gonzala

So I'm trying to replace the alternator on my 97 cherokee with the 160A from a 05 grand cherokee, so far it seems that it will fit with some minor modifications to the mounting bracket on the bottom but my questions/problems are about getting the electrical to work with each other.



so this is my old alt and I know power comes from the bolt in the center of the black connector on the left and goes to the PDC. Ground is the bolt on the far left I'm pretty sure. Now the brown piece just under the center of the unit with the 2 bolts protruding out of it are for the voltage regulator as far as I know.



This is the new alt......any ideas?

okcjeeper

No pics so not sure ..

gonzala

forgot to mention that the new alt is the bosch AL6553X. I'll try fixing the pictures, please let me know if it still is not working. Thanks

5-90

You're going from a Nippondenso to a Bosch - that's half of the problem (the 160A ND would look similar to the unit it's replacing.)

However...

The 8m/m post off of the side would be your B+ output stud. That's where the output cable will go (and you'll need to reterminate it. The one on your vehicle has a 6m/m or 1/4" ring on it, you'll need an 8m/m or 5/16" ring.)

The little two-pole plug at 12:00 on the back of the case looks like the field coil connexion - lemme check my catalogue:

Hm. Bugger. The only Bosch units I have listed for the GC are the #13872 (2001-2003 242ci, Bosch 132A) and #13777 (1999-2000 242ci and 1999-2000 287ci, Bosch 136A.) Both of those are similar to each other, with a side-exit B+ stud (6m/m on 13777, 8m/m on 13872,) and a two-pole field coil plug similar to yours. So, it is probable (but NOT certain!) that the field coil connexion is made the same way on the unit you're looking at.

However, you would have been better served with a 160A ND (they're out there - I've posted a couple of lists...) since that preserves the same connexions you already have.

You're going to have to find a mating socket to go with that plug - I'm not sure what style it is (I'm inclined to think it's a Deustch series connector, but I'm not certain.) If there is a ground connexion to be made, any convenient case screw will serve.

Good luck!

363

gonzala

Thanks for the info, my buddy said as long as I didn't use the alternator I could exchange it, I will look into the 160A ND unit, would you mind explaining what a field coil connection is?

gonzala

The wiring harness that connects to my old alternator, if I were to solder or use a spade connector to connect it to the 2 pins in the plug on the new alt would it work?

5-90

There are two sets of coils in an alternator - the "field" coils (also called "stator" coils) and the "rotor" coils.

The "rotor" is attached to the spindle, and is the magnetically "driven" coil.

The "stator" is attached to the frame of the alternator, and does not move.

There are two elements to power generation by the alternator. The first is relative motion between the coils - this is provided by the belt/spindle arrangement.

The second is a changing magnetic field. This is provided by the stator coils moving relative to the rotor coils (OK, it's the other way around,) and by a low voltage provided to the stator coils. This voltage is provided by the voltage regulator.

If you were to measure for voltage at the field coil terminals, you'd typically see something around 0.5-4.0VDC. You do not want your field coils to get full 12VDC battery voltage - this gets ugly fast!

Your alternator is essentially an electric motor in reverse (Trivia: if you turn a permanent magnet electric motor by hand, you will generate a voltage at the terminals. How much you generate depends on how fast you turn.) Specifically, it is an alternating current electric motor in reverse (this is done for manufacturing simplicity. The generation of alternating current is why we call alternators "alternators" and not "generators" - a generator worked on native DC voltage. I'll revisit this in a moment...)

If you were to open up an alternator, the giveaway would be that there are two solid sliprings for the brushes to make contact with, and not one segmented one. The segments on the generator (and starter motor) are necessary to provide reversion of the magnetic field - else the motor/generator wouldn't work. Recall I said the magnetic field needed to change.

The alternator generates a 12VAC supply internally (controlled by the voltage regulator - it actually regulates current output by controlling voltage. Just trust me on this one for the moment - if you want to know more, look up Ohm's Law and Watt's Law. Ask me again if you're still confused after that.) This 12VAC is then fed through a "rectifier" - a network of high-current diodes in the back of the alternator case that take that AC voltage and turn it into "flat" DC voltage. There's always a little AC leakage - ever notice that hum that changes with engine noise, when you're in between tracks on your CD player? That's "diode ripple" - it's caused by the slight "AC leakage" through the rectifier pack.

Alternators and generators work on the principle that you induce a magnetic field around a conductor when you pass a current through a conductor. The reverse is also true - when you pass a magnetic field through a conductor, you will also induce a current through it. The magnetic field needs to move - which is why you have a "stator" (static coil - doesn't move) and a "rotor" (rotating coil - moves.) The relative motion between the two coils is what changes the magnetic field, and keeps generating the current you use.

A similar principle is what makes ignition coils work. Think back to breaker points - you had to set "dwell" on them in order to make sure they were closed for a certain amount of time. When the breaker points were closed, the primary windings of the ignition coil were energised, inducing a magnetic field about the secondary. When the breaker points opened, the current went away - which forced the magnetic field to collapse. When the field collapsed, a current was induced in the secondary, which was routed to the spark plug to fire the spark.

The key difference there was that the coil was used as a "step-up transformer" - and took that 12VDC in and turned it into about a 25,000-50,000V spark (can't really call it AC or DC, since it was just one shot.) Relatively low current, very high voltage (Ohm's Law and Watt's Law again - voltage and current share a mathematical relationship.

Looking up how transformers work (and why they'll work on AC but not DC) would be potentially enlightening as well here.

gonzala

and I thought I knew everything I wanted to know about alternators lol, thanks for the info. But I'm still uncertain about what the "field coil connection" does specifically and if its possibly to connect the 2 wires from the harness to the 2 poles of the plug.

5-90

The field coil connection is the feed from the voltage regulator (in our case, in the PCM.)

That Bosch unit should still answer back to an external regulator, so I'm going to go out on a limb and say you should be able to adapt your harness connector, using a socket that mates with the plug on the back of the Bosch unit.

It really would have been much easier had you gotten a Nippondenso 160A tho - and there are some out there (they're actually a bit more common than the Bosch, by Jeep applications...)

gonzala

Thanks for the input, the reason I'm still asking about this alternator and not looking for the ND as I said I would is that I got this alternator for a great price and might not be so lucky with the ND so chances are I might get stuck with this one. So I thought it would be better to find out now while the topic was still fresh and not have to come back in a week or month to go digging for this info again

5-90

Fair enough. Just know that you're going to have to figure out how to attach to those two pins - reliably - and the ND would save you plenty of work at just that! Not to mention that the ND will also have the correct 6m/m output post, instead of the 8m/m on the Bosch...

How much is your time worth to you? That's a question to be asked before doing any sort of conversion like this (also, using the ND would give you the option of using a stocker replacement in a pinch - if you modify the wiring to accept the Bosch, you may not have that option. Always have options in the event of parts failure...)

gonzala

haha well, my time is actually worth squat right now and I don't have my "N" at the moment but will soon. So the jeep is to remain stationary for the time being. I will keep what you said in mind though, about going back to stock or another ND if I do end up using the bosch. I think it should be possible to put the current wiring setup back into place if I modify it any of the ways I've thought of. What ever I do I'll see about taking pictures and putting up a How To.