• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Too many lights, droping below 12 volts

R

[email protected]

NAXJA Forum User
hey i have a 99 with a 124 amp altenator. I also 4 aux lamps. 2 Piaa 520 fog and 2 Piaa 520 driving. each with 85 watt. when all of them are on along with the headlights after about 7 min. the volts drop to 12 volts. This is at idle. If the car is moving at at least 5mph then the volts go up to 13. Anyway what kind of altenator do i have to buy ( how many amps) in order to keep volts at at least 13 during idle? I am sure that if i left the car in idle for more then 10 min it would even drop below 12. Thanks.
 
Well with the '99 I have a similar issue...there is nothing aftermarket aside from the mean Green that puts out 100 amps at idle and almost 200 max.

I have one fo rthe XJ and two rover units heading to us, I'll let ou know how it goes!

RJ
 
[email protected] said:
hey i have a 99 with a 124 amp altenator. I also 4 aux lamps. 2 Piaa 520 fog and 2 Piaa 520 driving. each with 85 watt. when all of them are on along with the headlights after about 7 min. the volts drop to 12 volts. This is at idle. If the car is moving at at least 5mph then the volts go up to 13. Anyway what kind of altenator do i have to buy ( how many amps) in order to keep volts at at least 13 during idle? I am sure that if i left the car in idle for more then 10 min it would even drop below 12. Thanks.
Click to expand...

Well, the problem is that most alternators that put out more amps do it at higher rpm, then they can actually put out less amps at low rpm. Since you have no reason to run all those lights at idle, since you're not moving, if the amp drop bothers you just kill a couple of lights.

To me, your problem is the battery, not the alternator. A 124 amp alternator is pretty good, and most high output stock alternators put out good amps at idle. A good battery (high capacity, good condition) should hold above 12 volts for a good while at idle with that draw, I'd suggest checking the battery rather than the alternator. Also, be sure to check battery volts at the battery with a multi-meter. XJ's are notorious for voltage drops through the wiring harness.....you may not have a problem at all.

Personally, if you have a good battery, I wouldn't worry about it.
 
so the stock altenator produces 124 amps at idle? is that the way it works? How much does it produce at 1000Rpm or at 1500RPM? I haven't seen it drop below 12 yet, i am just guessing that it might. I guess i should just see what happens. Now what about those altenators they use for onboard welders or guys who use winches? thanks.
 
[email protected] said:
so the stock altenator produces 124 amps at idle? is that the way it works? How much does it produce at 1000Rpm or at 1500RPM? I haven't seen it drop below 12 yet, i am just guessing that it might. I guess i should just see what happens. Now what about those altenators they use for onboard welders or guys who use winches? thanks.
Click to expand...

No, they don't put out max amps at idle, just most stock alternators put out good amps at idle. To get better, you have to spend a lot of money. It is not unusual to have enough accessories to draw more than an alternator will put out at idle. The battery provides the extra juice, which isn't a problem with a good battery since you rarely sit at idle with everything on for very long. If your dash board voltmeter is showing 12 volts, it's just showing battery voltage, which isn't bad. I'd still check voltage at the battery in the situation you're concerned about before you draw any real conclusions.

Most people with winches run stock alternators and one battery. Some do upgrade to dual batteries and higher output alternators, but that's frosting on the cake. A stock alternator and decent battery in good condition will run a winch just fine.
 
The rated output of your alternator is probably at 2,000 RPM and is not linear. At 700 RPM, you'll be lucky to see 75amps or less.

50 amps for the lights, more for spark, radio, heater, on and on...
plus loss through the wiring and connectors.

Keep your lights pointed at the sun and the reverse input of photon energy should help charge your battery. :)
 
Sounds like it's possibly the battery. How many amps your battery rated at? After I added a winch, I burnt up two alternators. I think they were only 80 amp alts??? After the second one, I opted for the Mean Green 140 amp alt. and a good 850 amp battery. Have'nt had a problem since. However, when winching, I still need to bring the rpm's of the motor up (creating more amperage output from the alt.), to feed the winch and additional lights for an extraction.

As others have mentioned, take an amperage reading at the battery, gauges can be inaccurate. The battery is a reserve that stores energy. In ex... to start a vehicle. It also helps make up for what the alt. cannot produce at a given time. In ex... under a heavy load such as a winch, big lights, jump starting someone etc.... The alt. will recharge the battery after the load is lightened.

A 124 amp alt. is'nt bad at all. Take some readings at the battery and see if perhaps you need a bigger (higher amperage) battery for your set up. Good luck.
 
I had the same problem with my 98 even with an optima redtop, the alt would kinda crap out when on the trail and not revving the engine, I put in the mean green and have had no problems since, it was a tight fit, and I had to do some grinding, but my alternator squeak was gone and now I can run everything with no problem.
 
When the amperage draw exceeds the output the voltage will fall.. a battery with more reserve will help mask this problem..at an idle when I run my lights and my A/C at the same time, the voltage falls..the only real problem was the turnsignals would quit flashing at traffic lights...I replaced the mechanical flasher with an electronic flasher...I also installed a slightly smaller pulley on the alternator to get a little more RPM on the alternator at idle.
 
The first thing you need to do is to rip out the shoddy factory wiring and replace it with at least 4 gauge wire:

1. Alternator + to Battery +
2. Battery - to Chassis
3. Chassis to Engine block

Made a huge difference on my 97, and my system sees much larger loads than just those lights.

Josh
 
Wow, I guess I am lucky then. I have:

4 - 110W Bulbs in Hella 500's up front
3 - 55W lights on front of safari rack
2 - 85/150W H4 Headlights

add a TV, DVD, 1500 watts of audio, radar detactor, 2 cell phones, CB, and Radar/laser Jammer and mine never drops below 13V at any speed.......
 
tnomud said:
Wow, I guess I am lucky then. I have:

4 - 110W Bulbs in Hella 500's up front
3 - 55W lights on front of safari rack
2 - 85/150W H4 Headlights

add a TV, DVD, 1500 watts of audio, radar detactor, 2 cell phones, CB, and Radar/laser Jammer and mine never drops below 13V at any speed.......
Click to expand...
Sorry to resurrect an old thread, but I had too. Did you have "pimp your ride" build this bad boy. Do you really have all that electrical stuff in your XJ. If so does it go off-road ? Just curious.
 
[email protected] said:
hey i have a 99 with a 124 amp altenator. I also 4 aux lamps. 2 Piaa 520 fog and 2 Piaa 520 driving. each with 85 watt. when all of them are on along with the headlights after about 7 min. the volts drop to 12 volts. This is at idle. If the car is moving at at least 5mph then the volts go up to 13. Anyway what kind of altenator do i have to buy ( how many amps) in order to keep volts at at least 13 during idle? I am sure that if i left the car in idle for more then 10 min it would even drop below 12. Thanks.
Click to expand...


Sounds like the easiest solution would be an extended idle switch. It will boost the idle up to about 1000 RMP. This was used for fleet and police models of the XJ and was used for just this purpose.

Check this thread out. It even has part numbers for the labled swiches and a few pics.

http://www.naxja.org/forum/showthread.php?t=35197&highlight=extended+idle
 
try this..... the last time i checked, the oem alt only put out 98 amps at something like 3200 rpm... more like 60 -70 at idle if that...

http://www.bc4x4.com/tech/2004/jeepalt/

haven't had any probs yet, full lights w\hella's, a\c at full blast and stereo crankin'. no dips. btw, those in-dash amp meters suck. get under the hood for a good read.

and im out.......
 
boise49ers said:
Sorry to resurrect an old thread, but I had too. Did you have "pimp your ride" build this bad boy. Do you really have all that electrical stuff in your XJ. If so does it go off-road ? Just curious.
Click to expand...
:twak: :twak: :twak: :twak: :twak: :twak: :twak: you resurected an old thread just to throw some crap his way? Dont you have anything better to do?
 
boise49ers said:
Sorry to resurrect an old thread, but I had too. Did you have "pimp your ride" build this bad boy. Do you really have all that electrical stuff in your XJ. If so does it go off-road ? Just curious.
Click to expand...


Come on man:

tnomud

Last Activity: 08-01-2005 11:01
Offline
 
Really I was curiuos. All that boucing around has to be hard on it. Were is the harm ? ? ? ? Yeah I did throw a smart ass line in there. Sorry Man ! :hang:

I didn't notice he hasn't been on forever. Guess I was bored. Actually I was looking up Alt. Amp info.
 
Last edited:
Remember total watts of all your goodies divided by 12Volts equals the amp draw. At some point your gonna kill the battery no matter what. Better HD cables on stuff will help. I seem to see this a lot on stock motorcycles. Eventually the heat from to small wires leads to more loose connections then to more problems and failures.
 
You must log in or register to reply here.

Similar threads

W
Strange Charging Problem - 1992 XJ
Replies
3
Views
536
lawsoncl
L
cherokeefan_1
2000xj running hot
2 3
Replies
49
Views
5K
RCP Phx
R
FernGreen
Bad Fuel Pump Cause Poor MPG?
2 3
Replies
42
Views
3K
maxbraketorque
M
blondejoncherokee
RTF Property work day update - looking for volunteers
3 4 5
Replies
99
Views
9K
XJensen
XJensen
R
Upgrading Electrical
Replies
7
Views
2K
Overland
O
Back
Top