Basic jonboat battery questions for a newbie

[Chris at Tech]

If I be nice until Spring, my wife may let me get a jonboat in a few months

It's been a while since I've been in a classroom discussing voltage, current, etc. so let me burden you all with my silly questions...

1) Trolling motors that run off 24V.  Does that simply mean I need 2 batts to run this motor?  I assume if you have 2 of these motors, you need 4 batts right?  You can't run 2 motors off the same 2 batts, right?

2) is it generally a good idea to use another separate battery to run depthfinder, lights, livewell, etc, or is their power usage minimal enough to use the batts you're using for a trolling motor?  If it is a good idea to run other accessories on a different battery/set of batteries, how many batteries are sufficient to run these types of accessories?

3) all things being equal, if you look at 2 trolling motors with the same thrust, is it a better idea to get a 12V or 24V version?

4) lastly, would one see any difference in performance between one 80 lb thrust motor, vs two 40lb thrust?  I can't think of a single reason why there would be a difference...

Thanks all!

Chris

[Way2slow]

I will answer you basic electrical question and let the electronic jon boaters get into how many and what size motors.

First, yes it takes two 12V batteries to produce 24 volts. Two 12v 105 amp hour (Ah) batteries connect in series will give you 105 Ah at 24 volts. Connected it parallel, the will give you 12 volts at 210 Ah.

The higher the amp draw off a battery the lower the Ah rating. If the battery is rated for 105 Ah on a 20 hour rating, meaning that it is only having enough current drawn off it to take 20 hours to disharge it. Increase that draw so it disharges the battery in 4 hours it's only going to be about an 80 Ah battery. Naturally two motors are going to draw twice the current of one motor so if you try to run two motors off one set of batteries, you will significantly reduce your Ah capacity and over all run time from what you get if using two sets of batteries.

As for battery size and capacity, you will need to determine how many and what size motors you plan to run. Use the total amp draw these motors will place on your batteries and then multiply that total amp draw by how long you think you want to be able to operate at the amperage. Figure two motors @ 50 amps each = 100 amps and you want to be able to run at that load for three hours, that's 300 Ah's (150 Ah per motor) of battery your will need. Since 120 Ah 12V batteries are about as big as they get (and they would not be 120Ah at that draw rate), you would need to run four batteries in a series-parallel configuration on each motor (eight batteries total) to get that much run time. Cut the hours you would like to run at the load to 1.5 hours and you cut the battery capacity required in half.

Also, anytime you are connecting two or more batteries together, they must be the same type, age, Ah capacity etc. If two batteries are connected together and one goes bad, you must replace both if they have been charged more than 15 - 20 times or you will damage both batteries.

You also want to be sure to figure enough capacity you don't run the batteries down below 20% charge or you will greatly shorten the life of the batteries.

That much battery is also going to take some major size battery chargers. A bank of four 105 Ah batteries connected in series-parallel will require a 24 volt 25 amp charger to charge them.

As for electric boat setup, I will let the electric boat people cover that.

[fishbear]

I have a 14 ft. jon boat, and run 3 50 lb. thrust Minn Kota Enduras.  2 in the back, and 1 on the front.  They are 12V motors.

I run each one on a seperate battery, and I can go for 6-8 hrs. on Varner, as long as I am not running back and forth from one end of the lake to the other more than twice.

I also run my fish/depth finder off the battery that is hooked to the front motor.  I have not noticed it running that battery down faster.

I am however, a cautious person, and always leave one battery with enough juice in it to make sure I do not need a tow back to the ramp.  I just do not use one motor as much, as the day wears on.

This set up works for me, for now anyway.

[DEISWERTH]

I also would like to know what everybody else does to hook up there "extras",--depthfinder, radio, lights, aireators, etc.-- do you hook to your trolling motor/deepcycle battery or cranking battery? Do these type of things draw that much? I don't really understand what, when, say an aireator draws 1.75amps, it really means on a 12v battery. Thanks Doug

[senko_77]

chris, what size motor are you looking at?  it would be way more convienent to get a 24v because its way more battery efficient.  fishbears setup is two 55's.  55 is the highest you can go with a 12v.  an 82 is way more battery efficient because it draws less power from both batteries.  also, 1 82 is faster than 3 55's due to the prop size.  

i run all my electronics and livewell off of a small everstart group 24 battery.