donthelegend
NAXJA Forum User
- Location
- St. Louis, MO
After some discussion on another thread about larger than stock alternators and wiring, and some disagreement about output, I wanted to post up some numbers for how much current the alternator was producing with different loads.
Measurements were taken with an Extech MA120 AC/DC Clamp meter. It's no Fluke, but should be good enough for these purposes.
I tested on both my trail rig and DD XJ, with the clamp meter attached between the fuse/breaker and the PDC.
Test Setup 1: '97 XJ, stock alternator (unknown if it's the 90 amp or 117 amp version, I've never bothered to check), upgraded 4 gauge wiring harness, 120 Amp circuit breaker between alternator and PDC post. Aftermarket radio and speakers but no external amps. Headlights are Autopal H4s with the bulbs they came with, upgraded Putco relay harness.
I used to have two extra sets of driving/flood lights on the front of this jeep with upgraded bulbs in both, and a set of reverse lights, I would have liked to see the measurements with all of those running but I'm in the process of re-wiring some switches and upgrading to an LED lightbar so it'll be a while before I can get a measurement on extra lighting. Based strictly on the bulb ratings, I had about 400 watts in lighting, which would have been around another 30 amps.
My trailer isn't here or I'd have measured with the trailer lights running as well, not sure when I'll be able to get those measurements but I'll update when I can.
Anyone want to see something more specific tested? Problem with my measurements? Let me know. I looked around and didn't find anyone who had actually posted all the stock numbers so figured some might find it useful.
Measurements were taken with an Extech MA120 AC/DC Clamp meter. It's no Fluke, but should be good enough for these purposes.
I tested on both my trail rig and DD XJ, with the clamp meter attached between the fuse/breaker and the PDC.
Test Setup 1: '97 XJ, stock alternator (unknown if it's the 90 amp or 117 amp version, I've never bothered to check), upgraded 4 gauge wiring harness, 120 Amp circuit breaker between alternator and PDC post. Aftermarket radio and speakers but no external amps. Headlights are Autopal H4s with the bulbs they came with, upgraded Putco relay harness.
Measurements:
Test Setup 2: '99 XJ, 160 amp Durango alternator, upgraded 4 gauge wiring harness, 150 amp ANL fuse between alternator and PDC post. Aftermarket radio and speakers, but no external amp. Headlights are Autopal H4s with Hella 85/100W bulbs with DIY upgraded harness.- While cranking: 95-100 amps
- Hot Idle, nothing else on: 13 amps
- Headlights on High: 33 amps
- A/C on high (cooling fan on and blower motor on high): 70 amps
- Radio on w/volume turned up: 71 amps
Measurements:
Observations:- While cranking: 95-125 amps
- Hot Idle, nothing else on: 14 amps
- High Beams on: 33 amps
- A/C on (cooling fan on, blower motor on high): 71 amps
- Radio on w/volume turned up: 74 amps
- Higher current while cranking on the '99 XJ. The meter doesn't have the response time to see what's really happening so I just made a note of the peak measurement I saw. Out of curiousity, I swapped the 120 amp breaker from the '97 XJ in place of the 150 amp fuse on this XJ and after starting it 5 or 6 times in a row, it never popped the breaker. So that current didn't last very long, and the breaker doesn't trip instantly.
- Radio made a bigger impact on the '99 than the '97. I suspect this is mostly due to differences in standby power usage, and what the radio is doing when it's actually "off", as the headunits are different brands but both rated for similar output on each channel.
- I revved the motor while taking the top readings to see if I noticed any changes in current, and there weren't any on the '97. The '99 made a few extra amps when the radio was on but it was less than 5 amps extra.
- Apparently higher wattage bulbs aren't really higher wattage. Expected a difference between the headlight measurements but there wasn't a measurable one.
- The max power draw on a mostly stock '97-'01 XJ with no fog lights or driving lights appears to be about 75 amps.
- Stock alternators are capable of producing ~70 amps at idle
- A 150 amp fuse on a 160 amp alternator is fine if you don't need the last 10 amps (apparently I don't, as it hasn't blown once in 4+ years, but I've never run a winch either).
I used to have two extra sets of driving/flood lights on the front of this jeep with upgraded bulbs in both, and a set of reverse lights, I would have liked to see the measurements with all of those running but I'm in the process of re-wiring some switches and upgrading to an LED lightbar so it'll be a while before I can get a measurement on extra lighting. Based strictly on the bulb ratings, I had about 400 watts in lighting, which would have been around another 30 amps.
My trailer isn't here or I'd have measured with the trailer lights running as well, not sure when I'll be able to get those measurements but I'll update when I can.
Anyone want to see something more specific tested? Problem with my measurements? Let me know. I looked around and didn't find anyone who had actually posted all the stock numbers so figured some might find it useful.