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Newbie question about batteries and electronics

Old 07-12-2014, 03:43 AM
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Default Newbie question about batteries and electronics

I have 3 batteries on board my bay boat. One for the starter outboard 12v.
And two for the 24v trolling motor.
I have a gps/fishfinder that is now wired to the single starter battery.
It is now time to replace all batteries on board.
My question is can I wire the gps to one of the two batteries (deepcycle) that feed the trolling motor at 24 volts ? I would rather have the gps or any other electronics pulling from the deepcycle batteries rather than the starter battery.
Thanks in advance for any help
John
Old 07-12-2014, 08:57 AM
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What brand/model GPS do you have?
Old 07-12-2014, 09:12 AM
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It is an older garmin.
Old 07-12-2014, 09:15 AM
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The best solution would be to add a 4th house battery.
Old 07-12-2014, 09:34 AM
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Just to make it clear the trolling motor batteries are two 12v batteries wired to be 24v.
Stiletto I was hoping to avoid a 4th battery. that may be my answer though
Old 07-12-2014, 11:09 AM
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Originally Posted by stiletto View Post
The best solution would be to add a 4th house battery.
^^^^ this
Old 07-12-2014, 02:00 PM
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John,
the big question is whether or not the "older" Garmin can be hooked up to a 24v system, some can but w/o knowing exactly which model you have it would be hard for someone to say for sure. All of Garmin's specs are in 12-13v ratings, even their older/discontinued models. It might be worth calling Garmin's customer support Monday with your model just to check. Like Stiletto said adding a house battery would be the best so that, even with the minimal draw, the GPS doesn't draw down the TM batts.
Old 07-12-2014, 07:04 PM
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If the garmin can use 24v power source, that would be okay. Next solution is to use a 4th battery, next would be your starting battery, last would be 1 of the 2 trolling motor batteries. You will cycle them out of service faster than your starting motor battery.
Old 07-12-2014, 08:32 PM
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Yes you can wire it to 1 of your trolling batteries.
Old 07-13-2014, 04:47 AM
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Guys I am always afraid of draining the starter battery having the gps/fish finder on all the time.
My thought was to wire it to the first deep cycle battery running the trolling motor. I just dont know if it becomes 24v once you wire the two batteries together.
Old 07-13-2014, 07:06 AM
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It's still 12v as long as you use the pos and neg of the same battery.
Old 07-13-2014, 08:22 AM
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It is unlikely your GPS would be safe running on 24 volts and running off just the first trolling battery will unbalance the pair which will result in one running down before the other. When this happens, the battery with higher charge forces current through the discharged one which will destroy it rapidly.

One solution is the Trollbridge24. It keeps the trolling batteries in parallel so BOTH batteries are supplying power equally. When you turn the trolling motor on, it puts the batteries in series but next time the trolling motor is off they are put back in parallel so any imbalance in charge gets equalized by battery to battery current.

Before making a change, run a test with the GPS on the first battery (NEVER ON THE SECOND ONE) while the trolling motor is running to check that electrical noise from the trolling motor is not preventing the GPS from working.

You get the added advantage that when the main engine is running you can charge BOTH trolling batteries from the alternator which for many means they are independent from shore power.

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