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Second "House" battery in truck bed questions

Discussion in 'Technical Chat' started by pos3idon, May 15, 2011.

  1. May 15, 2011 at 1:57 PM
    #1
    pos3idon

    pos3idon [OP] Active Member

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    So I've searched around a bit and seen a number of different builds involving a second battery, I'm considering placing a battery in the bed to use on an extended road trip for lights and accessories while stopped.

    However I have the stock alternator and don't want to overload it, is there anyway I can setup the second battery so that it won't kill my alternator? Perhaps some sort of trickle charge setup?

    I'm just toying with ideas at this point so any advice is appreciated :)
     
  2. May 15, 2011 at 4:26 PM
    #2
    skytower

    skytower Well-Known Member

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    Without getting a better alternator, you have a few other options. Any time you add a second battery, you should use an isolator. The isolator will not let the 2nd battery to draw on the 1st battery. It also charges the 1st battery and then the 2nd, which keeps it from burning out the alternator.
    The problem arises when you run the second battery down till it's low or dead. Use a deep cycle battery for the 2nd, or you'll kill a regular battery after 3 or 4 discharges. Along with killing a battery, you'll kill the alternator. The alt is only designed to maintain the battery.
    The solution for when you know you will be draining the 2nd battery is to use a switch and a trickle charger. Leave the 2nd battery off till you can use the charger. Don't try to use the truck's inverter. It's still working the alternator.
     
  3. May 18, 2011 at 6:56 PM
    #3
    pos3idon

    pos3idon [OP] Active Member

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    Thanks for the advice, do you have a brand of isolator that you recommend?
     
  4. May 19, 2011 at 2:28 AM
    #4
    skytower

    skytower Well-Known Member

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    No, but, as with everything else, you get what you pay for. Match amp ratings with your alternator or larger.
     
  5. May 26, 2011 at 2:04 AM
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    WhatThePho?

    WhatThePho? Greg Graffin 2016

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  6. May 26, 2011 at 2:49 AM
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    JLink

    JLink Well-Known Member

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  7. May 26, 2011 at 2:58 AM
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    snowgod06

    snowgod06 UG legend wannabe

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  8. May 26, 2011 at 3:56 AM
    #8
    Caduceus

    Caduceus Well-Known Member

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    I don't know crap about batteries.

    However, maybe you could go to your local fire or EMS station. I know both of those rigs tende to have several batteries per vehicle. If they could direct you to their maintanence shop (sometimes off site for municipal departments), you might be able to talk to guys that deal with multi-battery vehicles on a daily basis. They might even show you the layout of what it looks like so you could visualize all the pieces and how they fit.
     
  9. May 26, 2011 at 4:30 AM
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    badguybuster

    badguybuster Well-Known Member

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    ^ Thats some good advice
     
  10. May 26, 2011 at 5:18 AM
    #10
    medic2230

    medic2230 Ditch Doctor

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    Totally different setup. That's for cranking amps wired in parallel. Batteries are not isolated.
     
  11. May 26, 2011 at 5:59 AM
    #11
    Caduceus

    Caduceus Well-Known Member

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    How do you know for sure? Are you one of the mechanics?

    Typically you dont' need that much power to start the vehicle - it's not like all your electrical systems come on the second you turn the key.. Think about it - whenever you're on scene you leave the engine running to keep the lights on (light bar, rear lights, flood lights, the house lights) and whatever else you need to turn on - suction, the 110/12 invertor, etc. Essentially that's what the OP is asking - how to keep his stuff running when he's stopped.
     
  12. May 26, 2011 at 6:15 AM
    #12
    medic2230

    medic2230 Ditch Doctor

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    If we run anything with the truck off...thus not charging, the batteries die and we don't start. Yes we do have a better reserve time but there is no isolated battery bank for starting and running stuff when the trucks are not running.

    If your on scene with regular lights not LED and leave it running at idle the truck will drain the batteries and it will not start up next time. That is why we have a high idle. Suction is 12 volt. We have a 2000 watt inverter for scene lights (2) 500 Halogen, printer, and ability to re-charge the cardiac monitor. We also use it for running a sawzall for extrication. The truck is always high idled when inverter is used because it will drain the system and shut the inverter off due to low voltage.

    I'm not one of the mechanics but I have done this for 16 yrs and know how an ambulance works.
     
  13. May 26, 2011 at 8:13 AM
    #13
    skytower

    skytower Well-Known Member

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    Starters draw hundreds of amps when cranking. More when cold, less when hot. I don't remember the exact numbers. Why is the starter lead so thick? Hmmm;)
    Semi trucks normally run multiple batteries. 12vdc in paralell for accessories, and 24vdc in series for the starter.
     
  14. May 26, 2011 at 1:52 PM
    #14
    Bryan139

    Bryan139 I have a spectacular aura

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    I cut some wires here. Added some wires there.
    I'm not sure I'm understanding this completely. Are you basicly saying without changing the alternator, just use a deep cycle and when you drain it, charge it externally when you get home?
     
  15. Apr 3, 2012 at 8:18 AM
    #15
    Shadetree

    Shadetree Well-Known Member

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    OEM alternators are sized to provide power for the maximum OEM electrical load of vehicle plus some extra power to slowly recharge the starting battery. The amount of power power produced is based on the engine RPM. When the load exceeds the power produced from the alternator, it is provided by the battery until the battery has been discharged. OEM alternators are not sized to produce power for large after market accessories or to recharge large house deep cycle batteries without the risk of overheating or other damage.

    Please see Section 5 in the Car and Deep Cycle Battery FAQ on www.batteryfaq.org for more information.
     
  16. Apr 3, 2012 at 10:22 AM
    #16
    skytower

    skytower Well-Known Member

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    Yes.

    Using a small battery charger matched to the wattage of the inverter might not be enough to recharge the battery. It would extend it's usage, but is pretty inefficient.
    A solar panel mounted on top of a cap, or a stronger alternator would be the way to go.
     
  17. Apr 5, 2012 at 9:54 PM
    #17
    joes06tacoma

    joes06tacoma Well-Known Member

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    Holy old thread revival Batman!:eek:

    While I'm here, just in case someone is reading this looking for my two cents, here it is:

    I have a small amount of experience with this. My buddy and I installed dual batteries in his Jeep. He has a 120A alternator, which was installed in place of the 90A stock alternator. It was a NAPA rebuilt alternator, so not a high dollar item. It was stock equipment for a 3/4 ton Dodge truck. Every electrical load in the Jeep is connected to the stock battery. The second battery is connected to the stock batterie's terminals and there is a continuous duty solenoid installed to break the connection on the positive cable with the key in the ACC or off position.

    Standard procedure with his Jeep is to take it camping, run the primary battery (stock location) down until the CD player starts to skip.:rolleyes: Then he restarts the vehicle using the second battery to "jump start" it. The alternator then recharges the primary battery.

    He's had this setup for close to ten years now. It goes through batteries for some reason. It has eaten several yellow top Optimas. I think that may be because the Optima yellow top isn't a true deep cycle. Or possibly because the Jeep isn't a daily driver anymore and it sits with the alarm set most of the time. But I seem to remember it ate batteries before....maybe because it's got a sound system without a cap installed.

    My main point here is that he's never had an alternator fail. I don't see any trouble with having a deep cycle in the bed that's only used for your camping loads. The alternator isn't going to have an issue with occasionally recharging the battery.
     
  18. Apr 6, 2012 at 8:39 AM
    #18
    skytower

    skytower Well-Known Member

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    Put it in the engine compartment. You will have to run thick gauge leads to a bed mounted battery. If you're still not convinced, be sure to put ot in a marine battery box. It'll protect it and keep the acid in.
     
  19. Apr 6, 2012 at 5:48 PM
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    joes06tacoma

    joes06tacoma Well-Known Member

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    How come? There's plenty of travel trailers out there with battery charge wiring through the trailer plug. They don't use more than a 10 gauge wire for that. As long as it's got a 30 amp fuse in it, I don't see the problem?
     
  20. Apr 7, 2012 at 4:16 AM
    #20
    Shadetree

    Shadetree Well-Known Member

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    There are a number of trade offs in battery placement on a vehicle. I have always been most concerned with safety first, capacity/performance and value matched to application. For example, no matter how well ventilated, I would never put a wet lead-acid battery in passenger or sleeping compartment. Instead I would use a AGM or Gel Cell VRLA Battery because of the dangerous gasses that are present during charging or mixing with salt water and fused wiring with less than a 5% voltage loss. In terms of capacity or performance, the applied temperature compensated charging voltages applied directly across the battery's terminals directly affect the charge of the battery and indirectly the health and service life. The value proposition is a function of the life cycle cost, average Depth-of-Discharge and maintenance. Heat, deep discharges and sulfation prematurely kill lead-acid batteries, especially deep cycle.

    For more information, please see the Car and Deep Cycle Battery FAQ on www.batteryfaq.org.
     
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