Alternator to PDC wire upgrade (late xj)

I'll try my best to explain my question:

Is the alternator wire that runs directly into the PDC to fuse locations #F8 & #F16 (labeled "60A ALT PWR1" & "60A ACT PWR2") connected with only one wire at the load side?

What I want to do is bypass the 2 60A fuses when I upgrade to a larger wire. Are the two fuses on one line? Can I piggy back ONE wire to bypass both fuses?

Or, is it possible to (instead of piggy backing) replace the wire inside the PDC?

When either method is done what happens to all of the other fuses and relays in the PDC? Should they ALL be upgraded?

Bare with me hear I'm new to this lol. Thanks.

ALWAYS run fuses or breakers. Just run it the way they designed, only use bigger wire.....

poorboy_616 said:

ALWAYS run fuses or breakers. Just run it the way they designed, only use bigger wire.....

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From what I've read the stock wire cannot be removed. I'm wondering if anyone out there has done it. I understand the fuse part. What I would do is run an inline bar type fuse within the wire that I replace the stock wire with. If I just piggyback the original wire than I'll just upgrade the stock fuses.

My question is do I have to piggy back the stock wire?

I'm probably making this too complicated and should just jump the wire.

I'm learning here as I type lol.

No. Disconnect the alternator lead at the QD fitting they use (whatever sort it is,) and then the alternator can be run - via a fuse - to the PDC screwposts where the battery cable connects. Electrically speaking, they're the same connection (the two posts connect directly to the Buss bars in the PDC. The fuses connect to the Buss bars in the PDC. Problem solved.)

You can even run the alternator output directly to the battery post, or down to the large post on the starter motor (I've seen that done, but I don't really recommend it...) as long as it goes somewhere that is "always hot."

If you want to source a kit, hit me backchannel, or check my site. I can set something up for you...

5-90 said:

No. Disconnect the alternator lead at the QD fitting they use (whatever sort it is,) and then the alternator can be run - via a fuse - to the PDC screwposts where the battery cable connects. Electrically speaking, they're the same connection (the two posts connect directly to the Buss bars in the PDC. The fuses connect to the Buss bars in the PDC. Problem solved.)

You can even run the alternator output directly to the battery post, or down to the large post on the starter motor (I've seen that done, but I don't really recommend it...) as long as it goes somewhere that is "always hot."

If you want to source a kit, hit me backchannel, or check my site. I can set something up for you...

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Thank you.
I'll check out your site and see where I'm at from there. I may go local but I haven't put a parts list together yet ($$).

I do have another question for you. What size fuse would you recomend for a rewound 160A alternator?

I know my stock is a 116A alternator (IIRC) and the fuse is only 60A so that's roughly 1:2.

Deadman 94 xj said:

Thank you.
I'll check out your site and see where I'm at from there. I may go local but I haven't put a parts list together yet ($$).

I do have another question for you. What size fuse would you recomend for a rewound 160A alternator?

I know my stock is a 116A alternator (IIRC) and the fuse is only 60A so that's roughly 1:2.

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There are two 60A fuses in parallel in your PDC. It's a cheeky way to get a 120A fuse. Not my favourite, but it can and do serve.

For a 116A, I use a 125A ANL (easer to get than a 120.) For your 160A, I'd use a 175A ANL. I like ANL fuses because they're relatively easy to get, can be changed quickly, are more durable than AGU (large glass tube) fuses, and they're easier to find and source than 10AWG fusible link wire (I still can't find that stuff in bulk!) The rule of thumb for "in between" stuff like this is to take the very next larger rating and use that. Since an "alternator surge" is typically several hundred amperes, that works.

I just don't care for the "two fuses in parallel" solution that ChryCo came up with, I'm just funny that way. If one fuse came from Harbour Freight and won't blow out, the other one lets go and the fuse that doesn't blow out becomes the centre of your brand-new electrical fire! Yech...

Gotcha.
Thanks for your help. I'll let you know if I want to purchase a kit from you.

Tom

I used one of Jon's kits on my 91 MJ. I have to say the kit is first rate and built with quality and functionality in mind. Now, getting to the topic: When installing the kit, I originally disconnected the factory alt-to-pdc wire by removing the factory wire from the alt and disconnecting the tube connector between the alt and PDC. I replaced it with the much heavier gauge kit wire from the alt to the PDC bolt-on 1/4" stud. Even though it is the same point electrically, I noticed my voltmeter dipping down to 10-11 volts during heavy load periods, which it did not do before w. the factory setup. Measuring voltages, the charging voltage was spot-on, and the "at rest" voltage after sitting a couple of days did not move either. I then reconnected the original factory alt-to-pdc wire in parallel with the kit wire, and the voltmeter did not dip anymore under load. WTF?? After discussing this with Jon via emails, we concluded that it has to do how the voltmeter picks up it's "sensing" voltage, which is at the PDC. Bottom line, since my charging and at-rest voltages were fine to the battery, I re-removed the original factory wire for safety so I did not have parallel paths from the alt to the PDC with different resistances due to the gauges of the two leads. It's been working fine for quite some time now, much better than the factory setup. Hope this helps.

comanche91 said:

I used one of Jon's kits on my 91 MJ. I have to say the kit is first rate and built with quality and functionality in mind. Now, getting to the topic: When installing the kit, I originally disconnected the factory alt-to-pdc wire by removing the factory wire from the alt and disconnecting the tube connector between the alt and PDC. I replaced it with the much heavier gauge kit wire from the alt to the PDC bolt-on 1/4" stud. Even though it is the same point electrically, I noticed my voltmeter dipping down to 10-11 volts during heavy load periods, which it did not do before w. the factory setup. Measuring voltages, the charging voltage was spot-on, and the "at rest" voltage after sitting a couple of days did not move either. I then reconnected the original factory alt-to-pdc wire in parallel with the kit wire, and the voltmeter did not dip anymore under load. WTF?? After discussing this with Jon via emails, we concluded that it has to do how the voltmeter picks up it's "sensing" voltage, which is at the PDC. Bottom line, since my charging and at-rest voltages were fine to the battery, I re-removed the original factory wire for safety so I did not have parallel paths from the alt to the PDC with different resistances due to the gauges of the two leads. It's been working fine for quite some time now, much better than the factory setup. Hope this helps.

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So if I'm understanding this correctly, what you're saying is that you originaly replaced the factory wire and got dips. Then you put the factory wire back on with the thicker wire and all was fine. Then you figured out that the meter was to blame and went back and removed the stock wire to put it back to the original upgrade?
I just want to be sure that what you're saying is that the meter readings can be inaccurate. Thanks

Deadman 94 xj said:

So if I'm understanding this correctly, what you're saying is that you originaly replaced the factory wire and got dips. Then you put the factory wire back on with the thicker wire and all was fine. Then you figured out that the meter was to blame and went back and removed the stock wire to put it back to the original upgrade?
I just want to be sure that what you're saying is that the meter readings can be inaccurate. Thanks

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Yes, the meter readings can be inaccurate. The older the IP meter, the more inaccurate it can be (it's hardly a test instrument - I use mine as "relative state of charge.")

Also, I'm not sure exactly where the IP voltmeter picks up its "voltage sense," but it's not at the battery and not at the alternator. So, moving the other end of the alternator output lead can change the reading - usually lowering it (due to conductor losses. The "sense lead" is, electrically speaking, likely to be "farther away" from the alternator than it used to be.)

That's why the first thing I advise people nothing electrical problems to do is to back-check the IP voltmeter with a DMM - which damn sure is a test instrument, calibrated better from the factory, and considerably more likely to hold calibration. If the voltmeter reading (at the battery, as a first step) is good, then use a grease pencil to draw a new "nominal" reading on the IP gage - as automotive meters are fair-to-middlin' at best. That's why I'd like to reconfigure my IP to take aircraft gages - I not only like the look, they're more rugged, calibrated better, and hold calibration much longer.

comanche91 is correct about our exchange (sorry, I can't recall your proper name at the moment,) and the only reason I stopped looking into things was because we'd decided that the problem described above is what he was having. Since he was getting nice, steady voltage at the battery (meaning the alternator was up to scratch for that current level, the regulator was working well, the brush pack, diode pack, rectifier pack, &c. was working well, ...) he decided we'd gone through enough and called it good. Note that he decided we'd gone through enough, not me.

Short form - yes, the IP voltmeter can be (and often is) inaccurate. Yes, relocating the alternator output can increase that inaccuracy.

The moral of the story? Don't believe all of your gages. Noviry v proviry. Translation? "We trust but we also verify."

Jon summed it up well. I did extensive testing with a multimeter under full load conditions after the kit was installed; both electric fans on, headlamps on, A/C running, and the blower at full blast. The multimeter readings across the battery terminals was a steady 12V at idle (even though the meter read about 10V), and when going up to 1500 RPM the voltmeter was centerlined and the multimeter reading was 12.5V. So it's a meter calibration/sensing problem. I have a new factory meter ready to install - just have not got around to it yet. And yes, I do not have the factory wire installed anymore. Don

Well thanks for the heads up. I'm not sure what I would have done when I got the readings seeing as how I'm still new at this stuff.

Deadman 94 xj said:

Well thanks for the heads up. I'm not sure what I would have done when I got the readings seeing as how I'm still new at this stuff.

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That's why we're here. If you don't know something - or aren't sure - ask! Just take notes when you get the answer, so you know for next time...

We've probably got some thousand years' collected XJ tech experience here, and 3,000-4,000 man-years' collected mechanical experience. I'm sure someone here will be able to help you if you have a question, just make sure to give the collective some time to answer your question (the right guy may not have seen it yet...)