

And the two from the field connections on the alternators. Current must flow to the ALT from the battery to energize the coils. The diodes in the diagram would act to block the current.

Diodes would not be necessary in this circuit. A diode could be used as a fail-safe but is not necessary.

So, after all this, wouldn't it be cheaper/easier to replace the bulbs in the lights he has with 12V bulbs or just buy the proper lights?

 

Yes, all true.

Didn't this thread start with a suggestion to just use different lights? That doesn't answer his question though. And of course I personally think my system is a good idea. It's not far off from the backup/Acc system I run in my truck.

 

I am pretty much lost on all the technical jargin and which way the electrons flow through this diode etc. I can see how the whole system would work together, but why it works is beyond me.

I'll be deployed until sometime next summer as of right now. I am a mechanic for the army, but schematics and electronics have always been a week area for me. All of the green and brown and yellow arrows in the diagrams above are just making my head hurt to tell ya'll the truth.

To put the issue at rest once and for all, simply swapping the bulbs (buying new ballasts) is not an option nor cost effecient. Each ballast is around $200 and the bulbs are non-replaceable. Another reason for wanting to do it this way is I just want to have something different.

 

Converting you truck to run on an alternative fuel would make it different. It would not be cost effective. Same with these lights. Not only is it not cost effective you run a very real risk of fire.

I am sorry about the headache...BTW, we didn't discuss PIV ratings and current rating of these diodes, so you are only getting half of the picture.

 

Exactly what I was getting at: if current flowed the direction of the green arrow through the first diode to/from ground, what was keeping it from flowing the same direction through the second diode to the left battery positive.

 

My drawing would not work, it looked good on paper but when I breadboard it, it does not work.
You are right the left battery would be a short to ground.

By the way the alternator Battery out windings are not excited by the BAT stud on the alternator as was stated. The Field winding is excited by the "A" wire and the alternator is turned on by the "I" wire that are not in the drawing so that it was easier to read.


I have no idea where he came up with an GM alternator from the drawings. I always talk Ford alternators. The drawing of the alternators and batteries was copied from another drawing on Battery Isolators as I did not want to take the time to draw the alternator.

All of my textbooks say the current flows against the arrow in a diode.
I still do not see anything wrong with my diagram and everything they have said about it is wrong.

I have heard of the Conventional Current but all the teaching and books I have had just said it has not been used for a long time and I have never used it 40 years working with electronics.
This below is about all they said about it it and when on to teaching electron flow.
“Conventional Current assumes that current flows out of the positive terminal, through the circuit and into the negative terminal of the source. This was the convention chosen during the discovery of electricity. They were wrong! “

I guess some still call a Capacitor a Condenser also.

 

I believe that the reason for the arrow on the diode is to point the direction of "conventional" current flow or positive to negative. That helps me discern whether or not there is a circuit through the diode.