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Battery different sizes for mobile set up

Discussion in 'Mobile Radio Systems' started by KO4LWS, Feb 25, 2021.

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  1. KO4LWS

    KO4LWS Ham Member QRZ Page

    I have an unused battery that pushes more amps than my truck battery. If I run a wire to the bigger battery to a smaller battery so the alternator will charge both, will the smaller battery draw from the bigger battery? And can I even do this?
     
  2. K6EEN

    K6EEN Ham Member QRZ Page

    Usually you want something like a smart "battery isolation manager" (BIM) to manage the charging between the two batteries. Or run the 2nd (non-vehicle) battery off of a 12V to 12V trickle charger with current limiting, so the radio only draws from the non-vehicle battery. Also can be a pain to figure out where to mount the 2nd battery, as most batteries vent fumes, so it needs to be not in the passenger compartment, like in a weather shield box in the truck bed (pickup) or on a tailgate rack (SUV).
     
    KB0MNM likes this.
  3. N1IPU

    N1IPU Premium Subscriber QRZ Page

    I run two golf cart batteries in a box and charge them with this https://www.amazon.com/Smart-Batter...8fb98&pd_rd_wg=xuWp7&pd_rd_i=B00400IYTK&psc=1

    You can do the same with one deep cycle battery . Trick is use a heavy gauge wire to avoid voltage drop depending on your run and Fuse or CB everything. Mine is overkill for general use and I went with an ambulance alternator and heavy harness for same but I also drive an inverter. Your alternator should do it with just one deep cycle depending on how you drive. Lots of short trips will kill it but if you do a lot of highway use you should be fine.
     
  4. K3XR

    K3XR Ham Member QRZ Page

    Going back to the early '70s I ran an extra battery in my VW Camper. There was a space on the opposite side of the engine for the battery. As has been pointed out there are dual battery isolators to separately charge each battery and prevent discharge of the vehicle battery.
     
  5. GJ6WRI

    GJ6WRI XML Subscriber QRZ Page

    There was an excellent webinar from the Orlando Hamcation a couple of weeks back about battery types and use. It's very informative. Here is the link.
     
    KB0MNM likes this.
  6. NG1H

    NG1H XML Subscriber QRZ Page

    Dual batteries are almost universal in diesel engines and is an option for most gasoline trucks. On older vehicles they just ran them in parallel with heavy gauge cables. The same wire size as runs to the starter. With more recent hall effect sensors it gets a little more complicated.

    Check with your vehicle manufacturer regarding their dual battery configuration. The advantage of this method is that you have additional capacity for starting the vehicle. The disadvantage is that when one battery goes bad the second one soon follows.

    A good (not HF nor cheap) battery isolator would be my second choice. The only disadvantages I know of is that not all allow you to use the second battery for starting and cost.
     
  7. KD4UPL

    KD4UPL Ham Member QRZ Page

    Batteries don't "push"amps. Current flow is based on the source voltage and the resistance of the circuit. I assume what you mean is that the bigger battery has a higher amp-hour capacity. Putting batteries in parallel will work but it works best if they are matched in size, type, and age. It sounds like yours are not matched. The "weaker" battery will tend to draw down the "stronger battery." It would be best, particularly with mis-matched batteries, to use an ACR, isolator, trick-L-start, or something to keep them separated.
     
  8. K2WPM

    K2WPM XML Subscriber QRZ Page

  9. KD4UPL

    KD4UPL Ham Member QRZ Page

    It would work but it limits you to only 15 amps and apparently costs over $100. A Blue Sea ACR would allow for greater charging amperage and costs more like $75.
     

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