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Old 12-11-2006, 02:52 PM   #1
The New Guy
 
1989 34.5' Airstream 345
San Diego , California
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Alternator? Batteries? Wiring?

I am a proud/frustrated owner of a 1989 345LE. I have owned it for about a year and have had fun figuring out and fixing all the little things. Here is the latest.

I use my MH frequently. I am a boondocker in So Cal. I let the MH sit for about 2 weeks, and did not cut off the battries. But I turned everything off. I noticed when I started it that it barley had enough juice to kick on. After running it for about an hour I thought it safe to turn off. Well, long story short I took the 2 year old auto battery to auto shop and the attemped to charge it. It did not charge. I replaced the chassis battery. All was good. Or so I thought.

My wife has been complaining to me that the Coach battries are not holding a charge for as long as they use to. So I thought I would do some checking with a digital multimeter. After driving the MH to my shop (25mins) I took the battries out, cleaned all contacts and checked their voltage. Chassi Batt: 11.75VDC Coach Battries: 12.92VDC and 12.88VDC. I let them sit overnight. And checked them the next day. Voltages were same pretty much -.03VDC. Well I figured the battries were ok. I hooked them back up and pluged the coach into house or shore power. I then checked voltages. Chassi: 11.70VDC (does not charge on house pwr) Coach: 14.4VDC. Which I read that anything over 13.8VDC is overcharging. So I have to adjust that somehow.

After a night of being hooked up to shore power, I took the MH off and checked voltages again. Chassi: 11.70VDC Coach: 13.8VDC. GREAT!! My battries are charging. So just to check the chassi battery and how well my ALT was charging, I turned on the engine and checked the voltages again. (note: I have noting inside the coach on except fridge on LP setting)
Chassi: 12.2VDC Coach 12.3VDC I know that is not the right voltage. It should be in the 13's or 14's right? While driving all light's, turn signals, and fans work. But gauge on dash shows 10VDC. I know that there are a few things that cold be wrong. where do I start. I am not that savvy when it comes to Auto stuff. Where is the Alternator located anyway? Any help at all would be great. Thank you all!
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Old 12-11-2006, 04:10 PM   #2
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Some quick thoughts. I put four alternators in my 1984 310 Limited until I broke down and bought a high capacity, 200 amp model. I have since been told that if you let your batteries get discharged a typical alternator will soon become over loaded and burn out because of the excessive draw of charging 3 batteries.

You need to be sure your Isolator is correctly installed (mine wasn't) and doesn't have excessive resistance (mine did).

My dash volt gauge was not accurate as wired, had to have a dedicated hot wire to it controlled by a relay.

Chassis batteries are not designed to be discharged very far and their life will be shortened if you allow them to become discharged.
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Old 12-11-2006, 05:32 PM   #3
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I also replaced my alternator with a high amp model 135 amps. Replaced the isolator with a higher rated one too. Also out a voltage meter on when shore power is on and see what charge rate your univolt provides.
I found if I left the univolt plugged in for a long time it fried the batteries, so I put the blade switch cut offs on them, and when parked on shore power or generator on, I cut the batteries out of the loop once charged.
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Old 12-11-2006, 06:20 PM   #4
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Just an FYI, if your chassis battery is 11.7 volts, it is completely discharged. Fully charged should be 12.75 volte, 75% charge is 12.5 volts, and 50% charge is 12.25 volts. You probably shoud replace the chassis battery with a new one (they are not that expensive) and check everything again. An Alternator is designed to keep a fully charged battery fully charged, and cannot charge a battery with anything approaching good results.
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Old 12-11-2006, 07:25 PM   #5
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1987 34.5' Airstream 345
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Had a similar problem with our 87MH345, original alternator and voltage regulator but new coach and house batteries. Dash voltmeter never showed anything over 12V, running 12V accesories like fridge or even dash AC, would put the voltage in the 10-11V range. Long story short, battery connect ("emergency start") solenoid was fused shut. Replaced both the solenoid and voltage regulator, the dash voltmeter now stays in the 13-14V range . Since I had to go with a 4-terminal solenoid, I wired the now new ignition post to the unused dash "Glow Plug" indicator for a ready visual of when the "emergency start" is engaged .
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Old 12-11-2006, 08:23 PM   #6
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It sounds like you may have more than one problem. The coach battery and charging system and the house batteries . If the house batteries are not lasting long you should have them load tested individually , there may be a cell going bad . On the coach it sounds like a regulation problem . A good mechanic can full field the alternator (which bypasses the regulator) to see if it is up to spec.. Some alternators have the regulator built in and some are external. As Buckwheat stated , the battery isolator can also cause low/no charge. Good luck
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Old 12-11-2006, 10:04 PM   #7
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1991 35' Airstream 350
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Troubleshooting

What, precisely, is your alternator output voltage?
What, precisely, is your Voltage at the isolator? All posts!
What, precisely, is your Voltage at the battery when charging with known good batteries?
What, precisely, is your time to full change on good battery--from 11.6 to 12.6 (or better, at rest) VDC??

Inquiring minds want to know........... Checking these out will tell you where your problem is likely to be. You may need new batteries, at the least. How old are they?

Best,

R
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Old 12-12-2006, 09:38 AM   #8
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1989 34.5' Airstream 345
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Quote:
Originally Posted by ralley
What, precisely, is your alternator output voltage?
What, precisely, is your Voltage at the isolator? All posts!
What, precisely, is your Voltage at the battery when charging with known good batteries?
What, precisely, is your time to full change on good battery--from 11.6 to 12.6 (or better, at rest) VDC??

Inquiring minds want to know........... Checking these out will tell you where your problem is likely to be. You may need new batteries, at the least. How old are they?

Best,

R
Where would I check the altenator output? Where is the Isolator located? I am really new to the whole automotive/RV fixing stuff. Once I know, I will check all of these voltages and update you all. The house battries are about 2 years old and are Interstate and are either SRM-27 or SRM-29. The chassi battery is less than 2 weeks old and is a EverStart from Wal-Mart the MAXX-1S with 875CCA.
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Old 12-12-2006, 10:12 PM   #9
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1991 35' Airstream 350
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Quote:
Originally Posted by ahmarquis8
Where would I check the altenator output? Where is the Isolator located? I am really new to the whole automotive/RV fixing stuff. Once I know, I will check all of these voltages and update you all. The house battries are about 2 years old and are Interstate and are either SRM-27 or SRM-29. The chassi battery is less than 2 weeks old and is a EverStart from Wal-Mart the MAXX-1S with 875CCA.
Measure the alt output directly at the alternator. There may be a rubber boot over the positive output. Use a good digital multimeter if you can. Do not run the alternator disconnected from the batteries.

The purpose of the isolator is to keep your battery banks from discharging into each other. The isolator is usually at the front of the vehicle, under the driver's side dash. Get to it by opening the front where you would check your engine oil. There are three posts, on an aluminum rectangle with fins. There will be wires attached to each of the posts. The center post receives the alternator output, and the two outer posts go to batteries and circuit breakers/fuses. There will be a voltage drop between the input and output. A big voltage drop--more than a volt--may indicate a bad diode in the isolator. A big voltage drop between batteries and isolator may indicate bad batteries, worn wires, short circuits, or just resident gremlins.

Search in this forum on isolator and you should find some pictures. It probably wouldn't hurt to clean up all connections with a dremel tool or emery paper as you check them for voltage.

Check all your ground straps. There is one on the rear of the engine block which runs to the frame adjacent, and one which runs from the rear of the battery box to the frame adjacent.

Finally, check the cables at the rear of your battery box for broken insulation by removing each in turn and inspecting each with a strong light.

I had a problem with symptoms similar to yours last year. I did all of the above, including replacing all batteries. I had 4 problems.

1. Bad alternator
2. Old batteries
3.Burned out fuse
4. Broken insulation on a battery cable, shorting out causing a very slow battery drain (several weeks from 12.6 to flat).

Best,

R
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Old 12-12-2006, 11:12 PM   #10
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If you have the P30 series chassis, then the Chevrolet Motor Home Chassis Service Guide has a fairly comprehensive test for the battery isolator. From 1987 onward, the isolator has four terminals labeled 1, 2, A, and E: 1=coach battery, 2=house battery, A=alternator, E=ignition. On a good system, voltage checks with engine not running should be: (key off) 1=12+, 2=12+, A=0, E=0; (key on) 12+ volts on all terminals. With engine running: all terminals should be 13.8 volts. On a faulty system with engine running, bad diodes would cause static battery voltages on terminals 1 or 2 (no charge from alternator to batteries); with key off you should never see voltage on terminal A (voltage present indicates a wiring fault). If the key is on and you have voltage on E but not on A, then the isolator is defective and should be replaced.
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Old 12-13-2006, 10:34 AM   #11
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1989 34.5' Airstream 345
San Diego , California
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Thank you all so much for the info...I will probably not be able to dive into this untill friday night or Saturday morning. But I will keep you all updated. I called a local shop yesterday and they wanted over $100 just to look at it. I think I can handel this one though...well, with a little help from the great minds in here. Thanks again. I am sure that this will not be the last time that I call upon you all for advice.
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Old 12-13-2006, 08:26 PM   #12
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Ah..new guy, some great technical stuff written already.., but to answer the questions you asked.

The alternator is located (looking down from the top of the engine) at the front right corner of the engine. It is belt driven. If this belt has any slack at all it will not help your charging situation, it needs to be very tight.

The isolator is generally located on the firewall directly in front of the driver under the engine access cover. You'll likely see it mounted there as it has pretty heavy duty wires running to three different locations on the box. Often blue in color.
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Old 12-13-2006, 08:52 PM   #13
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A two week old chassis battery @11.7 volts would seem to have been defective at purchase or a ground fault (short) is/has sapped the battery of its charge. One way to test would be to disconnect and charge the battery. Check its voltage (should be 12.7 -- if not, bad battery... if 12.7, a short exists. A multimeter with a current clasp allows sampling individual wires for amp movement. Good luck.
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Old 12-15-2006, 08:07 PM   #14
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1989 34.5' Airstream 345
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Ok so I took some pictures this evening of where the Isolator should be and of the engine so that maybe one of you coulf help me find the Alternator...I feel like an idiot. But anywho....I measured voltages at that thing that is where the Isolator should be. I had nothing at all post with the black lead on ground. Now I put the black lead on the exterior of that thing and the red lead on the post and I got 11.5 VDC Weird? I would think that thing is shot? Why are all the cables going to that one post? Is that right. I edited the images with Paint so that I could pick your brains. Any info would be a big help. I want to fix it this weekend.
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