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PostPosted: Wed Mar 27, 2013 7:43 am 
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Location: Rolla, Missouri
Hey Gang,

What size SLA batteries are you guys using for your trolling motors that you feel you are getting the best results with? Amp hours? 40-50 or other? I'll go with a lithium when I can afford it. For now I'm going to purchase a SLA just to get my setup going. Thanks for any feedback!

Carl


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PostPosted: Wed Mar 27, 2013 8:49 am 
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I have the Everstart Marine 24DC-6 75 AMPS Hours battery I purchased from Walmart. The battery lasts for a long time. In fact, I have never been below 50% when using it all day.


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PostPosted: Wed Mar 27, 2013 10:12 am 
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For lead acid your best bet is Adsorbed Glass Mat (starved electrolyte). The rating is at the C/20 current draw so a 40 amp hour battery is rated for 20 hours at 2 amp draw. The Peukert equation will determine how that decreases with additional current draw. So the poster above has 20 hours at 3.75 amps draw.

And for lead acid not going below 50% of capacity will give you a decent number of recharge cycles. From 300 to 500 if you use a very good charger. Deep discharges, even in a "deep cycle" battery will decrease the number of charges available.

So to size your battery, determine as best you can what your current draw might be using the motor as you intend. See if you can get a battery rated such that you are not exceeding the C/20 rating by much. The more draw the less total capacity. Lets say you decide to get that Wal Mart special and your motor draws 10 amps, most likely your real capacity will be more like 60 amp hours Still not bad as you would get six hours at that high draw if you don't care much about cycle life. If you want to keep the battery able to take more charge discharge cycles then the 10 amp draw would best be used for about three hours.

That is another advantage of the Lithium Ion battery. A better Peukert coefficient. Lead acid is about the worst for commercially available rechargable batteries. And the Lithium Ion can be discharged almost 100% and not lose cycle life which starts out higher than lead acid at about 1000 cycles.

Perhaps if you run some numbers you will discover as I did that Lithium Ion may have a higher initial cost but over the lives of the battery you will be much better off with Lithium than Lead Acid. And then there is the weight difference of four to one.

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PostPosted: Wed Mar 27, 2013 11:55 am 
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Location: Rolla, Missouri
AllElectric PA14,

I've seen pics of your setup before. What size LI battery did you get? I have a Minn Kota 30lb thrust. What would you recommend? You seem well educated on the subject. For arguements sake, let's say I plan on running low to mid power most of the time.

Thanks!

Carl


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PostPosted: Wed Mar 27, 2013 4:38 pm 
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Carl,

Having designed and built electric vehicles of all sorts, I have a pretty good working knowledge.

I just found a test run by a fellow on a five setting 52 pound thrust Minnkota transom mount trolling motor. He got 7 8.5 15 16.5 and 30 amps respectively for settings 1 through 5. So if we just ratio the 52 pound motor to the 30 pounds you have the five settings would draw 4 5 8.5 9.5 and 17 amps. At setting 3, most likely a good setting for you a battery with 75 amp hours like the one mentioned above would work very well over a long time period. You could easily use it for ten hours on the water at setting 3 all the time and be just over one half down on capacity. On full speed the battery would be depleted a bit over two hours and of course it would have shortened the cycle life. So to keep up the cycles you would use it for only a bit over an hour at full speed.

The Lithium Ion I got for my boat is 40 amp hours but is rated at 40 amps draw. I think you can see how Lithium has an advantage right away. So that sort of battery would last you over 4 hours at 3 speed or an hour and a half at full speed. So with greater cycle life you can actually run longer with a much lower rating battery in Lithium.

So at lower draw the big heavy lead acid battery would be the choice. At higher draw the Lithium takes over as leader with much less weight.

When we were in the Keys I ran the Yak in the channels between the key where we were camped and the adjacent keys. The current was 2.7 knots and the wind always seemed to be blowing against the direction I wanted to travel. The little 24 pound thrust motor moved the boat against all that, at a knot or so and I made headway. The battery ran that way for three hours straight and only dropped a few tenths of a volt. I have no idea how long it would run hard and the battery be depleted. I draw about 11 amps on high speed and only about 5 amps on low speed.

If you want to keep your purchase price low go with the lead acid if you can stand the weight (I carry two up so weight of the battery is more of an issue for me). That way you will get a good feel for electric power and not be out a lot of cash. And of course an on board battery for the motor runs the other electronics as well as charging your VHF radio or Cell phone. I use the Humminbird to read my voltage so I know how the battery is doing.

If you wanted to run Lithium Ion, I think the 40 amp hour would be the lowest capacity you should consider with a 60 amp hour being a real beast.

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PostPosted: Thu Mar 28, 2013 6:31 am 
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Location: Rolla, Missouri
AllElectricPA14,

Thank you so much for the info! This is a big help!

Carl


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