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Author Topic: Running Batteries in Parallel vs. one at a time  (Read 421 times)

Offline Yellowstoner

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Running Batteries in Parallel vs. one at a time
« on: Jan 10, 2019, 01:18 AM »
I made a homemade power source for a portable fish finder, light, USB chargers, and cigarette lighter adapter.  It's working great, but the offroad light really eats through the batteries.  It might last 4 hours or maybe a bit less.  So I ordered an identical battery with the thought of running them in a parallel situation to make it last longer.  However, now that it's arrived and I've done some googling on batteries, it seems like charging them in parallel is not advised, and also once one starts to not recharge to the full level, it may damage the other battery.  It's very easy to switch from one power source to the other inside the box, and the batteries themselves are relatively cheap ($20ish).

My question is this - is there any appreciable difference in battery lasting strength (amp hours) between running them in parallel versus one at a time?  IE, will it stay charged longer at a usable level if I run them in parallel versus running one down to nearly empty and then switching over my power cables?

Offline mvanhank222

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Re: Running Batteries in Parallel vs. one at a time
« Reply #1 on: Jan 10, 2019, 06:46 AM »
Probably not a lot of difference but with batteries doubling the available amps usually more than doubles the run time. You can run in parallel if the batteries are approximately the same age and can hold the same amount of charge. You may have been better off getting 1 larger battery eg. 1 15ah vs 2 7ah as long as that larger battery fit in your box. If you are going to charge 2 batteries at once connect the charger so the + is on one battery and the - is on the other battery that should help balance the charge.

Offline DANMAN

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Re: Running Batteries in Parallel vs. one at a time
« Reply #2 on: Jan 10, 2019, 02:45 PM »
Assuming your batteries are identical  and both batteries are 12v

In your sled    hooking batteries in parallel is fine if both batteries are good
plus to plus  ........  minus to minus

Then you hook your flasher plus to batteries plus  ..........    flasher minus to batteries minus

If you have only one 12v charger            You should separate  the batteries and charge the batteries individually

Be sure both batteries are fully charged before you go fishing.  Don't connect a full battery and an empty battery

Two 7ah are fine.........if one dies you still have a good one.  I find mine last about 4-5 years.  I get them on the ebXX for like 18 bux each delivered
   
to answer you direct question         should be no difference running one at a time vs two in parallel  ....  amp hours are amp hours

ditch the offroad light   .......go buy some LED tape strips on the ebxx for 5 bux for ten feet.  ............LEDS use very little "juice" vs incandescent

or get 2 of the free blue 24 LED flashlights at harbor freight   they use AAA batts

they have a hook you can use on your inside poles



PM me if you want to discuss

danman
DO NOT hook your 2  batteries in series    plus to minus   will give you 24 volts and pop your electronics!!

Offline tbern

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Re: Running Batteries in Parallel vs. one at a time
« Reply #3 on: Jan 10, 2019, 02:58 PM »
Why separate batteries hooked in parallel to charge separately? Batteries hooked in parallel on farm machinery are certainly not unhooked to use a separate charger to charge them if needed.

Offline Yellowstoner

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Re: Running Batteries in Parallel vs. one at a time
« Reply #4 on: Jan 10, 2019, 03:07 PM »






Pictures for reference - the off-road light is a 24-led model that I like for finding flags. Also shining at people who get too close to me.  I did pick up a smaller LED that’s usb powered for just tying on a new jig or putting on another worm.  The batteries are identical, except one is 6 months old and the other is brand new. I probably have only gone through a dozen charge cycles with the “old” battery though.

Offline slipperybob

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Re: Running Batteries in Parallel vs. one at a time
« Reply #5 on: Jan 10, 2019, 10:07 PM »
nice power box  :tipup:

For more information read my MN nice journal

Offline prospector

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Re: Running Batteries in Parallel vs. one at a time
« Reply #6 on: Jan 10, 2019, 10:55 PM »
Make sure you have fuses for the valuable electronics.

Offline Yellowstoner

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Re: Running Batteries in Parallel vs. one at a time
« Reply #7 on: Jan 11, 2019, 01:00 AM »
Make sure you have fuses for the valuable electronics.

I do, but I'm not quite sure how to tell what amp fuse to use for each piece of electronics.  I do have a fuse box in there though - it's mounted on the lid and has a little light that lets you know when a fuse blows.  The only piece I'd really be worried about is my fish finder.

Offline mvanhank222

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Re: Running Batteries in Parallel vs. one at a time
« Reply #8 on: Jan 11, 2019, 06:54 AM »
Looks like vexilars draw about 0.20 amps I would guess marcum and bird flashers would be similar. A graph would probably draw more. I know my Lowrance HDS units came with a 3amp fuse.

 



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