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  #1  
Old 11-22-2019, 04:15 PM
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mwood65 mwood65 is offline
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Alternator question

I apologize if there are threads already but I wasn't able to find them...



I have the stock Alternator on my 74' Cherokee which is I think 35 amps and wanted to change it out for something with a little more output for the lighting upgrade and other stuff I will be installing.


I would like to just find one that uses the stock brackets and would be just a swap out if possible, something like 60 amps to 80 amps would be good.


Anyone know what will work? Maybe just an OEM one from a later Jeep or something?
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Old 11-23-2019, 01:53 PM
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'74 uses a Motorola alternator. There are companies that sell Delco 10SI or 12SI alternators (what you want) that bolt in for the Motorolas. Search online and you should find them. There's also a bolt-on bracket that lets you use a regular Delco 10SI.

Do not use a more powerful alternator with your factory ammeter, or you risk a dash fire. There is a sticky thread at the top of the forum with discussion of how to bypass the ammeter.
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Old 11-24-2019, 03:40 PM
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I swapped out my 30 amp Motorola for a 150 amp Powermaster "Motorola replacement" alternator
http://www.powermastermotorsports.com/catalog.html


Powermaster is the only one I found with the direct replacement. The lower lug on the Motorola is only 1" wide, the later GM alternators they used were 2" wide. A GM style can be used but the mounting lug has to be modified.



The only problem I ran into was it contacts the oil filter but I think that is because '72 uses a short water pump. I think on later ones with 1/4" more spacing that wouldn't be a problem. It is a one wire alternator but has a plug for an idiot light but not amp meter.
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Old 11-25-2019, 05:11 PM
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Great!

Thanks for the input! I will shop around


Thanks for the info on the ammeter also, I will install an aftermarket one probably.....or go read the sticky first.
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Old 11-25-2019, 07:05 PM
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Quote:
Originally Posted by mwood65
Thanks for the input! I will shop around

Thanks for the info on the ammeter also, I will install an aftermarket one probably.....or go read the sticky first.


bypass the ammeter for the sake of your electrical system, and use a voltmeter


some links w picts


http://www.madelectrical.com/electrical-tech.shtml


before



after bypass


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Old 11-25-2019, 08:08 PM
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I'm sorry, but I have to disagree on the MAD bypass.
It's a poor wiring strategy.
Since all of the equipment is still getting power from the main splice, that design increases the wire length and adds junctions. It also increases the number of fusible links the current has to flow through.



The only thing it improves is the flow of current to the battery. But recharging is only temporary condition. With an alternator that can keep up with the loads, recharging should only be needed after startup - unless - additional equipment is being run.



An alterator with slightly higher output - especially at idle - should not be an issue.



An alternator with very high output can do serious damage to a severely discharged battery at driving rpms. That assumes the wiring doesn't give out. A voltmeter will not provide a clue of that disaster looming. Think out the whole package - first!
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Old 11-25-2019, 08:16 PM
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Quote:
Originally Posted by mwood65
I apologize if there are threads already but I wasn't able to find them...



I have the stock Alternator on my 74' Cherokee which is I think 35 amps and wanted to change it out for something with a little more output for the lighting upgrade and other stuff I will be installing.


I would like to just find one that uses the stock brackets and would be just a swap out if possible, something like 60 amps to 80 amps would be good.


Anyone know what will work? Maybe just an OEM one from a later Jeep or something?




How much more current will your modifications draw?
This is the starting point.
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Old 11-26-2019, 08:17 PM
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Bear with me here as I am very much NOT an electrical expert.....


Can't you put a voltage regulator inline before the ammeter to cut the current...(eh, I saw what I typed and think I answered my own question)


A voltage regulator cuts voltage but not amperage.?


Is there no way to reduce the amperage going into the vehicle but have the extra charging power going to the battery?



My battery is 12 volts but around 900 amps yet that doesn't all go to the wiring harness......right?


What keeps the 900 amps in the battery from frying all the circuits?


Somebody school me please on this kind of stuff.


I only know the basics....
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Old 11-26-2019, 10:55 PM
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Quote:
Originally Posted by mwood65
Bear with me here as I am very much NOT an electrical expert.....

I can be patient. After all, I still own the SJ after how many years?


Quote:
Can't you put a voltage regulator inline before the ammeter to cut the current...(eh, I saw what I typed and think I answered my own question)

Good!
Let's see if what you thought lines up my explanation.
Pretty much all car/truck ammeters are used to monitor current flow to and from the battery.
To do this the ammeter is placed between the battery and everything but the starter.


When the alternator is capable of producing enough power at a voltage above the batteries voltage, the alternator becomes the source of power.
If the battery battery is charged, on a simple setup like this 60s Plymouth-Dodge, current flow looks like this.


But if the battery is somewhat discharged and the alternator can supply the additional power to recharge it, then flow will look like this.



The 1960s Chrysler alternators and voltage regulators were the simplest, so lets start with them.

An alternator generates power when the spinning electromagnet moves electrons in the wires surrounding it. The spinning electromagnet is the rotor. The strength of the electromagnetic field is highest when we allow unrestricted current to flow through it. The 1960s Chrysler voltage regulator controlled the magnetic field by allowing full current, restricted current, or no current to the rotor. The switching could happen very rapidly or very slowly depending on what was needed. A grounded brush completed the circuit.

So that's the concept even though the Motorola has more wires.

Quote:
A voltage regulator cuts voltage but not amperage.?
The regulator cuts current flow through the rotor. It can do this on either the feed in or return to ground.
Its internal decision making is based on the voltage.
Current flowing out of the alternator depends on the need.

This makes more sense if we look at some things that need power.
The ignition in the schematic above is drawing about 2 amps, and the rotor is also drawing about 2 amps - although probably not steadily.
The battery is shown drawing 5 amps. Total of 9 amps current at that voltage.
When the battery is fully charged, it will draw zero. Then the current to the field will be reduced or not as long near its maximum.

For many things, the current drawn increases with increasing voltage.
A light bulb at 14 Volts will draw more current (and be brighter) than a bulb at 12.5 Volts.
A battery is only different in that the current drawn also depends on how close it is to fully charged. A fully charged battery will draw no current at 14 Volts. While a somewhat discharged battery could draw 30 amps at 14 Volts. But whatever the condition is, if a low battery is subject to a lower voltage it will draw less.

Quote:
Is there no way to reduce the amperage going into the vehicle but have the extra charging power going to the battery?
That's basically how the original system was designed to work.
The current flows to the equipment first, in part because a battery that is only slightly discharged isn't going to demand a lot of current when the alternator is only producing power around 13.5 Volts (at idle).

Here's a page from a 1960 Chrysler Master Technician's booklet that says just that.
http://www.imperialclub.com/Repair/L...148/page09.htm

Quote:
My battery is 12 volts but around 900 amps yet that doesn't all go to the wiring harness......right?
Exactly!

Quote:
What keeps the 900 amps in the battery from frying all the circuits?
Resistance!
As long as there is a device, even if its a small light bulb, only the current needed flows. The dome light is a perfect example.

But if the wire to the dome light was accidently grounded, resistance will be very low and then the battery will send a whole lot of current!! Since the dome light is on a fuse, anything more than the fuse rating and connection breaks. The fusible link is there to protect the main feeds and the ignition curcuit. It won't pop quick like a fuse, but its better than letting a 12 gage wire burn everything around it!
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Old 11-26-2019, 11:21 PM
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A couple more things worth mentioning.

Alternator ratings are kindof like small arms calibers. They are approximations and may or may not be useful for comparison.

Generally the current rating is based on something close to its maximum output at higher rpm.
While the original manufacture probably had some consistancy, aftermarket can easily cheat the numbers. They can make their units look better taking the current rating from powr output at higher rpm, or at a lower voltage.

Sometimes a higher rated alternator is for a specific need, and the higher output was achieved at the cost of poorer performance at low rpm.
That can be seen on this chart of from the AC Delco catalog.
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  #11  
Old 11-27-2019, 10:05 AM
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I used a Motorola replacement 10SI meant for marine use from Ebay.
The bottom flange, I had to grind down a bit and drill & tap a new hole for the "slider" bolt.
Easy enough to do and it's a lot cheaper than a Powermaster.
Doing it again, I might spend the extra money on a Powermaster - but then again, this way, I have a 10SI alternator with a face plate I can swap over if needed down the line.
I went one wire - stud to battery - and it charges just fine at idle with the fans on. If there's more to ask for from an alternator I don't know what it is.
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Old 11-29-2019, 09:14 AM
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i think you guys get way too concerned about the amp gauge in these things.
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Old 11-29-2019, 12:15 PM
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Quote:
Originally Posted by Ristow
i think you guys get way too concerned about the amp gauge in these things.
+1
Agreed.
"If maintained" the amp gauge is not a for sure eventual FSJ Car-B-Q waiting to happen. What causes fires is not the gauge failing but rather neglect. Terminals getting loose and corroded causing excess heat/fires. Every few years(10?) not a bad idea to remove the wires and clean the connections to shiny new and tighten the nuts securely. A dab of dielectric grease on assembly is good moisture, corrosion prevention. In the mean time occasionally reach up under the dash and check the connections are still tight. Keep'em clean and tight and you're golden.
Obviously running an non-stock 90A alt through a 60A gauge etc is a serious no-no. If you need to upgrade to a larger amp gauge...go with a quality brand name like VDO, Autogauge etc not the cheapest chinese crap available on ebay.
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Old 11-29-2019, 06:34 PM
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wow!

thanks for all the schooling nograin!


As for the question of how much power am I going to need...? I am not sure of how much I will end up needing in the end but would like to have 50-60 amps on hand. i don't foresee needing anymore than that. 50A would be plenty.


I am just upgrading the headlights to HELLA lights.

I plan on adding:
2 KC daylighters
An LED flood light on the back end (which won't draw much)
A new stereo
And lastly eventually a medium size winch (probably 9000lb.)
I know, I know. Everybody is going to say you need at minimum a
500,000 lb. winch...


With the off road experience and common sense I used to have, I have NEVER gotten really, really stuck.
In every instance I just needed a little help so I think a 9000# winch would be plenty.


Maybe I don't need even 50-60 amps? Who knows.
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Old 11-29-2019, 07:43 PM
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Are you putting your hella lights on relays? Great choice in brands btw... Is a good thing to do and you just use the former low and high beam wires to become signal wires for the relays. I just did this on a 01 dodge ram that is notorious for an undersized headlight circuit. Dim lights and warm wires. It made a big difference and is safer for the truck. I don't know much about your year rig, and the headlight wiring circuits and or if they could benefit from something like relays, but it takes the current flow off the vehicles circuits and puts it between the battery to the relays and to the bulbs. Full voltage and nice bright lights.

A 9K winch is fine. For a stronger pull, get a snatch block and tree strap and a short chain (when you are not attaching to a tree) and a shackle to hook it up. Double your line back through the pulley and it will be slower but pull a lot more than 9K. All winches are rated with one layer of cable on the drum. So two or three layers reduce the pull power. 9K is just fine for what you want to do. You probably knew all this, but I had to mention the snatch block or pulley.

For alternator parts. This place is great. I am putting a one wire Delco CS130 (slightly smaller case than a 10 or 12SI) on a bulldozer, and needed a really wide pulley for the big belt. Found the conversion pulley here.

https://www.aspwholesale.com/alterna...rts/delco.html

Anyway, good luck and happy wiring.
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Old 11-29-2019, 11:16 PM
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One thing I ran into with the Fitech EFI is it takes close to 30 amps by itself. I've read of people burning up 50 amp alternators because of the Fitech. With my 30 amp Motorola even using headlights was too much to keep the battery charged, and forget about running the quad high beams for more than a few minutes.



I figure bigger is better, some day I might want to run electric fans and seat heaters. I view the extra amperage as just reserve power. It's worth thinking about what distant future upgrades you might want, not just the ones in the immediate future.



The Powermaster also came with a paper where they had tested it at idle, mid range and high and gave the results. I remember at idle it produced more than 100 amps, I think it was 102, can't remember the exact numbers but they were pretty impressive.
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Old 12-01-2019, 11:55 AM
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Quote:
Originally Posted by mwood65
thanks for all the schooling nograin!
You're welcome!

Quote:
As for the question of how much power am I going to need...? I am not sure of how much I will end up needing in the end but would like to have 50-60 amps on hand. i don't foresee needing anymore than that. 50A would be plenty.
Whatever it adds up to, it will be best if the alternator wasn't being maxed out all the time.

I noticed in the '74 shop manual that 4 barrel equiped engines got a higher output, delta wound, alternator. A possible option. You'll have to find a shop that actaully deals with alternators that use soldered diodes. They could actually load a high output Motorola alternator at the rpm you need and tell you what the output is.

Quote:
I am just upgrading the headlights to HELLA lights.
A pair of 'vision plus' Hella HB2/H4 (or any H4 really) will draw approximately the same as stock 6014. As will GE's 'Nighthawk' halogen sealed beam.
Nominal rated power; high beam / low.
6014 60/ 50 Watts
H6024NH 65/ 50 Watts (This is the only version of the H6024 to draw 50 Watts on low)
HB2 and H4 60/55 Watts (HB2 also sold as 9003 bulbs)

To figure amps, divide the power in Watts by 12 Volts.
So 60 Watts divided by 12 V = 5 amps. That's minimum. The lamp will draw more at operating voltage of 13.5 to 14.5 Volts.
That can be seen here in Virgil's testing of H4 bulbs, two of which have nominal rating of 60/55 Watts but measured 73 Watts at 13.5 Volts.
https://www.candlepowerforums.com/vb...b-test-results
Bottom line is 5.5 or 6 amps will be fine for estimating.
Quote:
I plan on adding:
2 KC daylighters
An LED flood light on the back end (which won't draw much)
A new stereo
And lastly eventually a medium size winch (probably 9000lb.)
I know, I know. Everybody is going to say you need at minimum a
500,000 lb. winch...
Maximum current or power need for these you will have to get the info from the manufacture. Probably on the box or in the instructions.

Then add up all of the things that will be running at the same time.
And finally, which ones will be running when the engine is idling and which, if any, with the engine off.

All of the forward lighting can be placed on relays to reduce the number of connections and distance between the alternator and the lamp.

An electric winch can throw a wrench in the stock wiring.
There simply may not be enough power available from an alternator.
So it makes sense to attached to the battery - and this is what is usually done - right?
But the downsides are this. The battery gets really drained powering the winch. When done winching, the battery is really low, so it sucks as much power as it can from the alternator. The only regulation is the max the alternator can provide. This is when the charging circuit can get damaged.

I don't have an easy answer here. First find out what the winch's draw will be. Then figure out the best wiring and alternator scenario. It might include having a second battery isolated from the first. Lots of possibilities here.

As far as typical stock electric loads go I can offer the current draw I measured on my '85 GW.
Engine running and Alternator producing power at 14.3 Volts.
Heater Blower on max. -------------- 9.8 amps
Parking, marker and instrument lights 5.1 amps
Headlights, H4 --------------------- 9.0 amps
Total = 23.9 amps
Does not include rotor's field current because its an SI alternator. Figure another 2 - 3 amps.

Windshield wipers probably add another 5 to 7 amps. Need to look that up or measure.

So you can see that 30 amps was plenty even when driving in a wet, cold weather.
The use of electronic fuel injection, electric fuel pumps, fans, etc etc changed that. Another change with newer vehicles was the integration of A/C so that could be running at same time as defroster was blowing.
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Last edited by nograin : 12-01-2019 at 12:47 PM.
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Old 12-01-2019, 11:59 AM
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Just saw there is a power curve for the Motorola alternator in the FSM.

See page 74 of the electrical chapter!
https://oljeep.com/edge_74_tsm.html
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Old 12-01-2019, 03:44 PM
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This is what I use. The truck has a Holley Sniper. Voltage at idle drops to about 13V with the headlights and heater on, but I have the idle at 630 RPM. At 750RPM it's at 14.6V.



https://www.amazon.com/Electrical-Ad.../dp/B0081SB24G
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