My boat has an icebox that is on my list to convert after a few other expensive projects. I installed a small 120v. refrigerator under the nav table which I keep running at the dock and has been great for daysails. Can I power this with an inverter for a two week trip I have planned? Elcheapo
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If you have a way to recharge you batteries.
Sure you can use it for a two week trip if you have have a way to replace about 80 amps/day in your batteries. You will also need a large inverter to kick start that unit. The average 1/2 HP motor will take about 1800 watts to start it and 900 watts to run it. I suggest that you purchase Kollmann's "Do-it-yourself boat refrigeration" for detailed information on boat refrigeration.
Sure you can use it for a two week trip if you have have a way to replace about 80 amps/day in your batteries. You will also need a large inverter to kick start that unit. The average 1/2 HP motor will take about 1800 watts to start it and 900 watts to run it. I suggest that you purchase Kollmann's "Do-it-yourself boat refrigeration" for detailed information on boat refrigeration.
Power requirements
You don't state how large your battery bank is and what kind of charging system you have. One recommendation is to determine the 12 volt draw with an invertor plus all other items used on the boat when sizing your invertor and battery bank. Inverters have a large loss 20-30% when going from 12 to 110 volts and this needs to be accounted when calculating house battery size. Generally do not want to draw down the houe bank more than 50% on a regualr basis as it is hard on the batteries and will shorten thier life. I would suspect that the unit net from the battery bank draws more thean 80 amps per day. You also don't state how you recharge the bank. Stock engine alt, genset, solar, etc. This makes a difference in the total amount of electrcity put back as there is also overhead in charging (not 1 for 1 amp). Can you current system support those loads?? www.sv-makai.com
You don't state how large your battery bank is and what kind of charging system you have. One recommendation is to determine the 12 volt draw with an invertor plus all other items used on the boat when sizing your invertor and battery bank. Inverters have a large loss 20-30% when going from 12 to 110 volts and this needs to be accounted when calculating house battery size. Generally do not want to draw down the houe bank more than 50% on a regualr basis as it is hard on the batteries and will shorten thier life. I would suspect that the unit net from the battery bank draws more thean 80 amps per day. You also don't state how you recharge the bank. Stock engine alt, genset, solar, etc. This makes a difference in the total amount of electrcity put back as there is also overhead in charging (not 1 for 1 amp). Can you current system support those loads?? www.sv-makai.com
Invertor loss
I did some quick reading and reserach and determine that most companies advertise the maximum peak effecency. That is describe as the best you will be able to expect, but it does't tell you the conditions and the reading has not be forth coming to the details of how they arrived at these figures. Agreed under the conditions that manufactures test and rate and under the ideal or peak circumstances the loss figure is the maximum effecincy rather than the average. Example: 10 load tests and 1 hits a 90% conversion rate from 12-110 volts. What is the overall effeciancy? From the max number it is impossible to tell what to expect for all other 9 tests in this example. But the advertising of the max effecincy is 90% which the test supported. I beleive in the real world maunfacture literature is suspect as to the overall effecincies(couldn't find any average effecincy quotes). When sizing an inverter you are better off calcuating at an average rate so as not to undersize the inverter and battery bank sizing. This doesn't even get into the battery bank and the recharge after use. It isn't magic but it does take some reserach so as not to waste your money or to be comfortable with the day to day results. This is an excerpt from the linked Don Casey article. "Before you consider operating any AC appliance from an inverter, you should do the math. Let’s take a 700-watt microwave oven, for example. The PF of microwave ovens is typically around 0.6, so a 700-watt oven will draw around 10 amps (700÷ [120 x 0.6]). If your inverter does not deliver true sine wave power, an appliance inefficiency of around 30 percent comes into play, making the microwave draw around 13 amps (10 x 130 percent). Applying the times-10 rule, your battery bank has to deliver 130 amps at 12 volts, plus another 15 percent to operate the inverter. That makes the load on your battery around 150 amps while the microwave is running." This is a sailnet Don Casey link that does a good job of expalining the realities of power conversion. Very interesting especially when sizing a system.
I did some quick reading and reserach and determine that most companies advertise the maximum peak effecency. That is describe as the best you will be able to expect, but it does't tell you the conditions and the reading has not be forth coming to the details of how they arrived at these figures. Agreed under the conditions that manufactures test and rate and under the ideal or peak circumstances the loss figure is the maximum effecincy rather than the average. Example: 10 load tests and 1 hits a 90% conversion rate from 12-110 volts. What is the overall effeciancy? From the max number it is impossible to tell what to expect for all other 9 tests in this example. But the advertising of the max effecincy is 90% which the test supported. I beleive in the real world maunfacture literature is suspect as to the overall effecincies(couldn't find any average effecincy quotes). When sizing an inverter you are better off calcuating at an average rate so as not to undersize the inverter and battery bank sizing. This doesn't even get into the battery bank and the recharge after use. It isn't magic but it does take some reserach so as not to waste your money or to be comfortable with the day to day results. This is an excerpt from the linked Don Casey article. "Before you consider operating any AC appliance from an inverter, you should do the math. Let’s take a 700-watt microwave oven, for example. The PF of microwave ovens is typically around 0.6, so a 700-watt oven will draw around 10 amps (700÷ [120 x 0.6]). If your inverter does not deliver true sine wave power, an appliance inefficiency of around 30 percent comes into play, making the microwave draw around 13 amps (10 x 130 percent). Applying the times-10 rule, your battery bank has to deliver 130 amps at 12 volts, plus another 15 percent to operate the inverter. That makes the load on your battery around 150 amps while the microwave is running." This is a sailnet Don Casey link that does a good job of expalining the realities of power conversion. Very interesting especially when sizing a system.
short addition
Xantrex advertising states the full load effecincy is 85% for the Freedom 20, which is what we have. The 20-30% I quote may be a little high but Xantrex identifies a specific efficiency(full Load) 85% and a peak of 93%. Our link 2000 monitor confirms higher than advertized ineffeciencies. Again my point was not to be AR about the details but they do have a huge impact once you start using them. How many items have ever been bought the live up to or exceed expectations of the advertising. Sorry I didn't relize I wasn't logged in and could not go back and re-edit. link to Xantrex doc
Xantrex advertising states the full load effecincy is 85% for the Freedom 20, which is what we have. The 20-30% I quote may be a little high but Xantrex identifies a specific efficiency(full Load) 85% and a peak of 93%. Our link 2000 monitor confirms higher than advertized ineffeciencies. Again my point was not to be AR about the details but they do have a huge impact once you start using them. How many items have ever been bought the live up to or exceed expectations of the advertising. Sorry I didn't relize I wasn't logged in and could not go back and re-edit. link to Xantrex doc
It's OK
Cruising World did a inverter test a couple of months ago. From your location it's probably not aboard your boat yet. Anyway, they tested about a half dozen marine inverters. As I recall, they all came in at 91% efficiency, or so. Including my prosine 2.0. I'm not certain about that 85% number in your manual.
Cruising World did a inverter test a couple of months ago. From your location it's probably not aboard your boat yet. Anyway, they tested about a half dozen marine inverters. As I recall, they all came in at 91% efficiency, or so. Including my prosine 2.0. I'm not certain about that 85% number in your manual.
It was the November issue.
Page 62. Seven models tested. Efficiency ranged from 91.4% to 92%. I just re-read the efficiency part. The author didn't explain or test for differences at various loads, if any. The stated efficiencies were at full rated output. These were 2KW units.
Page 62. Seven models tested. Efficiency ranged from 91.4% to 92%. I just re-read the efficiency part. The author didn't explain or test for differences at various loads, if any. The stated efficiencies were at full rated output. These were 2KW units.
Possible
It is possible, we are kind of behind the times. that why I love these boards. I can learn a bunch for the next round of boat part buying sometime in the future. Now if I saw the test in Practical Sailor....
It is possible, we are kind of behind the times. that why I love these boards. I can learn a bunch for the next round of boat part buying sometime in the future. Now if I saw the test in Practical Sailor....
Those Casey numbers are what we see too.
Our inverter is true sine wave. 900 watts on the microwave draws an indicated 10 amps on the AC side and 100 amps DC. This is so much fun.
Our inverter is true sine wave. 900 watts on the microwave draws an indicated 10 amps on the AC side and 100 amps DC. This is so much fun.
Love it all
Love it all, this is where education starts. Much cheaper than buying and then regretting as you learn about what you should have got rather than what you bought. We just installed a Prosine after our Xantrex/ heart failed for the second time in 2 years(still have it though). First under warranty and second time not. We installed the prosine 1750 but haven't had much time to see how well it works. Not many choices here. It was cheaper even at inflated Caribe prices than shipping out for repairs. Now have a new interest in performace. I will keep an eye open for the CW with the inverter shootout.
Love it all, this is where education starts. Much cheaper than buying and then regretting as you learn about what you should have got rather than what you bought. We just installed a Prosine after our Xantrex/ heart failed for the second time in 2 years(still have it though). First under warranty and second time not. We installed the prosine 1750 but haven't had much time to see how well it works. Not many choices here. It was cheaper even at inflated Caribe prices than shipping out for repairs. Now have a new interest in performace. I will keep an eye open for the CW with the inverter shootout.
A cheap way!!
"VECTOR" manufactures a 1200 Watt inverter that sells for approximately $120. It will drive a small refrigerator that draws 1 amp or less. The problem is that starting the electric motor requires a bank of two group 27 batteries to maintain voltage above 11V during start up. The inverter has to be hard wired with a #2 gauge cable with a 200-250 amp fuse. $40. Do not install with more than 10 ft of round trip cable. If the refrigerator is cooled to its max before switching over to the inverter the draw on your batteries will be reduced. You do need a way to charge them batteries under way. If you overnight at marinas with shorepower where you can swith back to 110V and power your battery charger you can do it. If you plan to anchor out now you need to run a generator to power these items. The alternative would be to run your motor/alternator for a few hours every day or install expensive solar or wind powered cahrging systems. In reality the cheapest way is to put ice in your ice cooler. Every couple of days dock and replenish your ice and perishables. You can cool down your fridge to assist when tied to shore power. We just installed a small dorm fridge on an H-27 with the inverter described above. A 20 amp inboard battery charger will be powered at anchor by a Honda 2000eu generator. The fridge's draw on the batteries will be limited to 15 minutes per hour while under way. It is plugged in to a 110V power bar with an on and off switch. Opening of door will be maintained to a minimum and we will still carry an ice cooler to put the beer in and for drinks. Our trips on this boat are usually 3-4 days max.
"VECTOR" manufactures a 1200 Watt inverter that sells for approximately $120. It will drive a small refrigerator that draws 1 amp or less. The problem is that starting the electric motor requires a bank of two group 27 batteries to maintain voltage above 11V during start up. The inverter has to be hard wired with a #2 gauge cable with a 200-250 amp fuse. $40. Do not install with more than 10 ft of round trip cable. If the refrigerator is cooled to its max before switching over to the inverter the draw on your batteries will be reduced. You do need a way to charge them batteries under way. If you overnight at marinas with shorepower where you can swith back to 110V and power your battery charger you can do it. If you plan to anchor out now you need to run a generator to power these items. The alternative would be to run your motor/alternator for a few hours every day or install expensive solar or wind powered cahrging systems. In reality the cheapest way is to put ice in your ice cooler. Every couple of days dock and replenish your ice and perishables. You can cool down your fridge to assist when tied to shore power. We just installed a small dorm fridge on an H-27 with the inverter described above. A 20 amp inboard battery charger will be powered at anchor by a Honda 2000eu generator. The fridge's draw on the batteries will be limited to 15 minutes per hour while under way. It is plugged in to a 110V power bar with an on and off switch. Opening of door will be maintained to a minimum and we will still carry an ice cooler to put the beer in and for drinks. Our trips on this boat are usually 3-4 days max.
Efficiency will drop off rapidly
as the load drops. Then there is the power factor to consider when running a motor. For the refrigerator, I would not expect much over 30-35 percent actual efficiency. If you want max efficiency, get a DC model.
as the load drops. Then there is the power factor to consider when running a motor. For the refrigerator, I would not expect much over 30-35 percent actual efficiency. If you want max efficiency, get a DC model.
Refrigeration From An Inverter
Thanks Steve for recommending my books but for Elcheapo’s question about running a inexpensive 110 volt refrigerator from an inverter neither of my books will give the answer he is looking for. The 110 volt refrigerator that will fit under a chart table draws less than one amp at 110 volt AC. Cruising in waters north of Latitude 30 North and boat connected to shore power except for short cruises why not use an inverter to power the refrigerator. Here are the limitations that must be understood when adding an inverter to power a refrigerator: • The inverter must be designed for a refrigerator induction type motor. • Amp-hr rating of a battery is normally based on a maximum currant draw of 20 amps per hour. Exceed the 20 amps and the capacity is reduced this is known as the Peukert Value Effect. • If a battery bank is discharged by 100 amps it will take 110 amps to recharge it. • A standard 65 amp alternator with standard voltage regulator cannot replace 100 amps in six hours running time. • An inverter should be two and one half times the maximum current draw. Elcheapo my test shows that a three cubic foot GE refrigerator made in Mexico and sold for under $100 draws 0.6 (66 watts) to 0.9 amps (99 watts) at 110 volts AC, during compressor start up amperage momentarily jumps to 2amps AC. Your refrigerator running from an inverter should draw about 12 DC amps from the inverter when running. How much your refrigerator runs per hour will depend on how it is used. One dedicated group 27 battery for the inverter/refrigerator and a small amount of engine running time should take care of power for a weekend cruise. For two week cruises I would recommend two six volt Gulf Cart batteries in series and a high out put alternator and smart regulator. I would think a 600 watt inverter would handle the starting load of your small refrigerator. If you decide in the future to buy a boat ice box conversion refrigeration unit I do recommend my Twelve Volt Manual or for larger holding plate systems the Do It Yourself Boat Refrigeration Book.
Thanks Steve for recommending my books but for Elcheapo’s question about running a inexpensive 110 volt refrigerator from an inverter neither of my books will give the answer he is looking for. The 110 volt refrigerator that will fit under a chart table draws less than one amp at 110 volt AC. Cruising in waters north of Latitude 30 North and boat connected to shore power except for short cruises why not use an inverter to power the refrigerator. Here are the limitations that must be understood when adding an inverter to power a refrigerator: • The inverter must be designed for a refrigerator induction type motor. • Amp-hr rating of a battery is normally based on a maximum currant draw of 20 amps per hour. Exceed the 20 amps and the capacity is reduced this is known as the Peukert Value Effect. • If a battery bank is discharged by 100 amps it will take 110 amps to recharge it. • A standard 65 amp alternator with standard voltage regulator cannot replace 100 amps in six hours running time. • An inverter should be two and one half times the maximum current draw. Elcheapo my test shows that a three cubic foot GE refrigerator made in Mexico and sold for under $100 draws 0.6 (66 watts) to 0.9 amps (99 watts) at 110 volts AC, during compressor start up amperage momentarily jumps to 2amps AC. Your refrigerator running from an inverter should draw about 12 DC amps from the inverter when running. How much your refrigerator runs per hour will depend on how it is used. One dedicated group 27 battery for the inverter/refrigerator and a small amount of engine running time should take care of power for a weekend cruise. For two week cruises I would recommend two six volt Gulf Cart batteries in series and a high out put alternator and smart regulator. I would think a 600 watt inverter would handle the starting load of your small refrigerator. If you decide in the future to buy a boat ice box conversion refrigeration unit I do recommend my Twelve Volt Manual or for larger holding plate systems the Do It Yourself Boat Refrigeration Book.
DC Cooler
We used a Coleman DC cooler on our old boat. It cost $78 at Wall Mart including an AC adapter. We ran it on AC at the dock and plugged it into a cigarette lighter socket when under way. It drew 3.7 amperes continuous while under way. We bought another one after selling that one with the boat to keep things cold going to and from the lake in the van.
We used a Coleman DC cooler on our old boat. It cost $78 at Wall Mart including an AC adapter. We ran it on AC at the dock and plugged it into a cigarette lighter socket when under way. It drew 3.7 amperes continuous while under way. We bought another one after selling that one with the boat to keep things cold going to and from the lake in the van.
Conversion
Why not convert your present "ice box" to a refrigerator. I got a Norcold conversion unit fron Defender for mine. It will run on 12v or 110 AC. I don't remember what the draw is at this moment but it is very low, I had a similar unit in my previous boat and it worked beautifully. Dave A S/V Windsong Pearson 35
Why not convert your present "ice box" to a refrigerator. I got a Norcold conversion unit fron Defender for mine. It will run on 12v or 110 AC. I don't remember what the draw is at this moment but it is very low, I had a similar unit in my previous boat and it worked beautifully. Dave A S/V Windsong Pearson 35
I am blown away by my the wealth of knowledge out here. Thank you all for your insightful replies. I have decided to go for the coversion after doing some more research. My boat has the Balmar 75amp.alt with smart regulator and 375 amp house with a separate start battery. I have been on Kollmans' site and have it in my research list. Fair winds to all! Elcheapo
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