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  #1  
Old 02-27-2000, 03:44 PM
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Default Homemade dual battery isolator ??

I remember CJDave touched on how he creates his dual battery isolator with a heavy duty, constant service relay wired to an oil pressure switch. Here's the question...If you're cranking the engine (trying to start it) you don't have enough oil pressure to push the switch, right? So you are only on one battery to start the engine... If that battery is dead, how do you get juice to the starter...Can you run a second wire to the solenoid that is switched ( ) power, so you can flip the switch, turn the solenoid on hot, and jump yourself? Would you want to? It seems to me that it would be a lot easier to run my solenoid activation power off of the ignition switch...have it on accessory and you've got one battery. Key off and you've got one battery. Turn the key on, you've got two...winch, start, whatever. What am I not thinking of? This seems easier and cheaper....(which, if I've learned anything in my limited jeeping experience, is usually worse than harder and more expensive [img]/wwwthreads_images/icons/smile.gif[/img]).

Measure once, cut twice...or is that the other way around?
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Old 02-27-2000, 04:32 PM
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Default Re: Homemade dual battery isolator ??

Yep farmjeep, you are correct. I mentioned this to CJdave in one of the many replies to his post. He suggested that if you want to use both batteries for cranking (since the oil press sw will be open circuit as you said) have a manual toggle switch running in PARALLEL with the oil press sw that, when fliped on, connects the soleniod to ground enabling both batteries to be joined while cranking. i.e. if either the switch or the oil press switch is a closed circuit, the batteries are acting as one.
Have you built yours yet? I'm working on a tray to hold both batteries right now.

[img]/wwwthreads_images/icons/cool.gif[/img] Big Ed
<font color=red>'88 YJ, 4" susp,3" body,33's,283 Chevy V8,TH350,4.11's,D30,D35c</font color=red>
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Old 02-27-2000, 05:44 PM
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Default Re: Homemade dual battery isolator ??

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...
--------------------------------

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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Old 02-27-2000, 05:49 PM
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Default Re: Homemade dual battery isolator ??

I have been doing all the measurements for the cables, trays, and etc. I think I'm going to end up putting one battery in the stock location, and one on the opposite side of the engine bay...Here's another question that happened to come to me then...it seems as though the "primary" battery is the one that will be doing the most starting and cycling...would I want to put a deep cycle in as my primary and have a good starting battery backup...or have 2 deep cycles...or have two starters...or have a starting primary and a deep cycle backup?
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Old 02-27-2000, 07:03 PM
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Default Re: Homemade dual battery isolator ??

[img]/wwwthreads_images/icons/smile.gif[/img] Man, it's about time somebody posted the dual battery system in something besides the written word. There IS one little detail, however that has been in the back of my mind, and that IS....suppose little cousin Leroy sat his butt in your Jeep and played with the headlights, and went off and left them on. the next day, the primary battery is on it's kazooka, and the Jeep won't even fart, much less crank. In that case, the "shoo-fly" around the Hobbs is useless. The pushbutton "shoo-fly" (that's railroadese for SHUNT)needs to get power from TWO sources, and have a diode on each feeder. THAT would be the ultimate setup! And I don't think that I would mix batteries. The secondary battery is supposed to be the accessory battery so you won't play the radio too much, and have to walk home. You can drain it way down if need be.[img]/wwwthreads_images/icons/smile.gif[/img] Farmjeep, when corn season comes around you are going to have all the national magazines interviewing you, and wanting to know how you thought up all this custom Jeep stuff, yet still continue to feed a hungry nation. Raising food and fiber, folks; that's what it's all about.[img]/wwwthreads_images/icons/crazy.gif[/img]

CJDave
I never believe any statistics unless my moonguys [img]/wwwthreads_images/icons/crazy.gif[/img][img]/wwwthreads_images/icons/wink.gif[/img] made 'em up themselves.
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Old 02-28-2000, 12:33 PM
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Default Re: Homemade dual battery isolator ??

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...[img]/wwwthreads_images/icons/wink.gif[/img])

If Chris Columbus "Discovered" America (with 25 million already here), Can I Go "Discover" Florida?
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Old 02-28-2000, 01:03 PM
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Default Re: Homemade dual battery isolator ??

[img]/wwwthreads_images/icons/tongue.gif[/img] I'm still having a devil of a time explaining this to my moonguy [img]/wwwthreads_images/icons/smile.gif[/img] crew chief. He claims that the second battery could be down on it's kazooka if Ditzelfritz left the optional hamburger bum warmer on "low" and nobody noticed. So he's saying that to be sure that cranking could take place, that the by-pass needs to get it from either source, with diodes so it won't try to charge, or try to crank the jeep thru the control circuit. Normally, this moonguy[img]/wwwthreads_images/icons/smile.gif[/img] is pretty sharp, and he knows how careless his bunch can be about leaving things "on" when they are crocked and hanging around the Jeep. If they have enough beer, then THEY are down on their kazooka.[img]/wwwthreads_images/icons/crazy.gif[/img]

CJDave
I never believe any statistics unless my moonguys [img]/wwwthreads_images/icons/crazy.gif[/img][img]/wwwthreads_images/icons/wink.gif[/img] made 'em up themselves.
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Old 02-28-2000, 01:26 PM
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Default Re: Homemade dual battery isolator ??

I agree with CJdave's moonguy crew chief. The dead batt would be robbing cranking power from the secondary batt (which is fully) charged. In the ideal situation, you wound want a big ass diode to keep current from flowing INTO the primary batt during cranking only. However, big diodes can cost money, get real hot, and often still break! Even if the primary batt is completely dead, the secondary batt should still be able to crank over the motor, just like using jumper cables. Nice schematic mr rush, that's the way mine will look, no diodes.

[img]/wwwthreads_images/icons/cool.gif[/img] Big Ed
<font color=red>'88 YJ, 4" susp,3" body,33's,283 Chevy V8,TH350,4.11's,D30,D35c</font color=red>
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Old 02-28-2000, 02:07 PM
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Default Re: Homemade dual battery isolator ??

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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Old 02-28-2000, 02:50 PM
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Default Re: Homemade dual battery isolator ??

[img]/wwwthreads_images/icons/tongue.gif[/img] What is the drill if cousin Leroy runs the #2 battery completely down?[img]/wwwthreads_images/icons/crazy.gif[/img]

CJDave
I never believe any statistics unless my moonguys [img]/wwwthreads_images/icons/crazy.gif[/img][img]/wwwthreads_images/icons/wink.gif[/img] made 'em up themselves.
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