Lithium battery for trolling motor on dinghy

[tomfl]

From a thread about using an electric trolling motor on a dinghy this was posted

"My 40ah 12volt lithium battery weight 13lbs."

I have used an electric trolling motor on a small pontoon boat I use in spring fed freshwater rivers when taking pictures of wildlife. But always used flooded batteries and charged them up at my house overnight for use the next day.

While I considered using the lighter electric trolling motor on my dinghy adding a 60-70 pound flooded battery means in total more weight than a small gas outboard.

But if I could get a battery that weighed 13 pounds it would be a whole new ball game. I am talking about maybe going half a mile, or less, from my boat on a ball to the dock and back.

Can some of you smart EE guys set me straight. Am I wasting my time or is this a realistic idea.

[nimblemotors]

EV Source - CALB LiFePO4 cells

Get 4 of the 40ah cells and connect them in series for 12v.

I'd suggest you get 8 of them, and make two 12v batteries.
You use one to get where you are going, and use the second to return,
so you are never out of battery to get back.

[sstuller]

I lived aboard for five months on a mooring using a 30# thrust MinnKota for my dink. The battery was a 35 AH AGM motorcycle battery (wt. - 23#) that was recharged from a Harbor Freight 15 watt solar panel. I never needed shore power for recharging. This was the most reliable outboard setup I've ever dealt with. Thanks.

[tomfl]

OK I am still a little confused.

I t seems like I need to buy four of the EV batteries Jack linked to and connect them somehow which means something like 12-13 pounds or more. Not so sure how easy it is to charge them.

I found this battery on Amazon that seems similar in price and capacity but appears to me to not need to be put together. It also has what appears to be a charger from the same company.

linkAmazon.com: Battery Tender BTL35A480C Lithium Iron Phosphate Battery: Automotive

Turns out this battery is advertised as 35AH but some folks are claiming it is closer to 10AH the way flooded AHs are measured. I was able to find another battery company "Smart Battery" that is suppose to be better.

It seems both of these companies (probably along with any others I don't know about) sell charges that are specific to lithium batteries. All this will add to the cost and complexity of setting up this system.

On the other hand the AGM is more or less double the weight 13 v 23 but is much simpler and cheaper. For a ten pound increase in weight and easier charging I am leaning in this direction.

But I am still not comfortable with my knowledge of batteries. Anyone else want to weigh in please.

[nimblemotors]

It is very complicated to connect 4 batteries in series, the plus and minus thing is confusing. If they just used colors, like red and black, it would make it easy.

Trojan Battery Company

Charging LiFeCo 12v battery on the other hand is very simple, just apply a fixed 14 volts to the battery to charge it.

[a64pilot]

Tom,
The battery you linked to is I believe a motorcycle battery, and probably not nearly enough AH for what you want.
Lithium Iron Phosphate is a completely different animal than a LI-Po, I put in a Lithium Iron battery in my motorcycle a couple of years and and it has lived just fine without special chargers or cell balancing, a Li-Po wouldn't have.
I still think you will be happier with an infernal combustion motor, but that's just me.

[roverhi]

Lets see, the black wire is ground and the red is hot. That makes sense. But then there is this bunch with a black and white wire. Oh! that's AC power and black is the hot wire and white ground. Totally doesn't make sense. Yes wiring can be confusing and screwing it up can cost you a new prop or worse in a just a couple of hours.

Still, connecting cells isn't that big a deal unless it requires soldering which does require tools and some technique.

Originally Posted by nimblemotors

It is very complicated to connect 4 batteries in series, the plus and minus thing is confusing. If they just used colors, like red and black, it would make it easy.

Trojan Battery Company

Charging LiFeCo 12v battery on the other hand is very simple, just apply a fixed 14 volts to the battery to charge it.

[tomfl]

Originally Posted by a64pilot

Tom,
The battery you linked to is I believe a motorcycle battery, and probably not nearly enough AH for what you want.
Lithium Iron Phosphate is a completely different animal than a LI-Po, I put in a Lithium Iron battery in my motorcycle a couple of years and and it has lived just fine without special chargers or cell balancing, a Li-Po wouldn't have.
I still think you will be happier with an infernal combustion motor, but that's just me.

Thanks for the informative post.

I am on a ball in a marina in the Keys and often am only going a couple of hundred yards to the dock. Frequently I choke the motor, start it, and then am faced with the question of do I unchoke the motor before or after I tie off on the dock. This seemed like an idea place for a trolling motor. I still have one I use when taking pix of wildlife from my small pontoon boat because it is quiet.

I also put the dinghy on davits every night to keep the bottom clean so a reduction in weight would be another advantage.

But your point is well taken about what I now have working.

[nimblemotors]

Or a spot welder. This is one of the nicer things with the CALB cells I linked to, they just have bolts to connect them, and they sell straps and bolts designed specifically to attach them in series.
However, I did omit you must balance the cells before you connect them together, which means draining the cells individually until they reach 2.5v.
Then you can connect them in series for the 12v battery.

Originally Posted by roverhi

Lets see, the black wire is ground and the red is hot. That makes sense. But then there is this bunch with a black and white wire. Oh! that's AC power and black is the hot wire and white ground. Totally doesn't make sense. Yes wiring can be confusing and screwing it up can cost you a new prop or worse in a just a couple of hours.

Still, connecting cells isn't that big a deal unless it requires soldering which does require tools and some technique.

[ctsbillc]

Price for those batteries is pretty good.

If you go for it, make sure you get the battery management system as well. Unlike lead acid, these cells can be damaged very easily by overcharging - they don't equalize like lead acid cells do.

[nimblemotors]

Here is one of my 12v using the 40ah cells, compare its size to a T105 case next to it.
Tom, I can tack on a few bucks and sell it to you with a basic slow charger too if that helps. PM for details.
One really just needs a minimal constant voltage power supply to charge.

[thurman]

Yeah I know, it's an old thread. But if anyone else is still reading it...

And then there's the Torqeedo... Mine is a 503, and it seems to be good for about 2 miles on my 10' RIB at 3/4 throttle, which is about 3.5 knots. Has a GPS to let you know how far you've gone, and if you can get back with the charge remaining. The battery weighs 8.8 pounds, and the whole battery/motor combination weighs 28.4. Gas weighs nothing, since I don't use any. It has a 12 VDC input port on the battery, you can either use their charger, or just tap into the house 12 volts. If you don't own a trolling motor yet, check it out.