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Thread: How to incorporate dual alternators

  1. #1
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    Default How to incorporate dual alternators

    Hi,

    I have a ford E-350 build in progress (http://www.expeditionportal.com/foru...0-build-thread) and am planning on installing a second alternator. There's room for another one in the engine bay, (apparently it came with the ambulance package on these vans.)

    I'm planning a year-long trip overseas, and would carry a spare anyway, so I figure I might as well just install it now and have one less thing rattling around inside the van. The main goal of this is redundancy.

    So the question I have is, should I:
    1. Hook up the second alternator to van's electrical system and then install a split-charge system, or
    2. Create a dedicated "house" circuit where the second alternator is only connected to the house batteries, leaving the vehicle's stock electrical system untouched?

    The advantage of (1) is that if one of the alternators fails, I don't have to do anything to get things running again. In fact, it seems like I may not even know if one of the alternators has failed unless I install some sort of monitoring system (so that could be a disadvantage).

    With option 2, I wouldn't have to purchase and install a split-charge unit, but I probably would have to run some additional wiring to connect the second alternator to the house batteries. In the event that either alternator failed, I'd have to re-wire or jump power to either the house system or the starting system, and without a split charge unit, I'd have to be moving wires around all the time to make sure all of the batteries stayed charged.

    Just typing this up is making me think that I should go with option 1 and get some kind of current sensor so that I'd know if one of the alternators had failed.

    Anything I'm overlooking here?

    Thanks!
    When Sparks Fly

    “There are no foreign lands. It is the traveler only who is foreign.” – Robert Louis Stevenson

  2. #2
    I would recommend going with invisible option 3.

    3. Upgrade stock alternator to high-output unit.

    You could purchase a H.O. Large-case conversion kit and just have a single, more reliable alternator. However, if you are stuck on using a stock dual alternator setup (non-large case), I would recommend option 2. - running a "house" alternator directly to the battery(s). I understand the allure of redundancy in the system, unfortunately option 1 (as you have realized) will require a custom harness to run both alternators with the OEM electronics. Frankly, this may not even be possible without the PCM and engine harness from a dual alternator model. In the stock setup, the PCM senses each alternator and sends a DTC when there is a fault. Even on the stock dual-case system, the battery light may not indicate if only one alternator goes down.

    Cliff notes:

    1. May be impossible without PCM, harness, and possible other proprietary OEM parts
    2. Add a second OEM or high-output non-large-case alternator wired only to the battery(s)

    3. replace single OEM unit with Large-case 6G High-output unit

    If you have any other questions, I will be happy to help.
    Fastlane Parts and Supply

    fastlaneparts@gmail.com

    Offering Mechman High-output charging systems and accessories.

    ebay store: http://stores.ebay.com/Fastlanesupply
    don't see it in my store? send me an email!

  3. #3
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    Fastlane, thanks for the information. Definitely some considerations I wasn't aware of!
    When Sparks Fly

    “There are no foreign lands. It is the traveler only who is foreign.” – Robert Louis Stevenson

  4. #4
    Add a second alternator and run its output to the house battery bank. If your main alternator goes sideways, jump the vehicle batteries over to the second alternator and you're up and running in 10 minutes. Those Ford alternators are for sale pretty much everywhere so getting a broken alternator replaced or repaired should not be problematic. I wouldn't bother with a split charge or battery isolators if you have a provision for a second alternator, nor would I spend a bunch of money on a high output alternator. Just go with good quality Ford 3G units...maybe take a spare regulator to throw in the glove box, and call it good. New, quality, aftermarket 3G at 130 amps should run you under $150.

  5. #5
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    Every alternator I can remember having failed was due to worn out bearings. When it happens - you'll know it.

    One thing to think about is that normal voltage regulated alternators are pretty poor battery chargers.

    I'd rig the second alternator to the house bank using an external 3-stage regulator:

    http://sterling-power-usa.com/advancedregulators.aspx

    That will insure a tip-top charge to the house battery, which, unlike the engine battery, will benefit greatly from a proper charge routine.


    AND I'd rig a split charge relay with a dumb solenoid and a manual switch so I could tie the primary and aux batteries manually in case of alternator failure. Cut the belt off the failed alternator, flip the solenoid switch, keep going.
    ...
    ...
    Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
    Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker

  6. #6
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    > One thing to think about is that normal voltage regulated alternators are pretty poor battery chargers.

    That's good to know.

    I found a few threads on installing the second alternator (one here: http://www.powerstroke.org/forum/99-...tor-setup.html). It sounds like if I'm not going to tie the second alternator into the stock electrical system, I should just need the mounting hardware and a new serpentine belt, but not the Ford wiring harness. Then I'll run my own cabling back to the voltage regulator and house batteries.

    I guess I'm assuming that the alternator isn't relying on any signals coming from the car's computer to operate properly. So it's just a matter of connecting the output of the alternator to the voltage regulator?

    That sounds like a good way to go as long as I can find the mounting hardware, as it gets me a backup alternator, plus a charging profile that should be more friendly to the house batteries.

    Thanks for all the great info!
    When Sparks Fly

    “There are no foreign lands. It is the traveler only who is foreign.” – Robert Louis Stevenson

  7. #7
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    Quote Originally Posted by witt View Post
    So it's just a matter of connecting the output of the alternator to the voltage regulator?
    Output of the alternator goes to the battery. Voltage regulator goes to both - senses battery state and engages the alternator clutch (energizes field coil) to control the alternator as needed.
    ...
    ...
    Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
    Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker

  8. #8
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    Serpentine belt? Ouch. If one alternator locks up or starts smoking from a bad bearing...then what? How do you bypass it?
    ...
    ...
    Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
    Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker

  9. #9
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    Hmm. Was watching a youtube video on how to install the second alternator, and it sounds like you need a different (longer) belt for the dual setup. One could probably keep spare belts for each of the single alternator configurations in case one of them died, assuming that the shorter belt will clear the pulley on the dead alternator.

    As usual, the more I look into the details of this the more complicated it gets!
    When Sparks Fly

    “There are no foreign lands. It is the traveler only who is foreign.” – Robert Louis Stevenson

  10. #10
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    Quote Originally Posted by witt View Post
    Hmm. Was watching a youtube video on how to install the second alternator, and it sounds like you need a different (longer) belt for the dual setup. One could probably keep spare belts for each of the single alternator configurations in case one of them died, assuming that the shorter belt will clear the pulley on the dead alternator.

    As usual, the more I look into the details of this the more complicated it gets!

    Or, if the alternators are the same, if one failed you could move the good one to the location for which you have a spare, shorter belt.
    ...
    ...
    Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
    Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker

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