My CJ7's electrical system anatomy

[jdcaples]

I'm looking for some help.

Today I tried to start my Jeep for the first time in two or three weeks.

The battery was putting out 6.8 volts so I put the my charger on it and when it got to 70% charged, I started the engine and kept the charger on "monitor" mode watching the alternator charge to 100%.

The battery's about 6 months old, Sears Die Hard Platinum 4 year something something.

I pushed a button on the charger to show me the voltage and it was 13.1, dropped to 12.2 and pretty much hovered there.

I've never had to diagnose anything electrical.

Should the voltage be closer to 14.4 volts?

Here's the alternator

View attachment 17007

I think I have a 3 wire alternator. Am I correct?

The battery attaches to this thing (outlined in red):

View attachment 17008 View attachment 17009


I'll have to pull off some conduit to know for sure, but I'm pretty certain the alternator is attached to it as well.

What is that thing called? Is that the voltage regulator?

Is the voltage being less than 14.4 a problem?

If so, where do I start looking for the issue?

I'm not looking to pinch pennies here. I just want the electrical system to be "healthy."

Thanks for any guidance you can offer.

-Jon

 

[caveman]

The fact that the battery was dead after 2 or 3 weeks leads me to think that your battery is the problem. You might want to have it checked. The thing outlined in red is your starter selenoid. It has nothing to do with the charging system.

 

[Torxhead]

When the engine is running, the alternator should be charging at around 14.5 volts. A fully charged battery should read around 12.5 volts, with engine off. That "Thing" is a starter relay. 6.8 volts after sitting 2-3 weeks is a bit light and indicates an issue of some sort. The first thing I would consider would be the battery wiring and weather it is secure. From there you should check for a battery drain, like a short circut.

 

[PaRenegade]

^^ What Torx said. The battery gets charged at a higher voltage but will only hold about 12.5 volts. It's so the battery can catch up quicker while still under load, is the way I always looked at it. But when I get a battery that is showing it's voltage in the single digits it's usually due to a bad cell, beit from low water, it froze, whatever, and it will never recover. Being that it's only 6 months old, take it back now, it's faulty.

 

[jdcaples]

Thank you, everyone.

I'll verify the connections, the integrity of the wiring and get a new battery.

Much appreciated!

Oh, am I correct in determining that's a 3-wire alternator, or is more information required?

-Jon

 

[PaRenegade]

Yes, that's what I would consider a 3 wire alternator.

 

[jdcaples]

I'm back. On a hunch, I connected my fluke tester to the alternator "BATT" post and to the negative side of the battery. I started up the Jeep and at fast idle, the voltage seen was 14.1. When the idle kicked down after warming up, the I saw 13.1 v. I turned on the heater fan, the headlamps and the hazard lights. That's when I saw 12.1-12.2 v.


Is my test indicative of someone that knows enough to be dangerous; a bogus conclusion based on a lack of understanding of DC current?

Is there a new alternator in my future, or is it still the battery?

Thanks

-Jon

PS: the previous owner installed an alarm system. Does that qualify as a parasitic drain that might explain the battery being so discharged? I totally forgot about the alarm until I went out there and accidentally set it off.

 

[Torxhead]

I am sure that an alarm system could cause a battery drain, some guys just install a hidden switch somewhere that will break the circuit to the coil wiring so the vehicle will not start. You might try running a jumper wire from the alternator housing to the battery negative to see if that bumps up the voltage any. The black headlamp ground wire could be extended to the battery negative as well. One of the things that make a CJ simple is the use of sheet metal and cast iron to conduct electricity rather than use a wire. Sheet metal and cast iron are not good conductors anyway especially combined with paint, grease, and corrosion. The battery condition and the alternator can be checked and should be before replacing. Also running that red wire on the alternator that goes from that nylon plug to the back of the alternator from that nylon plug to the hot side of the relay will help the charging system. This way that alternator "Sense" wire reads battery voltage instead of volts being sent to the battery.

 

[jdcaples]

I thought I'd complete the thread.

I charged the battery to 100% out of the vehicle. It kept 12.4 volts and something north of 97% over night. I charged it to 100% installed it and drove about 5 miles to the nearest Autozone store.

Autozone's website says they test charging systems w/o removing components. I called to confirm an OBD port wasn't a pre-requisite.

After I asked for a free charging system test, one of the employees grabbed a test tool that looked like an 18"x7" purpose built computer and connected it to the battery.

The battery tested fine, but it was only at 60% charged so I was told that charging system couldn't be tested. Apparently the charging system test needs the battery at 100%.

I drove home. After inspecting the wiring connections, I decided to test the alternator with my PSC-12500A charger/tester (I forgot it can test alternators), but all it tells me is the % of output, which is basically meaningless to me.

It said 38%.

I took the alternator to the local NAPA store.

It was a zoo. I left the alternator to be tested and came back a bit later.

The person that tested it wasn't there and didn't write down any metrics on a piece of scrap paper that said, my name and "bad."

They were still pretty busy so I decided to gamble instead of demanding a retest.

I bought the only alternator in stock that would fit: a 55 amp reman, part number 2134011B (one grove pulley). I suspect it was replacing a 37 amp alternator, but even it was the optional 60-something alternator, I didn't care.

Even though the store was busy, I noticed it was clocked at 9. I needed it at 3. They clocked it for me and tested it before I left. They're awesome, but I was losing daylight and rain was correctly forecast for the next few days.

I installed the alternator and the used the PSC-12500A to test its output. It came back "100%" for its alternator test.

The alternator charged the battery to 100% at idle in less than 5 minutes.

24 hours later, the parasitic drain bled the battery down to 70%, but it held voltage above 12. The alternator did it's job in a few minutes of engine running, bringing the battery to 100%.

When it stops raining, I'll chase down the parasitic drain.

I want to thank sincerely thank the members that educated me, helping me through this.

-Jon

PS: I realize that some of you think the battery's faulty. I'm willing to discount the Autozone battery test and replace it, but I want to knock out the parasitic drain before I put a new battery in the Jeep.

 

[SCSEAJAYSEVEN]

WAIT! Are you telling me that is stops raining in Seattle? When?

I think you do have a parasitic drain on your battery somewhere. You will continue to have problems until you find it. In the mean time consider this:

12.5 volts (+/-10%) is the constant voltage for a static automotive battery.

14 volts (+/-10%) is the constant voltage for an alternator output that runs through the electrical system and keeps your battery charged.

As loads are added, i.e. wipers, blower motor, headlights, turn signals or hazard lights on, these will bring the voltage down and the alternator works to keep about 14 volts on the electrical system.

If you have only one tool that you will always need for electrical testing on vehicles, it will be a multimeter. Analog meters are good, but a more accurate meter is a Digital Volt Meter (DVM). You can test the integrity of your charging system very quickly with one of these. If you have a FLUKE meter, I don't think you can get one much better than that.

At fast idle, your alternator is putting out all of the voltage and amperage that it will ever put out. No need to race the engine, it is working as hard as it ever will at that speed. With the volt meter, you see 14.1 volts. That is good. At idle speed, you see 13.1 volts. that is good also. With all the accessories on you see 12.1 volts. Not so good.

When you are at a stoplight with all of the accessories on, your alternator is not compensating for the load placed on the battery. That is OK because when the light changes, you are driving and the engine is above idle again and the alternator is compensating for the load on the electrical system.

One very simple thing you can do, is turn on all electrical systems that load your system while idling, hook up your Fluke meter to the battery correctly, and adjust your idle speed up until you get about 13 volts. The battery is happy, the electrical system is happy and you will be happy too!

That drain on the battery is your problem, find that and you will be even happier!

 

[jdcaples]

Thanks, SCSEAJAYSEVEN

It actually stopped raining this afternoon, but I didn't get home until dusk.

I'll be looking for the parasite tomorrow morning since it's supposed to be mostly dry. Sunday it's supposed to just be cloudy.

Monday the day job gets in the way again.

'preciate your post

-Jon

 

[jdcaples]

About the parasitic drain: I pulled all the fuses, which was diagnostically fruitless and disheartening.

Fast forward to today, every aftermarket add on that didn't work is gone.

I have room under the hood for a coolant recovery tank and maybe a oil system pre-charger

It's nice having no parasitic drain, having bright headlamps. It's nice that my turn signal lamps no longer cause an electrical oscillation between 12v & 14v. I love my new 1/0 battery cables (yes, decadent). The alternator's putting out 14.446. The battery after two days of idle is still at 13 volts.

How'd this happen?

Painless wiring harnesses are not painless - not mentally, not physically - and getting to happiness sucked; but I'm happy, 'cuz everything works when it's on and everything's actually off, when it's off.

Bottom line: Never. Ever. Ever. Again.

-Jon