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Topic: Alternator issue, no power to battery.  (Read 101 times) previous topic - next topic
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Alternator issue, no power to battery.
Hey guys I have an issue here with alternator replacements on my E350 1989 ford econoline lazydaze. Two alternator replacements and neither of them will give power to my battery. The batter will sit at 12.5 volts and once the engine starts it drops to 11.7 v. I have checked the regulator and it was also replaced. The battery is also new. I had one of my mechanics come out and verify the wiring and the only thing we cannot verify is the fuse of the alternator. Normally we would expect a fuse box in the engine compartment but there’s nothing there. I have read that it would be a fusible link but cannot locate it. Any help finding this thing is appreciated. I ran into a similar issue not too long ago but resolved it by just replacing the alternator after several swaps. Thanks in advanced
1989 Ford E350, unknown floor plan
Re: Alternator issue, no power to battery.
Reply #1 –
Quote from: Val.M  - 
Hey guys I have an issue here with alternator replacements on my E350 1989 ford econoline lazydaze. Two alternator replacements and neither of them will give power to my battery.

The alternator's output goes to the isolator (the blue box shown in the photo). The isolator distributes power to the starting battery and the coach battery and prevents one battery from discharging into the other battery when the engine is off and generated power is not available.
Has the isolator been checked to see if the diodes are still good and pass power in one direction? This is where I would start looking. There may be a fusable link in the wire running from the alternator to the isolator.

Older alternators used a separate regulator; besides checking the regulator, the regulator's wiring may have faults.

Larry
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Alternator issue, no power to battery.
Reply #2 –
Quote from: Larry W  - 
The alternator's output goes to the isolator (the blue box shown in the photo). The isolator distributes power to the starting battery and the coach battery and prevents one battery from discharging into the other battery when the engine is off and generated power is not available.
Has the isolator been checked to see if the diodes are still good and pass power in one direction? This is where I would start looking. There may be a fusable link in the wire running from the alternator to the isolator.

Older alternators used a separate regulator; besides checking the regulator, the regulator's wiring may have faults.

Larry

Hey Larry,

Thanks for your reply. Yah the isolator was one of the first things checked. It does pass and we disconnected it in one of the tests to see if it was at fault. We also checked the external regulators wiring as well such as field wiring and light method. It did pass and the alternator seemed to be the culprit. When the vehicle runs off the battery it kicks power throughout the coach and there’s lights functioning.  Once the engine is off there’s very little power. Which is one of the reasons why we believe it could be a faulty fuse for the alternator as that’s the only thing we can’t eliminate. We will definitely check that fusible link.
1989 Ford E350, unknown floor plan
Re: Alternator issue, no power to battery.
Reply #3 –
Hi Val;  Your comment: ...when the vehicle runs off the battery it kicks power throughout the coach and there’s lights functioning.  Once the engine is off there’s very little power..."    How is the separate house battery?  That battery is charged through the isolator, but once the engine is off, the chassis battery is prohibited from supplying power to the coach. Strictly there to start the engine, run the headlights and such.
  The 'house' battery usually is somewhere in the coach, but sometimes in older motorhomes under the hood also. Sounds to me like the house battery isn't doing it's job to support lights, water pump, space heater, refrigerator, etc.
   When the engine is running, the voltage on both batteries should be the same, about 14.6 volts if you have a diode isolator.  Older coaches may have a small relay that connects the batteries together, so that the alternator can charge both at once.  Much newer coaches after about 2012 have the same relay arrangement, but a bigger more robust relay to prevent 'diode drop' in voltage across the isolator.    RonB 
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB