Converting to dual alternators

[JasonS]

To store the electricity made by the 12 volt alternator. Now I can add any 12 volt goodies that I want.

There are other ways to do it - 24 volt inverters, dual output alternators, etc, but I liked this set up the best.

Why not connect the 12V alternator to the existing, first 12V battery in your 24V system?

 

[gimpyrobb]

Not too familiar with electric stuff, huh?

 

[JasonS]

Not too familiar with electric stuff, huh?

On the contrary, I have an advanced degree in electrical engineering. I have not done this before but I do not see any reason why it will not work. I'd love to debate the merits of the idea if you are up for it.

Here it goes:

You have two series 12V batteries in a 24V system. The lower battery operates at 14V nominal above ground. The second operates at 28V above ground. The concern with tapping the lower battery is that it will discharge that battery more than the upper battery. Still with me? You want the lower battery to stay at 14V, right? Take your second, 14V alternator, and connect it to the lower battery.

Why do you think that the world will end if you take a 14V source and connect it to a 14V battery?

 

[JasonS]

I guess you never heard about dinosaurs going extinct. What do you think caused that?

That was clearly beyond the capability of 14 VDC. Way beyond 28VDC, too.

 

[rat4spd]

Think deep cycle.

 

[DUG]

Why not connect the 12V alternator to the existing, first 12V battery in your 24V system?

I don't have any advanced degrees - I do have Rat4Spd on speed dial.

The REASON that I did not wire the 12 volt alternator to the existing 1st or 2nd battery in the 24 volt system is because I want them independent of each other. COMPLETELY.

This way, when I'm at DIRTBAG and I drain the 3rd battery (wired to the 12 volt alt) from running a microwave for burritos or a blender for margaritas, I still can start my truck. I won't need a jump, I won't need a push, I won't need anything, since I left the 24 volt side alone. And, as a side benifit, if a battery on my 24 volt side takes a dump, I can steal the 3rd battery to try and help things out.

Call me racist - but my 12 volt stuff doesn't mingle with my 24 volt stuff. 12 volts are for toys, 24 volts is to get me home.

 

[nk14zp]

DUG I used a 24volt napa relay for my 12volt alt. Used a switch first and forgot to turn it off and drained the 12volt batt.

 

[DUG]

DUG I used a 24volt napa relay for my 12volt alt. Used a switch first and forgot to turn it off and drained the 12volt batt.

What drained the battery? The only thing I have hooked up now is a voltmeter

 

[JasonS]

I don't have any advanced degrees - I do have Rat4Spd on speed dial.

The REASON that I did not wire the 12 volt alternator to the existing 1st or 2nd battery in the 24 volt system is because I want them independent of each other. COMPLETELY.

This way, when I'm at DIRTBAG and I drain the 3rd battery (wired to the 12 volt alt) from running a microwave for burritos or a blender for margaritas, I still can start my truck. I won't need a jump, I won't need a push, I won't need anything, since I left the 24 volt side alone. And, as a side benifit, if a battery on my 24 volt side takes a dump, I can steal the 3rd battery to try and help things out.

Call me racist - but my 12 volt stuff doesn't mingle with my 24 volt stuff. 12 volts are for toys, 24 volts is to get me home.

No problem. Yours is a completely valid reason to keep them separate. You may want to invest in a battery like a Concorde AGM which is meant to be used that way. SLI batteries will not last long if deeply discharged. The point of my first post was simply that it doesn't HAVE to be that way.

 

[nk14zp]

My OTR truck does.EDIT It does have a duel output alt.

 

[tm america]

dh it does work with the heater hose in either location .. you might have to angle the fitting toward the back of the motor a little but it clears no problem..i'm in the process of getting a plasma table right now so i will be making several different brackets and other specialty things for mvs...i love the hobby and do my best to keep prices down and quailty up..i like to make my mods match the trucks they are going on..i was thinking about making some grill gaurds for the m35 that have little m35s cut out rather than the expanded metal ones that are stock,.There are other things like mounting brackets for ac or hydraulic pumps for the multi fuel...these are just a few of the other things i'm working on right now to..i would also like to make some guards for the rear composites on the deuce as well...maybe with the same m35 cut outs as the grill guards..they would be availible with or with out the plate brackets and plate light... ...

 

[JasonS]

You can not charge 2 batteries in series with a 24v alterntor and charge the first battery seperately with a 12V alternator with a commom ground, at the same time.

Show me a working/existing system that does this.
QUOTE]

I have explained electrically why it can work. If you are sure that it "can not" work, it should be easy for you to explain why.

 

[rat4spd]

You can not charge 2 batteries in series with a 24v alterntor and charge the first battery seperately with a 12V alternator with a commom ground, at the same time.

Show me a working/existing system that does this.


I understand there are special alts for this, bit we were talking about simply adding a 12v alt to a deuce and charging a single(of the original 2) battery.

Consider that the 12v alternator is grounded to the engine, and your batteries are referenced to ground at 24v. Now connect your 12v alternator to the center of your two batteries. What have you just done? You just created a nice short to ground. You'd do just as well running a jumper cable from your 12v between batteries to your frame.

Let us say you isolated your 12v alternator from ground. Which voltage regulator is going to charge the first battery? They are both seeing the same voltage drop across that battery.

 

[DUG]

And now we know why I keep Rat4Spd on speed dial.

 

[JasonS]

Consider that the 12v alternator is grounded to the engine, and your batteries are referenced to ground at 24v. Now connect your 12v alternator to the center of your two batteries. What have you just done? You just created a nice short to ground. You'd do just as well running a jumper cable from your 12v between batteries to your frame..

I am not sure that I understand your comment. Are you suggesting that power will flow back into the alternator? Aside fron a few nanoamps reverse current through the rectifiers, power will not flow back into the alternator.

 

[JasonS]

Let us say you isolated your 12v alternator from ground. Which voltage regulator is going to charge the first battery? They are both seeing the same voltage drop across that battery.

Common automotive alternators are simple constant voltage sources (single stage charging). Each alternator simply trys to output it's set voltage 14, 28, etc. The charging rate depends on the battery state of charge, state of health, and the impedance of the alternator.

 

[rat4spd]

I am not sure that I understand your comment. Are you suggesting that power will flow back into the alternator? Aside fron a few nanoamps reverse current through the rectifiers, power will not flow back into the alternator.

I have since realized that. In my world, we have reverse current relays that protect against that.

Edit: to emphasize what DH said, and i previously said, which voltage regulator is going to do the charging?

 

[JasonS]

The 24 volt alt is charging 2 batteries in series. It is a poor setup but in ideal conditions(2 identical batteries drawing the same identical load) it works OK.

Not sure why you think it a poor system. All of the really large systems use series connected 2V batteries. It gets difficult to balance parallel strings of batteries.

If you were to add a 12v alt that simultaneously charged the first(chassis grounded) battery, that battery's condition would not be identical to the other battery's condition.

Now, you will have a (possibly) fully charged first battery and a second battery that is in some lesser state of charge. The 24v alt has no way of measuring either battery separately. It cannot charge either battery separately, so it will never charge either one or two correctly.
QUOTE]

This is not really true. Again, alternators do not measure or have any idea of what is going on (modern 2 and 3 stage alternators excluded). Each battery will see 14V. Obviously, the lower battery sees 14V. The second battery sees two items in series with it, a 28V source (alternator) and a 14V drop (lower battery). Mathematically, the top battery sees the difference between the 28V alternator and the 14V lower battery. I'll leave it up to you to do the math.

 

[JasonS]

Why such resistance to opening your mind and thinking about problems and instead burying your heads in the sand?

 

[JasonS]

YOUR WRONG, I'll let you show me a real life system.

And yet you don't even know enough to BEGIN to argue why.