And for the rest of us, who cruise weekends and a few weeks now and then, we don't rack up that many cycles, perhaps 100 in 5 years and 200 in 10 years. Northern holiday cruisers are even more challenged to rack up high cycles, with the boat out of the water half the year.
Even using shallow cycle designs, which we are not, we'd be hard pressed to hit the cycle limit within 10 years if we took them to 60 %, and we would just hit it in 5 years at 80% discharge. With standard deep cycle batteries, we could discharge to 80% far more times than we will ever spend the night on the hook. The batteries will die of corrosion, failure to recharge, or failure to water first.
This has been my experience. I use relatively small battery banks and discharge past 50% regularly. I do recharge as soon as possible and I do check the water. I typically have gotten 7 years, whether cruising frequently or not, before I loose enough capacity I replace them (never complete failure, such as a shorted cell).
Why what some would consider an undersized bank? Because on a multihull, weight is worth money. My boat cost $20/pound and I feel every pound saved is worth $20 in performance. Otherwise, I would have purchased a slower boat. Carrying an extra battery (75 pounds) costs $1500 in weight penalty.First, I don't believe adding a battery would extend the battery life in proportion to the added purchase cost; they would last perhaps 15% longer and cost 25-50% more to replace. The $1500 weight penalty stands. The only upside is additional reserve capacity, which isn't worth $1500 to me.
(That's 25 degrees C, not 250C like it says)
I've had enough different boats to understand that for each boat, my answers to these questions would have been
different.
- How big is the bank? A single group 24 battery is minutes to change, but a big bank of traction batteries is a project.
- How critical is power failure? An outboard can be pull-started, a big diesel is a problem.
- What charging sources are available? How many days between full charging?
- How often is the boat anchored-out? Are we talking thousands of cycles or hundreds during the life of the battery?
I need to look into this farther.
If you're looking at a small lithium solution, check out the Valence U1-12RT model from LithiumWerks. It's got 40Ah capacity and will charge at C/2 from empty in 2.5 hours (20A * 2hrs + 30min cell balance). It's got an integrated BMS, absorbs at 14.6V, and floats at 13.8V. Valence is not a fly-by-night far eastern piece of junk, this unit is UL and CE marked and used in the DaVinci surgical robots. I'm integrating the 24V versions in another piece of commercial medical equipment and have been abusing 15 different systems in the lab for three years without any hiccups. As an aside, conventional wisdom is that lithium systems don't like to sit at 100% SOC but I hold mine in float 24/7/365 with the manufacturer's blessing.
ReplyDeleteDrew, I have thought of going to a small battery too. My loads primarily the autopilot and depth sounder. Currently I have a starter on my OB, but I could easily just pull start. I recon I could save ~60lbs. That’s a lot of beer.
DeleteBen
Entourage
F-27F