Does anyone know where I can find a good reference that covers power managment on a sailboat? I have a 1992 Hunter 28 that has a stock 55A automotive charging system and two batteries that are rated for 85AH and 75AH. An electircal engineer friend of mine (who has owned a Cal 33 for 15 years and does lots of cruising) said that the automotive charger will only charge a battery to 85% and that you shouldn't draw a battery down below 50%. This means that the 85AH battery is good for 36AH and the 75AH is good for 32AH. Some of the items that draw current are pretty easy to caluclate - for example, two cabin (1A each) for three hours is 6AH, the anchor light at 1A for 6 hours is another 6AH, the VHF radio at .5A for 6 hours is another 3AH. However, the use of the fresh water pump and the cycling of the bilge pump are more difficult to calculate. How do you manage your power consumption so that you can be sure of starting the engine every time you need to?
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Easy answer.
The easy way: an isolated starter battery that is NEVER used. I never use position #1 on the battery switch. It goes to a new 900CCA AGM starter battery. Whenever I am on the boat the switch is on #2. That is tied to the house bank. I start the engine on that bank and do everything else on that bank. My charging system is set up to charge both banks using a combiner. I have a meter so that I can always be sure the charging system is working and that the starter battery is fully charged. Still I have the same chart with all the amps calculated. I think I got a copy from an article on Sailnet. Try the Related Link.
The easy way: an isolated starter battery that is NEVER used. I never use position #1 on the battery switch. It goes to a new 900CCA AGM starter battery. Whenever I am on the boat the switch is on #2. That is tied to the house bank. I start the engine on that bank and do everything else on that bank. My charging system is set up to charge both banks using a combiner. I have a meter so that I can always be sure the charging system is working and that the starter battery is fully charged. Still I have the same chart with all the amps calculated. I think I got a copy from an article on Sailnet. Try the Related Link.
Have you ever . . .
had circumstances where you were on the hook and the juice in battery #2 just wouldn't keep the anchor light or the cabin lights going and you had to switch to bank #1? Sounds like you run your engine enough that you never get close to battery #2's capacity. Do you have a procedure you follow to run you engine for an hour a day to charge both batteries (and get the side benefit of having hot water)?
had circumstances where you were on the hook and the juice in battery #2 just wouldn't keep the anchor light or the cabin lights going and you had to switch to bank #1? Sounds like you run your engine enough that you never get close to battery #2's capacity. Do you have a procedure you follow to run you engine for an hour a day to charge both batteries (and get the side benefit of having hot water)?
Added batteries.
No, I have never needed the starter battery. But that is because: 1) we seldom go out for more than three nights, and 2) we have three house batteries with room for a fourth. We often motorsail and always motor in/out of anchorages and marinas. This more than compensates for battery usage. We have a backup with a 2000W Honda generator. This is primarily for running the A/C away from the dock. But it will top off the batteries in pretty short order. A nice quiet alternative to the 55-amp alternator. For the kind of sailing that I do I would add batteries before the expense of solar panels or a wind generator.
No, I have never needed the starter battery. But that is because: 1) we seldom go out for more than three nights, and 2) we have three house batteries with room for a fourth. We often motorsail and always motor in/out of anchorages and marinas. This more than compensates for battery usage. We have a backup with a 2000W Honda generator. This is primarily for running the A/C away from the dock. But it will top off the batteries in pretty short order. A nice quiet alternative to the 55-amp alternator. For the kind of sailing that I do I would add batteries before the expense of solar panels or a wind generator.
Steve, I recommend installing a Link 20 monitor. See the link I included on this page. I use a Link 10 in my H260 since I have only one bank. With these units you know exactly how many amp-hours have entered and left the batteries and what the state of charge is at all times in real time. It's done by installing a current shunt in the negative battery cable. To get a full charge you need a different voltage regulator. Good Questions!
Batteries
Steve, I'm not sure that your electrical engineer friend is totally accurate. I suspect that the alternator you have would charge that last 15% into your batteries, it would just take a long time and is not worth the engine run time. He is right that your normal running range is the 50% to 85% range. But think of it like this...if you are fully charged when you leave the dock (preferably with a good three stage charger), you will have the full 50% of both batteries before you need to recharge (ssuming your engine will start from a 50% discharged battery). From there, recharging to 85% capacity with the alternator is reasonably efficient, but will still require several hours or more run time from the engine. The advice you have received here is all good. Protecting your engine starting source is a good idea, whether by having a dedicated start battery or only using one of your two down to 50% before you recharge. The Link 20 is a good way to monitor the system. You should do an energy audit to determine use and evaluate that against your sailing desires. If you intend to spend more than a night at anchor without providing some recharging source (alternator, generator, of dockside power) then you may want to consider additional battery capacity. I'm not sure that your current battery capacity warrants a larger alternator. If your bilge pump or fresh water pump are running enough to have a big impact on amps used, you need to figure out why you are sinking or talk to the wife and kids about the lmited supply of fresh water. You have the rest figured out for usage. On our 290 we went with two Group 27 AGM house batteries (200 amp hours) and one Group 27 AGM dedicated start battery. We have the stock 55 amp alternator in that boat and we can anchor out for two nights if we are fully charged and careful and then have to recharge for each additional night with about 1.5 hours of engine run time. We always tried to plan our local voyages with those parameters in mind rather than just running the engine while at anchor. Hope this helps. Dan Jonas (S/V Feije II)
Steve, I'm not sure that your electrical engineer friend is totally accurate. I suspect that the alternator you have would charge that last 15% into your batteries, it would just take a long time and is not worth the engine run time. He is right that your normal running range is the 50% to 85% range. But think of it like this...if you are fully charged when you leave the dock (preferably with a good three stage charger), you will have the full 50% of both batteries before you need to recharge (ssuming your engine will start from a 50% discharged battery). From there, recharging to 85% capacity with the alternator is reasonably efficient, but will still require several hours or more run time from the engine. The advice you have received here is all good. Protecting your engine starting source is a good idea, whether by having a dedicated start battery or only using one of your two down to 50% before you recharge. The Link 20 is a good way to monitor the system. You should do an energy audit to determine use and evaluate that against your sailing desires. If you intend to spend more than a night at anchor without providing some recharging source (alternator, generator, of dockside power) then you may want to consider additional battery capacity. I'm not sure that your current battery capacity warrants a larger alternator. If your bilge pump or fresh water pump are running enough to have a big impact on amps used, you need to figure out why you are sinking or talk to the wife and kids about the lmited supply of fresh water. You have the rest figured out for usage. On our 290 we went with two Group 27 AGM house batteries (200 amp hours) and one Group 27 AGM dedicated start battery. We have the stock 55 amp alternator in that boat and we can anchor out for two nights if we are fully charged and careful and then have to recharge for each additional night with about 1.5 hours of engine run time. We always tried to plan our local voyages with those parameters in mind rather than just running the engine while at anchor. Hope this helps. Dan Jonas (S/V Feije II)
For those of you looking at power management, "Sailboat Electrics Simplified" by Don Casey, Part of the International Marine Sailboat Library is an excellent resource.
I noticed there was no mention of using more energy efficient lighting such as LEDs. They make a huge difference if lighting is used extensively in the evenings. The new LED anchor lights look to be very miserly when it comes to consumption as well. I will be looking into this further this year since I'm in the process of purchasing a 28.5 for some cruising. Anyone using LEDs?
I have an LED anchor light
that draws about 1/10 of an amp as opposed to the standard one that used over 1 amp. Also have 2 led fixtures installed in the cabin above the berths and one red/white led fixture in the cabin. I use a small battery powered led hung from the boom for when I'm on the hook. LED's are great.
that draws about 1/10 of an amp as opposed to the standard one that used over 1 amp. Also have 2 led fixtures installed in the cabin above the berths and one red/white led fixture in the cabin. I use a small battery powered led hung from the boom for when I'm on the hook. LED's are great.
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