Keeping the batteries on board in tip top condition is key not only so that they don't crap out on you when most needed but also because I don't like spending money on replacements needlessly. Nothing destroys a battery faster than incomplete and improper charging. Unfortunately on many a boat that is the norm rather than the exception. Although most boats will have some sort of charging circuit fed from the engine alternator this obviously only puts a charge into the batteries when the engine is running. Considering that most boats sit idle most of the time and the engine is not running it is easy to see that the batteries stand a very good chance of being undercharged almost consistently.
When the engine is fired up the alternator puts out a hefty charge but this soon drops after the battery has accepted its initial top up as it were. It is a well known fact that the last 10% of charge is the hardest to get the batteries to accept. Batteries on boats will often accept what is known as a surface charge and the alternator not knowing any better will shut off thinking that the battery has reached full capacity when in truth it has not.
What is need therefore then is some sort of smart charger that can overcome these problems especially on boats that are used infrequently yet still keep the batteries operating at optimum output.
To address these problems I have installed a Guest 36082 charger on the boat. The picture above shows the charger attached to a mounting board with one set of leads already connected. The charger is a 12 volt charger, 24 volt systems are also available and the makers claim it is suitable for wet lead acid, AGM and gel batteries. You can see a couple of black leads coming from the bottom of the unit these are for the 120 volt supply and connection to a remote monitor, which could be useful in many cases as the charger will often be mounted in an out of the way location where the front mounted LED status lights on the unit itself will not be visible.
Connection is a simple affair and consists of connecting the black and red leads to the battery which are protected by in line circuit breakers, shown below and connecting up the mains supply. Once connected and plugged in the LED lights give an indication of the battery condition. There are two lights, a red and a green. If the battery is at all flat the red light comes on to indicate that the charger is putting out the maximum amount of power to bulk charge the battery. After several hours depending on the battery and it's condition at the time the unit was fired up both the red and green will come on showing that the battery has entered the finishing stage; the voltage is held at 14.6 volts while the amount of amps delivered to the battery is slowly reduced. It is at this stage that charger 'tops up' the last 10% which is so hard to do with the engine charging circuit. Finally the red light goes out and steady green indicates that the battery is being held in the float or maintenance stage and is now fully charged.
It is worth noting that the battery can be maintained in this condition with the charger connected for many weeks of months if need be with no ill effects as unlike cheap automotive style chargers there is no chance of overcharging and boiling off the electrolyte.
Things got a little more complicated however when I added on the optional alternator module. This module connects to the studs on the charger and one set of battery leads, instead of being connected to the second set of studs are connected to the outputs on the base of the module. This module then directs excess charging current from the alternator when the motor is running to the second or house battery bank once the cranking battery is fully charged. this automatic charging relay is fully potted to prevent the ingress of moisture and like the charger appears well made.
The battery charger with the alternator module attached.
I must confess that I had one or two problems with the wiring, the diagram and instructions could be clearer but I worked it out in the end. The other problem with the alternator module is that it is only rated for 60 amps but many alternators will put out more than this, but in my case I was connecting the unit to an alternator with maximum output of 45 amps so all should be well.
I've been using the charger for some time now and it most definitely keeps the batteries in better shape. Once I plug the boat into shore power I can leave the boat knowing that when I come back my batteries will be in good shape and there will be power aplenty to fire up the motor. The charger is pretty small and with the alternator module is just over 10 inches high and 6 inches wide so it will fit almost anywhere although it should be mounted vertically.
A quick trawl of the web revealed both charger and module available for between 150 and 200 dollars which I think is well worth the money compared to replacing failed batteries prematurely.
A quick trawl of the web revealed both charger and module available for between 150 and 200 dollars which I think is well worth the money compared to replacing failed batteries prematurely.
Posted by: Tony | May 17, 2011 at 03:40 AM
Can you provide me with a diagram on how you connected the alternator module?
Posted by: Captain Ryan Boyd | May 06, 2017 at 11:01 AM
Ryan
I no longer have the manual, but as I recal the connections are very straightforward and the wiring diagram that comes with the module lists out how these are made. It also tells you what size cables to use to avoid voltage drop. Do not use undersized cables or the performance of the unit will be disapointing.
Posted by: mark | May 29, 2017 at 08:48 PM