Power Management Ideas (12 V)?
- Thread starter Kings Gambit
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A couple of observations and alternatives.
Any time you start moving heat around a boat you need to consider doing it in novel ways that do not require electricity. Reducing the amount of heat you need to move around is the most effective way of keeping the cost down and that means having the best insulation around your reefer that you can muster and having efficient systems.
Using battery voltage to determine SOC is pretty easy and CHEAP. You probably don't need to know down to the fractional AH how full the batts are and can live with +-5% SOC. Read this to see why:
http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf
Did I mention it was cheap?
If you are considering solar, wind, hydro for powering a heat moving device like a reefer/freezer then I'd recommend you consider using an engine driven compressor and holding plate type of system before you go out and cover your boat with solar panels. Embrace the horror of diesel power and consider for a minute the following scenario. After a long pleasant day of sailing and walking around the destination town with the first mate you return to the boat and fire up the engine, you begin to draw down the reefer/freezer holding plates, the alternator/inverter/electric stove cooks your meal, the water is heated for the shower later, the batteries get charged up, the AC (also belt driven) cools cabin down and all it cost is a quart of diesel. You could also accomplish this with a genset and inverter but I’m thinking that running an A/C unit and heating water this way would be kinda hard to implement.
I'm not trying to say this is a great solution. It is a solution at one end of the possible ways of doing it. A boat totally covered with solar panels would be at the other end. Neither is very palatable. Somewhere in the middle is the solution that can work for you.
The real key is to reduce your consumption with insulation and efficient systems.
I made a spreadsheet that helps get a handle on balancing loads, production and storage on a boat. After playing with it for a while I came to the conclusion that big alternators are not that great an investment unless you can use the output as you consume it. Storing it in a battery (90%) for use later (90%) is not an efficient way of using the electricity (81% efficiency max overall). By storing the AH in the batteries you throw away no less than 19% Then there is the battery acceptance issue that totally kills the big alternator idea unless you have a huge battery bank. Far better to turn on the high amp load while that alternator is running and use the current directly (or through an inverter). Also when you turn things on and off can make a significant difference in your battery SOC and times between recharges. If you, for instance, just run the reefer during the day when the solar can supply (use as you produce again) the current and use the holding plate to "coast" through the night you can see some significant reduction in AH consumed and not really tell the difference in reefer temps. If you turn on the alternator and charge just as you enter the hour that you most deeply discharge the batts your acceptance rate will be better and you get more AH into your batts for your quart of diesel. There are some really dumb things you can do that totally kill your SOC also.
Any time you start moving heat around a boat you need to consider doing it in novel ways that do not require electricity. Reducing the amount of heat you need to move around is the most effective way of keeping the cost down and that means having the best insulation around your reefer that you can muster and having efficient systems.
Using battery voltage to determine SOC is pretty easy and CHEAP. You probably don't need to know down to the fractional AH how full the batts are and can live with +-5% SOC. Read this to see why:
http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf
Did I mention it was cheap?
If you are considering solar, wind, hydro for powering a heat moving device like a reefer/freezer then I'd recommend you consider using an engine driven compressor and holding plate type of system before you go out and cover your boat with solar panels. Embrace the horror of diesel power and consider for a minute the following scenario. After a long pleasant day of sailing and walking around the destination town with the first mate you return to the boat and fire up the engine, you begin to draw down the reefer/freezer holding plates, the alternator/inverter/electric stove cooks your meal, the water is heated for the shower later, the batteries get charged up, the AC (also belt driven) cools cabin down and all it cost is a quart of diesel. You could also accomplish this with a genset and inverter but I’m thinking that running an A/C unit and heating water this way would be kinda hard to implement.
I'm not trying to say this is a great solution. It is a solution at one end of the possible ways of doing it. A boat totally covered with solar panels would be at the other end. Neither is very palatable. Somewhere in the middle is the solution that can work for you.
The real key is to reduce your consumption with insulation and efficient systems.
I made a spreadsheet that helps get a handle on balancing loads, production and storage on a boat. After playing with it for a while I came to the conclusion that big alternators are not that great an investment unless you can use the output as you consume it. Storing it in a battery (90%) for use later (90%) is not an efficient way of using the electricity (81% efficiency max overall). By storing the AH in the batteries you throw away no less than 19% Then there is the battery acceptance issue that totally kills the big alternator idea unless you have a huge battery bank. Far better to turn on the high amp load while that alternator is running and use the current directly (or through an inverter). Also when you turn things on and off can make a significant difference in your battery SOC and times between recharges. If you, for instance, just run the reefer during the day when the solar can supply (use as you produce again) the current and use the holding plate to "coast" through the night you can see some significant reduction in AH consumed and not really tell the difference in reefer temps. If you turn on the alternator and charge just as you enter the hour that you most deeply discharge the batts your acceptance rate will be better and you get more AH into your batts for your quart of diesel. There are some really dumb things you can do that totally kill your SOC also.
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