Monthly Archives: June 2013

Lithium Iron Phosphate Batteries

Using Lithium Iron Phosphate Batteries to Repower

Lithium Iron Phosphate batteriesAnyone interested in replacing their marine batteries should read the story of catamaran owners who recently repowered their boat. They replaced their AGM deep cycle batteries with marinized lithium iron phosphate batteries – for a lot of good reasons. Lithium iron phosphate batteries outperform lead-acid across the board:

  • Charging efficiency – Lithium accept charge much more quickly – without having to slowly charge  the last 15 – 20% typical of lead acid. Kill your generator sooner!
  • Discharge efficiency – Unlike lead acid (AGM, gel, or wet cell), lithium batteries can be discharged quickly without heating excessively and losing much of their rated amp-hour capacity.
  • Depth of Discharge – Lithium batteries can be routinely discharged to 70%, versus 50% for lead acid batteries.
  • Internal resistance – Lithium batteries are highly efficient, returning nearly the same number of amp-hours as were required to charge the battery.
  • Storage – Similar to AGM, lithium iron phosphate batteries have very low self-discharge rate, allowing long-term battery storage without concern for the batteries going flat.
  • Stable output – Lithium batteries maintain their full nominal voltage, even when being heavily discharged – until they're 70% discharged.
  • Expected life – Lead acid last approximately 1,500 cycles if they're not discharged beyond 50% too often, while lithium claims 5,000 cycles at 70% discharge.
  • Cost – Lifeline AGM were priced at $3,600 with 252 usable amp-hours, versus Winston lithium batteries, which cost $2,365 and provide 280 usable amp-hours.
  • Weight – The lithium deep cycle battery bank weighs 157 pounds (71 kg), while the AGMs they replaced totaled 423 pounds (192 kg).
  • Environmental – Lithium batteries are far less toxic than lead acid batteries.
  • Safety – Lithium batteries don't generate flammable gasses while charging. Perhaps of interest – you can watch a LiFePO4 battery being cut and crushed while still powering a light.

The downside is that you need to have an effective battery management system which both limits the voltage while charging and shuts off loads if the voltage while discharging drops too low. Violating either of these rules can substantially reduce battery life.

Battery management system for lithium iron phosphate batteriesIf you're interested in reading a bit more about lithium iron phosphate batteries, there's a thread at cruiserforum you can peruse – or you can fire up your favorite search engine.

I'm still just thinking about installing lithium iron phosphate batteries, but they look good from here!

Outboard Weed Guard

Outboard Weed Guards


In my area (western Lake Erie), June brings weeds – lots of weeds. I've hunted all over for an outboard weed guard to keep weeds from balling around the propeller. It's no surprise that outboards don't have much thrust or steerage when the prop is weed covered. In addition, weeds clinging to your propeller could damage the seal or block cooling water intakes – either of which can ruin your whole day.

The best solution has been to put the outboard in reverse for a few feet to let everything unwind and disperse. That solution hardly qualifies as an outboard weed guard though. If you're at the tiller and the gearshift isn't easily reached, constantly putting the motor in reverse is a nuisance and a distraction. It can be a disaster if weeds strike as you approaching an obstacle. This year I'm going to fight back. I didn't find a suitable outboard weed guard, but I did find a weed cutter that may work well.

Moss HawgThe weed cutter is a fairly tough plastic, intended for fishing boats commonly used in heavily vegetated waterways. The cutter is called “Moss Hawg“, and it's designed to fasten easily to electric trolling motors motors commonly used while fishing. As it turns out, the Moss Hawg can be modified to fit many small outboard motors by cutting the plastic support ring and gluing it to the bottom end of your outboard. The ring feels like HDPE, a plastic which doesn't glue well. Fortunately, West System markets G/Flex, a glue which is both resilient and tough – and engineered to stick well to plastics, as well as metals, glass, wood, fiberglass, etc. According to the developer, it will even stick if applied underwater! The picture to the right shows it glued to Thumbnail - Moss Hawg outboard weed guardthe bottom end of my Bigfoot (click to enlarge). The support ring for the Moss Hawg is round, and the casing at the bottom of the Bigfoot isn't – so the G/Flex between the two is fairly thick in places. Regardless, the G/Flex has a firm hold of both the Bigfoot and the Moss Hawg, and the serrated blades sweep the hub right up to the roots of the blades.

I saw my first group of weeds yesterday, and will report back in a month or two – as soon as I have a solid feel for how well the combination works. It's not an outboard weed guard, but if it cuts weeds as advertised, I'll be a happy camper!