Sense wire for 12si alternator - JeepForum.com

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post #1 of 22 Old 06-09-2012, 03:50 PM Thread Starter
TadaoBaba
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Sense wire for 12si alternator

Hi there, searching hasn't found the exact answer I am looking for. I am replacing my alternator (with a Powermaster 47294), and have read JeepHammer's explanations that the alternator sense wire is better connected somewhere downstream, rather than back to the BATT lug on the alternator. I've got an 80 CJ5, and I am looking for a good place to run this wire. I've upgraded most of the charging wires, added the requisite extra grounds, and have my headlights, electric fans etc. running off relays.

Where is a good location to run the sense wire, exactly? Is the starter solenoid not far enough away? How about running to the positive battery terminal? I'm looking for some specific ideas, other than just "down stream."


Last edited by TadaoBaba; 06-09-2012 at 07:23 PM.
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post #2 of 22 Old 06-09-2012, 06:48 PM
hutch1200
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bump....me too

I've also learned that sometimes... when people don't agree with you .... its best to hold them down and kidney punch them till they agree with you
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post #3 of 22 Old 06-09-2012, 06:57 PM
parker007
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why not just put in 1 wire regulator and just run 1 wire to batery they cost maybee 15 dollars, i belive the wire you talk about originaly went to either ignition switch or charge light.
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post #4 of 22 Old 06-09-2012, 07:22 PM Thread Starter
TadaoBaba
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1 wire has been thoroughly been covered as being the weak way to go. Hard on alternators and electrical systems.
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post #5 of 22 Old 06-09-2012, 07:52 PM
lucdog
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Agree on the light of ignition. I've been running mine on the ignition for half of last summer. And the last 2 months (trail only keep)

I seem to remember on the 1 wire, JeepHammer stated, the only drawback to the 1 wire was that in can draw down the battery over a period of time when not used. I don't remember anything about hard on the alternator, or other electrical. I wasn't that long ago.

Bill

1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1979 J20
1980 CJ5 trail Jeep.
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post #6 of 22 Old 06-09-2012, 08:03 PM Thread Starter
TadaoBaba
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Yeah - I'm not looking for one wire info, though. Want to do it three wire, with an excite (stock) and a sense.
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post #7 of 22 Old 06-09-2012, 08:07 PM
lucdog
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Quote:
Originally Posted by TadaoBaba
Yeah - I'm not looking for one wire info, though. Want to do it three wire, with an excite (stock) and a sense.
I realize that, you brought it up in your post before mine. And your info wasn't correct.

1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1979 J20
1980 CJ5 trail Jeep.
1983 CJ7
1989 YJ the CJ to YJ.
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post #8 of 22 Old 06-09-2012, 08:21 PM
lucdog
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The postive Lug on the battery or the battery side of the solenoid would be the only place down stream I can think of. Since the battery connection on the alternator always has 12 volts, and since it's connected to the hot side of the solenoid, and the sense wire is the same gauge . What I mentioned above is the only logical choice as I see it.

1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1979 J20
1980 CJ5 trail Jeep.
1983 CJ7
1989 YJ the CJ to YJ.
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post #9 of 22 Old 06-11-2012, 01:40 AM
hutch1200
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I sent J-Hammer a PM 2 days ago to see if he was OK. No word. Hope & pray all is well. Anybody nearby to check on him? Should be a thread?

I've also learned that sometimes... when people don't agree with you .... its best to hold them down and kidney punch them till they agree with you
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post #10 of 22 Old 06-11-2012, 02:09 AM
BagusJeep
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Quote:
Originally Posted by hutch1200 View Post
I sent J-Hammer a PM 2 days ago to see if he was OK. No word. Hope & pray all is well. Anybody nearby to check on him? Should be a thread?
He cruised past yesterday but has not posted for near a month.

BagusJeep lives in Bali.

1981 CJ7 258ci - Bagusjeep
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post #11 of 22 Old 06-11-2012, 05:20 AM
jay-h
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The main purpose for the sense wire is so that the battery gets proper voltage, so I would put it there. Normally (unless your wiring is bad) battery is pretty close to alternator voltage, but sometimes not.. For example if you are using a solid state battery isolator for two batteries, there is a voltage drop and the sensor wire should be on the downstream side.
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post #12 of 22 Old 06-11-2012, 06:24 AM
bentshackle
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I originally wired mine into the feed to the horn relay, per JH's instructions.

Then I had a not so insignificant parasitic drain from my alt with the key off. I probably just need a new regulator but I changed it to sense off of a switched feed on the back of my fuse block instead. I get 14.8V at idle with everything electrical on.

Figured it only needs to sense with the ignition on so why does it need a constant feed? Sorry I can't remember which circuit and I'm not at home to go find it. I just get back in there with a test light and found one that fit my criteria.

Last edited by bentshackle; 06-11-2012 at 06:25 AM. Reason: clarity.
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post #13 of 22 Old 06-11-2012, 06:34 AM
John Strenk
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On some jeeps the sense wire connects to the (+) on the ignition coil. Probably to make sure the power to the coil has the proper electrical voltage at all times. Some go to a junction just off the ignition switch. Some travel am inch to the output post on the alternator.


If you put it on your battery then the battery will be OK but you can have a big drop in power going to your electronics and your jeep won't run right and you will waste money slowly in gas costs.
.
If you put it on your electronics the the battery can get over charged and you will have to buy new batteries more often.
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post #14 of 22 Old 06-11-2012, 07:31 PM
flashpointmax
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Quote:
Originally Posted by John Strenk View Post
If you put it on your battery then the battery will be OK but you can have a big drop in power going to your electronics and your jeep won't run right and you will waste money slowly in gas costs.
Help me out with an understanding of why this would be the case. After the engine starts the voltage going to the primary of the coil is normally reduced down to around seven or eight volts because it's fed through a resistive wire. IMO I'd think any potential above that level would be sufficient and not impact the firing system.
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post #15 of 22 Old 06-11-2012, 07:32 PM
jay-h
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Quote:
Originally Posted by John Strenk View Post
...

If you put it on your battery then the battery will be OK but you can have a big drop in power going to your electronics and your jeep won't run right and you will waste money slowly in gas costs.
.
If you put it on your electronics the the battery can get over charged and you will have to buy new batteries more often.
While this is true, then you're treating the symptom. Ideally the battery should be getting the correct voltage (so it doesn't overcharge). If the circuitry has excess voltage drop, that should be addressed as a primary issue. Otherwise you're putting bandaids on the problem.
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