alternator question

[99chero]

So i noticed that when I have my sound system, rear defrost, blower on high and head lights on that my charging volts go down to about 11 volts and back up when I turn something off. my question is what would be a good, higher output alternator to put in my 99 4.0 cherokee sport and what other mods (if any) I would have to do?
Thanks
Jhery

 

[5-90]

First things first - is this at idle? How much sound system? Have you verified this with a DMM at the battery, instead of relying upon the gage in the IP? What year?

I ask all of these for good reasons -
1) At idle, an alternator is good for about 40% or so of max output. Ramp crankshaft speed up to 1200-1300rpm, and you can get full output.
2) If your system is a huge drain, it's going to try to soak up that 40% at idle.
3) The IP gage is known for being more of a "relative state-of-charge" indicator, than a reliable, absolute instrument.
4) Just because your moniker is "99chero" doesn't specifically mean that we're talking about a 1999 - you could have more than one rig. Also, what engine? The 4.0 often got a "larger" alternator than the 2.46L.

Repeat the tests using a DMM to verify your system voltage, and check at idle and with a helper holding 1200-1300rpm (you don't need to have the vehicle moving, you just need to have the crankshaft going a bit faster.) If increasing the crankshaft speed tends to increase the system voltage under load (it should,) then consider whether you're going to be running all that stuff at idle or not - upgrading your alternator may be the right answer to the wrong question... If you're going to be running your stereo at idle, for instance, are you likely to be running all of that lighting with it? Especially if you're running the rear defog and the blower fan (both of which tend to draw a lot of current?)

 

[originalxj]

Ehhh... it's a 99 4.0L he kinda said that.

To answer his question, Mean Green makes a nice unit. As well as Powermaster and the unit from Premier Power Welders. I know the Mean Green and Powermaster bolt right up, don't know about the other. But I imagine it does require very little.

There has been discussion about a ZJ/WJ alternator having more amps. Anyone want to chime in?

 

[99chero]

Yeh this was at idle, i have yet to check wit a DMM because thats in my tool box and the building that my box is in is closed for the semester (still in school) and my system, i think the amp is about 400 watts, nuttin too crazy, just to run 2 12 inch sony xplods rated at 1200watts a piece. stated in my previous post, my vehicle is a 1999 cherokee sport with the 4.0. I know that the volts increase when you increase the RPM, the reason for my concern is that at idle with the loads on it used to drop to about 13volts at idle now it goes down to 11-12v but yeh i havent check the actual charging volts b/c of no DMM at the moment. I also plan on running some more lights and a bigger system eventually so i figured a high amperage alternator might be in order down the road.

 

[5-90]

Ehhh... it's a 99 4.0L he kinda said that.

To answer his question, Mean Green makes a nice unit. As well as Powermaster and the unit from Premier Power Welders. I know the Mean Green and Powermaster bolt right up, don't know about the other. But I imagine it does require very little.

There has been discussion about a ZJ/WJ alternator having more amps. Anyone want to chime in?

OK - I missed that.

The rest is still valid. The idea of using a ZJ/WJ/Durango unit (136A) has some merit, although the mounting usually needs to be modified.

But, let's figure out what the problem actually is before we go about solving it - no sense spending money that doesn't have to be spent, right?

 

[99chero]

I just mainly want to do it as a precautionary measure for when I do get more lighting and bigger amp that i wont kill my alternator

 

[jeepster_259]

i bought a direct fit 120 A alternator (rebuilt) off ebay for $60 from a vender called Alterworks. works great and is an upgrade from the stock 90 A alternator and actually tests out at 133 A.

Autozone sells reman. ones for $150. Or you can go the junkyard route and get a 136A alternator from a 97-99 Dodge ram or durango V8. may require slight grinding to bracket.

 

[stewie]

i have a 136A alt out of a 97 ZJ in my 95 xj. it works quite well. the only problem i have right now is that my battery is quite old and needs replacing. i can run my headlights, offroad lights, and taurus fan without a problem.

the zj alt did require a little grinding to the alt bracket on my engine. a dremel took care of all of it. and i am still able to put a stock xj alt in there if for some reason i was wanting or needing to go back (reverse compatable)