| A little confused.... [message #229965] |
Fri, 15 November 2013 18:54  |
jme8ro
Messages: 34
Registered: October 2013
Location: Arkansas
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OK here is the deal. New bags, new shocks, remodeling almost done and looking retro and fabulous. For a girl I think I am doing ok. However with my limited knowledge of engines diagnosing problems seems to take forever. But I am learning and am excited to expand my knowledge. So here is my dilemma. My rv runs great and all seems well. However, while I am driving down the road my headlights will become dimmer until they die all together. It will stay running but no lights. But if I turn it off it won't start due to dead battery. I checked/replaced fuses. Did a volt test which said the alternator was putting off about 10 volts. I know it should be about 13-14. So I decided to try to test the isolator. This is where I have questions. I have been reading through archived posts to determine the process. That part I understand. So here is my questions.
1)where is the isolator located? I found pics of what it should look like.
2) Do I test the isolator with it running?
3) If I take the wires off the isolator to see if the problem persists, where do I put the wires to run it and see if the lights still go dead?
4) Where can I find a combiner and what specs should I look for when choosing one?
5) Any suggestions that might help?
My knowledge of my big bird engine is still limited but expands each day and I am super stoked about learning more. Any suggestions/answers would be a great help. This is a project I have taken on alone so while confident I can get this I am a little ignorant as to some technical terms. Just saying you are talking to a determined yet somewhat confused blonde chick lol. Thanks
Jeanette E., Central Arkansas-1975 GMC Glenbrook
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| Re: A little confused.... [message #229967 is a reply to message #229965] |
Fri, 15 November 2013 18:58  |
Otterwan
Messages: 946
Registered: July 2013
Location: Lynnwood (north of Seattl...
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Where did you check the voltage? It sounds like your alternator either died, lost a belt, or is not hooked up.
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: A little confused.... [message #229970 is a reply to message #229967] |
Fri, 15 November 2013 19:01 |
jme8ro
Messages: 34
Registered: October 2013
Location: Arkansas
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My alternator belt is new, it is hooked up and running. I have a battery charger that will also test the alternator voltage.
Jeanette E., Central Arkansas-1975 GMC Glenbrook
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| Re: A little confused.... [message #229971 is a reply to message #229970] |
Fri, 15 November 2013 19:27 |
Otterwan
Messages: 946
Registered: July 2013
Location: Lynnwood (north of Seattl...
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| jme8ro wrote on Fri, 15 November 2013 17:01 |
My alternator belt is new, it is hooked up and running. I have a battery charger that will also test the alternator voltage.
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I would take you alternator to the local auto parts store. They can test it for you.
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: A little confused.... [message #229973 is a reply to message #229970] |
Fri, 15 November 2013 19:43 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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1. Isolator is located on the firewall in the engine compartment, behind the hood access door on the passenger side of the GMC. OEM isolators are blue in color (the ones that I've seen), and have three posts for electrical wires. the center post is connected to the alternator, the other two posts are connected to the two batteries, the engine battery and the house battery. The assumption here is that the P.O. did not do anything strange. For photo of isolator:
http://www.appliedgmc.com/prod.itml/icOid/986
2. Isolator can be tested for diode function without the motor running. Test for voltage function should be done with the motor running. Center voltage should be in the range of 14.4v, both outer posts should read 0.7 volts lower (taken with motor running).
3. I don't follow this question. Taking the all wires off the isolator, the output of the alternator stops at the alternator. There is no alternative path for it to follow. However, if you are testing the isolator for diode function, removing the wires is a good idea.
4. Where did you measure the 10 volts? Across the battery? At the center post on the isolator? If from the alternator (remember center post of isolator), either your alternator is toast, or the belt is slipping. The alternator should be putting out 14.4 volts.
5. Any possibility that your batteries are low on water? Does your battery charger bring them up to 13 volts or so? Disconnecting the wires on the battery sometimes help getting a full charge.
I have found on 2 coaches that the P.O. had connected both the house battery and the engine battery to the same post on the boost solenoid. This is a bad idea, as one battery will kill the other battery unless they are very closely matched.
JmK or Jim Bounds are your source for parts. They understand what you need and you do not have to chase for it.
Combiner looks like this:
http://www.appliedgmc.com/prod.itml/icOid/868 (follow the installation instructions carefully, do not cut any wires shorter.)
Keep asking questions.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
[Updated on: Fri, 15 November 2013 19:44] Report message to a moderator |
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| Re: A little confused.... [message #229974 is a reply to message #229973] |
Fri, 15 November 2013 19:48 |
jme8ro
Messages: 34
Registered: October 2013
Location: Arkansas
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I measured the voltage for the alternator across the battery as per the instructions with the battery charger I bought. Thank you for the advice I will try this. Also can the alternator be taken off without removing the alternator belt? I just replaced the belt. How do I know if it is the belt slipping? I have checked it out and it seems to turn and be straight. Sorry for the novice response,like I said I am learning as I go.
Jeanette E., Central Arkansas-1975 GMC Glenbrook
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| Re: A little confused.... [message #229975 is a reply to message #229974] |
Fri, 15 November 2013 19:53 |
jme8ro
Messages: 34
Registered: October 2013
Location: Arkansas
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I thought I read that you can connect the outter wires to the battery and the center to the isolator plate? I may have read wrong I just thought there was a way to bypass the isolator to test the alternator. If I test the alternator at the battery and the isolator is at fault, will the alternator reading be accurate or would a faulty isolator effect the reading?
Jeanette E., Central Arkansas-1975 GMC Glenbrook
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| Re: A little confused.... [message #229977 is a reply to message #229975] |
Fri, 15 November 2013 19:55 |
jme8ro
Messages: 34
Registered: October 2013
Location: Arkansas
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And how do I know If my battery is low on water? I am not sure that the battery I am using holds water? This is new info to me. Do I need a battery that holds water? Can you expand on this? Thanks
Jeanette E., Central Arkansas-1975 GMC Glenbrook
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| Re: A little confused.... [message #229978 is a reply to message #229975] |
Fri, 15 November 2013 20:03 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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I think you would end up with a runaway alternator, resulting in its death. The alternator senses its output as a control function.
Generally the isolator is a pass or fail item. I do not believe that they fail half way. If you have voltage at the center post and voltage at either end of the isolator (testing against ground.), the isolator is good. The difference between the voltage on the center post and the voltage at either end post should be about 0.7 volts. The voltage on both end posts should be very close to the same. If there is a difference, the isolator has failed.
By the way, 10 volts is the charge of a "fully charged battery" with a dead cell. You can pull the battery and have it tested at most auto parts stores for free. (Of course, they want to sell a new battery, if it is bad.)
Look for messages 229948 and 229966 and follow the thread. This was a current discussion on isolators, etc.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: A little confused.... [message #229979 is a reply to message #229977] |
Fri, 15 November 2013 20:09 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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All Lead-Acid batteries have water in them. You will find the water hiding under the caps that run down the center of the battery. Some batteries have two rectangular caps that when pulled off reveal 3 separate battery compartments. When pulling the caps, do not splash the liquid on yourself or anything else for that matter. Acid is bad stuff.
The inside of each battery compartment will have some method of determining the water level. Generally, there will be a short tube going down with either a line or an edge that is the desired water line. Add distilled water (slowly) to bring the water up to that level. If the cell is completely dry, the battery is toast, and cannot be brought back to function.
Hope this helps.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: A little confused.... [message #229981 is a reply to message #229978] |
Fri, 15 November 2013 20:13 |
jme8ro
Messages: 34
Registered: October 2013
Location: Arkansas
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ok I know this is a stupid question but I have a multimeter. However I have never used one. Where do I put the ground side when testing the isolator? And can I remove the alternator without removing the alternator belt? Feeling really in the dark about this one but I am sure I can do this. I appreciate all the help. It is much appreciated. Please bare with me on the questions. Seems everything I have to do is an hours long process of research but I am learning and will be more knowledgeable in the end for it.
Jeanette E., Central Arkansas-1975 GMC Glenbrook
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| Re: A little confused.... [message #229982 is a reply to message #229965] |
Fri, 15 November 2013 20:13 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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Janette, testing an alternator by only checking the voltage doesn't really test it. It has to be tested under load. An battery can be checked in place and also the alternator if you tell them that the center terminal of the isolator is the output of the alternator.
You cannot change the alternator without loosening the alternator and taking the belt loose. You don't have to remove other belts however, just loosen the adjuster nuts and rotate the alternator so there is enough slack in the belt to get it over the pulley.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: A little confused.... [message #229983 is a reply to message #229965] |
Fri, 15 November 2013 20:14 |
jme8ro
Messages: 34
Registered: October 2013
Location: Arkansas
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so my battery is not one that holds water. It seems to be a regular battery. Do I need one that holds water in order for it to work with my rv. It starts and runs fine its just the drain I am noticing.
Jeanette E., Central Arkansas-1975 GMC Glenbrook
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| Re: A little confused.... [message #229986 is a reply to message #229983] |
Fri, 15 November 2013 20:30 |
Dennis S
Messages: 3046
Registered: November 2005
Karma: 2
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| jme8ro wrote on Fri, 15 November 2013 20:14 |
so my battery is not one that holds water. It seems to be a regular battery. Do I need one that holds water in order for it to work with my rv. It starts and runs fine its just the drain I am noticing.
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Jeanette,
Please tell us -- do you have to recharge the battery in order to start the GMC or does it recover after a while.
All regular batteries hold water --
see this video for how to add water -- the battery shown is somewhat unusual bu the video is the best one I found.
http://www.youtube.com/watch?v=YGQUfgqNt2k
and this one is OK -- but you should use gloves --
http://www.youtube.com/watch?v=q2WthPyx9p4
You don't want to overfill the battery -- so be sure you know where the fill line is....
Dennis
Dennis S
73 Painted Desert 230
Memphis TN Metro
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| Re: [GMCnet] A little confused.... [message #229991 is a reply to message #229987] |
Fri, 15 November 2013 20:55 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Senior Member |
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Testing voltage at isolator with multi-meter:
1. Set multi-meter on 20v DC range.
2. Ground lead goes to base of isolator or a metal spot on the firewall
3. Positive lead is used to touch and get a reading at the isolator posts. With the engine running, the center post should read 14.4 volts or very close.
Both end posts should read 0.7 volts lower than center post. This amount represents voltage drop across the isolator diodes. Much difference and the isolator is suspect, especially if one post reads 0 voltage.
4. Without the engine running, the end posts voltage will tell you the level of both the engine battery and the house battery. Should be close to 13 volts or a little less, depending upon state of charge in the battery. If a difference of 2 volts, that lower voltage battery is suspect. Remember each post is connected to a different battery, the isolator's purpose is to isolate the batteries from each other, but to allow a charging path from the alternator.
You may have a maintenance free battery with no method to check water level. Does not mean that the battery does not have a bad cell. All batteries will age out. Style or type of battery is not important as long as it is the correct voltage and cranking power for the engine.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: A little confused.... [message #229992 is a reply to message #229981] |
Fri, 15 November 2013 20:56 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| jme8ro wrote on Fri, 15 November 2013 19:13 |
ok I know this is a stupid question but I have a multimeter. However I have never used one. Where do I put the ground side when testing the isolator? And can I remove the alternator without removing the alternator belt? Feeling really in the dark about this one but I am sure I can do this. I appreciate all the help. It is much appreciated. Please bare with me on the questions. Seems everything I have to do is an hours long process of research but I am learning and will be more knowledgeable in the end for it.
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Before you pull anything off, you still haven't determined if the alternator is putting out. The red lead from the multimeter should be touched to the center terminal of the isolator and the black lead can be touched to the aluminum plate that the diode is mounted on. Set the multimeter to 20 V DC or higher(or anything over 12) and you should see 13V or more with the engine running. Let us know what you read and we can go further.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: A little confused.... [message #229995 is a reply to message #229965] |
Fri, 15 November 2013 21:09 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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All batteries have electrolyte (acid). Some have service caps to allow you to replace distilled water as it evaporates. Your coach has a chassis battery and a house battery. When working on wires, replacing alternator etc. FIRST disconnect the NEGATIVE at the battery. We want you to be safe and not have a coach fire.
John Lebetski
Woodstock, IL
77 Eleganza II
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