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Thread: how many volts should the alternator put out??

  1. #1

    Post how many volts should the alternator put out??

    I've been having troubles with my headlights burning out prematurely. I was thinking that the alternator could be putting out too much voltage and thus heating up the bulbs too much. I checked the voltage last night. With the Jeep off, but the ignition in the on position the battery read 11.90 volts. with the Jeep on and at idle or upto 3000 rpm the voltage was at 14.9 volts. 14.9 seems to be too high, what do you guys think. Do you think this could be a problem for any of the other systems in the vehicle??

    TIA

    Steve

    ------------------
    '90 XJ 3.5" with 30X9.5 BFG AT's on AR 767's, 3" coils and spacer from rusty's and RE AAl with MJ shackles. Rusty's Cat-back with flowmaster 3-chamber, air tube with K&N filter, Tuffy security box, Hella E-Codes 100/80W with custom harness, Hella 500 driving lights 100W bulbs, Rusty's tow hook's and brackets, JKS Gen II disconnects
    To be installed: Rusty's transfercase skid, Rusty's motor mounts

    non-jeep photos
    '90 XJ 3.5" with 30X9.5 BFG AT's on AR 767's, 3" coils and 3/4" spacer from Rusty's, RE AAl with MJ shackles. Rusty's Cat-back with flowmaster 3-chamber, air tube with K&N filter, Class 3 hitch and Warn Reciever shackle, Tuffy security box, Hella E-Codes 100/80W with custom harness, Hella 500 driving lights 100W bulbs, Optima Red Top and 160 Amp alternator, Rusty's tow hook's and brackets, JKS Gen II disconnects, Rusty's motor mounts, Rusty's transfercase skid, C4x4 double-tube rocker guards, HI LIFT
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  2. #2
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    steve, that is certainly a little out of spec. i don't know about the specific tolerances of the xj to increased voltage, but i think the factory spec should be right around 14, from upper 13's to lower 14's. i sit right at 14. getting close to 15 certainly sounds like a caution flag to me, but i'm not really an electrical whiz-i just have some idea of what is considered normal. i would definately agree that being nearly a volt from average could be a problem, though i don't really know, again much about the specific tolerances here. in short, i agree with your suspicion
    push the seat back a little lower-watch light bend in the blower. planets align. a king is born.

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    Make sure you have the electricl system checked before you trust those gauges. My ZJ was running at the line before the 14 volt line, which I think it about 12.7. I took it in for the test, it was running at a perfect 13.7 Those gauges are really cheap, even my oil pressure gauge is off.
    '02 WJ Laredo V8; Selec-Trac; Silverstone

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    your alt puts out 14.8 volts it is fine at 14.9it has to be that much higer to push currant in to battery to charge it
    Originally posted by Steve - Vancouver, BC:
    I've been having troubles with my headlights burning out prematurely. I was thinking that the alternator could be putting out too much voltage and thus heating up the bulbs too much. I checked the voltage last night. With the Jeep off, but the ignition in the on position the battery read 11.90 volts. with the Jeep on and at idle or upto 3000 rpm the voltage was at 14.9 volts. 14.9 seems to be too high, what do you guys think. Do you think this could be a problem for any of the other systems in the vehicle??

    TIA

    Steve


  5. #5

    Post

    The voltmeter I was using is a very accurate one that I borrowed. It is accurate to two decimal places. I will get the charging system checked soon. I will be getting a new battery, so I don't want the alternator to hurt it if there's a problem.

    Thanks

    Steve

    ------------------
    '90 XJ 3.5" with 30X9.5 BFG AT's on AR 767's, 3" coils and spacer from rusty's and RE AAl with MJ shackles. Rusty's Cat-back with flowmaster 3-chamber, air tube with K&N filter, Tuffy security box, Hella E-Codes 100/80W with custom harness, Hella 500 driving lights 100W bulbs, Rusty's tow hook's and brackets, JKS Gen II disconnects
    To be installed: Rusty's transfercase skid, Rusty's motor mounts

    non-jeep photos
    '90 XJ 3.5" with 30X9.5 BFG AT's on AR 767's, 3" coils and 3/4" spacer from Rusty's, RE AAl with MJ shackles. Rusty's Cat-back with flowmaster 3-chamber, air tube with K&N filter, Class 3 hitch and Warn Reciever shackle, Tuffy security box, Hella E-Codes 100/80W with custom harness, Hella 500 driving lights 100W bulbs, Optima Red Top and 160 Amp alternator, Rusty's tow hook's and brackets, JKS Gen II disconnects, Rusty's motor mounts, Rusty's transfercase skid, C4x4 double-tube rocker guards, HI LIFT
    Jeep Pics

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    You can't measure alt output at the battery. Too many variables, length of cable terminal condition, battery condition etc. that could influenece the reading Check this site for info on how to diagnose charging probs. Good Luck
    http://www.motorage.com/edindex/039772.htm

  7. #7
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    Check out this guy's site. Has plenty of explanation for this issue & how to fix it!
    http://www.olypen.com/craigh/tech.htm

    ------------------
    1990 XJ - "Gonzo Guinea Pig"
    30 x 9.5 Sidewinders, 1992 GDI 3-row radiator, Accel 8mm wires, Bosch Platinum +4 plugs, Rusty's Airtube, K&N 9" filter, Dynomax exhaust & muffler, (Hey! Anyone seen my cat? Heeere kitty!), NAPA Orbital/Optima dry cell battery, 1/0 ga battery cables & alternator hotwire.
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    1990 XJ

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    1st - Stock electrical gauges are not perfectly acurate but are usualy consistent so they are a good reference. If you have a range that it usualy runs within, that is probably where it needs to be to indicate proper performance.

    2nd - Alternators generaly produce much higher voltage and current than the application they are designed for needs. This is to allow for resitance in the circuit (voltage drops) and added load. At the battery, you can measure the voltage accross the battery and the current flowing but this won't tell you much unless you are testing the battery.

    3rd - The voltage regulator is the component that should "regulate" the voltage in the system. In general, if the voltage or current measurements are too low, it is an indication of a problem with the alternator, too high is an indication of a problem with the regulator.

    4th - Different vehicles are different and I have not needed to identify weather the Cherokee alternator is internaly regulated or not.

    If you understand the difference between voltage, resistance, and current, then you can use the manual and some diagnostic tools to check these components out yourself. But if not (and really even if you do), most battery retailers will diagnose your system on the spot for free. Just go get it checked.
    Jonald
    07 JK Unlimted Rubicon

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    The Cherokee's voltage-regulator is built into the alternator. If the regulator's bad, you need to buy a whole new alternator for $79 at AutoZone if you trade-in your old one. As for the voltage, 14.9 is too high, it should idealy be 13.8 or maybe 14.2 at the max. If you don't correct it, like you said, you stand the chance of royally screwing up your battery!

    ------------------
    - Joe

    AOL IM: JeepGrand4

    '86 2.8L 2dr XJ Laredo:
    Mods to date: a chrome exhaust tip, a full-width rear-deck, a 300 watt Jensen stereo system, 30x9.50 Liberator All-Terrains, custom 3" lift, rear sway-bar removed, custom roof-rack for spare tire, roof-to-crossbar mouting rails switched over from rubber mounts to 1-1/4" fender washers(VERY strong), custom reciever hitch, Pro Comp ES-3000 shocks all around.
    Plans include bar-pin eliminators, custom front sway-bar links, KC lights, custom dual exhaust system, and a new paint job.
    - - - - - - - - - - - - -
    '96 5.2L ZJ Laredo:
    30x9.50 Libertor A/T's are the only mod so far
    - Joe

    AOL IM: JeepGrand4

    1986 XJ Laredo 2.8L V6 2dr - my first vehicle, over 208K miles and still kickin'

    1996 ZJ Laredo 5.2 V8 - bought off my dad for $2,000 in June of '05 with only 97K miles on it! :jammin:

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