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Unread 12-20-2007, 01:23 PM   #61
JeepHammer
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Quote:
Originally Posted by weatherford
I am installing 2 batteries on my CJ-5 and was wondering what the difference between jumping a dead battery off with another jeep and just putting a switch to isolate the batteries or run both. It seems to me it would be the same? I have read the threads on the subject but still wondering.

OK!

This is a good question...

On the most basic type of dual battery system, the two batteries are wired directly together,
Charge and discharge as one unit.

Roughly, this is what your current battery and starter system look like.



I show the extra wires to the starter solenoid mostly because they will come into play later, and I want you to be familiar with them.
............................

You will need batteries of the same Size, Age & Kind.
Meaning you can't run one old battery with one new battery,
One small battery with one large battery,
One 'Starting' battery with one 'Deep Cycle' battery.



There is no 'Redundancy' built into this system, it's simply more 'Reserve' energy to get things started.

Like running one VERY LARGE battery.
If you leave something turned 'ON' it's going to run both of them down since they are both directly connected to each other.


-------------------------------------------------------

An "ISOLATED" battery system could be talking about two different things, so we'll cover them one at a time as not to confuse the issue...

There are two kinds of 'Isolators', Battery isolator, and Charge Isolator.

1. Battery Isolator.
Commonly referred to as a 'Battery Isolator/Combiner' so it sounds more important! It's just a solenoid or relay in actuality.

Breaks the connection between batteries when you shut the vehicle off so if you leave something turned 'ON', it can't run both batteries down.
AND,
There are two BASIC ways to do this,

A. By using a Large capacity solenoid called a 'Continuous Duty' solenoid that connects the batteries together at full amperage output at all times when the key switch is 'ON'.
This is what most after market system use as a 'Battery Isolator'... Cheaper for them to buy, and easier for them to integrate in their 'Kits'.



This is basically a second starter solenoid that is 'ON' when the vehicle is running.
This version uses an oil pressure switch to connect the second battery to the system.
Some hook to an already overworked ignition system feed.

My version also has a 'Self Rescue' switch, so if the primary battery is completely dead, you can power the ignition with the second battery.

One draw back is, IF that isolator solenoid fails, you won't know it until you actually NEED to self rescue, and that is a Bad time to find out it failed!

Another draw back is it runs TWICE the current through your starter solenoid than was intended when you are cranking the engine.
(Which isn't a big deal if you have a good quality starter solenoid, but if you have one of the 'Discount Sore' kind...)
....................................

B. Two batteries feeding two starter relays.
This system has the advantage of having two COMMON type starter solenoids you can get at any auto parts stores,
And if one fails, it doesn't keep the second one from starting your vehicle.



This diagram DOES NOT show any way to charge the second battery, that is in the next diagram, I left it out to simplify the diagram...

This is called 'Seamless Operational Integration', or in Jeeper slang, 'Redundancy'.
If one battery or solenoid fails, you won't even know it until you do your maintenance on the batteries and cables.

Since the second battery MUST have a way to charge, and you want to keep the two separated when the key switch is 'Off' and the engine isn't running...
The system has to be 'Smart'...
It has to know when the engine is running before connecting both batteries together for charging...



Some systems use the key switch, but if someone leaves the key switch in 'Accessory' or 'Run', it will discharge both batteries since they are connected together.

An easy, but elegant solution is an oil pressure switch.
(The oil pressure switch I use is for Chevy pickups, Car Quest p/n PS 127.)
When the engine is running, the alternator is charging, and both batteries should be hooked together so they can charge at the same rate.

When the oil pressure comes up, it connects both batteries, and does just that, automatically,
Again, 'Seamless Operational Integration'. No extra step by the operator to make this work.
...................

The only exception is if you leave something on, and run down the 'Primary' battery to the point it can't even power the ignition switch...
Then you will have to use a 'Self Jump' or 'Rescue' switch to use the second, Isolated battery to get everything started and running...



This shows the addition of a cockpit 'Self Jump' or 'Self Rescue' switch.
It's a MOMENTARY switch, meaning when you let go of it, it will return to the 'Off' Position.
Activate the switch with one hand, and turn your key switch with the other, and you can 'Self Rescue'.
------------------------------------

NOW...
IF you have a winch, or some gigantic output alternator, you will probably need to run a Relay in the charging circuit, since deeply discharged batteries from winch use will draw more current than the oil pressure switch is intended to handle...

In this diagram, the oil pressure switch activates a 70 Amp automotive relay, and that should be plenty for even the largest of the 'Mega Output' alternators...



The oil pressure switch is a common one used on Chevy pickups for several years
(The oil pressure switch I use is for Chevy pickups, Car Quest p/n PS 127.)
The relay is easily available, and completely reliable, and will keep the contacts in the oil pressure switch from having to carry too much current.
One of the common uses for that particular relay is for the starter solenoid on Harley Davidson motorcycles, so it WILL carry some amperage.
----------------------------------------------------------------------------


2. CHARGE ISOLATORS.

A "Charge Isolator" is a gadget that will allow you to run two (or more) dissimilar batteries next to each other.

Be aware, The Charge Isolator has nothing to do with Combining the batteries together for extra starting power, it's simply there to make sure dissimilar batteries don't kill each other trying to get charged.



As you can see in the diagram, you will need to connect the two batteries together to load them.
If you run dissimilar batteries, Deep Cycle with Starting, or Larger with smaller, or an older battery with a new one, each battery will demand a different charge rate.

With a charge isolator, Each battery has it's own voltage regulator, so theoretically, no battery gets under or over charged.

Common isolators will charge up to 3 or 4 different Age, Size or Types of batteries (or battery banks).

If you use the same Age, Size, Types of batteries in your dual system, a charge isolator won't be necessary in most cases.


Last edited by JeepHammer; 12-20-2007 at 03:46 PM..
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Unread 12-20-2007, 03:40 PM   #62
LSUtiger
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http://www.jeepforum.com/forum/f8/dual-batterys-493384/ This was a page over.
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Unread 12-20-2007, 04:07 PM   #63
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If you use a continuous heavy-duty solenoid similar to that offered by Wrangler Power Products, that will work well. Normally, that solenoid is activated by the ignition 12 volts, so the batteries are isolated unless the ignition key is in RUN. That way, they'll both charge when the engine is running, but will not be connected to gether when the engine is off and you're using the auxiliary battery for such chores as winching.

Wrangler also makes a three-position switch deal, but they want a fortune for it -- about $150 if I remember right. But you can make your own wiht a three-position togle switch and a couple of panel lights. With that setup, the three positions do the following:

1. Connects the batteries together as I described above.

2. Never connects the batteries together - good if your auxiliary battery shorts out or is very low, so it won't suck up your alternator when you start the car.

3. Connects the batteries together with power from the auxiliary battery -- good for the situation you described. So if your main battery is really low (like you left your headlights on overnight), if you put the 3-position switch in the 3rd position, it ties the auxiliary battery in parallel to the main battery immediately, so you can use the power from the auxiliary battery to start the car.
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Unread 12-20-2007, 05:17 PM   #64
JeepHammer
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Quote:
Originally Posted by OldSailor

3. Connects the batteries together with power from the auxiliary battery -- good for the situation you described. So if your main battery is really low (like you left your headlights on overnight), if you put the 3-position switch in the 3rd position, it ties the auxiliary battery in parallel to the main battery immediately, so you can use the power from the auxiliary battery to start the car.
Got a diagram on that three position switch application?
Or can you explain how you wired that further?

As I get it, in the normal 'Run' postion, both batteries are tied to together for charging,
For me, that would be controlling the charing relay...

One position is 'Off' where neither battery gets charge.

And the third is just selecting the 'Primary' battery,
OR,
Secondary battery for single charge?

Am I close?
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Unread 12-20-2007, 05:18 PM   #65
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Quote:
Originally Posted by LSUtiger
Clearer question and objective this time.
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Unread 12-20-2007, 08:35 PM   #66
weatherford
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I understand this now but what is the bad thing about having a switch for left battery and right battery or bothand off. If 1 runs down you could just switch to the other one. Start the jeep and switch it to both? I am sure there is a reason. Would it not be the same as jumping it off with booster cables?
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Unread 12-21-2007, 03:12 AM   #67
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No diagram, but here's how I wired mine.

The heavy duty solenoid has two hi-amp terminals. A heavy duty battery cable goes from each battery positive terminal to one of the two hi-amp terminals. There are two low-amp terminals that activate the coil of the solenoid. One of those goes to ground. The other low-amp terminal is where the 12-volt source goes to activate the solenoid and tie the two batteries together. That terminal goes to the center contact of the 3-position switch mounted under the dash.

One of the outer terminals of the 3-position switch goes to a 12-volt line that is hot when the ignition key switch is put in the RUN position. The other outer terminal of the 3-position switch goes to the positive lead (through a fuse) of the auxiliary battery.

So. when the 3-position switch is placed in one of the outer positions, the center wire will be connected to the RUN wire. In that position, the batteries will be tied together when the ignition key switch is placed in the RUN position, so the batteries will charge when the engine is running. When the 3-position switch is placed in the center position, no voltage will be connected to the center wire, so the isolation solenoid will not activate, and the batteries will never be tied together. When the 3-position switch is placed in the other outer position, the 12 volts from the auxiliary battery will be connected to the center wire, which will activate the isolation solenoid and tie the two batteries together.

Yes, one could accomplish the same thing as the last position by jumpering the two positive battery terminals together with a jumper cable. But I ask you, as long as you have an isolation solenoid in the vehicle, why not take the time to install a $4 3-position siwtch, get about $1 worth of 16 gauage wire, and spend 20 minutes wiring it as I describe. Then, when the main battery is low, you don't have to get out in the ice and snow, lift the hood, get out your battery cables. hook the ends to the batteries, start the engine, unhook the jumper cable and stow it, close the hood, and get back in the cab. Instead, all you have to do is flip one switch on the dash!
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Unread 12-21-2007, 10:22 AM   #68
weatherford
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Sorry for the confusion. I was wanting to put a 4 way switch on battery box with no solenoid. Just hook batteries up so you could run left battery, or right battery or both batteries and shut off all. You could run off right battery, if it went dead just switch to left and start it up. Then switch to both to charge both batteries. Or you could run on both for more power. I was told that if one battery was dead and you switched to both position to recharge it it would explode the dead battery. This is where I got confused. Switching to that position would be just like jumping it off with cables? I am not trying to be cheap just simple. I go in remote places and battery failure is not an option. I dont mind lifting the hood to switch positions on switch. My thoughts are the more wires and ect. you have the more chance of something going wrong. I have bought a duel box from wrangler nt and 2 yellow tops to go in it.
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Unread 12-21-2007, 10:55 AM   #69
JeepHammer
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Quote:
Originally Posted by weatherford
Sorry for the confusion. I was wanting to put a 4 way switch on battery box with no solenoid. Just hook batteries up so you could run left battery, or right battery or both batteries and shut off all. You could run off right battery, if it went dead just switch to left and start it up. Then switch to both to charge both batteries. Or you could run on both for more power. I was told that if one battery was dead and you switched to both position to recharge it it would explode the dead battery. This is where I got confused. Switching to that position would be just like jumping it off with cables? I am not trying to be cheap just simple. I go in remote places and battery failure is not an option. I dont mind lifting the hood to switch positions on switch. My thoughts are the more wires and ect. you have the more chance of something going wrong. I have bought a duel box from wrangler nt and 2 yellow tops to go in it.
Yes.
Manual Battery (bank) isolator switch.
Popular in marine applications.
Check any marine application web site


Since one battery will be completely isolated, you will have to run some kind of charge circuit to it, and I'm afraid a battery charge isolator is the only way to do that...
With out connecting the two batteries together so they could potentially discharge...
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Unread 12-21-2007, 10:56 AM   #70
kundilini
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Cool I was planning to do this and now by this spring it will be in thanks!
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Unread 12-25-2007, 12:42 PM   #71
petey156
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where can i get a continuous heavy-duty solenoid?
advance
napa
autozone....

thanks
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Unread 12-26-2007, 09:05 AM   #72
JeepHammer
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Quote:
Originally Posted by petey156
where can i get a continuous heavy-duty solenoid?
advance
napa
autozone....

thanks
NAPA that services big trucks, or any big truck parts house would be where I'd start.
Big trucks use continuous duty solenoids that will work for our Jeep applications.

The one used by Wrangler looks suspiciously like the accessories continuous duty solenoid used by big trucks like Peterbuilt and Kenworth, and by a lot of boat manufacturers, but I can't get a good enough look to tell for sure...

A lawn mower starter solenoid will work also, just don't expect it to live as long as one of the big continuous duty solenoids that are built for this very application...
But a $8 or $10 each, it's a well priced alternative, and a 'Quick Fix' off the shelf if you need one to get you up and running on the road somewhere!
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Unread 12-27-2007, 09:14 AM   #73
buddy
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JeepHammer, you definitely know more about how all of this works than I do. There is no disputing that.

Quote:
Originally Posted by JeepHammer
Since one battery will be completely isolated, you will have to run some kind of charge circuit to it, and I'm afraid a battery charge isolator is the only way to do that...
However, there is now something called an Automatic Charging Relay, which is similar to an isolator, but is solid state & has no diodes to go bad.


250 amp version


120 amp version


60 amp version

They are a little expensive, but are a much more reliable item than a traditional isolator. Basically, they are "smart" relays.

Also, they are dual sensing, so you can hook up an alternative power source, i.e., solar panel, shore power convertor, windmill, etc. & it will charge you're system automatically.

Just more information for this great thread!

Later,
Buddy
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Unread 01-03-2008, 11:21 AM   #74
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Thanks Again! You Guys Are The Top Of The Mountain!
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Unread 01-09-2008, 10:37 AM   #75
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The reason for fine wire is that the electrons (current) travel on the surface of the conductor (wire). So the finer the wire, the more surface area in a given size of cable. The only problem I see with the dual battery "self jumping" feature is that if one battery is dead (or severly drained down) the charged battery will loose some of it's power "back feeding" into the low battery in the schematics shown. The 2 circuits would need high amp diods which act as "check valves" to allow current flow towards the starter only and not back to the low battery.
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