Battery Box for Trolling Motor

It’s winter and outdoor projects are limited. As soon as it turned the new year I made a reservation to camp for the Fourth of July. Camping is very popular in Colorado and it is difficult to get into a summer campsite. I know the Fourth of July is very crowded but it is also a good time for family being together especially at a lake.

Last summer I purchased an inexpensive Intex raft for our camping fun at the lake. We went out in it a couple of times but found rowing it to be more exercise than I could handle. This was mostly due to the chop in the lake which is unavoidable with summer motor boat traffic.

Chop from Motor Boats
Chop from Motor Boats

I looked at trolling motors but many were sold out for the year or the cost was high. I vowed to return to the project in winter when demand would be lower. Right after the new year I read reviews and recommendations for trolling motors. Then I calculated the thrust that was needed for our little boat. We could have used a 30 lb thrust motor but I opted for the larger 46 lb thrust from Newport Vessels. The extra thrust uses more battery power but will also move faster through rougher water.

Newport Vessels Trolling Motor
Newport Vessels Trolling Motor

But the electric trolling motor requires a battery system to run. The 46 lb motor uses 40 amps or 480 watts at full power. It can run for approximately an hour using a 40 amp hour rated battery since it is not used at full speed the entire time. Even though lithium batteries are not recommended for trolling motors because they maintain higher voltage through the use period I knew that the entire boat with floor, motor and batteries would begin to get really heavy to carry from the camp site to the lake. The difference in weight between the lithium batteries and lead acid is extreme. A 55 amp hour lead acid battery weighs about 45 lbs and a 20 amp LiFePo4 battery weighs 5.4 lbs. Although lithium batteries are usually much more expensive than a marine battery, I was able to buy three 20 amp hour LiFePo4 batteries for around $200.

LiFePo4 20 amp batteries
LiFePo4 20 amp batteries

I knew about wiring batteries in parallel from using 12 volt battery banks in the RV. So I purchased a couple of cables and terminal ends. The screws that came with the batteries were too short for two cable ends together so I bought some stainless machine screws at the hardware store. I also bought lock washers for all the screws.

Box for Assembly
Box for Assembly

Next I selected a box for the battery system. The first box I ordered was not as large as the published measurements and the batteries didn’t fit. Then I bought an inexpensive tool box from harbor freight, but it didn’t appear to be sturdy enough. Finally I found this deeper box that was also wide enough for the batteries.

Batteries in Box
Batteries in Box

After these basic purchases the costs began to add up. The lithium batteries require a special charger, then I wanted to be able to charge the rechargeable air pump on board if needed so why not add a 12 volt charging port? We might need USB ports. What self-respecting Intex inflatable boat would be without them? And finally the meter that comes on the motor does not accurately read the remaining power in the batteries so I needed a special meter too. Ten terminal lugs were not enough for all the cables I had to make. I upgraded the 50 amp fuse to a switch type, added a cut off switch, then decided to change the inappropriate battery meter on the socket panel to install an Anderson Powerpole socket. Lots of supplies were needed that I didn’t have on hand like extra power pole plugs, and a crimper. Then I found the cut off switch needed 3/8″ lugs so ordered those and decided to run the neutrals to a separate junction block and I bought screw on covered battery terminals.

Sample battery box
Sample battery box

I looked at several sample battery box builds. I found that most information about these boxes was on YouTube videos. I am not fond of videos because they often have a very slow presentation of the information. I scrub through them and find the part I’m interested in takes longer to find than the amount of information I get. I prefer text and photo examples. Much quicker access to the information I want. I did watch a couple of videos and the one modification I would have liked to have made was to install a trolling motor plug instead of the terminal posts.

The socket panel came with separate wires for each function and each red had a nice 10 amp fuse and holder. But the example wiring was to wire all the plugs to the switch, which made more sense. I tried to use the terminal ends that came with the hot wiring but I could not get good connections so I had to use some terminal ends that came with another device. I just used the three separate wires for the neutrals.

Socket panel wiring
Socket panel wiring

I had to build a wire for the Anderson Powerpole plugs however and that required learning how to crimp wires for the sockets. I had several mistakes using the crimper and the advertised “click” seemed to be elusive but finally I got the hang of it and was able to wire the two sockets. I also had to purchase more 1/4″ terminal ends for this light weight wire.

Under the hood—Shut off and terminals
Under the hood—Shut off and terminals
Lid wiring with negatives installed
Lid wiring with negatives installed

I tried placing the batteries in a separate tray but that raised them just enough that the inset tray would not fit so instead I surrounded the batteries with the dense foam that came in the smaller box. I had decided to keep the smaller box for a power tool.

The lid has all the wiring connections for use. The two large wires attach to the 50 amp breaker on the positive side and the shut off switch on the negative.

Lid with circuit breaker and shutoff switch
Lid with circuit breaker and shutoff switch

I had to wait for the larger lug nuts and that is when I decided to add a negative terminal block for all the negatives I was connecting. Plus I ordered more large size heat shrink. So the updated wiring includes a negative terminal and a bit of wire management.

Lid and tray with cable management
Lid and tray with cable management

I had to move the wires out of the way so the handle indent fit over the tray handle for a tighter fit. Notice the zip ties that keep the heavily wired lid attached to the box.

I guessed the final weight was about 30 lbs but I was over. It is only 24.2 lbs. That is pretty good for all it contains and I will be able to haul it with the boat and motor.

Total Weight: 22.4 lbs
Total Weight: 24.2 lbs

And it can charge through the Anderson power pole connectors and runs the trolling motor!

Charging through the power pole connection
Charging through the power pole connection
Motor running with battery box
Motor running with battery box

Ready for summer!

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