Using an A-B switch on trolling motor??

**mitrisin** · 01-22-2012, 05:14 PM

I have a 12v trolling motor and have a second trolling motor battery on board in a 16ft boat I use mostly for crappie fishing and do a lot of trolling with my trolling motor. I also have a BPS charger to charge my trolling motor and my starting battery. I was wondering if it would work to put an A-B swithch on my trolling motor bank and hook up both batteries. One like the Perko with an A or B or A+B switch. I guess I could charge the batteries using the switch and would it hurt the charger to charge the batteries in the A+B position? Anyone see any problems with this? It would be a lot easier to flip the switch than physically swap the batteries while fishing. Also are there any switches out there smaller than the Perko (5 1/4" diameter)?

**Cray** · 01-22-2012, 06:23 PM

It is a good idea but I would not use the cranking battery for trolling motor unless it is a deep cycle like your trolling battery. If it is still not good idea to run down cranker. I would get another troller with a few dollars more than your perko switch. Hook your 2 Trollers together positive to positive, negative to negative. Hook charger to one and charge both at same time. Every now and then after charger kicks off let battery settle for hour or so and disconnect one if you have a meter and check voltage on both just to make sure they are both toping off.
I have never found a switch that would carry the load of trolling motor any smaller than the Perko if that is the direction you decide to go. Good luck which ever way you go

**Reel Man** · 01-22-2012, 08:03 PM

Blue Sea makes a mini disconnect series that is quiet a bit smaller than the Perko's that will handle up to 300 amps. It will also mount behnd a panel, on the front of a panel or flush mount.

**mitrisin** · 01-22-2012, 09:10 PM

It is a good idea but I would not use the cranking battery for trolling motor unless it is a deep cycle like your trolling battery. If it is still not good idea to run down cranker. I would get another troller with a few dollars more than your perko switch. Hook your 2 Trollers together positive to positive, negative to negative. Hook charger to one and charge both at same time. Every now and then after charger kicks off let battery settle for hour or so and disconnect one if you have a meter and check voltage on both just to make sure they are both toping off.
I have never found a switch that would carry the load of trolling motor any smaller than the Perko if that is the direction you decide to go. Good luck which ever way you go

Thans Cray, I have a second trolling motor battery and do not connect my cranking battery to my trolling motor. I just am trying to decide if it would be better to connect the two batteries in parallel, or use an A-B switch to use one and then the other with the option of using A+B.

**catch fillet** · 01-22-2012, 09:24 PM

I have same as you--2 batteries--never thought about A B switch.Now I am wondering.

**Cray** · 01-22-2012, 09:49 PM

Originally Posted by mitrisin

Thans Cray, I have a second trolling motor battery and do not connect my cranking battery to my trolling motor. I just am trying to decide if it would be better to connect the two batteries in parallel, or use an A-B switch to use one and then the other with the option of using A+B.

In that case I would go with A/B switch.

**mitrisin** · 01-22-2012, 11:07 PM

In that case I would go with A/B switch.

Excuse my ignorance, What is the difference.

**Corker** · 01-23-2012, 05:45 AM

There is a difference and the A/B switch is a good idea.

When you set up a parallel bank of batteries, both feed power to the load (your TM) at the same time--but they also feed each other. Since batteries age at different rates, the weaker of the two will pull amps from the more powerful. Unless you're monitoring them with a gauge (not likely since you're busy fishing), both could be drawn down to a marginal level of performance.

With a switch, you start the day set to the weaker of the two batteries. Run that one down to a moderate level of discharge. A fully charged battery will read 12.6 volts or higher. At the 50% level, it will read 12.2 volts and you should switch to the fresh battery. If you draw it down any lower, you shorten the battery's life.

I switch my batteries at lunchtime. By saving the stronger battery for the second half of the day, you have a good idea how much trolling time remains. On TMO lakes, knowing that I'm switching to a fully charged battery at lunchtime means I can fish all afternoon and not worry about having enough power to get back to the dock. Remember--in an emergency you can always switch back to the first battery and do what you must in order to get home.

Those with more battery knowledge & experience may advise differently, but it's reasonable to assume that two batteries in parallel will take no more charge than the weaker of the two. This would deprive you of the extra energy the stronger battery is capable of holding. With an A/B switch set to A, B, or off, your charger(s) can stay connected to both batteries and charge both to their maximum capacity at the same time.

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