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post #1 of (permalink) Old 12-10-2002, 07:16 PM Thread Starter
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A Few Dual Battery Questions!!

Well since this topic has been heavily discussed you guys will be happy to know that I read through all the old post and only have a few questions!

First off I already have an oil pressure switch but nothing is plugged into it, just a wire on the end of the sender for the oil temp gauge. Should something be plugged into the pressure switch? and should I get a new one when I do the dual batterys? Napa part # OP6620

Second I have a few questions about the Wiring diagram, I guess it is TR's. Do these have to be special solenoids? I obviously already have one running and wanted to get a second cheap one like it for the second battery. but I found this napa part number ST95 and it is $30, so I am guessing it must have different rating.
#4 on the diagram is just any switch you want to use for in the dash mount right?

And my final questions are just going to confirm the charging process. When the switch is off only battery 1 will be getting charged and used until the oil pressure builds up. Then both will be getting charged. Will the 2nd battery then only be used when the switch is on?

And then wired this way if the lights got left on the switch could just be turned on to use battery 2 for start up? Thanks for the help. Mike
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post #2 of (permalink) Old 12-10-2002, 09:04 PM Thread Starter
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Re: A Few Dual Battery Questions!!

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post #3 of (permalink) Old 12-11-2002, 08:33 AM
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Re: A Few Dual Battery Questions!!

1. The solenoids are Continous Hold solenoids. They're made to be working ALL the time...
2. Change the oil pressure switch.
3. Isolating Solenoid is Part Number ST95, 80 Amp, continuous duty, 3-terminal, 16-20 ohm coil.
4. I'm not a fan of this type of install.
5. I favor a fully isolated dual battery system using a quality isolator .
6. Both batteries can fail when placed in parallel without isolation if one fails.
7. This circuit will provide for self-Jumping. One battery is disconnected until oil pressure builds. The second battery is the one you use as the jumping battery..
8. For self-jumping you use
a. Jumper cables, or
b. Move the starter cable to the second battery, or
c. A use second set of starter cables and starter relay, or
d. A battery management circuit.
9. When the oil pressure swtich is on both batteries are charging/discharging.
10. So the loads are in common until the engine's turned off.
11. I favor splitting the circuits to one or the other of the batteries under all conditions.
12. Remember,
a. If one battery is starting to fail,
b. Both are going to take on the charactericts of the bad one.
c. It's like two buckets of water
d. With a common pipe in the bottom
e. And a hole half way up one of the buckets.
f. Because both buckets share a common "bottom" they also cant' be filled any furhter than the bucket with the hole.
g. Try to overfill the "good" bucket only means the "bad" bucket will drain the "good" one down to it's level.
h. In a non isolated dual battery system this can lead to:
h1 Over charging.
h2. Regulator problems.
h3. Alternator problems.
h4. Battery problems.
i. The problem is that often the owner doesn't notice it till it's too late. This is a gradual process.
j. In fainess to this system, using Optima batteries would be a good choice to lesson the problems associated with this sytem.
13. So as you now understand, if one battery is not fully charging... the second one also will not fully charge no matter how fast that alternaor is turning.
14. This limits your ability to "go to the power well," so to speak, and may compermise your ability to self-jump.
15. Here's a good Dual Battery write up I like.
16. A good dual battery installation is neither hard, nor too expensive, but it does take planning and some work.
17. Study hard, think more, ponder some, and pay your money and take your choice.
18. Best of luck on your choice. [img]images/graemlins/grin.gif[/img]

Last edited by LEVE; 03-24-2009 at 07:45 PM.
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post #4 of (permalink) Old 12-11-2002, 10:37 AM
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Re: A Few Dual Battery Questions!!

</font><blockquote><font class="small">In reply to:</font><hr />
using a quality isolator.

[/ QUOTE ]
This is the key point if you go this route. The 20 specials from an auto parts stores are not great, spend the $$ for a good one. When I did large stereo installs we used to use isolators until we started checking voltages and realized how much voltage loss the isolators have (some up to 2 volts, not counting loss in cable runs), so we started using the large relays instead. There are some isolators that have very little voltage loss, but expect to pay good money for it.
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post #5 of (permalink) Old 12-11-2002, 03:13 PM Thread Starter
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Re: A Few Dual Battery Questions!!

Hi thanks for the lengthy reply, I see why the isolator method would be better. How much is a good isolator going to cost? Around $50? I am poor so was hoping the easy way with 2 new batterys would be ok. For now I will probally just end up building the tray intil I figure out exactly what I want to do.

This may sound dumb but how long does a battery take to drain? Since I want to wait to do it the right way I could probally just put a second battery in the tray (not hooked up) for now incase the other one dies. Mike
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post #6 of (permalink) Old 12-11-2002, 03:30 PM
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Re: A Few Dual Battery Questions!!

1. An good isolator can run $35 on up... sky's the limit depending on the marketing hype and the name. IMHO an diode's a diode's a diode...
2. The length of time it take drain a batter depends upon the load. A small load can run for several weeks... like a stereo memory. A large load like a welding with a battery can drain a battery very quickly.
3. Remember with an Optima that you can mount them in ANY orentation...so if they don't fit somewhere uprght, they may fit on their sides.
4. I like Optimas.
5. You may want to look a the Exide Select Orbital battery... It's a little less cost.
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post #7 of (permalink) Old 12-12-2002, 06:18 AM
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Re: A Few Dual Battery Questions!!

</font><blockquote><font class="small">In reply to:</font><hr />
Remember with an Optima that you can mount them in ANY orentation

[/ QUOTE ]

That is not quite right [img]images/graemlins/grin.gif[/img] Try putting them on their side with the sideposts down on yer metal floor [img]images/graemlins/laugh.gif[/img]

B.t.w. Over here in the U.K. we've seen quite a few problems with Optima's lately, so many in fact that a lot of the suppliers here don't stock them anymore. They've switched over to the Exide Select Orbital ones and say that they are better than the Optima's although I haven't got any experience with either of them. Just what I've heard and read...
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post #8 of (permalink) Old 12-12-2002, 07:12 AM
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Re: A Few Dual Battery Questions!!

It maybe more than you want to spend but you can buy a duel battery kit from summitracing.com for about 100 bucks. That will give you a 250amp solenoid and all the wire to run it. Also 4wd.com has it also, but it cost a little more. Here is the link to that site.

http://www.4wd.com/shopwrangler/Prod...oductSku=40102
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post #9 of (permalink) Old 01-17-2003, 05:40 PM Thread Starter
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Re: A Few Dual Battery Questions!!

Well it is just about that time. After more planning and research I was going to do the isolator way but now am thinking of the solenoid way.

It seems that the only pro to an isolator is that if one battery fails they both wont. The cons are that it is expensive and puts a major strain on the alternator.

The solenoid way seems to cost less, and I also read that is how stock vehicles come that have dual batterys. If I am using 2 brand new batterys of the same kind wouldn't this method be fine?

Now according to the TR diagram if something gets left on, I could just flick the switch and battery number 2 would start the jeep? I wouldnt have to use cables across the 2?

and the final question: say i didnt want to use a continous hold solenoid connecting the batterys and didnt use the oil pressure switch. then just wired this solenoid to a switch. wouldn't this allow the battery to only be charging and discharging when the battery is on? thanks for the help.
Mike
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