dual battery question

[bennylt]

I am planning out my electrical for a restore I'm doing.

15ft starcraft jet star conversion into a fishing boat.

I am not going to have much electrical draw, but i think i want dual batteries anyway.

The batteries will run

a 55lb thrust 12v trolling motor
standard safety lights
interior led strip lighting.
bilge pump
single display fish finder
one or 2 auxiliary ports for charging cell phone or whatever.

The motor right now is a 30HP pull start, no power trim or anything. so I don't have starting needs at the moment, but I will eventually upgrade to a 40-50hp electric start with power tilt/trim etc..

anyway. I plan on doing 2 batteries but what I don't know is; is it better to connect them in series and run everything off of that single 2 battery source, or have essentially 2 seperate electrical systems. One battery for boat power. and one just for trolling motor.

If separate, once I add powered engine components, which system should that run on?

I can see benefits of each having to do with simplicity and a single massive power source by doubling the batteries. But a redundancy and possible backup (by swapping a battery) by having them separate.


FYI. the reason for the big trolling motor on a small boat is that Several of my local lakes are electric motor only, so I will frequently be relying on my trolling motor for ALL propulsion. And on my bigger fishing trip to Canada in September it is ALWAYS very windy and choppy, so I use a trolling motor very heavily and at higher power levels.

Part of my reason is this. We are currently using a 30Lb motor on a similar sized boat and it eats through a charge, we have had to quit early since the single battery on that boat would get so low we were afraid of not being able to start the gas motor. so I definitely want a bigger trolling motor, AND a dual battery.

 

[alldodge]

anyway. I plan on doing 2 batteries but what I don't know is; is it better to connect them in series and run everything off of that single 2 battery source, or have essentially 2 seperate electrical systems. One battery for boat power. and one just for trolling motor.

if this is a 24V trolling motor then the batteries have to be in series, now if it is a 12V then it needs to be in parallel.

And on my bigger fishing trip to Canada in September it is ALWAYS very windy and choppy, so I use a trolling motor very heavily and at higher power levels.

Part of my reason is this. We are currently using a 30Lb motor on a similar sized boat and it eats through a charge, we have had to quit early since the single battery on that boat would get so low we were afraid of not being able to start the gas motor. so I definitely want a bigger trolling motor, AND a dual battery.

I would say get two batteries group 27 or 31 deep cycles now and use them for everything. Anything other then the trolling motor won't make much of a difference. When you get the new outboard, buy another battery for it.

You could also go with a 24V trolling motor for more power and use the same two batteries now. Still going to need a charger

 

[Silvertip]

On a 15 foot fishing boat you simply do not need a 24 volt trolling motor. Two group size 31 batteries are also overkill. a pair of 27's keeps the cost and weight down and should run the motor all day and into the evening easily. And as was pointed out, only if you do end up with a 24 volt motor would the batteries be connected in series. To stay at 12 volts but double the capacity you wire them in parallel. If this was my boat there would one group size 27 or 31 and if you can't fish all day with that battery I would be looking for issues with the motor. Weight and space are issues on smaller boats.

 

[bennylt]

My mistake. yes parallel. it is a 12v trolling motor.

 

[bennylt]

I'm just not sure about a single battery for everything having had issues with that in the past.

So I would like as much capacity as possible if only running one system. It sounds like running the trolling motor on one battery and the boat on another is not what you guys favor.

So 2 batteries in parallel is probably the better choice?

I'm not overly concerned about the weight of 2 vs 1 battery. going to 3 would probably be excessive though.
Both will go in the bow, and I am running a tiller steer, so having extra weight in the front is actually a good thing. for now at least.

If i go to a 50 HP in a couple years I'm not sure i want to do a tiller setup or not. seems heavy and tiring.

Although now that I have thought more about it. for the time and cost to redo the setup for a bigger motor (since the max on this boat is still only 50HP), I might as well just get a different boat at that time instead.

 

[gm280]

I have to say that unless you plan on trolling pretty fast on some really windy days, I can't see any need for a 24 volt trolling motor on your setup. I had a bass boat and could troll all day long and not even drain my 12 volt capability even a little, and it certainly was not a 55lb trolling motor either... JMHO!

 

[Silvertip]

You have no large electrical draw except for the troller. Your engine is a pull start. I Don't understand the need for two big batteries. If you eventuLly go electric start then a group 24 for the engine is a simple addition. But it is your boat and your money. Whatever lights your fire.

 

[Grandad]

Think about what's most important to you. Since you plan on changing to a larger electric start motor and are worried about getting it started for the trip home, I would use 2 batteries, independently able to operate your entire electrical system on each battery via a selector switch. When you've trolled until one battery gets low, you can switch to the other battery for a sure electric start or use the extended capacity of the second battery to cautiously troll some more. Assuming the batteries are identical, you'll know what to expect from each when held in reserve, especially if you rotate their use so that their capacity characteristics remain consistent. As they age, one will likely begin to fail shortly before the other, so replace both at the same time. - Grandad

 

[bennylt]

I really appreciate all of the thoughts and opinions. Even if they don't fit my situation now, it is still knowledge to keep in my head perhaps for a different time, or to help someone else.

The waters have been muddied here so please let me rephrase my question without boat length etc.

Here is my situation

I need to run a 12V 55LB trolling motor at relatively high power for very extended periods of time. 8-12 hours of heavy use.

I frequently fish in very windy conditions and on electric power only lakes so the trolling motor is not only used to position the boat, but to run all over the lake as the main propeller. So yes I do need to run fast in very windy conditions.

This is the exact motor. http://www.minnkotamotors.com/Trolli...unt/Endura-C2/

Other battery drains are minimal consisting of Lights and fish finder, cell phone charger etc.

I have had trouble in the past with a single battery (even a new one) lasting long enough.

I improved things by increasing the trolling motor from a 30Lb to 55Lb which has proven to be more efficient.

I am transferring this experience to a new boat with a clean slate electrically.

I want to go to 2 batteries this time. My investment is not significant.

Under which setup will I have have the most remaining power at the end of the day?

1. 2 identical batteries run in parallel on a single electrical system.

2. 2 batteries run individually on a single system with the ability to change between them

3. 2 batteries on separate systems. 1 of which is dedicated to the trolling motor only. these may be different series batteries.


Okay. now shoot.

 

[UncleWillie]

2 identical batteries run in parallel on a single electrical system.

This will give you longest operating time time without throwing switches.

2 batteries run individually on a single system with the ability to change between them

You will need to switch batteries half way through, but the total time will be the same as in parallel.

2 batteries on separate systems. 1 of which is dedicated to the trolling motor only. these may be different series batteries.

You are only using 1 battery so the time will be half of what you would get with 2 batteries. There is no free Lunch!

Assuming that the motors draw an average of 35 amps, and you have 100AH batteries that you are willing to repeatedly deplete by 70% of their capacity...
Each battery will operate for ~2 hours. You will need 6 batteries dedicated to the trolling motor to operate for 12 hours.
Plus a 7th battery dedicated to start the gas engine, so you can get back home predictably.

Your hourage will vary depending on the actual Battery Bank Capacity and the Current Draw.
But, 2 batteries operating a 55# motor, aggressively for 12 hours, is not a reasonable expectation.
A 2hp Gas Engine may be more practical for your intended use.

 

[bennylt]

Interesting. Well a gas motor is out of the question since I'm running around a lot of No Gas lakes. where electric is the only motor allowed. the biggest lake is 239 acres and no gas, and that is a lot of ground to cover to get to different spots just on a trolling motor.

I'm not sure about the math coming up with 7 batteries, I can run about 8 hours on the single battery. that is up from about 6 hours with the 30Lb motor. So I think adding a second battery will easily get me to my 12 hour mark.

It looks like no advantage to one over the other for switch vs. parallel, so I'll probably do the switch since to me I feel I'll have more control over the situation. when the first indicator goes down, that is my signal that I am more than half way done with my day. Flip the switch, Fish a few more hours and head in. It will still be a LOT longer than when the indicator gets low in the single battery, then heading in then feeling short changed.

 

[Silvertip]

You should not be surprised that trollers will typically power a boat to 3.5 MPH max. Your 55# motor will draw well in excess of 40 amps at the fastest settings so the bit about maximize efficiency is out the door as there is no saving at high throttle setting. For your use, you seem to be limiting yourself to very high AHr batteries in the group size 31 range. What are you fishing for that you need to troll so fast?

 

[UncleWillie]

....I'm not sure about the math coming up with 7 batteries, I can run about 8 hours on the single battery. That is up from about 6 hours with the 30Lb motor. So I think adding a second battery will easily get me to my 12 hour mark....

You originally stated ...

... I use a trolling motor Very Heavily and at Higher Power Levels...

If you are getting 8 hours out of a 100AH battery and are Not running it dead flat; That would indicate you are drawing ~10 amps average.
That is Not running a 30#, and especially not a 55# motor, at anything you would commonly describe as, "Very Heavily and at Higher Power levels"
10 amps is well less than half power. Heavy use would give you less than 2 hours with the 55# motor. Hence, the 6 battery Quote.
1 batteries lasting 8 hours, indicates your use may better be described as, "Continuous, but at Low Power Levels."

 

[bennylt]

My battery is a Deka 810 Amp marine battery. this. http://www.lowes.com/pd_599945-50656-DC31DT_0__?productId=50183761

Is that a 100AH?

It lasted 6 hours with the 30# motor. it now lasts about 8hrs with the 50# motor.

I am adding a second battery because I want the total sum to be above 12 hours.

Whatever the math is or whatever your definition of "heavy use" is... it is just semantics, that is my situation.

If the other stuff really matters to you, here is my reason. Maybe it isn't appropriate for your situation, but it is for mine.

I am NOT "trolling" at all technically. I fish primarily on electric only lakes. No gas motors allowed. It is a very common PA thing. My region is also very windy.

So try to think about every time you fire up your gas motor to run to a different part of the lake. I am instead running my trolling motor full out at those times, then using it as usual to fish. Repeating all day, in the wind.

Discuss...

 

[UncleWillie]

A little web searching shows your battery has a 225 min Reserve Capacity @ 23 Amps. That works out to 86AH.

The 810Amp spec is the (MCA) Marine Cranking Amp spec. 810 Amps for 30 Seconds at 32F.



I realize that "Heavy Use" is a matter of opinion, but that was all the info we had to go by.

If you are getting 8 hours from your current battery, then 2 of them will give you twice the run.

And parallel, or one at a time, will be equivalent.

 

[poconojoe]

To play it safe, I would use the batteries separately and switch between them. This way when one has run down, you know you still have a full one left. If they are tied together in parallel, you might risk running them both down and you would be stuck. This is what I do when using my Jon boat. (I'm Also in PA)

 

[bennylt]

A little web searching shows your battery has a 225 min Reserve Capacity @ 23 Amps. That works out to 86AH.

The 810Amp spec is the (MCA) Marine Cranking Amp spec. 810 Amps for 30 Seconds at 32F.



I realize that "Heavy Use" is a matter of opinion, but that was all the info we had to go by.

If you are getting 8 hours from your current battery, then 2 of them will give you twice the run.

And parallel, or one at a time, will be equivalent.

Awesome. Thanks for the input! I appreciate it. Now i know more about batteries! I'm going to be getting new wire and whatnot in the next week or so to do the wiring.