Alternator Wiring Revisited

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Alternator Wiring Revisited

November 25, 2016, 02:08:55 pm

Some time ago, I had a thread about problems with the way a new replacement alternator was wired by "one of the top five diesel mechanics in the country." The bottom line is he wired the engine battery to the alternator output. The alternator did charge the engine batteries, but put too high a voltage on the house batteries.

I have done some more investigating. There are two small wires, one attached to the sense terminal and the other attached to the ignition terminal on the alternator. Today I measured the voltage on each of them. With the engine off and the ignition switch off, they both read zero volts. With the engine off, but the ignition switch on (and the annunciator dinging like a banshee), they both read zero volts.

It seems that the wire attached to the sense terminal is not connected to the engine battery. It also seems like the ignition terminal is NOT attached to a location that is "hot" when the ignition is on. Trying to track these wires down was difficult because they disappear into a large bundle with many other wire looms and MANY zip ties.

My understanding is that I can remove those two wires from the alternator. Then run a new wire from the engine battery plus to the sense terminal; and a new wire from an ignition switched location to the other terminal. I also need to remove the battery plus from the alternator output, and connect it to the proper terminal on the isolator.

If I do that, can I expect that my alternator will now provide the proper voltage to charge the engine and house batteries? If I just add the new sense wire, will it work without making an excite connection? I have done a lot of reading on the forum message threads (think I had 33 pages of hits with the search term "alternator"), and am now very confused about whether it needs to be excited externally, or is actually self-exciting? Especially since I did not have a voltage on the current excite connection now. (The alternator is supposed to be a new "no-name" replacement for my OEM alternator according to the above mentioned "expert.")

Based on my brief description of where I am now, is there any hope that I can get it to work properly? This question may be moot after tomorrow, because the Power Ball lottery is expected to be over $400 million dollars. But since my chances of winning are only 1 in 192 million, I need a backup plan. Although it would be nice to get a new brushless alternator.

All suggestions and advice appreciated.

Thanks,

Trent

Re: Alternator Wiring Revisited

Reply #1 – November 25, 2016, 02:37:57 pm

Perhaps one of those wires is the 6 volt for the battery isolator ? DON'T ASK HOW all I know is that when I didn't have one of the connectors hooked up the isolator didn't function at all.

Re: Alternator Wiring Revisited

Reply #2 – November 25, 2016, 02:47:01 pm

Trent,
We just went through some alternator fun. I will try to convey what I think I learned.
The alternator used on our 99 U270 is a special alternator that was modified by the factory to function correctly with our power divider.
A rebuilt alternator of the same part number that had not been modified would not work correctly in that the power divider takes up almost a volt of juice and in order to maintain both the house and chassis battery it had to be bumped up in output.
Working with Brett Wolfe was invaluable to figuring out what voltages should be seen where, and under what conditions.
While the truck dealer had a hard time believing it, when we got the right alternator in it has worked as needed.
Maybe someone with more knowledge of electrical systems can jump in here and make more sense than I have.
Len

Re: Alternator Wiring Revisited

Reply #3 – November 25, 2016, 02:51:12 pm

Trent, hard to believe you're still wrestling with alternators. If you have the Foretravel standard non self excited DUVAC alternator then it takes two wires (in addition to the B+ output wire) to make em work properly. No reason you can't hook a couple wires to the terminals on alternator, run em both to the battery terminal for a test only, not permanently. Crank it up and read the output. Should be in the neighborhood of 14 volts.

Then take the temp wires off, throw them away, and find the problem with connections on original harness. You can't leave it connected and floating, and the original harness is much higher quality than any field wired setup is likely to be. The Foretravel elec. schematic is pretty clear on where these should be connected, no need to reinvent the wheel.

Here's how it should work: (The standard original factory setup, not the temporary test)

Key off. One of the two wires is hot. This is the Sense wire. The other wire is not hot. That is the Excite wire. (Make sure they are going to the proper posts on back of alternator, common mistake to reverse these.)

Key on. Both should be hot.

Check this first.

Re: Alternator Wiring Revisited

Reply #4 – November 25, 2016, 03:22:54 pm

Additional Info:

The sense wire, as Lenspeiser noted, is what adjusts the output of the alternator to counter the voltage drop of the isolator.

The excite wire is what turns your alternator off and on. It won't work without being excited if it's the standard Foretravel alternator.

It is possible to modify a standard alternator to be Duvac. I posted this procedure years back. This is where DUVAC alternators come from, they are factory conversions. They add a sticker on back that says "converted to duvac."

It is also possible to modify a standard alternator to be Duvac that is also self excited. That's what I did and have run for several years. In this case you don't use an excite connection, just the sense.

Finally, it is also possible to install a Delco alternator which will probably outlive the coach. $$$$

Re: Alternator Wiring Revisited

Reply #5 – November 25, 2016, 08:09:18 pm

I see no problem in just running new wires (see below). BUT, make sure to trace and disconnect the original wires (you don't want stray hot wires back there).

Sense terminal of alternator to any connection on the chassis battery side of the diode-based battery isolator.

Ign/excite terminal to any source that is only hot with ignition on (remote start panel is a nearby source).

Re: Alternator Wiring Revisited

Reply #6 – November 25, 2016, 09:21:15 pm

I recently had similar problems, my alternator was replaced from a three wire to a four wire. The PO ran a exciter wire from the ignition to the rear of the coach. Brett was a big help for me. Take your time and follow Bretts sugestions and you won't go wrong. I by no way want to offend anyone responding to this thread. Clean terminals at battery, isolator, and Alternator are essential. Take readings at battery {both sets} with engine off and then running at about 1200rpm. Becareful not to cross the sense wire and exciter wire. Don't ask me how I know.

Re: Alternator Wiring Revisited

Reply #7 – November 25, 2016, 11:31:02 pm

My goal in posting was to provide a simple way to troubleshoot the function of a Duvac alternator. So many people have struggled needlessly with this issue, primarily because many mechanics and technicians are not familiar with this style alt. They are really quite simple in function and very straightforward to prove out and troubleshoot.

As far as running new wires, well sure you can do that but for what purpose? Wires rarely go bad. You've still got to locate both ends of the old wires. You need to disconnect them so you don't have a hot wire loose in your harness, at least one member here fried his wiring harness due to a loose excite wire that grounded to an engine component. The existing wiring has overcurrent protection....you will need to add this as well if you run new wires to new points. Your old wires are color coded, labeled, and have oem spec terminations on them, are specified for service around oil, heat, per amperage, for engine room use. Call me picky but as a retired industrial electrician I always prefer to see things fixed rather than workarounds in the form of duplicate circuits. That's my recommendation but it's not my coach so as was so succintly said, "do what makes you happy."

Re: Alternator Wiring Revisited

Reply #8 – November 25, 2016, 11:47:37 pm

Chuck, some of this stuff is pretty obvious if you are familiar with it. For many it is not so obvious. As many hve found out it is not the wire that fails it is the crimp-on connector. Puttin a crimp on cap on an old wire and running a new one is sometimes the easiest way. When I put in my Delco and a new isolator the wiring was different and I spent quite a bit of time making sure I had it right

Thanks for helping others understanding the four wire Leese Neville wiring. Every perspective helps

Re: Alternator Wiring Revisited

Reply #9 – November 26, 2016, 03:34:51 am

Quote from: wolfe10 – November 25, 2016, 08:09:18 pm

make sure to trace and disconnect the original wires (you don't want stray hot wires back there).

Brett,

Since my voltage measurements are zero on both of those wires, could I just remove them from the alternator and hook a signal tracer to it and find where it goes?

Quote from: wolfe10 – November 25, 2016, 08:09:18 pm

Ign/excite terminal to any source that is only hot with ignition on (remote start panel is a nearby source).

Since my alternator has been (almost) working without voltages on the excite line, can I assume it is now self-exciting?

Brett, Chuck, and the rest of you who have been helpful:

My original alternator was the standard L=N with all four inputs. This is a "new" no-name alternator that supposedly replaces it. Since it is about 15 years newer than my old one, I suspect it might now be self-exciting. The fact that this alternator has been generating voltage seems to confirm that, right?

Bubba had tied the engine battery to the alternator output and it was putting 14.2-14.6 volts on the engine battery. The house battery seemed to be getting the default alternator output of up to 15.6 volts. Is there and explanation for that observation? Remember that I have *now* determined that the sense terminal was not getting a voltage applied to it.

To get my Echo-Charger to work, I had to put the two battery banks on the proper isolator terminals. while they are tied together in storage, I just put the boost on occasionally to avoid depleting the engine batteries.

BTW, I replaced the two "old" yellow tops I had with three new red tops about a year ago. The yellow tops were sitting on my patio and have been in my living room while I have been experimenting with replacement lights and LEDs. (No, DW is not happy about that.) Any way, it has been many months since I last charged them. When I checked them yesterday, they read 12.83 and 12.86 VDC. I replaced them because they did not hold a charge very long in the RV. Guess I better spend some time looking for an unusual drain in my engine battery circuitry.

I will hook up a temporary input for the sense and excite terminals and crank the engine up and read my two battery gauges (and move the isolator wires to the proper posts). If I don't go over about 14.6 VDC, then I think I can blame the runaway coach battery charging to lack of a sense connection. One last thought: does the alternator regulator set that default charging rate, and is that something that the end user can change?

Thanks for all the help,

Trent

Re: Alternator Wiring Revisited

Reply #10 – November 26, 2016, 09:05:14 am

Trent,

I would sure start with the wiring diagram and check for the appropriate wire number where it is supposed to be. I agree with others, wires seldom fail, it is the connections that do.

Re: Alternator Wiring Revisited

Reply #11 – November 26, 2016, 09:50:48 am

Trent, if you have a 103450 regulator on the new alternator it is non adjustable. If the alternator has, indeed, been modified for DUVAC all you should need is the sense wire. It sounds like it is self excited given it is producing without an excite wire.

Brett's suggestion above is right on, do this then hook up a sense wire and see if output is proper.

Re: Alternator Wiring Revisited

Reply #12 – November 26, 2016, 09:58:27 am

Quote from: TulsaTrent – November 26, 2016, 03:34:51 am

My original alternator was the standard L=N with all four inputs. This is a "new" no-name alternator that supposedly replaces it. Since it is about 15 years newer than my old one, I suspect it might now be self-exciting. The fact that this alternator has been generating voltage seems to confirm that, right?
Trent

Yes, quite possible that the no-name replacement is self exciting. Should have wiring instructions with the alternator, or from the no-name manufacturer.

There are a LOT of imitation products out there styled as "replaces .....". Some are fine, others are junk.

So, when shopping be very aware of "replaces" vs "name brand". This is especially true of air dryers-- lots of "replaces" junk out there.

Re: Alternator Wiring Revisited

Reply #13 – November 26, 2016, 10:53:23 am

Agree, we need to determine what the "no-name" replacement alternator is. Is it a "L-N" type, or a "Delco" type? Most Foretravel folks are familiar with the L-N type and the DUVAC 4-wire hookup.

If it is a Delco type (which most truck shops will install as a replacement), this will only work properly if it has B+ voltage present on the output stud to energize the ASIC voltage regulator chip at startup. If it is a Delco type alternator, this may be why the mechanic connected the chassis battery to the output stud - to get it to work.

FYI for reference, see the attached Delco bulletin. Delco alternators work fine with an isolator (I installed a Delco 40SI in my '91 U300), provided you use a diode isolator with an ignition terminal, or the Sterling ProSplitR isolator with an ignition terminal as some have installed.

Note (as stated in the Delco bulletin) that on a Delco alternator, there is no excite terminal, the "I" (ignition) terminal is NOT the excite terminal, connecting 12V excite to the "I" terminal can damage the alternator.

Re: Alternator Wiring Revisited

Reply #14 – November 26, 2016, 11:15:51 am

When I route the new sense wire, should it have a fuse? I have some heavy duty fuse assemblies that come with 30 amp fuses. You can place any standard size automotive fuse in the holder. Would 10 amps be more apropos?

Thanks,

Trent

Re: Alternator Wiring Revisited

Reply #15 – November 26, 2016, 11:31:03 am

Trent,

Neither the sense nor the excite (ign) wire carry much current. I don't recall either having a fuse as original equipment, but your wiring diagram will show that.

If you have a link to your actual alternator wiring/installation instructions you have, it would end a lot of this speculation, as we can verify how it should interface with your electrical system.

Re: Alternator Wiring Revisited

Reply #16 – November 26, 2016, 01:31:25 pm

Quote from: wolfe10 – November 26, 2016, 11:31:03 am

If you have a link to your actual alternator wiring/installation instructions you have, it would end a lot of this speculation, as we can verify how it should interface with your electrical system.

Boy, wouldn't that be nice. It was a turnkey installation. Bubba "fixed" it with a new alternator, then gave me my key to turn. (Shoulda known when the equipment charge on the bill was less than $400.) It does have the two extra terminals on the back labeled "sense" and "ignition," or something like that. It is really difficult to access with all of the engine "plumbing" above and behind it. Unlike Leonardo, it is difficult for me to read with my inspection mirror, standing on my tippie toes.

Trent

Re: Alternator Wiring Revisited

Reply #17 – November 26, 2016, 01:46:05 pm

Can you post close up photos of front and back?

Re: Alternator Wiring Revisited

Reply #18 – November 27, 2016, 11:56:30 am

Trent, in Reply #9 you asked: "One last thought: does the alternator regulator set that default charging rate, and is that something that the end user can change?"

I did not see any answers to your question, so I will attempt to answer it.

The regulator, which attempts to control the output voltage of the alternator (normally 14.6 volts), is a separate component from the alternator. Fifty years ago regulators were in a separate metal box attached to the firewall or fender well. Today, most regulators are mounted inside the alternator and in some cases, invisible. The Leece Neville alternator in my Foretravel has a "three step" regulator which is visible on the top side of the alternator away from the drive belt. It is attached to the alternator with four small bolts, such that it can be removed and adjusted (14.6v, 14.2v, or 13.8v, thus the "three step" name). Most regulators are sealed components and are not adjustable, however, they are available in different set points (common are 14.6v and 14.0v). Replacing a regulator involves dismantling the alternator, which is not difficult to do.

So, if by "default charge rate" you meant voltage, the answer is normally "yes", however, if by "default charge rate" you meant amperage, the answer is "no". The regulator attempts to set the output voltage of the alternator, and the load (or limit of the alternator) sets the output amps. If the demand for amps is more than the alternator can provide, the output voltage and output amps are set by the load with the regulator holding the alternator to maximum output.

The regulator in the alternator on my Foretravel is set to 14.2 volts while the output of the alternator is actually 14.4 volts. I accomplished this with a resistor in the sense voltage circuit. So, "yes" the output voltage of the alternator can be adjusted.

Re: Alternator Wiring Revisited

Reply #19 – November 27, 2016, 12:30:14 pm

Quote from: P. Wyatt Sabourin – November 27, 2016, 11:56:30 am

The regulator in the alternator on my Foretravel is set to 14.2 volts while the output of the alternator is actually 14.4 volts. I accomplished this with a resistor in the sense voltage circuit. So, "yes" the output voltage of the alternator can be adjusted.

Be aware that for coaches with the diode-based battery isolator (which was standard from Foretravel), alternator output is approx. .7 VDC higher than what reaches the batteries. The diode-based isolator "charges" that .7 VDC and turn it into heat. That is why the large cooling fins on the isolator.

It is also why there is a sense wire that goes to the chassis battery side of the isolator. It "fools" the alternator into putting out the high voltage which is reduced in the isolator to correct charging voltage.

Re: Alternator Wiring Revisited

Reply #20 – November 27, 2016, 05:42:31 pm

Tried to get pictures today, but Mother Nature wanted to show how much power she has. Will try again tomorrow, assuming the ground dries some.

Thanks for all of the knowledgeable answers,

Trent

Re: Alternator Wiring Revisited

Reply #21 – November 28, 2016, 12:42:11 pm

Thanks Brett, I forgot that the voltage at the alternator is 0.7v higher than the voltage at the batteries ( caused by the diode based battery isolator). I do not use the battery isolator because I have just one battery bank for both start and house.

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