Is my stock alternator and battery up to powering this?
03-19-2017, 06:07 PM
#1
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Is my stock alternator and battery up to powering this?
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.
(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.
Last edited by Charley3; 03-19-2017 at 08:04 PM.
03-19-2017, 07:04 PM
#3
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Year: 2000
Model: Cherokee (XJ)
Engine: 4L, 6 cylinder, 190 hp, 225 ft lp torque
I'm no expert, but I'll give it a go. Your headlight high beams should be 65w each, 130w total for those. Does the aftermarket coil draw more than the stock coils? To me it sounds like everything you mentioned is what the system was designed to do. I would say that yes your stock alt and battery (if in good condition) are up to the challenge.
Just an example: lets say 250 w total. That converts to 21 amps. The stock alt is rated at 117 amps. I think your ok.
Just an example: lets say 250 w total. That converts to 21 amps. The stock alt is rated at 117 amps. I think your ok.
03-19-2017, 08:02 PM
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I'm no expert, but I'll give it a go. Your headlight high beams should be 65w each, 130w total for those. Does the aftermarket coil draw more than the stock coils? To me it sounds like everything you mentioned is what the system was designed to do. I would say that yes your stock alt and battery (if in good condition) are up to the challenge.
Just an example: lets say 250 w total. That converts to 21 amps. The stock alt is rated at 117 amps. I think your ok.
Just an example: lets say 250 w total. That converts to 21 amps. The stock alt is rated at 117 amps. I think your ok.
Last edited by Charley3; 03-20-2017 at 02:15 AM.
03-20-2017, 08:14 AM
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Year: 1990
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Engine: 4.0
Ohms Law -
Volts x Amps = Watts
Equation can be rearranged to solve for amps, given volts and watts.
Amps = Watts/Volts
200/14 = 14.28 Amps
Solve for the rest of your components, add them together, and subtract for Alternator rating.
Volts x Amps = Watts
Equation can be rearranged to solve for amps, given volts and watts.
Amps = Watts/Volts
200/14 = 14.28 Amps
Solve for the rest of your components, add them together, and subtract for Alternator rating.
03-20-2017, 11:05 AM
#7
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If you are worried do the big 3 upgrade before you change your alternator or battery. Those 18 year old wires can get pretty corroded. I did mine with 0 Gauge OFC wire. Overkill but the kit wasn't much more than the cheap wire kits.
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03-21-2017, 02:41 AM
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What other cables should I upgrade?
03-21-2017, 02:41 AM
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Yes. I did that. I'll post my results below.
03-21-2017, 02:43 AM
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Model: Cherokee
Heaviest Load Scenario (not likely to happen much, if ever)
I've done some more research. Here is what I learned for a heavy load, worst case scenario.
Wipers 12 Amps under load (like snow on windshield). Usually around 2 to 4 amps. Amps depends on load. i.e. - resistance (snow or ice increase load for example)
=====
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.
500W for mildly upgraded exterior lights (parking lights, blinkers, tail lights, brake lights, backup lights)
100W 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 2018W, which is 158 Amps at 12.8V.
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 316A rated alternator to perform well at idle and just above idel. Obviously I won't be buying a 316A alternator. I don't even know if anyone makes one that scookum.
At 1500+ rpm (maybe 1400 rpm) an alternator makes 100% of it's potential. So at 1450+ rpm I need a 158A alternator. So a 160A alternator from a Durango or Grand Cherokee V8 would be perfect.
However, several of the above items draws are based on worst case scenarios for that item. For example the wipers power draw I used is for when they're pushing snow.
A 160A Durango alternator sounds good, or maybe a 160A from a Grand Cherokee V8? However, do I really need that much? Probably not.
Wipers 12 Amps under load (like snow on windshield). Usually around 2 to 4 amps. Amps depends on load. i.e. - resistance (snow or ice increase load for example)
=====
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.
500W for mildly upgraded exterior lights (parking lights, blinkers, tail lights, brake lights, backup lights)
100W 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 2018W, which is 158 Amps at 12.8V.
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 316A rated alternator to perform well at idle and just above idel. Obviously I won't be buying a 316A alternator. I don't even know if anyone makes one that scookum.
At 1500+ rpm (maybe 1400 rpm) an alternator makes 100% of it's potential. So at 1450+ rpm I need a 158A alternator. So a 160A alternator from a Durango or Grand Cherokee V8 would be perfect.
However, several of the above items draws are based on worst case scenarios for that item. For example the wipers power draw I used is for when they're pushing snow.
A 160A Durango alternator sounds good, or maybe a 160A from a Grand Cherokee V8? However, do I really need that much? Probably not.
03-21-2017, 02:45 AM
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Medium Load (or slighly heavier than medium). This is a likely scenario for me.
OK. So I refigured everything with a more likely medium load situation.
Wipers 12 Amps under heavy load (like snow on windshield). Usually around 2 to 4 amps. Amps depends on load. i.e. - resistance (snow or ice increase load for example)
=====
150W front wipers heavy load (clearing snow). i.e. -worst case load.
50W front-wipers light-load (full-time low-speed rainy weather)
50W rear-wiper heavy-load (clearing snow).
16W front-wipers light-load (rainy weather)
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.
500W for mildly upgraded exterior lights (parking lights, blinkers, tail lights, brake lights, backup lights)
300W since most of time I won't be stepping on brakes or in reverse.
100W mildly upgraded interior lights (all interior lights on - like when door is open)
25W interior lights when driving (dash and controls only)
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.
In this scenario I'll use 35W for my calcuations since I don't listen to loud music.
320W for mildly upgraded horns. Stock horns use around 250W. So 320W is reasonable for upgraded horns.
Since this is a light load scenario I'll use 0W for horns.
=====
Total 1261W, which is 99 Amps at 12.8V at medium draw. i.e. - typical situations that may 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 198A rated alternator to perform well at idle.
At 1500+ rpm (maybe 1400+ rpm) an alternator makes 100% of it's potential. So at 1400+ rpm I need a 99A alternator. A 117A alternator would do nicely at 1400+ rpm. Probably would do well enough at 1200+ rpm. So based on that a 117A alternator will do.
However, a 136A alternator would be much more ideal, IMO.
A 160A would be ideal for worst case scenario heavy-load power, but I'd rarely need that much power. 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 altenator. No more and no less.
I'm leaning towards getting a 136A alternator. Though of course I'm open to advice and suggestions.
Wipers 12 Amps under heavy load (like snow on windshield). Usually around 2 to 4 amps. Amps depends on load. i.e. - resistance (snow or ice increase load for example)
=====
150W front wipers heavy load (clearing snow). i.e. -worst case load.
50W front-wipers light-load (full-time low-speed rainy weather)
50W rear-wiper heavy-load (clearing snow).
16W front-wipers light-load (rainy weather)
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.
500W for mildly upgraded exterior lights (parking lights, blinkers, tail lights, brake lights, backup lights)
300W since most of time I won't be stepping on brakes or in reverse.
100W mildly upgraded interior lights (all interior lights on - like when door is open)
25W interior lights when driving (dash and controls only)
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.
In this scenario I'll use 35W for my calcuations since I don't listen to loud music.
320W for mildly upgraded horns. Stock horns use around 250W. So 320W is reasonable for upgraded horns.
Since this is a light load scenario I'll use 0W for horns.
=====
Total 1261W, which is 99 Amps at 12.8V at medium draw. i.e. - typical situations that may 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 198A rated alternator to perform well at idle.
At 1500+ rpm (maybe 1400+ rpm) an alternator makes 100% of it's potential. So at 1400+ rpm I need a 99A alternator. A 117A alternator would do nicely at 1400+ rpm. Probably would do well enough at 1200+ rpm. So based on that a 117A alternator will do.
However, a 136A alternator would be much more ideal, IMO.
A 160A would be ideal for worst case scenario heavy-load power, but I'd rarely need that much power. 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 altenator. No more and no less.
I'm leaning towards getting a 136A alternator. Though of course I'm open to advice and suggestions.
03-21-2017, 02:46 AM
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I probably have a 117A alternator now. Not sure. I'll check later this week. I haven't yet done the lighting, horn, or stereo mods. The only electrical mod I've done so far is install a relay harness for my headlights. At this moment my headlights are still stock wattage.
A 117W alternator would be plenty for me if my idle was at least 1400 rpm, but I kind of want a 130A or 136A alternator. I think a 160A would be overkill and cause unnecessary drag on engine and reduced gas mileage.
I'm interested in hearing advice for how to increase my engine idle to 1400+ rpm, and/or info on sources for a 130A or 136A alternator and install instructions.
A 117W alternator would be plenty for me if my idle was at least 1400 rpm, but I kind of want a 130A or 136A alternator. I think a 160A would be overkill and cause unnecessary drag on engine and reduced gas mileage.
I'm interested in hearing advice for how to increase my engine idle to 1400+ rpm, and/or info on sources for a 130A or 136A alternator and install instructions.
03-21-2017, 02:49 AM
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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. Nothing special. Does that need upgrading?
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. Nothing special. Does that need upgrading?
03-22-2017, 08:03 PM
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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. Nothing special. Does that need upgrading?
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. Nothing special. Does that need upgrading?
Alternator charging wire to Battery positive
Battery negative to chassis ground wire
Engine Block to chassis ground wire
03-22-2017, 08:10 PM
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Year: 1990
Model: Cherokee
Engine: 4.0
It is not likely you will exceed your current alternator's capabilities. If you do for a brief period of time, you will run the battery down a bit. Likely not enough to cause the jeep to not restart. I would suggest you leave the electrical alone until you actually have an issue. Either the stock alternator fails, or you consistently run the system above it's abilities. At that point, swap in the 160 amp unit. Go big or go home I say, you don't drive an XJ for mileage.