alternator problem?

[jeepman3071]

This is for my 2000 Jeep Cherokee 4.0L. I have some electrical accessories on it including some 100 watt off road lights wired to come on with the high beams, as well as heated seats.

I could run all this stuff with my factory 117 amp alternator and didn't have any problems. Well the factory alternator had a bearing that went bad, so I bought an Autozone rebuilt alternator. It worked, but didn't seem to charge well enough at idle. I recently replaced that alternator with a "high output 150 amp" alternator from eBay. It is basically a stock alternator that has been rebuilt to put out 150A. I also upgraded the alternator cable to some larger gauge wire while doing this mod. All connections are clean and tight.

What I have noticed is that the idle charging problem has worsened. If the Jeep is idling with no lights or anything on, the dash gauge reads 14 volts. If I turn on my high beams (and off road lights) while idling the dash gauge will spike to 12 volts, and the headlights and dash lights will dim. If I press the throttle a bit (say up to 1000 RPM) while doing this, everything gets bright again and the volt gauge returns to 14 volts. If my electric fan kicks on while idling at a light, the same thing will happen and the volt gauge will spike to 12 volts until I get moving. It almost seems like the alternator can't handle the load placed on it at idle, but is fine otherwise.

If I'm cruising down the road everything is fine, this only happens at idle. Could I have gotten two bum rebuilds, or is something else the problem?

 

[SwampSurvivor]

Isn't that generally the side effect of getting a higher capacity alternator that wasn't originally designed as such?

If you want to keep this alternator for the 150A capacity, install the high idle switch.

 

[Skid]

Higher output alternators have thicker windings and will put out higher amounts of current at high RPM, but lower amounts of current at low RPMs such as idle because there are fewer windings.

 

[Skid]

http://jgdarden.com/batteryfaq/carfaq5.htm

You could try a smaller pulley (may need a different belt as well). (smaller on the alternator end)

 

[razel]

+1 to above. Also before making another comparison, make sure your battery is fully charged. A weak battery is a bigger demand on your electrical system than a strong, full battery.

Good job on upgrading the alternator cable. Since you already did one, you might as well upgrade what the car audio guys refer to as the 'Big 3'. On top of that try to find a chassis ground for your off-road lights. Those are not solutions to your idle problem, but it will at least keep your electrical system healthy.

 

[wrcsixeight]

The alternator ratings are usually fairly ridiculous. Expecting an alternator to make its rating at idle is unwise.

My '130 amp' alternator cannot make more than 32 amps at hot idle speeds. Couple hundred more rpm and it will make 65 to 70, but I need 3200+ rpm to exceed 110.

I'd not worry about it, and just make use of a battery charger afterward, if idling a lot, to get maximum service life from the battery.

Making sure the battery is fully recharged can mitigate the issue somewhat too. Too many people act as if alternators are magical instant battery rechargers, but time at high voltages are needed for the battery to absorb all it can and reach full charge. About 4 hours to go from 80% to 100% charged no matter how big and shiny the alternator is.

The amps the battery can accept at these high voltages and higher states of charge, are quite low.

You can throw more money at it by finding an alternator which claims to have high output at idle speeds.

200 watts is only 20 amps or so depends on the voltage and what voltage the lamps are rated for at 200 watts, probably 12.8, and higher voltages they get brighter and draw more than 200 watts.

The Hvac blower motor on high is likely 16 to 18 amps.

These additional lights serve no purpose being on at idle anyway. I'd put a manual switch on the relay so they can be turned off when the high beams are activated and this obscene amount of light is not needed, if it ever is.

My desire for hideously bright high beams is mostly to blast the person back who is blinding me with theirs. PEEing contests are so ridiculous.

 

[SwampSurvivor]

Are there overdrive pulleys available for the alternator?

I'm going to be installing the "ext idle" switch on mine that raises RPM to 1100. Will be nice for running accessories, lights, etc while idling. The ECU is pinned for it and it was an option on the police package Cherokees. It would allow the engine to run at 1100 to get more output from the alternator while idling with all of the lights on.

 

[HerrStig]

Originally Posted By: Miller88
Are there overdrive pulleys available for the alternator?

I'm going to be installing the "ext idle" switch on mine that raises RPM to 1100. Will be nice for running accessories, lights, etc while idling. The ECU is pinned for it and it was an option on the police package Cherokees. It would allow the engine to run at 1100 to get more output from the alternator while idling with all of the lights on.
+ 1 Pully selection is often overlooked. YOu'll need a SMALLER one.

 

[Donald]

Maybe find a rebuild shop to rebuild your original alt. They almost always know whats going on with starters and alternators. They are getting harder to find however.

Maybe put a switch for your off-road lights. Do you always need them with on with the high beams?

Some high amp alternators require dual belts. High amp alternators are somewhat common on marine engines.

 

[440Magnum]

The first problem (parts-store reman not putting out at idle) is typical of the rebuild process where nothing is carefully matched or optimized. The biggest factor is probably a mistmatched rotor and stator set that could have come from two slightly different-model alternators. Or it could be lossy cheap diodes, undersized wire if they re-wound the rotor or stator, or who knows what. This is why I like to use a local rebuilding shop (Texas Alternator and Starter, in my case).

The second problem (lower idle output from a modified alternator) is the nature of the beast. When you increase the peak output, you tend to compromise the low-RPM output because increasing the wire size for higher peak output means fewer turns per phase, which means lower flux density at lower RPM => lower output at low RPM. The graphs plotted earlier show it perfectly.

IMO, the best answer for uprating a 2000 XJ alternator is to get an unmolested 135A Nippondenso alternator off of a circa 2000 Durango or Ram truck, grind the middle of the "C" shaped bracket from the XJ to clear it, and use that. You can find writeups on how to do it on most of the Jeep forums.

 

[SwampSurvivor]

Originally Posted By: 440Magnum
The first problem (parts-store reman not putting out at idle) is typical of the rebuild process where nothing is carefully matched or optimized. The biggest factor is probably a mistmatched rotor and stator set that could have come from two slightly different-model alternators. Or it could be lossy cheap diodes, undersized wire if they re-wound the rotor or stator, or who knows what. This is why I like to use a local rebuilding shop (Texas Alternator and Starter, in my case).

The second problem (lower idle output from a modified alternator) is the nature of the beast. When you increase the peak output, you tend to compromise the low-RPM output because increasing the wire size for higher peak output means fewer turns per phase, which means lower flux density at lower RPM => lower output at low RPM. The graphs plotted earlier show it perfectly.

IMO, the best answer for uprating a 2000 XJ alternator is to get an unmolested 135A Nippondenso alternator off of a circa 2000 Durango or Ram truck, grind the middle of the "C" shaped bracket from the XJ to clear it, and use that. You can find writeups on how to do it on most of the Jeep forums.



One of these days, I'm going to head to the junkyard and get one of those, make sure it mounts up to the Jeep and have it rebuilt.

 

[xxch4osxx]

I heard that a dual rectifier alternator is better for high output. Not sure if that is true or not.

 

[zzyzzx]

Sounds like a normal alternator to me. I would stop tying to fix the non-existent problem.

 

[jeepman3071]

Thanks guys for all the help! I'll try to post a video once I get home of what it is doing. That makes sense about the modified alternator, and maybe the rebuilt one from Autozone just wasn't putting out as much amperage at idle as the factory alt. I have a used factory alternator that I may swap in, or I might drop the cash for a genuine Mopar one. Rebuild shops are hard to come by in this area.

I don't need the off road lights on with my high beams, but I use them on back roads because of all the deer. I do have them on a switch, and have upgraded the main battery and ground cables. The terminals are brass and very clean/tight.

My main concern is the electric fan will make the voltage spike to 12 volts if just the low beams are on, which was never the case before with the factory alternator. I came to a stop light last night and the fan clicked on and my headlights got extremely dim until I hit the gas.

I did look into the larger case Chrysler/Dodge alternator, but it requires grinding the block and timing cover a bit in addition to the bracket. I was fine with the bracket, but I didn't feel comfortable grinding the timing cover.

 

[jeepman3071]

Here is a video showing what happens at idle:

https://www.youtube.com/watch?v=v-Buiq3x5mw

 

[mjoekingz28]

My old Z acted like that when I cheaped out and used a smaller battery from a Sunbird, AND then I added an underdrive pulley set. Man, i sure did mess that car up trying to make it faster. Bolt ons are [censored], you pay big money to make the car worse, but that was at the turn of the century, maybe they are more honest now and make decent products that make the vehicle better!?

 

[wrcsixeight]

If the low beams and the fans coming on drop the battery voltage to 12.0 volts nearly instantly, the battery is on its way out, or extremely undercharged.

If it is extremely undercharged, then it will be on its way out in short order.
Are these the radiator fans?
Do you know anybody with a DC clamp on ammeter?

What is the battery resting voltage in the morning before you start it?

 

[jeepman3071]

Originally Posted By: wrcsixeight
If the low beams and the fans coming on drop the battery voltage to 12.0 volts nearly instantly, the battery is on its way out, or extremely undercharged.

If it is extremely undercharged, then it will be on its way out in short order.
Are these the radiator fans?
Do you know anybody with a DC clamp on ammeter?

What is the battery resting voltage in the morning before you start it?


The fan is the factory aux. radiator fan that clicks on when the coolant reaches a certain temperature. I wired it to a switch to demonstrate in the video.

One thing I have noticed is that the Jeep will turn over really slow after sitting over night. This is more apparent in the colder weather, but it has been happening for a couple months. If the engine has been running recently (like going into a store) it will crank right up fairly quickly.

I used my battery load tester to test the voltage.

This is what it reads after sitting over night, the Jeep is stone cold. It shows about 12.5 volts.

This is with the load switch on the tester in the "on" position. The battery is testing borderline weak on the gauge. This is an 800 CCA battery. I have done this test after it has been run for a bit and the battery will test a little higher, but still closer to the weak range.

This is the voltage reading after completing the load test.

 

[jeepman3071]

I'd also like to add that this battery was fully charged with a battery charger on the 2 amp mode two days ago.

 

[wrcsixeight]

Is this a flooded battery?

Those readings on the load tester and your observations when driving are at odds, in my opinion.

I know people love the low and slow charging method, and love the soothing green light on modern automatic chargers, but most times a good Hydrometer would prove the charger is a dimwitted liar, and higher voltages for longer periods of time are needed to fully charge a battery to the maximum of the remaining capacity.

I've found that my Flooded battery actually responds better to higher amp charging, but it is a deep cycle, and is cycled daily. Low and slow for 5 days at 13.6v has not maxed out the specific gravity on this battery. 14.9v applied for 2 hours after 5 days of 13.6v, did get me to 1.285 specific gravity.

A Turkey baster style glass hydrometer with temperature compensation is a much better flooded battery tool than most load testers, in my opinion.

I'd like to know the amp draw of that factory fan, at the 110 watts of low beams should be cakework for most any alternator at idle speed.

Have you ever measured the difference in voltage at the headlamp plugs compared to battery voltage with the lights on?

My lights noticeably dimmed at hot idle when I had ~2.5V of drop on the original wiring. When a relayed 12 awg harness was installed, and voltage drop was reduced to 0.3V, I can no longer notice dimming at hot idle, even with a depleted battery.

Light output was also increased by ~30%, and few vehicles who pass me on the freeway have more light on the road ahead. And, These are just sealed beams getting 14.6v most of the time.

You say you upgraded the alternator cabling. Does this include the ground from battery to engine? The positive is only half the circuit.