alternator not charging

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alternator not charging

October 17, 2021, 12:33:41 pm

I am having problem figuring out why my 98 u295 charging system isn't working. I replaced the alternator and several electrical solenoid. I think there is a breaker that has popped but I can't find one. My alternator would charge properly then it would drop voltage then go back up. I have charged the batteries and hook them up and all the batteries would lose charge even with the battery disconnect off. The only one to hold a charge is the chassis battery but the alternator won't recharge it. Voltage on the 2 white wires (excite and ignition) is very low under 0.4v. Any ideas on where to look to fix this problem. Then alternator is a neville alternator.

Re: alternator not charging

Reply #1 – October 17, 2021, 12:46:58 pm

What is voltage at the SENSE TERMINAL?

Re: alternator not charging

Reply #2 – October 17, 2021, 12:52:37 pm

Basic things first:
All battery cable connectors clean and tight.
Alternator ground cable to block connection clean and tight.
Battery isolator properly connected to alternator and both battery banks (refer to 12V Automotive Wiring diagram for your coach).
The "SENSE" wire should be always HOT and connected either directly or indirectly to read START battery bank voltage.
The "EXCITE" wire should only show battery voltage when the ignition switch is "ON".
Verify all voltage readings with a good quality multimeter. Take readings directly at the batteries/alternator/isolator - do not go by the dash voltmeter.

Re: alternator not charging

Reply #3 – October 17, 2021, 01:26:43 pm

How's the isolator.

Re: alternator not charging

Reply #4 – October 17, 2021, 01:31:06 pm

Tnalaskan wrote; "I replaced the alternator and several electrical solenoid."

Oh goody. Let's change a bunch of stuff at the same time.

Back to basics: The sense wire goes to the Chassis battery. If you have a battery isolator, use the chassis battery terminal on the battery isolator. The excite wire* goes to the ignition terminal on the ignition switch, so you're looking for a wire that has battery voltage when the ignition switch is in the on or run position, and no voltage when ignition off. Now check and see if there is electricity coming out of the alternator. At the alternator.

*No excitation, no output.

Re: alternator not charging

Reply #5 – October 17, 2021, 01:50:41 pm

I'm wondering. Did you replace the L-N with another L-N or did you switch to a Delco? The delco's are much simpler to hook up. But different enough to get you going in the wrong direction.

Re: alternator not charging

Reply #6 – October 17, 2021, 03:27:28 pm

If you changed the alternator then it's most likely not modified as a DUVAC output so it won't work with an isolator in the system unless you have it modified. Typical symptom.

Re: alternator not charging

Reply #7 – October 17, 2021, 03:39:06 pm

Quote from: Twig – October 17, 2021, 03:27:28 pm

If you changed the alternator then it's most likely not modified as a DUVAC output so it won't work with an isolator in the system unless you have it modified. Typical symptom.

A non-DUVAC alternator (for example a Delco Remy with a sense wire) will work with an old DIODE based alternator just fine, but it won't compensate very well for the nearly 1 volt loss though the old Diode based isolator. Much better choices are out there now to isolate house and start batteries that don't have the voltage losses and can provide smart charging solutions.

You do not have to use an inefficient DUVAC modified alternator and old technology diode based isolator in your Foretravel.

Re: alternator not charging

Reply #8 – October 17, 2021, 04:10:58 pm

Quote from: Roger & Susan in Home2 – October 17, 2021, 03:39:06 pm

A non-DUVAC alternator will work with an old DIODE based alternator just fine, but it won't compensate very well for the nearly 1 volt loss though the old Diode based isolator.

Actually, the second half of this statement is correct. A "regular" alternator (no sense terminal) when coupled with the diode-based isolator will leave charging voltage about .7 VDC below what it should be. So, I would suggest that is NOT what you want.

Two choices:

Stick with your diode-based battery isolator and a DUVAC alternator.

OR

Use a "regular" alternator with "alternative" battery isolator.

There are several quality battery combiners on the market.

If you want strictly KISS theory, a simple marine ON-OFF switch works just fine. Install at the foot of the bed so you can easily reach it. Alternator B+ and chassis battery to one lug. House battery to the other. Switch OFF and alternator charges only the chassis battery. Switch on and both banks are charged. On also give you an easy high-amp battery combine and also allows your converter or inverter charger to keep both banks up.

No "this is the only way" here. Choose an option you are comfortable with.

And, yes, we may be jumping the gun here. If you need more help with diagnosing your current set up, just let us know. We WILL need to know exactly what alternator you have (what terminals it has) and what battery isolator you have. From there, troubleshooting is pretty straight forward.

Re: alternator not charging

Reply #9 – October 17, 2021, 05:30:00 pm

Too many variables being added here. His system worked, he replaced the alternator and nothing else pertinent and now it doesn't work. No sense changing anything. Spend 50 bucks to get the DUVAC done and be on your way. Overthinking sometimes kills a budget.

Re: alternator not charging

Reply #10 – October 17, 2021, 05:46:58 pm

Quote from: Tnalaskan – October 17, 2021, 12:33:41 pm

I replaced the alternator and several electrical solenoid.
Voltage on the 2 white wires (excite and ignition) is very low under 0.4v.
Then alternator is a neville alternator.

Tralaskan wrote that he replaced his alternator with a Leece Neville.

He has no excite voltage. No excite, no alternate. He needs to have +12V with the ignition key on.

Now I ask: Did Foretravel use solenoids in 1988 to separate the batteries when the engine was not running?

Re: alternator not charging

Reply #11 – October 17, 2021, 08:25:24 pm

I don't know what coach you have but some have a resettable circuit breaker for the sense wire

Re: alternator not charging

Reply #12 – October 18, 2021, 12:44:03 pm

Quote from: red tractor – October 17, 2021, 08:25:24 pm

I don't know what coach you have but some have a resettable circuit breaker for the sense wire

Tnalaskan wrote "98 u295"

Re: alternator not charging

Reply #13 – October 19, 2021, 10:13:47 am

Quote from: red tractor – October 17, 2021, 08:25:24 pm

I don't know what coach you have but some have a re-settable circuit breaker for the sense wire

"I" had him confused with a guy fixing an '88 and my '86 Rockwood . . .

Re: alternator not charging

Reply #14 – October 24, 2021, 06:44:29 am

Quote from: Twig – October 17, 2021, 05:30:00 pm

Too many variables being added here. His system worked, he replaced the alternator and nothing else pertinent and now it doesn't work. No sense changing anything. Spend 50 bucks to get the DUVAC done and be on your way. Overthinking sometimes kills a budget.

What do you mean get the duvac done?

Re: alternator not charging

Reply #15 – October 24, 2021, 08:25:05 am

DUVAC is a type of alternator control/wiring that allows correct battery charge when using a DIODE-BASED BATTERY ISOLATOR. That type of isolator drops voltage by about .7 VDC. The DUVAC allows the correct post-isolator voltage to the batteries.

Basic alternators have a B+ for alternator positive and a ground-- often through contact with the engine, but sometimes a separate ground.

Additionally, DUVAC alternators have a SENSE terminal that connects through a small gauge wire (no significant current carried) to the chassis battery side of the isolator. It tells the alternator to raise voltage by that .7 VDC that is lost in the isolator.

There is also an IGN terminal that is supplied voltage only when the ignition is on.

Re: alternator not charging

Reply #16 – October 24, 2021, 10:43:53 am

Quote from: Tnalaskan – October 24, 2021, 06:44:29 am

What do you mean get the duvac done?

Tnalaskan, let's go back to basics and back in time for a moment.

All an alternator is at heart are two pieces. A spinning electromagnet and a coil of wire.
What do you need for an alternator to produce electricity? Carbon brushes riding on slip rings to power the spinning electromagnet, the brushes do wear out with time and the electromagnet requires a push from the battery to get things going.

The coil of wire is something for the moving magnetic field to cut through making electrons move i.e. making electricity, and is arranged in three sets of North-South pairs. That's why there are three diodes to turn, to rectify, the alternating current into direct current for the battery.

In the beginning, voltage regulators were separate from alternators. Today voltage regulators are built into the alternator. Pretty common today is the "One Wire" alternator that only requires the battery cable be connected to the output post of the alternator. There is usually a connection to the "generator" light to tell you when the alternator is not creating electricity and to start making things complicated THAT wire also provides the initial excitation electricity.

Some alternators do come with a third wire called the sense wire that don't really conduct much current but provide the alternator's internal regulator a measurement of voltage at the load. In this case load equals battery, and in our application when wired to either the battery directly or to the output terminal of a diode based battery isolator automatically corrects for the 0.7V "Diode Drop*" introduced by the diodes in the isolator.

The DUVAC, aka the Leece Neville DUVAC is the original as Leece Neville was the original supplier, back in the 1960s for heavy duty i.e. over the road truck and police application, alternators. I *think* DUVAC is an acronym for Dual Voltage Alternating Current alternator. Alternating current because that's what alternators create, alternating current that is then rectified to become direct current.

If you Google alternators and sense wires I think you'll find that Delco manufactures products suitable for use with a diode isolator.

If you want help finding the source of your problem I need voltage measurements made while your finger or a light bulb grounds the B+ lead.

*You really don't want me to expound on this subject because I'll take you through electron tunneling, quantum mechanics and time travel. Well, maybe not the time travel but take it as gospel truth that there is a 0.7V drop when electricity flows through a diode.

Re: alternator not charging

Reply #17 – October 24, 2021, 11:30:08 am

Hi! Me again!

Prestolite - Leece Neville Alternators.

IdlePro Extreme Alternators from Prestolite & Leece-Neville

Re: alternator not charging

Reply #18 – October 26, 2021, 02:28:21 pm

Quote from: wolfe10 – October 17, 2021, 12:46:58 pm

What is voltage at the SENSE TERMINAL?

Below .4v.
I realize putting all the info in the original post.

Re: alternator not charging

Reply #19 – October 26, 2021, 02:32:32 pm

Quote from: Old Toolmaker – October 24, 2021, 11:30:08 am

Hi! Me again!

Prestolite - Leece Neville Alternators.

IdlePro Extreme Alternators from Prestolite & Leece-Neville

I just put a new leece-neville alternator in. there is no power to the ignition or excite wires. I don't know where to look to check the source of the power to those 2 wires.

Re: alternator not charging

Reply #20 – October 26, 2021, 03:06:03 pm

For the SENSE terminal, you can make a jumper from any small gauge wire. Connect one end to the chassis battery terminal of the battery isolator. Obviously, between it and ground should read exactly the same as chassis battery voltage.

And, you can temporarily connect another small gauge jumper from either outer lug on the battery isolator to the IGN terminal for testing.

Re: alternator not charging

Reply #21 – October 26, 2021, 04:40:29 pm

There should be a circuit breaker near the boost solenoid for a protected start battery voltage source for the sense wire.

Re: alternator not charging

Reply #22 – October 26, 2021, 07:02:06 pm

Not sure but you should be able to get an ignition hot from the remote start panel. It will only have 12 volts with the key on.

Re: alternator not charging

Reply #23 – October 26, 2021, 09:23:58 pm

Quote from: Tnalaskan – October 26, 2021, 02:32:32 pm

I just put a new leece-neville alternator in. there is no power to the ignition or excite wires. I don't know where to look to check the source of the power to those 2 wires.

If you want to see your new alternator work, you can temporarily connect the ign terminal to any source of battery voltage.

Same thing goes for the sense wire.

What wires did you have for the old alternator? There's the big wire for the output terminal. And a medium sized wire for 12V+, and a skinny wire for sense. Maybe a ground wire, although alternators generally ground through the mounting points to the engine to the chassis.

Re: alternator not charging

Reply #24 – November 26, 2021, 04:19:57 pm

Quote from: Roger & Susan in Home2 – October 26, 2021, 04:40:29 pm

There should be a circuit breaker near the boost solenoid for a protected start battery voltage source for the sense wire.

That helps but i have no idea where to look to find that.

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