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There are a couple of ways to do the dual battery thing. See the attachment for the way I intend to do mine. It may give you an idea or two....
Or, it may just be a waste of time... I never know...
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Your stock ignition switch is way over taxed the way it is.
Adding something else to it, especially something high drain, may be, 'the straw that broke the camels back', so to speak...

Attached is a rough wiring diagram of the set up I'm going to use.
It uses a remote switch. Mine will be mounted in dash, but some might want to hide the switch, or put it under the hood.

Factory Starter Solenoid,
Self explanatory.

Continuous Hold Solenoid,
Large truck or Heavy equipment supply house, and Maybe NAPA. $13 for mine.
(They may call it a large accessory really.)


Oil Pressure Switch,
Normally open 10 lb. Hobbs switch is what I have planned. About $10 at NAPA.

Self Start Override Switch, any automotive flip switch or normally open push button.
$2 at NAPA.

I use 2/0 (not 2 Ga) fine strand welding cable for all of the heavy battery to starter connections. I use solid copper ends, crimp them down, solder them, and use heat shrink tubing.
I don't have failures.

Hope this helps some, Aaron.

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 

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That's why I power my oil pressure switch and bypass switch from the SECOND battery, so the solenoid cam be triggered even if the first battery is missing!

Have a look at the diagram again....

(define: 'kazooka' please.../wwwthreads_images/icons/wink.gif)

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 

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I get what you are saying now! You are saying that if the primary battery is completely 'kazooka', then you are worried that it will absorb the current being produced by the second Un-kazooka battery...

That shouldn't be a problem if you just flip the switch and hit the key.

A completely kazooka battery doesn't have any polarity, so it's just a giant capacitor at first...
It should start even with a completely kazooka primary battery.

If you are worried about someone leaving the override switch on, use a momentary push button, like an old time starter button.

Take a look at the new diagram. It takes the kazooka primary battery out of the circuit entirely... That should stop the problems...
It takes a 1/2" or 9/16" wrench and two minutes before you try to start the vehicle....

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 

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I guess I'm still not getting it. I don't see how the #2 battery could be drained with the engine off on my diagram...
Someone please point out the flaw.
If the engine and override switch are both off, how can #2 get drained? What did I overlook?

I would really like to see the diagram you are talking about with the diodes... Anybody able to post it?
(The best ideas are stolen ones, the R&D are done, so somebody post!)

If you want low cost diodes that will take all charging and load in a vehicle except the starter, try half of the rectifier bridge out of an alternator. Fords work the best for that...

Later folks, and thanks for the help. Aaron.

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 

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IT WORKED!!!! DON'T KILL THE BOX!!!!

Almost a real schematic!
That should loose 90% of the home builders....
I see what you are talking about now...
Dual isolation both directions.
I don't know why I couldn't get a grip on that...
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I think if I was going to go to the trouble to build and maintain that, I would just use the voltage cut outs like my Cad uses.
The voltage drops below 12.0 volts, the cutout disconnects the battery from the cars load centers.
You have to turn the key to get it back.
Comes in handy when I leave the interior light on all night./wwwthreads_images/icons/tongue.gif
You loose all your radio pre sets, but the friggin' thing starts!!! And I don't have to drag jumper cables in the rain!
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I intended to run everything off of both batteries when vehicle is running, and nothing off of the second battery when the vehicle was not running. If I ran the first one down, the second would be a self jump...
Maybe come in handy for tobacco juice welding too...../wwwthreads_images/icons/wink.gif
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I can't believe this thread went this long and not one harsh word! COOL!
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Z50K2
For the question about the continuous hold solenoid, It will handle very large amp loads for a short period of time.
The ones I have are rated at 130 amps continuous, and 300 amps momentary. That should be enough to jump a hard to start Jeep.
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1&2 are continuous hold solenoids.
3&4 are Oil pressure switches.
5 is a 'Either/ Or' manual selector switch.

When the oil pressure comes up, the continuous hold solenoids are pulled in, and the batteries can charge on a common line.

The #5 switch allows either battery to be used to start the vehicle.

I think I would use a three position switch rather than a double throw on #5.
Three positions would allow the center to be 'Off', instead of draining one battery all the time by keeping one of the continuous hold solenoids activated continuously.

It is a good idea, but pretty busy...
It wouldn't take much of a diode to do what you want here. One diode out of a alternator rectifier bridge should do the trick, and do it cheaply. There are normally at least three positive and three negative diodes in a rectifier bridge.

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 

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*Blackjack* said,

*you could use pressure switches, but i prefer spst switches (i am a manual control kind of guy). this would require three toggles to run the system (a drop in the bucket to the total number that is planned for my jeep)*

I'm that fat, lazy, Cad driving kind of guy, I like it automatic.
Too many switches confuse me. (so does anything to do with a woman or the IRS...)
I was thinking Hobbs switches because of CJ Dave's original design...
Sorry dude! Didn't mean to butcher your schematic....
It is sound thinking, and someone did put a lot of thinking into that design...
Talented bunch on this thread....
That's probably why I had to have it spelled out for me.... I can be a little thick headed at times. This was one of them...
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*acemeck* asked,
*Would the system you drew up have double the available amperage if 6 volt batteries were used in series/parralell fashion? Probably complicating things too much but I just couldn't resist.*

In parallel, like it is in both diagrams, the voltage would stay the same, but double amperage.
(like jump starting a car)

In series, the amperage would effectively stay the same, but the voltage would double.

In series/ parallel with 6 volt batteries, you would have to have a screw loose to mess with it!
I used to do everything from large trucks with series/ parallel switches on 6 volt batteries that charge on 12 volts and start on 24 volts.....(Insane!)
To golf carts that have three sets of 6 volt batteries wired for 12 volts, and those three 12 volt feeds wired in series for 36 volts! And it has a separate 6 volt battery to kick the switches with...! (what the hell were the designers thinking!? Or Smoking?)
That will make you crazy in a hurry!
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*StooperWilly* asked,
*Can you label the components to your latest diagram? I see you have numbers on the things but can you make it easy for the electrical illiterate?*

Yup, I can.
Read the post that goes with the diagram. (it's down toward the bottom a little...)
I name and discuss the switch functions...

The little red thing with the arrow head in the box is a diode.
A diode is a one way check valve for electricity. It goes through one way, but not the other. The arrow indicates the direction it will go.
You will need a diode that will handle about 3 amps for this application to be safe.
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If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
 
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