Is stock alternator and battery up to powering these things all at same time? - JeepForum.com
 
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post #1 of 14 Old 03-19-2017, 05:39 PM Thread Starter
Charley3
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Is stock alternator and battery up to powering these things all at same time?

Is my 99 Classic XJ stock alternator and battery up to powering 100w high-beams, Kolak ignition system (MSD coil), heater-defroster fan, windshield wipers, and the stock radio all at the same time?

(I have spark-plugs gapped wider than stock to get the most from my MSD coil. My MSD coil is rated to be 1/3 more powerful than stock coil.)

Maybe that's a stupid question. I don't know. I'm not an electrical expert.


Edited in Later. To clarify what I mean about headlights: My high-beams are 100W each. That's 200W for headlights. I have a relay harness and 100/55W bulbs.


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post #2 of 14 Old 03-20-2017, 10:55 PM
Moezer
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that's the best way to kill your alt or battery, a good battery will go a long way tho,

I have stock alt and a 995 cranking amp bat and 800+ cold cranking amps, I'm powering my winch led lights and my 55 watt each head light along with an E fan and I think 100 wattx2 spot lights if my radio is on and heat blasing on high my batt dipps a bit then goes back up over 14Vts also if I turn on the e fan it stands still at 14v
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post #3 of 14 Old 03-21-2017, 12:31 AM
festerw
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IIRC the Classic trim came with a 117 amp alternator so you should be fine as long as you're you're not sitting at idle for extended periods.
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post #4 of 14 Old 03-21-2017, 12:48 AM Thread Starter
Charley3
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Heavy Load - Worst Case Scenario

I've done some more research. Here is what I learned for a heavy load, worst case scenario.

=====

150W front wipers (when under load, such as clearing snow). i.e. -worst case load.

50W rear wiper (when under load, such as clearing snow).

330W MSD Ignition

150W fuel pump

240W for electric engine fan + electric interior heater/AC fan. I don't have info on these separately. I only have info on them both on high (which can happen in deep snow where engine can get hot and need heat in cabin).

115W for two stock or near stock wattage low-beam headlights. I am including this in my total power figure since I could be idling with low-beams on at a traffic light in Summer at same time my engine electric fan is on.

Note: 185W for upgraded high-beams. However, I'm not including this in my total power figure since I'd only use high-beams when driving 40+ on highway at night, and in that scenario my electric engine cooling fan wouldn't be coming on.

65W for mildly upgraded exterior lights (parking lights, blinkers, tail lights, brake lights, backup lights)

50W mildly upgraded interior lights

50W (to 75W) mildly upgraded stereo. I probably won't ever crank it above 50W, but to be safe I'll use 63W for my calculations.

320W for mildly upgraded horns. Stock horns use around 250W. So 320W is reasonable for upgraded horns.

=====

Total 1533W, which is 120 Amps at 12.8V (heavy load scenario).

With engine at idle 750 rpm the alternator puts out 40% of its potential. Just off idle at around 1100 to 1200 rpm alternator puts out about 50% of its potential.

So based on that ^ I need a 240A rated alternator to perform well at idle and just above idle. Obviously I won't be buying a 240A alternator. I don't even know if anyone makes one that scookum.

At 1400+ rpm an alternator makes 100% of it's potential. So at 1400+ rpm I need a 120A alternator. So a 128A or 130A alternator would be perfect for worst case scenarios, IMO.

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post #5 of 14 Old 03-21-2017, 01:18 AM Thread Starter
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Medium Load (or slightly heavier than medium) - This is a likely scenario for me.

OK. So I refigured everything with a more likely medium load situation.

=====

50W front-wipers light-load (low-speed rainy weather)

16W front-wipers light-load (rainy weather)

275W MSD Ignition

75W fuel pump

240W for electric engine fan + electric interior heater/AC fan. I don't have info on these separately. I only have info on them both on high (which can happen in deep snow where engine can get hot and need heat in cabin).

115W for two stock or near stock wattage low-beam headlights. I am including this in my total power figure since I could be idling with low-beams on at a traffic light in Summer at same time my engine electric fan is on.

Note: 185W for upgraded high-beams. However, I'm NOT including this in my total power figure since I'd only use high-beams when driving 40+ on highway at night, and in that scenario my electric engine cooling fan wouldn't be coming on.

65W for mildly upgraded exterior lights (parking lights, blinkers, tail lights, brake lights, back up lights).

50W mildly upgraded interior lights (all interior lights on - like when door is open)

40W (to 75W) mildly upgraded stereo. I probably won't ever crank it above 50W.

0W horns. Since this is a light load scenario I'll use 0W for horns.

=====

Total 926W, which is 72A at 12.8V (medium load scenario). i.e. - at typical situations that are likely to occur.

With engine at idle 750 rpm the alternator puts out 40% of its potential. Just off idle at around 1100 to 1200 rpm alternator puts out about 50% of its potential.

So based on that ^ I need a 144A rated alternator to perform well at idle.

At 1400+ rpm an alternator makes 100% of it's potential. So at 1400+ rpm I need a 72A alternator. So a 117A alternator would be great at 1400+ rpm. I think I already have a 117A.

However, a 136A alternator would be much better.

A 160A would be to much. A larger alternator increases drag on engine, which decreases fuel economy. So there is a benefit to getting an appropriate size alternator. To small an alternator doesn't make enough amps. To large an alternator needlessly increases drag on engine and wastes gas and engine torque and HP. So the key is to have an appropriate size alternator. No more and no less.

I'm leaning towards getting a 136A alternator, or maybe a 150A aftermarket alternator. Though of course I'm open to advice and suggestions.

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post #6 of 14 Old 03-21-2017, 01:34 AM Thread Starter
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I'm interested in hearing advice for how to increase my engine idle to 1400+ rpm and info on sources for 130A, 136A, or 140A alternator and install instructions.

What is the largest plug-and-play direct bolt in alternator I can get? What are my options if I'm willing to do slight modifications?

What is the "Big 3" wiring upgrade I keep hearing about?
Is that referring to 3 ground wires, or something else? I've already replaced my battery cables pos and neg wires with 00 wires, and I also upgraded the wire that bolts from battery to alternator. All that came with my Jeeper and Creepers 00 battery cable upgrade. Is there another wire (or more) that I need to upgrade?

I have a standard wet cell G34 battery. Does that need upgrading?

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post #7 of 14 Old 03-21-2017, 05:21 AM
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I had/have a 150amp off of EBay. I had to modify the bracket for it to fit. There are 160-200 amp ones on EBay, that are advertised to fit the stock bracket. I bought a 136 amp from NAPA, that should fit the stock bracket. I plan to upgrade the wire (4 ga) and use a 150 amp fuse. NAPA has a 150 amp fuse. Need to add anther post at the PDC. Where the green fuse link is at.
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post #8 of 14 Old 03-21-2017, 05:45 AM Thread Starter
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Quote:
Originally Posted by 75SV1 View Post
I had/have a 150amp off of EBay. I had to modify the bracket for it to fit. There are 160-200 amp ones on EBay, that are advertised to fit the stock bracket. I bought a 136 amp from NAPA, that should fit the stock bracket. I plan to upgrade the wire (4 ga) and use a 150 amp fuse. NAPA has a 150 amp fuse. Need to add anther post at the PDC. Where the green fuse link is at.
Why are you buying a 136A if you already have a 150A? What am I missing there? Can eBay sellers be trusted? I've been ripped off several times buying things from eBay. I'm pretty leery of eBay. But if you've already dealt with the seller and they were good then I'd be likely to trust them too.

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post #9 of 14 Old 03-21-2017, 07:47 AM
75SV1
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I was having issues with the accessory drive. It started before I installed that alternator, but got worst after that. I decided to replace that alternator with a more stock one. I found that the harmonic balancer elastomer came lose. Also, the thrust bearing and surface on the crank is bad. Long story. I don't believe the alternator is bad. Just the 136 amp is a direct fit.
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post #10 of 14 Old 03-21-2017, 11:16 AM
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I don't see anything in the calculations that shows replacing the stock alternator is required. Don't forget that the battery is a reservoir of amperage that is easily and quickly refilled, and that one very seldom idles for an extended period of time at full power usage.

The obvious first modification is to activate the Extended Idle function. If you really think greater alternator changing capacity/output is required, have the local alternator shop custom build one in the stock case.

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post #11 of 14 Old 03-21-2017, 12:39 PM
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I had a 117 amp alternator in both my XJs, they had a 9500lbs. winch, and winching at high idle I never drained the battery. I find it extremely unlikely you would need anything but a standard alternator in your XJ with the basic stuff you have + a set of high- power bulbs. You are overthinking this whole thing.


ZJ 5.9s have a 150amp alternator; they only have an e-fan, which draws something of around 40amps constant load at high speed. At e-fan start-up, it's even more than that. The surface area of the blades is about three times that of the XJ aux. e-fan, XJ e-fan probably doesn't draw much more than 20amps max - if even that.
I've never managed to drain the battery or overload the charging system on my niner, not even when using a winch.

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #12 of 14 Old 03-21-2017, 05:21 PM Thread Starter
Charley3
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Quote:
Originally Posted by CJ7-Tim View Post
I don't see anything in the calculations that shows replacing the stock alternator is required. Don't forget that the battery is a reservoir of amperage that is easily and quickly refilled, and that one very seldom idles for an extended period of time at full power usage.
You're probably right. I had a math error that overstated my needs by 38A. I corrected that in my earlier posts.

Quote:
Originally Posted by CJ7-Tim View Post
The obvious first modification is to activate the Extended Idle function. If you really think greater alternator changing capacity/output is required, have the local alternator shop custom build one in the stock case.
Those are good ideas. I especially like the idea of beefing up stock alternator (though it probably isn't needed).

Warning: I often edit my posts a few times to get them complete or correct errors.
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post #13 of 14 Old 03-21-2017, 05:32 PM Thread Starter
Charley3
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I probably don't need a larger alternator, but humor my curiosity.

How much can a stock 117A alternator's Amps be increased with extra windings?

What are the largest available bolt-in plug and play alternators?

I don't want to modify mounting brackets.

Warning: I often edit my posts a few times to get them complete or correct errors.
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post #14 of 14 Old 03-22-2017, 12:33 AM Thread Starter
Charley3
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Quote:
Originally Posted by 75SV1 View Post
I had/have a 150amp off of EBay. I had to modify the bracket for it to fit. There are 160-200 amp ones on EBay, that are advertised to fit the stock bracket. I bought a 136 amp from NAPA, that should fit the stock bracket. I plan to upgrade the wire (4 ga) and use a 150 amp fuse. NAPA has a 150 amp fuse. Need to add anther post at the PDC. Where the green fuse link is at.
Please keep me posted on your 136A alternator mod.

I like to know how it works out for you.

Please let me know after you've installed it if it was indeed a direct bolt-in plug and play.

Also please post the part number.

Warning: I often edit my posts a few times to get them complete or correct errors.
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