wolfe10
Texas
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Truck55 wrote:Pretty sure I have and isolator of some type. Just not sure where it is. If it is faulty could it keep it from charging?
Thanks
Dan B
In a word, YES.
Again, trace from alternator output toward batteries and/or from batteries toward the alternator to find it. There are both diode-based isolators and solenoid-based isolators.
Brett Wolfe
1993 Foretravel 36' U-240
Cat 3116, Allison 3060
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YC 1
Yuba City Calif.
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Joined: 01/11/2005
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Truck55 wrote:It will start and charge and run great for a few mins. Then it will quit charging and the engine will go dead. It is as if all electicity is cut off to the engine. It will then start right back up and charge and run great for a few mins. again before doing the same thing again. I have always been a shade tree mechanic, just know about enough to get me in trouble. LOL.
There must be something that I am missing.
Thanks
Dan B
Since the engine is going dead you are losing the voltage to your ignition system. Turn on your headlights and tell me if they go dead when your engine dies. Some main supply line is opening up. You do not have an alternator problem.
I would like to cite just one incredibly strange problem a couple of years ago. A cutomer parked in our lot, engine would not start, we jump started her. As soon as she put vehicle in gear the engine would die. We charged her battery for a few minutes and jump started her again. As soon as the vehicle was put in gear and a bit of load on the system was placed. It would die instantly. Now I have been doing this type of thing for 30 years and have only seen this once.
We grabbed an old battery, because it was handy, replaced her battery with it, started it, and off she went. I cannot figure out what the issue was with her battery.
On one other situation 25 years ago, a BMW, exactly 20 minutes with any load on the battery, as little as 1 amp, and the voltage would drop to 8.5 volts. You could set your watch by it.
So, just in case. You might want to swap the battery out for a quick test.
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Tenn Stud
Northeast, TN
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Some alternators and/or regulators have over voltage relays. All Aircraft do. with the engine dead and the ign switch on, Measure the voltage on the largest post on the back of the alternator from the post to ground. The measure the field voltage( on the back of the alternator) from post to ground, Post those voltages. I would guess you have a ground problem or a shorted cell in a battery. On a 12vdc solenoid most all will hold engaged as low as 7.5vdc. If you can hear it drop out AND you have 12vdc+ on the back of the alt it is not the alternator or the internal regulator. Like a poster ahead of me stated a battery will not discharge that fast. How long will it run with the emg start switch engaged? Or take a jumper cable and jump from the pos post on the house batts to the pos post on the chassis batt see if it will keep running
* This post was
edited 08/12/08 08:37pm by Tenn Stud *
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Golden_HVAC
Fulltime, CA, USA
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I see DANGER!
You must have a great big short to ground someplace.
I think you will find a battery or alternator charge wire that has rubbed against something, and is shorted to ground, causing the votlage to drop. Perhaps the +12 wire going to the jacks, or starter motor? Check the alternator to battery wire. If your batteries are not under the hood, then check the wire that runs from the fuse center to the batteries.
Also check the +12 line towards the generator.
I think you will find that one of those battery cables is shorted someplace. Did you think about trying this at night? You can see the ark from the wires better at night. Keep a fire extinguisher on hand!
Fred.
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Tenn Stud
Northeast, TN
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Here is a thought that you might consider. you say you hear a click then the engine fails to run but, You can start it right back up and it runs ok for a few minutes. You should have a boost fuel pump in the fuel tank that will run for a few minutes after starting the engine that pump is controlled by a relay, I wonder if that is what you are hearing and your you are running out of gas causing the engine to fail. That pump would run again as soon as you hit the starter
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Truck55
Florida
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Ok if I had a dead short, wouldn't it short just as soon as i turned the ign on?
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Dan B
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Truck55
Florida
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Ok guys here is some more info. Chassis battery with MH running is at 13.62v. Both house batteries are 6.74. Tonight I started her up and she was running and charging great. Did so for about 5 min then voltage went down to 9.62 at the battery for a few seconds then went back to 13.62. Engine kept running the whole time. I checked the voltage of the relays for the battery disconnects. The chassis relay read 0 while alt was charging and when it would quit charging the voltage went to 12.80. I could hear and feel the relay clicking. The relay got very hot almost too hot to touch. For some reason it was doing much better today than when I originally posted. But the relays click and then the voltage goes down to about 10v. not 0 as it was at first. The only thing i did was to operate the disconnect switches in the coach several times. when it is charging right i can rock the house batt disconnect switches and hear it click when it stops charging right it won't click when rocking it.
Anyway what i am asking is Should the relays get to hot to touch? These relays are by the solenoid valves under the hood. Does anyone know of a good way to check the relays. I am beginning to think that my problem may lie somewhere between the disconnect switches in the coach and the relays under the hood.
Maybe you guys can shed some more light on this for me.
Thanks
Dan B
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YC 1
Yuba City Calif.
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Truck55 wrote:Ok guys here is some more info. Chassis battery with MH running is at 13.62v. Both house batteries are 6.74. Tonight I started her up and she was running and charging great. Did so for about 5 min then voltage went down to 9.62 at the battery for a few seconds then went back to 13.62. Engine kept running the whole time. I checked the voltage of the relays for the battery disconnects. The chassis relay read 0 while alt was charging and when it would quit charging the voltage went to 12.80. I could hear and feel the relay clicking. The relay got very hot almost too hot to touch. For some reason it was doing much better today than when I originally posted. But the relays click and then the voltage goes down to about 10v. not 0 as it was at first. The only thing i did was to operate the disconnect switches in the coach several times. when it is charging right i can rock the house batt disconnect switches and hear it click when it stops charging right it won't click when rocking it.
Anyway what i am asking is Should the relays get to hot to touch? These relays are by the solenoid valves under the hood. Does anyone know of a good way to check the relays. I am beginning to think that my problem may lie somewhere between the disconnect switches in the coach and the relays under the hood.
Maybe you guys can shed some more light on this for me.
Thanks
Dan B
The relays should not get to hot to touch. An easy approach to determine if the relay is bad is to first disconnect you negative battery terminal, then disconnect the relay wires, the big ones that is, and then stack them together so the relay is not in the circuit anymore. You could build your own bypass jumper if this is difficult and just add a temporary nut to hold them.
I'm doing this with no visual of your solenoids so your mileage may vary on how to bypass the them.
I am very curious about that voltage reading across the battery of 9 volts for a few seconds. Only a couple of things could cause this. One is a cell shorting out and the other which could produce some massive smoke and fire would be a serious short in the electrical somewhere.
As you are doing any test you need to have a fire extinguisher and a set of bolt cutters or a serious set of wire cutters handy. If you have a serious short and manage to get it to stay shorted you could end up in a dangerous situation in just an instant. Batteries and the power they can supply is phenominal. Keep the cutters very handy and if needed be prepared to cut the negative lead of the battery off.
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Truck55
Florida
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Thanks again to all of you for the helpful advice. Today I took house batteries and had them tested. Found one of them to have a bad cell. Even though they were only a couple of months old. Put them back in and all problems went away. She started and was charging great. Seems I was getting a voltage drop and the alt was trying to charge a bad battery which it is not designed to do.
Thanks again to all of you on this forum Without all the good advice I never would have figured my problem out.
Thanks again to all of you
Dan B
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randandchris
MI
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Joined: 09/26/2008
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Dan, How was your dead chassis fixed?
Just bought a used RexAir and woke up to a completely dead chassis in the boonies. An auto repairman cleaned the burned wiring and replaced what he thought was an ignition solenoid but still didn't run till he jumped the solenoid with 12v. Turned out what was needed was a battery isolator relay.
Why design an RV to be a walk home when a part fails that doesn't/shouldn't have anything to do with starting it?
Rand
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