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post #1 of (permalink) Old 12-15-2007, 05:55 PM Thread Starter
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Electrical Question

I have a dual battery kit in my cj7. I have 2 brand new optima red tops in there. My volt gauge always shows about 11.8 volts when idling with nothing on. If I test the posts on my batteries, they are around 12.2 or so.

I hooked up a voltmeter to my gauge, it was reading correctly... so the gauge works and is within margin.

when I turn on my electrical stuff...

heater... it drops to about 11.0 volts
heater + lights... it drops to about 10.4 volts
heater + lights + compressor... it drops to around 10.2 volts

I understand it dropping, but it seems like it's very marginal here? shouldn't it always be over 12 volts?

I tested my alternator at the local store, they said it was fine. I pulled fuses, to see if there was a load on something else, and there wasn't. I tried the old headlight test on the wall to see if they got brighter when I turned the engine on, they don't really change much (probably from good optima batteries)

My question is, is this normal with my setup?
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post #2 of (permalink) Old 12-15-2007, 07:23 PM
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No. You have a problem. It should be 14 to 14.5 with the engine running. Could you have a slipping belt? Loose connection? What happens to the voltage if you turn the idle speed up some?

Where did you have the alternator tested? Some of those places don't do a very good job.

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post #3 of (permalink) Old 12-15-2007, 07:39 PM
 
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I would also look at the ground connection between the dash volt gauge and the battery. In order for the gauge to read the correct system voltage, the ground connection has to be good.

I had similar symptoms once with my 1986 XJ; it turned out to be the ground strap between the firewall ground connection and the engine block was frayed. I ran 3 #10AWG sized wires home run to the negative battery post and the problem disappeared.

Good Luck!!
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post #4 of (permalink) Old 12-15-2007, 08:03 PM
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I agree with checking for belt slippage, and make sure that all connections to the alternator are correct. Also check the voltage regulator. When I bought my 73 cj5, I drove it from Atlanta to Memphis,and almost home before my optima red top gave out. The local big name auto parts place gave me 3 seperate alternators and even though they said that all three were working properly, they werent. After the second one was tested "OK" I drove it to the next town, and had it tested by a competitor. it to was bad, I took it back, got another one and did the same thing.All three were reading 11.something. This time, I purchased one from the otherguys and we all lived happily ever after. They even let me keep the voltage regulator they put on to test my old one, which wasn't bad. You did good buying the optima!
Just my .02
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post #5 of (permalink) Old 12-15-2007, 10:23 PM
 
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I'm sort of having issues, similar...
While idling fast 900-950rpms... I'm reading 14.5-15v.... (nothing on).
While idling at 700-750rpms... I'm reading 13.5-14v.... (nothing on).
Warm idle with lights on... I'm reading 12.5-13v....
Warm idle with dual flex-a-lite fans running... I'm at 11.5-12.5v....
Warm idle with lights and fans... I'm at 11.5-12v....
While driving with nothing on I'm around 13.5-14.5....
While driving with the fans and lights on I'm at 12.5-13v....
While driving with fans and lights with the blinker it jumps from 12.5 to 11.5 (as the turn signals goes on and off)... Any thoughts?
I think with the fans & lights on they draw way too much energy for this Alternator to maintain or charge... (Constantly).
Any suggestions on what alternators I should look for in the JunkYard? V-Belt perferably... Something of 115amps or bigger?
post #6 of (permalink) Old 12-16-2007, 06:44 AM
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You don't need a bigger alternator. You just need one that works properly. You might have a slipping belt. If not that, you probably have a bad diode or two. Find a shop that can test the alternator under load all the way to its rated current output.

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post #7 of (permalink) Old 12-16-2007, 07:08 AM
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I know people that run the "optima" batteries, I have always ran the largest Interstate Megatron battery that will fit in my tray and have had no problems whatsoever. Most stock Jeep alternators, the older ones, without A/C, power windows, etc. are only rated for approx. 63 to 68 amps running under load. I have had both of my latest alternators rebuild by a reputable shop where they replace everything except the case. When I had the last two done they upped them to 94 amps, the guy told me they could do 120 amps but it wouldn't work properly below 2000 rpms, He told me the 94 was a good replacement because it works just fine at a low RPM. I ran a new ground to the dash and firewall and also ran a separate ground to the alternator itself from the battery and my voltage will not drop below 13.5/14.0 volts with everything turned on. Since I have done this all my lights are brighter the heater fan is smoother and everything electrical works better. The cost was only a whoppin 64.00 and it was better than buying new. By the way the first one I had rebuilt was a "new" rebuild and it never worked correctly and cost more than getting mine rebuilt by the Amish folk. This is just my .10 worth and what I know to be factual, I only do what works, for me.

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post #8 of (permalink) Old 12-16-2007, 07:18 AM
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My CJ does something very similar to [email protected]'s. The battery still charges so I have not worried about it. The lights, chevy heater, and blinkers all impact my voltage reading.

-- mike
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post #9 of (permalink) Old 12-16-2007, 07:56 AM
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Battery life no matter how good they are is only good for about 3 years, anything more and it starts to put a load on and wear out your alternator. Just because it works and has juice don't mean nothing, I replace my batteries when they become 3 years old no matter what, course I get them for free when I need them, but I still replace them after 3 years. I have found my alternators last longer. This is only my .10 worth and I only do what works, for me.

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post #10 of (permalink) Old 12-16-2007, 08:05 AM
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I

If one of the batts is bad. Even a new one can be. Like a bad cell or something it will draw alot and will drop the total volts the system is putting out.. The optima that i had in my truck was going bad. It had something like 11.6 and when the motor was running it was only 12.5 I did the alt swap and looked at every thing and i found out much later after spending money i did not need to spend that my batt was failing. A new cheap-O batt from Wal-Junk fixed everything.
I know they have Batt testers at some of the parts stores but i dont know if they will find stuff like that..

Good Luck

Note: Some of the other things posted could be it to..

88 YJ SOA2.5" 2"BDY Locked F/R Chevy 4.3 NVG241OR 4.56's 36x12.50
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