It is now the end of February and I have completed 6 projects and have 9 others already in progress. The biggest and most challenging so far was the electrical system upgrade and modifications....are you in the mood for a riddle?
How many amps does a 60 amp alternator produce?
How many amp hours can you get out of a 300 amp hour battery?
I found that boat electrical systems are extremely complex. Unlike your car where the battery is only used very briefly to start the engine and then the alternator drives the electrical systems while the car is running. A sail boat battery starts the engine, the alternator runs for a few minutes until you clear the marina, raise the sails and shut the motor down. From that point on, your electrical devices draw from the batteries, and boats have far more electrical devices than cars. To exasperate the situation, if you are at anchor (that means no shore power) you are running off batteries for days at a time. You can start the motor to spin the alternator to recharge the batteries. However deep cycle batteries take many hours to recharge....get the picture?
My first task was to expand the amount of battery capacity and to improve the charging system to get a quicker re-charge at anchor. I started off by asking for advise from other sailors. Which turned out to be "Get a Balmar Multi Stage Regulator, you can charge you batteries in 1/3 the time"
Well this seemed like good advise and I went directly to Second Wave and picked one up for $154.00. When I tried to install it, I found out that my alternator was not externally regulated and the device was useless.....lesson learned.
I figured out that if I wanted to do this, I would have to do my own research and lots of it. There are entire volumes of information on the subject and I spent a horrendous amount of time getting myself up to speed. Along the way I made some very interesting discoveries:
Although the standard flooded lead acid battery is over 100 years old, it is still widely mis understood.
There are tons of new (and expensive) high tech devices to help you run and monitor your batteries and charging systems, but they are rife with trade-offs. For example, external electronic regulators charge your batteries faster but they are more prone to failure than the simple internal regulators built into the alternator.
Battery isolators designed to prevent one weak battery from drawing down another also introduce a voltage drop on the input side of the circuit. If you do not account for this, you can get incorrect measurements and over charge your batteries.
...it goes on from there.
I ended up designing a system that suited my needs, was pretty close to idiot proof, and provided a some level of redundancy (Just in case). I went "off the page" of conventional wisdom and came up with a pretty unique solution...here it is.
I changed out the stock 60 amp internally regulated alternator for a 90 amp internally regulated alternator. There are 120, 150, and 200 amp alternators, but they require a major reconfiguration of the engine pulley system and mounts to support them. Also, for every 30 amps of power they generate, they draw 1 horse power from the engine. With a 23 HP engine, I would not have enough power left over to spin the propeller.
I stuck with an internally regulated alternator and traded shorter charge times for reliability.
I dropped in a single marine grade start battery in the engine compartment. It is physically isolated from the remainder of the batteries / electrical systems. With this configuration, you can't accidentally drain down the engine start battery because a selector switch was left in the wrong position. The trade off is that the battery is also isolated from the alternator and will not be charged by the engine. I should be able to get 20 starts before it needs to be recharged and I have a back up battery.
By installing a dedicated start battery, I can now use both large deep cycle batteries to run the house electrical systems. Prior, I used only one battery to start the engine and run the house systems and kept the other in reserve....so I essentially doubled my house capacity.
The boat came with a three circuit charging unit that is capable of monitoring and charging three battery banks when the boat is connected to shore power. I rewired it to charge all three battery banks.
I stuck with "Old school" flooded batteries. Gel Cells, AGM (Advanced Glass Mat), and the hot new spiral wound batteries are pretty expensive. And it turns out the only true way to measure the charge of a battery is with a hydrometer, which can not be used on any of the high tech batteries.
Answers to the questions above....
A 60 amp alternator will produce 60 amps only when it is spinning at it's maximum of 6000 RPM. The output falls off sharply at lower RPMs and heat reduces it further. With a normal cruising engine RPM of 1200 - 1500 RPM and a ratio 1 - 2, the alternator is spinning at about 2400 to 3000 RPM...when heat is factored in, you are getting 8 to 10 amps if you are lucky.
A 300 Amp Hour battery should be capable of powering a 1 amp device for 300 hours, or a 10 amp device for 30 hours. However, completely draining a battery can shorten it's life. Deep Cycle batteries are built to take a deep discharge, but it is recommended that you do not run down a deep cycle battery beyond 50% (some say 70%) of its capacity. Conservatively, you can get 100 amp hours out of a 300 amp hour battery.
