EagleXJ

Background: This is a 98 XJ Classic. So this is what I have going on: I'm wiring five, 35w HID lights into my jeep; this is going to give me a grand total of 9 lights on my rig: the 5 and then the 55w headlights and my 55w fogs. This has got me a little concerned for my alternator. According to my research, the 55w lights are going to pull 15-20 amps each and the HIDs will pull 20 amps on start-up and 3-6 amps once warm. Assuming the HIDs are warm, thats 90 amps in lights! Granted, I will rarely have more that 2 of the HIDs lit up at a time, I still want to have the ability to light everything up if I need to.

I punched my vin# into the decoder and it said that my XJ has a 117 amp alternator. First question:
1. How can I check to make sure this is correct?
If this is indeed correct:
2. Will it hurt the alternator to be putting out close to its maximum?
3. If so, how close is safe?
4. Anyone have any kind of pall park idea of how many amps a standard sterio would draw, how 'bout heat?

94XjSport94

You will NEED 40 amp relays. Probably run two lights you're adding to 1 relay. Properly wire them up, that includes correct wire gauge.

You can pull the alt and have it tested an auto parts store and see what it's putting out.

You should be ok, that is a lot of lighting and I would also look into upgrade your battery cables, check out Kelly's WIP.

Dan91

1. P=IV, watts=voltage times current. So I=P/V. 55w/12v= ~4.5amps per light. So right there your total comes way down to a reasonable number. I know the HIDs take a lot when warming up, but that's a relatively short time, so not too much to worry about.
2. Biggest problem with maxing your draw from the electrical system is gonna be horsepower loss to spin that alt. Being at max output I'd guess the alt would get pretty hot, effectively shortening it's life.
3. Dunno
4. Really depends on your speakers, head units, choice of amps/subs etc.

EagleXJ

So I had all my lights running tonight while my engine was at idle. After about 30 seconds the engine bumped up a few hundred rpm; is this just so it can keep enough power flowing?

mentalbreakdown00

It was the ECM revving the engine to keep alternator output suffencient. The alternator on these is ECM controlled

wrapstar

Id get a 02 durango alt. Takes minimal grinding to fit plug and play and its 160 amps. I run one with proper wiring and dual batterys with isolator. I can have the stereo on "bumpin" with 260watts of light and use my winch with no issue or dimming.

mentalbreakdown00

I cannot remember now which one I have I think I got the ZJ alt on it a while back, not bad for $20

cleenrob

get a zj 136 amp alt.and kelleys wip cables. i run that set up with my taurus fan wired up and i barely get any voltage drop. id say with all your lights its a VERY good idea to upgrade

EagleXJ

Thanks for the help and advise!

5-90

1) If there is still an ID tag on the alternator with an OEM #, post that and someone should be able to run it for you.
2) It does shorten its life a bit, but not really enough to worry about. However, the lower the percentage of max capacity your alternator "lives" at, the longer your service life will be - because it will result in less heat. ("Heat is the enemy.")
3) You can run it at full rated output until something gives - usually the rectifier diodes, if it's an electronic fault. Otherwise, the brushes go - they're wear parts anyhow.
4) "Stereo." I think the OEM stereo runs something like 30-40W x 4 channels (120-160W total,) plus a couple of amperes for the head unit. Assuming 40W/channel, that's 160W/12VDC (nominal) or 13-1/3A. Add, say, 4A & change (probably high,) and that's about 18A - 20A at the outside.

If your stereo is still OEM, heat should not be a big problem. However, if you add an amplifier (especially for a sub driver,) I do recommend that you mount it with useful airflow - fully half of the case's surface area will be heat sinks anyhow, so you just need to add airflow. (If using an enclosed driver in a ported box, I like to put the port and amplifier such that the port will stir the air over the amplifier, aiding convection and improving airflow and head dissipation.)

If you'd like to upgrade your alternator, it will take some grinding to fit a higher-output unit, as 117A is the max for that frame size in COTS/OEM parts. However, a 136A or 160A unit may be fitted - however, I strongly recommend upgrading your wiring as well, which will allow you to increment your fuse protection upwards and take full advantage of the new alternator (if you're going to mount a larger alternator, it is usually assumed that you will be using the capacity. When I fitted my "special" that was done for me - 175A rated, 198A actual max output - I increased the wiring as well. My alternator typically "lives" at about 50A or so output - but if I NEED the full 198A, I have access to the full 198A (I can clip in booster leads and throw a full surface charge on a dead battery in about five minutes, running at 1200rpm or so.)

yarom

On my 98 Limited I definitely run into issues when everything was on.

I am running a pair of PIAA 580s (85W) a pair of PIAA 520s (65w), a pair of PIAA 520s (fog 65w), upgraded H4 headlights (85w), 3 VHF radios, a GoLight search light, an Alpine amp powering the stereo and some 12V instruments for navigation... I am not talking about the winch, which rarely sees use and is connected directly to battery #2...

Despite the fact I have two Optimas yellow, isolated, I definitely saw a voltage drop when a bunch of stuff was on. I also got interference on some of the radios. The 117A factory alt could not recharge the batteries and run all that stuff at the same time. The engine also kept idling higher when stationary...

I got a 160A on eBay, for $119 shipped. Drops in and bolts on with no grinding at all. Definite improvement in power, less radio interference and headlights shine brighter. I did replace the big PIAA driving lights with a 40" LED bar, saving a few hundred watts and that helped quite a lot...

JJCIII

I've got a 220 amp alt in my zj with a big 3 upgrade for charging an optima tellow top and have zero voltage drop. My setup is only for audio since any voltage drop on a system that normally only runs at 13.8 will cause the sound to be less crisp and also too much voltage fluctuation causes issues. In my opinion if you don't atleast go with the durango alt then I recommend using l.e.d. lighting to save your alt. If you your rig needs current high enough to automatically up the rpm to compensate then the alt won't last long. A smaller alt pulley MAY give you some results.