July 18, 2002
Batteries

This week SetSail asked our cruising contributors about the batteries. What type do you use (manufacturer and design)? How many amp hours? How often do you charge and at what voltage? What kind of voltage regulator do you use? How old are the batteries? How many cycles do you expect before they die? To what level do you normally allow them to drop before charging?

Fortunately, Steve Dashew did all the battery research for our boat, a Sundeer 64, before we bought it, so all we have done is to build on the excellent base we found ourselves with.

We were provided with 1800 amp hours of wet cell batteries, arranged in 2 banks of 6x1.5v single cell units manufactured by Tudor. Each 1.5v unit is about 6"x6"x24" and very heavy, so they are mounted in the keel space and are part of the ballast for the boat.

As it is a good idea to cycle batteries between about 90% and 40% of charge--that way they get "exercised" and should give the longest life--we need to be able to replace about 900 amp hours during each cycle. This is where we decided to depart from Steve's original thinking, which was to use the main engine on which are mounted two Brute 210 alternators, driven by belts off the front pulley (we are British, so if you are American then pulley = sheave). The maximum output of a Brute 210 is 210 amps under ideal conditions. These never occur; instead we get about 160 amps initially, dropping to 130-140 under normal charge conditions. Due to the crankshaft loads they are geared very low.

To get any acceptable charge rate, the engine needs to be running at over 2200rpm, and as the load is something like 15bhp on an engine capable of generating 140bhp (about 110bhp at 2200rpm), we didn't like to run the main engine at light loads for such extended periods.

So we installed (Steve said "Think of the weight....") a DC generator, based on a gearbox-less Yanmar 18bhp diesel, with a shaft mounted on the flywheel, from which we run another two Brute 210s from twin belt pulleys.

With this setup we can run the Brutes at more optimum speed, which produces a charge rate of about 280-300 amps. This means we run the generator for 3 hours every three days--we use about 250-300 amps per day. We have used this now for 8 years and although we have beefed up the original generator design wherever it broke, which of course like anything else it has a number of times, we are very happy with it.

If a Brute fails, we can swap the units off the main engine until we can get it repaired, something we have done several times. If the generator is broken, we can still use the main engine to charge. If the main engine is broken, we can still sail and run the generator. Due to our reliance on 12v, we believed this resilience in the system was crucial.

We avoided an AC generator for three other reasons.

First, all the main systems on the boat are 12v, such as the fridge/freezer and watermakers, so it seemed daft to create 110v then use it at 12v.

Secondly, the maximum charge rate for the battery chargers we investigated was about 120amps, so it would take us about 8 hours to replace 900 amps.

Finally we already had a 3kw inverter, so that takes care of the AC loads we need for the washing machine, microwave and so on.

The regulation control for the DC generator is manual/automatic in that the charge voltage can be adjusted by a control on our Transpo 911R regulators. We have remote mounted this on the chart table switch panel alongside the generator controls so it can be easily managed. This also makes it very easy to perform equalizing charges, regularly needed with deep cycle batteries.

We also have an amp hour counter/ammeter display to monitor where we are in the discharge/recharge cycle. With this and the adjustable voltage regulator control, we can easily optimise our charge times, and as we only need to do it every 3 to 4 days it is hardly a chore. On passage, we run the generator every day for an hour to ensure we have topped up batteries in the event of bad weather or other problems.

Using such high charge rates, we use a lot of battery water. To create this, we use the fresh water flush system on our watermakers. Setting the pressure at about 150psi, rather than the 850psi we normally use when processing seawater, this 'double' processing of fresh water produces water with minimal salts so is ideal for the batteries. We have a production run every time the batteries are topped up, about every 6 weeks or so.

The batteries are now 8 years old, we have lived on the boat all that time and after approximately 800-1000 cycles they still provide 1800 amp hours. So, good choice Steve!