Dual batteries in e350

Discussion in 'Domestics' started by billj, Aug 27, 2017.

  1. Mobile Dan

    Mobile Dan wrench

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    What is your plan for the ground circuit? Some vehicles only run a smaller wire between batt and frame. If you plan to ground frame battery with a short cable to a spot on nearby frame. you may want to add equal wire to front frame area for underhood battery.
     
  2. billj

    billj MR BILL

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    Yes, the ground wire I have will connect to the frame maybe 18" from the battery box. I imagine the idea of running a similar ground wire from the underhood battery is be sure both batteries are equally well grounded. I found out once what it's like to have a poor ground in our mini-stock, shot sparks from gauges to dash, dash to body, roll bars to me.

    Anyway, please take a look at my rough schematic and see if I have all this straight in my head. I may add a couple 80 amp fuses at the battery positives and a cut off switch on the frame battery under the hood. Daul battery schematic 3.png
     
    Last edited: Sep 10, 2017
  3. Mobile Dan

    Mobile Dan wrench

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    Ok....I would think wire labeled "factory ground" would connect to underhood battery.

    A possible upcoming challenge would be the "true ignition power source" thing. Hopefully your can find a fuse that has power when key is "on" and while "cranking", but not when key is "off". Piggyback connection at that fuse might be the way to go.
     
    Last edited: Sep 11, 2017
  4. Mobile Dan

    Mobile Dan wrench

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  5. billj

    billj MR BILL

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    Mobil Dan...Thanks for catching my Daul battery schematic 4.png mistake on the schematic, Factory ground should be on under hood battery. Posting modified schematic

    Question to everyone at BAT: What the heck is Hot while cranking, but not with the key in off position? aka: "true ignition power source"
     
  6. Mobile Dan

    Mobile Dan wrench

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    Hmm...what needs to be working during both cranking and running? Well, you've got to have spark and gas, so maybe fuel pump, ignition coil, injectors.
     
  7. billj

    billj MR BILL

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    See any problem with tapping into " hot when key on" side of fuel pump fuse?
     
  8. Mobile Dan

    Mobile Dan wrench

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    I would think it should work. But it might be helpful to add a relay to reduce power loss to fuel pump. Are you the same guy I helped to wire up some relays to get fog/driving lights added to some kind of small SUV?
     
  9. billj

    billj MR BILL

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    Yes sir! A 2005 Ford Escape. Still have it, 108,000 miles. Don't drive it much, but we bought a 2011 Escape, sold that, and now a 2014 Escape, but I still like the '05 and the fog/driving lights work great

    What about the idea of mounting a switch in the cab that controls the isolator. The switch would be powered by the Frame battery and have an indicator light on the dah that comes on when the isolator is energized .

    Well, Mobile Dan, when you have time, which direction would you go? I've had some experience with relays (as you know). So I'm open to ideas.
     
    Last edited: Sep 12, 2017
  10. billj

    billj MR BILL

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    Trying to contact Mobile Dan. Are you out there friend?
     
  11. Mobile Dan

    Mobile Dan wrench

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    I think a switch/light connected to frame battery would work. The only downside would be that if you switched on isolator to charge frame battery, but shut off the engine later at the end of your day, and did not switch off the isolater, in the morning BOTH batteries would be discharged because to isolator would stay energized and keep the batteries connected until they were both so low that there was not enough power to keep the isolator energized.
     
  12. billj

    billj MR BILL

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    What was your relay idea Mobile Dan?
     
  13. Mobile Dan

    Mobile Dan wrench

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    [​IMG] Wire it like this diagram, but change info on diagram to read "+12V (from fuel pump fuse, a true ignition power source)" for pin 86.
    Also change to read "+12V (to right hand small terminal on isolater shown on your homemade schematic) for pin 87.
    Info for pins 85 and 30 would remain the same.

    Wiring in a relay in this way would greatly reduce the amount of power to be "stolen" from the important fuel pump circuit to keep that large isolater relay energized.
     
  14. jd

    jd Hero Member

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    Let me gently and humbly poke back into this... I'm reluctant since I'm not a pro mechanic, and much of my experience is dated. But it IS experience, and what I drew on recommending an Isolation Relay is based on owning Ford-based Class C motorhomes. We've had two over the last over 20 years, and both used isolation relays. I'm very active on an RV forum, and the popular setup that works and is relatively trouble free is isolation relay. Electronic solutions that are diode based are not recommended. The gold standard is Intellitec's "BIRD" which allows Either Coach (sometimes called House, which would be Bill's lighting battery in this case) OR Chassis (the starting battery) to be charged when the Other is being charged. So when driving, the Chassis would charge the House. When parked on a powered RV site or running an onboard generator, House would charge Chassis. I don't have one and the Chassis battery hasn't required charging, even when camped for 60 days. I didn't recommend it to Bill because he doesn't plug his van into a 120 VAC shore tie. If he did, and used a Battery Charger on his Lighting Battery, BIRD would charge Chassis as well. Bill's problem statement doesn't seem to require that.

    Most RV's with Isolation Relay have "Aux Start" and all it does is apply 12 VDC to close the Relay, so House (Lighting) helps Chassis. I didn't suggest including that because I wasn't sure of Bill's wire size. He could be running wire that's plenty for powering the lights, and charging from the Alternator that was NOT adequate as a "Jumper Cable." Intellitec BIRD, in the GAS version, allows Aux Start also.

    Since both of our RV's already had Isolation Relays, and I never had to work on them, I don't know which exact Fuse/Circuit/Terminal the "True Ignition" came from.
    The Ford Van Owner's Manual should be a good start. If Bill can confirm the Year Model, I'll see if I can find a Manual on line and look. Simply stated,
    START: Fuel, Ignition, Cranking
    RUN: Fuel, Ignition, Accessories (Radio, A/C, etc.)
    ACC: Accessories only
    So, what you want to find is Fuel or Ignition. I'll help if needed. Seems you could pull the respective Fuse and tap in with an adapter like pictured above. That would only power the Isolation Relay's Coil. NOT the load to charge or use the Lighting Battery

    The "Bosch" relay pictured above might not be adequate for Isolation. They're rated around 30A. If I'm reading right, using a Bosch type relay as a Slave to the Isolation Relay's control coil. Ford Vans are that way. A fender liner mounted Relay powers a Solenoid on the Starter. Chrysler used to use a small Relay (like a Bosch) between Ignition Key Start and the Starter Solenoid. It's in no way a bad idea to insert a small relay to supply power to the Coil (small terminals) of the Isolator. Again, the RV's I've known do not, but it wouldn't hurt anything unless the "Bosch" is a super cheap one and becomes a point of failure.

    Bill should either:
    Break Interior Lights OFF of Chassis and ONTO Lighting along with the LED's or
    Leave Interior ("Dome") as is, and wire the LED's separately

    Lots of words, but I hope I've helped.
     
  15. Mobile Dan

    Mobile Dan wrench

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    Yes, "using a Bosch type relay as a Slave to the Isolation Relay's control coil" is a good description of the proposed setup.

    I think Bill's goal is to keep rewiring to a minimum and just add a "frame battery" that will boost power when cranking and be recharged when engine is running. Also...isolated from electrical use (depletion) when key is off.
     

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