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  #1  
Old January 18th, 2007, 07:29
92DripCherokee's Avatar
92DripCherokee 92DripCherokee is offline
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Why not wire alternator directly to battery?

My 92 4.0 has a long run of skinny 10 gauge wire from the alternator + side to the starter relay.

Is there a good reason why there's no shorter, heavier guage wire running directly from the alternator's + side to the battery? (fused of course)

It looks like the whole system was designed to save Chrysler some copper!

Does anyone have pics of their rewired 91 up charging system, upgraded alternators and all?
(Sometimes I wish I had a Renix cherokee! Damn things seem more serviceable.)

Last edited by 92DripCherokee; January 18th, 2007 at 07:34.
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  #2  
Old January 18th, 2007, 08:01
XJING XJING is offline
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Re: Why not wire alternator directly to battery?

http://www.olypen.com/craigh/charge.htm
http://www.olypen.com/craigh/elec_system.htm
Good reading and write up.
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  #3  
Old January 18th, 2007, 08:31
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92DripCherokee 92DripCherokee is offline
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Re: Why not wire alternator directly to battery?

That "olypen" writeup does cover the 91' and up, but it describes a different circuit arrangement than what I see on my jeep.


The olypen write up describes the alternator + wire running directly into the PDC, which on my jeep it does not.

On mine, the hot circuit goes from alternator b+, to starter, then battery, and finally to the PDC.

I'm going to find a charge circuit diagram in the mean time, but if anyone has pics of this kind of "bypass", i'd really appreciate it.
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  #4  
Old January 18th, 2007, 08:33
lighthouse jim lighthouse jim is offline
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Re: Why not wire alternator directly to battery?

the olypen site is good! thanks
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  #5  
Old January 18th, 2007, 08:43
lighthouse jim lighthouse jim is offline
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Re: Why not wire alternator directly to battery?

5-90 has a good site--he offers sets of large gauge wires made up for particular applications. I just installed a set and love them, and he has a lots of tech insight, too.


http://www.geocities.com/JeepI6Power/index.html
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  #6  
Old January 18th, 2007, 14:21
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Re: Why not wire alternator directly to battery?

Why not run it directly to the battery? No particular reason, I suppose - other than accountants making engineering decisions.

Electrically speaking, you can run the alternator output to any terminal that has a direct connection to the battery anode - I've even seen it run to the start motor mains post (which is always hot!)

In later models with the PDC, you can run the alternator into the bottom of the PDC (OEM location,) to the input post on the PDC, and to the battery anode - all are the same connection, electrically speaking. However, once you move the alternator output lead from its original location, you will want to do something to restore fuse protection - because it's either going in through a fusible link, or a pair of MAXI60 fuses in the PDC. That's why I have ANL fuses and blocks (also provides for upgrading protection when installing an uprated alternator.)

10AWG is rather puny for a mains lead tho - that should be 6AWG or larger (larger, if you're going to uprate your alternator. I think 6AWG is right on the ragged edge for OEM output ratings, but that's in keeping with "beancounter engineering." An engineer would put in 4AWG or 2AWG to make himself comfortable - the cost difference is minimal, and Jeeps have a history of being modified anyhow.)
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  #7  
Old January 18th, 2007, 15:27
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Re: Why not wire alternator directly to battery?

Slaughterama by Gwar?
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  #8  
Old January 18th, 2007, 15:48
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Re: Why not wire alternator directly to battery?

Quote:
Originally Posted by dizzymac
Slaughterama by Gwar?
Ayuh.

casm already got it backchannel, but I haven't come up with a suitable replacement yet...
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  #9  
Old January 18th, 2007, 19:58
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92DripCherokee 92DripCherokee is offline
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Re: Why not wire alternator directly to battery?

Well the +12 stud on the back of my alternator is so stubby, i dont see how i can piggyback a second wire on top of it and still tighten the nut,

is it safe to just completely omit the old run from the alternator to the starter and replace it with a run of 4 gauge straight to the batt (fused at 125 amps)?
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Old January 18th, 2007, 19:59
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Re: Why not wire alternator directly to battery?

Ayuh - that's what you end up doing with one of my kits. The 1AWG cable goes from the alternator to the fuse block, then another run from the fuse block to the battery.
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  #11  
Old January 20th, 2007, 08:11
gjxj gjxj is offline
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Re: Why not wire alternator directly to battery?

I suspect they dont go direct to battery simply because that area is more prone to corrosion and more frequently messed with during battery changes.

If you make a run from alternator to battery you really should do away with the run to the starter. You dont want an alternate path through small wires from battery to starter fo obvious reasons.
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  #12  
Old January 20th, 2007, 09:16
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Re: Why not wire alternator directly to battery?

I just put on 1 AWG Wire From Jon Kelley 5-90. I love it! Totally suggest doing this!! I have picture if anybody needs.
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  #13  
Old January 20th, 2007, 09:24
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Re: Why not wire alternator directly to battery?

If you run the alt straight to the battery, you will no longer be able to run the engine without a battery.

Stock, you can start the engine, then remove the battery and it will still run, because the alt is supplying all the engines demands.

Also, the volt reg senses the voltage & current needed for the vehicle, NOT the battery. It supplies this and charges the battery at the same time. That way, the battery will charge up AND the vehicle will run.

If you send all this straight to the battery, then as soon as you turn the vehicle off, the battery will be low, since the alt will only be supplying what is needed to recharge the battery. Stock it supplies the vehicle AND recharges the battery. If it goes straight to the battery, it will only charge the battery, while the battery is being sucked down at the same time by the vehicle.

The alt cannot instantly do a full recharge on the battery. So, if you run the alt to the batt, after you start and stop the engine a few times with a short recharge period, you will slowly kill the battery. You lose the full electric power to the vehicle with the excess recharging the battery. Now, you only charge the batt, and you are doing so at the same time it is being drained.

It's kinda like running my laptop off AC while the battery is being charged. If the AC only charged the battery (same as running the alt straight to the batt), I wouldn't be able to use it (like I am now) while the battery is being recharged, until the battery has been recharged enough to run the computer.

Also the battery is kinda a backup power supply for the vehicle. Stock, the alt supplies the vehicle, and when the alt dies, the battery does this until it dies. You don't even need a battery if you jump start it.

If you run the alt to the batt, it will work the same way, but the battery won't be at full charge when it takes over, and it won't nearly as long, since as the alt is dying, the battery charge is dropping. You lose the redundant safety factor of 2 power sources running the alt to the batt straight.

If the gage of wire is what concerns you, upgrade it, but don't run the alt to the batt only.

Last edited by TRCM; January 20th, 2007 at 09:32.
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  #14  
Old January 20th, 2007, 09:38
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Re: Why not wire alternator directly to battery?

Well said TRCM,

I'd say that'd be your reason why!
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  #15  
Old January 20th, 2007, 09:43
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Slo-Sho Slo-Sho is offline
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Re: Why not wire alternator directly to battery?

Spoken like a true bookworm.

Disconnecting the vehicle's battery while the alternator is charging is a great way to destroy voltage sensitive electronics. Oh and the battery is the main supply for the vehicle, the alternator charges the supply (battery).

The main output stud on the alternator is always 'HOT'. FYI.

Last edited by Slo-Sho; January 20th, 2007 at 09:46.
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