LiFe Batteries

I’ve installed half the LiFe battery pack and controller (prototype).

LiFe batteries require some special control electronics to Charge and ‘Balance’, so this was quite involved (see picture). However they seem to work well.

My Battery Management System consists of all this, as well as a USB link to the computer so I can monitor the charge progress of all 5 Cells.

To test, I drove the boat for 30 minutes at mostly top speed, with two people (dad and I) on-board.

The battery pack is 17V, 100AmpHour, so I expected it to be half empty…

There was no noticeable change in Battery voltage (16.7), it doesn’t seem discharged at all..

This is a change from Lead Acid batteries, which noticeably change their voltage as they go flat (eg 13.6 Volts to 11 volts). The LiFe battery doesn’t let on that it is going flat at all..with only a small change from Full to Empty.

All in all, the LiFe battery had no trouble driving the boat around at 60 Amps peak, and didn’t go anywhere near flat.. from the Cell voltages, I would say I used < 30%. 


So, a summary of the test:

Battery voltage is good: 17 volts gets the boat to max displacement speed;  prop + motor + 17V is about right.

LiFe batteries are awesome,  last 3 or 4 times longer (will take 6 years for me to confirm this) than Lead Acid, voltage changes very little,

less than half the weight..Image

The Life battery 5 cells = 17 Volts




The Battery management system,

Charger, cell balancer, over discharge protection, over current protection, with USB connection for monitoring with a PC







Water Test, and improved bearing.


Water Tested at 12 V.

It was good to finally put the boat in the water.

The controller electronics were covered with a plastic container…and barely holding together with wires all over the place.

But the point was to test the shaft, motor and prop.

Happily, the shaft did not leak, and the boat ran fine at 12V.

I motored out to a mangrove island and back, a return trip of 400 Metres, with my cousin on board also.

After that, I decided to run it at 24V, For a brief moment I felt un-imaginable thrust, and then the controller blew up.

Over the next few days..

While Fixing the electronics and testing I discovered the bearing (Trailer roller bearing) had failed, it was squeeking and grinding like a piece of rubbish  It was never suitable for this application (high RPM).


I have replaced the bearing with a Deep groove sealed ball bearing (spec in the picture)

It just so happens that it fits nicely in a rubber hose coupling (65mm). So now the bearing assembly looks like this (see picture).



It runs ALOT smoother. The rubber hose coupling helps to absorb any vibration. And I believe it will improve the reliability of the bearing and all other parts (motor and shaft).


The whole thing fits together quite nicely.. There are 50mm pipe couplings pushed in to hold the bearing. These are clamped in place with the hose clamps. The shaft is held within the bearing by collar and screws into the shaft.

Ready for more water time.

A friend wants to go fishing, he has faith that the boat will safely take him fishing at night, and get him home as well.

Probably because he hasn’t seen the controller prototype.. a tangled mess of wires, and electrical tape…







Sanding. Waiting. Sanding. Waiting

Epoxying the shaft in the boat.

Cut a hole so that half the shaft is above the floor, and half below.

Looks about right.

Now to epoxy it in place. Each layer of epoxy is a messy time consuming process, and before each new layer, the previous layer has to sanded.. after it has cured for 5 hours (1 day).

In my opinion, this is the worst part of the process, always. Polyester resin would be quicker. But I am using epoxy. Slower, but stronger.

Note: two- part epoxy has to be measured and mixed exactly, or it will either get hot and go hard very quickly, or stay soft and gummy and not set.

Note: Using a few drops of white pigment to give the epoxy the white colour.

Note: All parts of the boat hull that are connected to epoxy are sanded right back to the glass with 40 grit and then 80 grit sand paper.

I am finding the following tools most useful: Coarse flat Rasp, a round Rasp, Small Electric Sander.

When I am sanding, I wear disposable overalls, gloves. I hate epoxy dust…. here are some pics: …now I’m going to ‘Bunnings’ to buy more cheap(ish) paint brushes because the Cheap Shop (dollar store) is closed.


The bottom of the boat has a nice channel that fits the 50mm shaft-pipe nicely.


Epoxy and Chop-Strand glass slapped on. When it is hard, the Coarse Rasp will make short-work of the excess Mat and epoxy.

19mm Ply inserted between shaft and hull, 19mm ply prop-guard Fin. 1 layer of Chop-strand Glass. Sanded, Filled out with epoxy, Sanded, epoxy…

Pushing water

The whole assembly running at 24V, With the aluminium (expensive) prop installed…

Top speed is decent, a bit of vibration, mainly due to the motor not being perfectly aligned.

But I am going to go ahead and install this in the boat..

The Electronics need refinement, but the mechanical (Shaft, bearing, prop, motor) are go for take off.


Jaw coupling arrived, fits !

The Jaw coupling arrived. It is beautiful.

I sourced it from an Auto-parts store, Each half can ordered to fit the shaft size one requires.

The rubber insert absorbs misalignment and shock, this can be replaced and bought separately if it wears out.

The whole coupling cost only $79  !.

So I can test the whole assembly…Here is a clip of it rotating.


There is a bit of vibration, Once the prop is in a water tank I will test it at Max RPM and get some data, if it doesn’t fly to pieces.

Max RPM ~2000, will be the true test of the coupling, bearing and shaft. There is a good chance something will break catastrophically… we will see.. today hopefully.

Cutlass Bearing , mounted in low cost pipe fittings

The cutlass bearing arrived, and it fits nicely inside standard PVC pipe fittings from Bunnings (hardware store). I will see how this works, and then epoxy it in place later to make it permanent. Note on construction: The pipe fittings are glued with PVC glue (they had to be tapped into place with a hammer; very tight fit), the cutlass bearing will be epoxied in place, after first roughing-up the inner PVC pipe wall with a rasp and coarse sand paper, so the epoxy adheres well.  This makes a complete unit that can be removed and replaced simply by unscrewing the 50mm pipe fitting from the end of the 50mm shaft tube (‘shaft log’). Too easy !