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Old 11-03-2019, 05:29 PM   #1
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Thumbs up 1982 Tiffin Allegro - chassis charging system

Picked up a new to me 1982 Tiffin Allegro. This unit is in pretty good condition for it's age with quite a few recent upgrades. Having an issue with the chassis charging system.

Chassis - 1981 Chevrolet P30

Synopsis
1) half way into the 30 mile drive home the headlights started going on/off - but not in a fashion that would indicate a short.
2) Woke up to a dead battery. Unable to start engine. Voltage 11.3. Replaced corroded headlamp switch and dimmer switch for good measure.
3) Battery wouldn't charge with stand alone charger. Replaced what appeared to be a fairly new battery.
4) New battery voltage (at battery) - 12.3.
5) Starting motor - Voltage jumps to 13 at idle.
6) Turning on headlights and brights - voltage drops to 12.1 at idle.

I pulled off the coach engine cover. I'm not sure where the alternator is... Where should I start? My strengths are with the internal house systems. Light mechanical I can muddle through with some direction. The apparent lack of access to the engine area is a mental roadblock...

For now the battery is hooked to a multistage charger.
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Old 11-03-2019, 07:05 PM   #2
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Update:

I located the alternator however it's position prevents the viewing of the label. It looks very new. My guess is a standard alternator was put in that isn't providing the power required.

I know Lestek supplied the alternators in this area of motor homes. Would anyone know the model # that came in the 1982 (81 chassis) Allegro? I want to search for a drop in replacement before I look at other possible solutions.
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Old 11-03-2019, 07:12 PM   #3
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May not be the alt , motorhomes have some draw on battries over nite ... If you have a voltmeter remove posstive cable and check for draw .. lots of relays on rvs that can corrode and cause problems.
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Old 11-03-2019, 07:14 PM   #4
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You could have a short causing the battery to draw down.. Sounds like your alt is putting out ...
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Old 11-03-2019, 08:45 PM   #5
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Shouldn't I expect to see no change in voltage when I turn the headlights on? If it's a short I'm wondering if it's in the circuit the headlights are on given the voltage drop. I'll do a draw test tomorrow.
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Old 11-03-2019, 08:46 PM   #6
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Quote:
Originally Posted by mangocat1 View Post
Shouldn't I expect to see no change in voltage when I turn the headlights on? If it's a short I'm wondering if it's in the circuit the headlights are on given the voltage drop. I'll do a draw test tomorrow.
You should see a drop when you turn the headlights on !
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Old 11-03-2019, 08:55 PM   #7
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unhook the battery overnite and see if it'll start in the morning .. There are tons of draws on these RVs ... steps, lights in bays ...
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Old 11-03-2019, 11:30 PM   #8
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I would suspect the headlights to be a separate issue. Many an older vehicle has the same problem with the headlights going on and off after being on a few minutes or so. The issue is usually because of high resistance in the old wiring and wiring connections. Most often bad grounds. The high resistance slowly makes the circuit breaker inside the headlight switch heat up until it cuts off. It cools for a couple of seconds then the lights comes back until it repeats the cycle if not immediately. Sometimes a new headlight switch alleviates the issue a bit but it is rarely the root cause. You mentioned voltage drop testing. If you are familiar with that then you should have little problem finding the issue. Now that you know what to look at.

It sounds like the system is charging, not sure how well, but working. I consider 12.4 volts the minimum for a "good" and resting battery so something is on the iffy side there. Many vintage type alternators didn't put out much at idle so about anything much is often OK. You want to focus testing on how it's doing at about 1500 RPM to check on the alternator's health.

Parasitic drains can be difficult to track down in cars, much less with all the extra stuff in an RV. Rule of thumb for the average car with everything you know of normally shut down would be a battery drain of 50 milliamps at the most. That accounts for a dash clock and/or a radio that remembers your radio stations, stuff like that.
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Old 11-04-2019, 03:59 AM   #9
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I suspect that the boost solenoid, that connects the house and chassis batteries, has been jumped.

The draw of the solenoid, along with the house loads, are drawing down your chassis battery. The chassis and house batteries should not be connected together, if the engine is off.

Headlight switchs have circuit breakers in them. See if all of the headlamps are on, high and low beam. That can overload the switch. Bad grounds make dim lights but not overloads.

Even a cheap 60 amp replacement alternator will bring the battery voltage up above 13 volts, if not overloaded. Bad connections can effect that.

A new battery that checks at 12.4 volts is discharged or running something. A battery resting voltage is 12.6 or 12.7 volts. You may have a bad volt meter.
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Old 11-04-2019, 08:58 PM   #10
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Ran through a draw test this afternoon. Volt meter was reading 10.5 amps (!!) with no key in the ignition. No Chassis systems on. Ran through the fuse box pulling and reinserting fuses with no luck. Pulled and reseated the direct wire connections in the fuse box. This seems to have done the trick. Draw is now .001 amps.

Reconnected the battery and started the motor. Volt meter reads 17 volts at the battery. Turned on all exterior lights including high beams and fog lights. Volt meter read 17.3 volts. Isn't 17 volts too high?... The journey continues.
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Old 11-04-2019, 10:48 PM   #11
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Yup, 17 volts is to high.

If its equipped with a battery isolator, the alternator may be miss-wired or the wrong one.

See if you have a volt reading on the big wire on the alternator, with the engine off. If not, there should be a smaller wire on it that has 12 volts to control the voltage regulator.
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Old 11-05-2019, 06:33 PM   #12
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Discovered 2 issues:

1) My volt meter is bad. The voltage reading on my battery charger and the in cab gauge match. Both are in the 12.3ish volts range. Volt meter was reading 16.5 - 17.

2) The alternator does not belong in this motor home. Itís a 7273-9a - 73 amp. Voltage dips to 11.9 when loading up the system and the motor running. With no load the voltage is around 12.3. Recommendations?

Battery isolator seems to check out.
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Old 11-05-2019, 06:43 PM   #13
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12.3 volts in not a charging voltage. That's the voltage of a low battery, not being charged.

Check the alternator output at the alternator, it should be above 13 volts. Even if its only a 73 amp alternator.

Next check the voltage at the center terminal of the battery isolator. That should match the alt voltage.

Then check the voltage at each side terminal of the battery isolator. They should each be about 1 volt less then the center. If one is not, the isolator is bad.
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Old 11-05-2019, 09:09 PM   #14
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Turns out my volt meter battery was just low. Fresh battery now... will rerun tests tomorrow.

Battery posts read 12.2V with motor off.
Battery posts read 12.4V with motor on.

What I had posted previous is below

++++++++++++++++++++

Using inaccurate volt meter -

Alternator no engine - .35 volts
Alternator engine on - 19.35 volts (dash meter does rise a bit)
Isolator center post - 19.78
Isolator left post - 18.65
Isolator right post - 18.63
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