patzfan4eva
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If I have an invertor, is there any value to having a AC/DC Fridge or will AC work just fine. Amp hours always confuse me.....
AC/DC Fridge
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Moonstruck
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A DC fridge works just fine. If you have no need to run energy hungry things like A/C, you need no generator for AC current. A twelve volt boat is simple. Your charging system is more important that a generator. If you are hanging on a hook for long periods, and don't want to run your main engine, an AC generator may be in order.
patzfan4eva
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I been reading about AC fridges and they seem to use less amp then DC fridges, but I'm not sure how much the invertor uses to convert. The primary reason for this question is my Norcold is dead and If I can function properly with a $150 fridge as opposed to $900 unit I want to go that route.
David: I had an AC/DC fridge with an auto-switching device built-in that ran the fridge on AC when available (eg: on shorepower or when inverter was on...which was always when we were off shorepower). This auto-switching device failed....and I have now learnt this is pretty common and that they have a life typically of only about 5 years in continuous use. Replacing them is expensive. When the auto-switch failed, the fridge switched itself to run only on DC....but wasn't staying as cold as normal. Investigating this problem was what caused us to find the auto-switch had failed. The fridge wasn't operating well because we had excessive voltage drop in a too-indirect DC cabling...which had been disguised by the shorepower/inverter operating properly & delivering full voltage until the auto-switch failed.
Rather than do the costly replacement of the auto-switch, the advice I got from 2 marine refrigeration techs was to direct-connect the fridge to the house battery bank buss (with appropriate fusing & cable sizes of course) to be sure to get the full 13+ volts to the fridge. The compressors of these fridges are VERY sensitive to voltage drop, despite indicating that they run at a wide voltage tolerance (mine said on its compressor label 10-14v or similar). They'll run at low voltage, just not very effectively.
The refrig techs also pointed out that modern inverter efficiency is 'good', but still only 85-93% (my Victron inverter, a quality unit, states that it is 87% efficient). So you are using up to 15% more battery power on the inverter vs a direct-connect to the House bank. That's not a small % for a big consumer like a fridge. So my advice would be to go the DC route but to do it properly.
Having said all that though, your 2nd post makes a good point: standard domestic fridges are much cheaper than 12v models. Often they are better insulated and more energy-efficient too...maybe enough to offset inverter losses, though that is a guess. But domestic fridges don't come with door locks and you will certainly need to do something about that. So if you have a quality inverter, a good size battery bank (800Ah+), external regulators to large (120A+) alternators & can fit locks to fridge and freezer compartment doors to stop them flying open in a seaway...then go the standard domestic AC route by all means.
Finally, AC or DC, you can help you fridge's efficiency by ensuring it is well-ventilated around the compressor/behind the fridge. In tight spaces, installing a brushless, super-low-draw computer fan adjacent the compressor and wired to run off the compressor circuit so it comes on when the compressor cycles, is a huge efficiency booster, particularly in hot weather. Suitable computer fans are less than $20 at any computer parts place. I installed one with a remote on/off switch so I can turn it on when days are hot: it reduced the fridge's cycling-on times noticeably.
Rather than do the costly replacement of the auto-switch, the advice I got from 2 marine refrigeration techs was to direct-connect the fridge to the house battery bank buss (with appropriate fusing & cable sizes of course) to be sure to get the full 13+ volts to the fridge. The compressors of these fridges are VERY sensitive to voltage drop, despite indicating that they run at a wide voltage tolerance (mine said on its compressor label 10-14v or similar). They'll run at low voltage, just not very effectively.
The refrig techs also pointed out that modern inverter efficiency is 'good', but still only 85-93% (my Victron inverter, a quality unit, states that it is 87% efficient). So you are using up to 15% more battery power on the inverter vs a direct-connect to the House bank. That's not a small % for a big consumer like a fridge. So my advice would be to go the DC route but to do it properly.
Having said all that though, your 2nd post makes a good point: standard domestic fridges are much cheaper than 12v models. Often they are better insulated and more energy-efficient too...maybe enough to offset inverter losses, though that is a guess. But domestic fridges don't come with door locks and you will certainly need to do something about that. So if you have a quality inverter, a good size battery bank (800Ah+), external regulators to large (120A+) alternators & can fit locks to fridge and freezer compartment doors to stop them flying open in a seaway...then go the standard domestic AC route by all means.
Finally, AC or DC, you can help you fridge's efficiency by ensuring it is well-ventilated around the compressor/behind the fridge. In tight spaces, installing a brushless, super-low-draw computer fan adjacent the compressor and wired to run off the compressor circuit so it comes on when the compressor cycles, is a huge efficiency booster, particularly in hot weather. Suitable computer fans are less than $20 at any computer parts place. I installed one with a remote on/off switch so I can turn it on when days are hot: it reduced the fridge's cycling-on times noticeably.
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Moonstruck
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You will lose at least 10%, but more like 12% of power in a inverter. A fridge will run better, and use a little less power with a true sine wave inverter. The compressor may run slower and run longer on a modified sine wave inverter. Also a modified sine wave can cause the start up amperage to be higher. However that only lasts a few seconds at most.
I run a 115 volt Sub Zero fridge/freezer from an inverter, but also have a generator.
CPseudonym
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A well placed piece of Velcro about 4 to 6 inches long makes a fantastic fridge lock. Not the yachtiest looking thing but darned effective.
Tom.B
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I don't see how this is accurate. A voltage drop is a voltage drop. When a load is on the batteries and they are unable to stay at 13.5V, voltage is going to drop everywhere. Not just on that circuit.
Tom-
Phil Fill
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A lot depends on what is running on AC and or the inverter. If its just the refrigerator and a couple of items not problem. But if you have a lot of AC stuff, like heaters/water heater/batter chargers etc then they have to be turned off and on so only the refrigerator is running. On the Eagle its to much trouble to have just an AC refrig. It would be better to just have a DC refrig.
motion30
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The amp rating on the ac fridge look low because that is for 120volts when converting to 12 volts tru your inverter multiply by a factor of 10 plus the loss% tru the inverter I have had both 12 volt is better for me
patzfan4eva
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I asked my mechanic who said that in his opinion, with the money I'll save on an AC unit, I can purchase additional batteries to help power it thru the invertor.
BruceK
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Also add solar panels to your system to feed the batteries, via a good regulator. Your batteries will love you for it and live longer in better shape.180watts of panels gives enough charge run a 12v fridge on a sunny day with batteries staying full. BruceK
They seem to use less amps than a DC refrigerator because you're looking at the current (amps) draw at 120 volts for the AC refrigerator and at 12 volts for the DC refrigerator. Multiply the current draw of the AC reprigerator by ten, then add ten percent to that and you'll have the current drawn from your batteries by the inverter to run the refrigerator.
If you want the most efficient refrigerator for your boat (and it matters if you're using it away from shore power or while anchored), buy yourself a quality, marine, AC/DC refrigerator to replace the failed one. Nova Kool and Isotherm are well thought of brands to consider.
Running a battery charger from an inverter?
That would be the elusive "perpetual motion machine".
I think it's the other way around. Not the cost, but the insulation and efficiency. Plug something into a wall outlet in your home and efficiency isn't that important. There's a nationwide electrical grid available to power it.
On a boat, there's just a battery or two. Quality marine refrigerators are designed around efficiency.
patzfan4eva
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You know....you guys are supposed to help me by making it easy to buy a AC fridge!!! Thanks a lot!
I'll check into this further with some of the electrical engineers here at work and get there opinion as well. But $1300 (Nova Kool) $1150 (Norcold) etc versus $170 is hard to swallow without a significant argument for them.
I'll check into this further with some of the electrical engineers here at work and get there opinion as well. But $1300 (Nova Kool) $1150 (Norcold) etc versus $170 is hard to swallow without a significant argument for them.
Ask yourself this question - If a 120 volt AC "dorm" refrigerator powered by an inverter from 12 volt batteries was a reasonable and less expensive alternative than a "real" AC/DC refrigerator, wouldn't the entry level boat manufacturers like Bayliner and Glastron do this instead of installing an AC/DC refrigerator in their boats?
You didn't bother to post the capacity of your inverter, how it was installed, or your battery bank capacity. Is the inverter rated for continuous duty?
Remember, an AC/DC refrigerator runs and draws power until the thermostat determines that it's cold enough, then it shuts off. An inverter would have to run 24/7 to provide power even when the thermostat is satisfied.
Unless your electrical engineers are boaters and experienced with boat electrical systems, their advice is more apt to lead you astray than to set you straight.
BTW: You have what appears to be a pretty nice boat. Why screw it up with a dorm refrigerator? You'll have to put a real one in when it comes time to sell the boat anyway. Think of it as an investment.
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patzfan4eva
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Ron,
All very good points, I'm just being cheap. LOL! I'll find out what my invertor is rated for before any decisions are made. Someone has to explain to me why the same size fridge differs by over $1000 from "Dorm" to "Marine" use!!
All very good points, I'm just being cheap. LOL! I'll find out what my invertor is rated for before any decisions are made. Someone has to explain to me why the same size fridge differs by over $1000 from "Dorm" to "Marine" use!!
CPseudonym
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...I'll have 4 x 220 amp/hour batery nak. I will only use AC refrigeration. A freezer and a refrigerator with a 2500 watts inverter
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motion30
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I ran a undercounter 120v fridge for 2 years Ran off a mod sine inverter no problem no problem underway did use more juice while at anchor I replaced it with a 12voly unit just seemed like the right way to go
motion30
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I found one on ebay new for $700 waco
When we bought Hobo she had a ~ 5 cft Sub-Zero fridge and a ~5 cft Sub-Zero freezer with ice maker. The first 24 hours at anchor 400 plus amps, Yikes 
. We replaced both with a SeaFreeze custom, (4" of insulation), combination 6 cu ft fridge and 3 cu ft freezer. The fridge runs off a Danfoss BD35F compressor and the freezer uses a DB50F. We have a 1100 amp house bank. We have left the boat for 4.5 days at anchor and still had over 50% of the house bank remaining when we got back.
If you're a weekend cruiser, the AC fridge off the inverter makes some sense. We have met many cruisers with Grand Banks, Selene's, Nordhavns, Krogens, etc. who can't leave there boats unattended for more than 24 or 36 hours. In 4.5 +years we have never turned them off (except to defrost the freezer) or have we had any compressor issues. If we lose the freezer we still have the fridge or if we loose the freezer we can turn up the thermostat and have a fridge and a few barbecues. Danfoss utilizes the same electronic module in the both units so if you are into spares you only need one. I think you know what we like.
. We replaced both with a SeaFreeze custom, (4" of insulation), combination 6 cu ft fridge and 3 cu ft freezer. The fridge runs off a Danfoss BD35F compressor and the freezer uses a DB50F. We have a 1100 amp house bank. We have left the boat for 4.5 days at anchor and still had over 50% of the house bank remaining when we got back. If you're a weekend cruiser, the AC fridge off the inverter makes some sense. We have met many cruisers with Grand Banks, Selene's, Nordhavns, Krogens, etc. who can't leave there boats unattended for more than 24 or 36 hours. In 4.5 +years we have never turned them off (except to defrost the freezer) or have we had any compressor issues. If we lose the freezer we still have the fridge or if we loose the freezer we can turn up the thermostat and have a fridge and a few barbecues. Danfoss utilizes the same electronic module in the both units so if you are into spares you only need one. I think you know what we like.
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ksanders
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Well put!
Boat manufacturers don't put 120 volt units in their small cabin cruisers because they know that a inverter, properly installed plus the price of the AC fridge will cost more than the DC fridge.
I have no issues with a full sized household fridge on a large boat, if you re-work the cabinets to make it look nice. The problem is household fridges seem to change sizes by a couple of inches every couple of years. This makes replacement problematic.
Marine fridges seem on the other hand to come in pretty standard sizes. Our 10 year old norcold was replaced by a vitrifrigo that dropped right in.
On a smaller boat, cheaping out on the fridge will just tell prospective buyers the kind of maintenance you did on your boat.
It is all in the amps.
Get a true reading of the amp usage of whatever fridge you are looking at. Add 6 amps, continuous, for the inverter to just sit there and wait while the fridge is off, and add that 6 amps to the draw of the fridge when running. add it up over 24 hours and you have the usage. Now your charging system needs to put all of that back into your batteries, every day, without fail. That is just for the fridge. Don't forget to add in all the other loads that you have aboard. When you have the total, double it, as your charging system can't be expected to run at max output all the time.
I doubt your $150 AC only will come close to the efficiency of a DC only, if only due to having to run the inverter all the time. Under no circumstances go to another AC/DC, as you get the worst possible draw while operating on DC, due to the Norcold AC/DC being actually an AC only with a built in inverter. Get a Danfoss or equivalent DC only and watch your draw drop. In my case, I was able to reduce the no of batteries carried to 1/2 when I made the switch from Norcold AC/DC to Danfoss DC only.
Get a true reading of the amp usage of whatever fridge you are looking at. Add 6 amps, continuous, for the inverter to just sit there and wait while the fridge is off, and add that 6 amps to the draw of the fridge when running. add it up over 24 hours and you have the usage. Now your charging system needs to put all of that back into your batteries, every day, without fail. That is just for the fridge. Don't forget to add in all the other loads that you have aboard. When you have the total, double it, as your charging system can't be expected to run at max output all the time.
I doubt your $150 AC only will come close to the efficiency of a DC only, if only due to having to run the inverter all the time. Under no circumstances go to another AC/DC, as you get the worst possible draw while operating on DC, due to the Norcold AC/DC being actually an AC only with a built in inverter. Get a Danfoss or equivalent DC only and watch your draw drop. In my case, I was able to reduce the no of batteries carried to 1/2 when I made the switch from Norcold AC/DC to Danfoss DC only.
Our boat came with a Norcold AC/DC undercounter refrigerator/freezer. It was installed by the previous owner the year before we bought the boat, which was in 1998. While not the most efficient thing in the world, fourteen years later it is still working as advertised.
A few years ago it acted like it was getting ready to die on us, but today we're not sure if it was or we were having a battery issue. We were all prepared to replace it with a stainless steel AC/DC Isotherm but the Norcold "fixed" itself (or it liked the new kind of batteries we installed at the boat at about the same time) and it has been running fine since then.
While a more efficient refrigerator would be nice, and we really like the Isotherm that was in line to replace the Norcold, we follow the philosophy of not replacing anything on the boat unless it fails or no longer does the job we need it to do.
We are well aware of the repuation of these AC/DC units and while it may die tomorrow we attribute its long life to the fact that from the day we took delivery of the boat the Norcold has never been turned off. Even when the boat is in the yard for painting, the groundpower cable is still hooked up.
We like the AC/DC capabilites because at the dock should the AC fail the refrigerator will not switch over to DC and run the batteries down thus depriving the boat of power for the bilge pump which Murphy's law says that we would need at that very moment. (We turn off the DC breaker for the refrigerator when the boat is in its slip, that's why it won't switch over).
When we're using the boat we switch the Norcold over to DC which means we don't have to have the inverter going in addition to the refrigerator. Our boat has a generator so we can throw a charge back into the batteries when needed.
So we like the flexibility an AC/DC refrigerator/freezer gives us. It works well with our boat's very simple and basic electrical system. Other people prefer all AC or all DC. It's just a matter of preference, the boat's electrical system, and how one uses the boat.
A few years ago it acted like it was getting ready to die on us, but today we're not sure if it was or we were having a battery issue. We were all prepared to replace it with a stainless steel AC/DC Isotherm but the Norcold "fixed" itself (or it liked the new kind of batteries we installed at the boat at about the same time) and it has been running fine since then.
While a more efficient refrigerator would be nice, and we really like the Isotherm that was in line to replace the Norcold, we follow the philosophy of not replacing anything on the boat unless it fails or no longer does the job we need it to do.
We are well aware of the repuation of these AC/DC units and while it may die tomorrow we attribute its long life to the fact that from the day we took delivery of the boat the Norcold has never been turned off. Even when the boat is in the yard for painting, the groundpower cable is still hooked up.
We like the AC/DC capabilites because at the dock should the AC fail the refrigerator will not switch over to DC and run the batteries down thus depriving the boat of power for the bilge pump which Murphy's law says that we would need at that very moment. (We turn off the DC breaker for the refrigerator when the boat is in its slip, that's why it won't switch over).
When we're using the boat we switch the Norcold over to DC which means we don't have to have the inverter going in addition to the refrigerator. Our boat has a generator so we can throw a charge back into the batteries when needed.
So we like the flexibility an AC/DC refrigerator/freezer gives us. It works well with our boat's very simple and basic electrical system. Other people prefer all AC or all DC. It's just a matter of preference, the boat's electrical system, and how one uses the boat.
I totally agree the AC/DC Norcold is not particularly efficient compared to what's available today. But we see no advantage in replacing it at this point since it still insists on working properly. The higher power draw has not been a problem for us so far, even on our longer cruises to Desolation Sound and the like. Given my schedule that limits us to only one longer cruise a year and the fact that on these cruises we rarely spend more than a couple of days at any one remote location, the main engines are running almost every other day if not every day. Plus we have the 7.5kw generator. So battery power has never been an issue for us so far.
The same is true for the two and three day cruises we take throughout the rest of the year.
The Isotherm we would replace the Norcold with is also AC/DC but it uses a Danfoss compressor and it's much more efficient than the Norcold with it's odd little self-inverted AC unit.
The same is true for the two and three day cruises we take throughout the rest of the year.
The Isotherm we would replace the Norcold with is also AC/DC but it uses a Danfoss compressor and it's much more efficient than the Norcold with it's odd little self-inverted AC unit.
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jeffnick
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If we all believed we should do it because that's the way it's done there would be little progress and no fun. Besides, no 2 of us do the same kind of boating...should we all boat the same because we have the identical specified AC/DC fridge. Well, I think not and part of the fun is seeing what works best for me. I can't boast that I have a 'better' marine fridge, but my $160 chest freezer, brine brick and remote line thermostat are not only making me happy, but providing unlimited flexibility and entertainment.
It's funny that when we're growing up we are told that we are individual, different and special. Then as we get older our doctors, preachers, and everyone else want us to be identical...in the way you act, your weight - blood pressure and chemistry, the way you drive, what you eat, how much you save for retirement.
If you want to be a sheep, fine. I prefer life with a little more excitement.
It's funny that when we're growing up we are told that we are individual, different and special. Then as we get older our doctors, preachers, and everyone else want us to be identical...in the way you act, your weight - blood pressure and chemistry, the way you drive, what you eat, how much you save for retirement.
If you want to be a sheep, fine. I prefer life with a little more excitement.
Reply to Tom at Post #7: tom, our voltage drop was caused by long cable runs from battery to circuit breaker panel to fridge and a too-small cable diameter, not by an issue with the battery itself. Running a larger cable a shorter overall length direct to the fridge moved the volts back up substantially. The Danfoss compressor, which is a great piece of kit, is nevertheless very voltage sensitive.
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Reply to Ron at Post #14: Ron, I can assure you that modern household fridges are better insulated than most marine types. First, just take a look at their comparitive wall & door thicknesses. Second, a quote from the refrigeration section of Victron's 'Energy Unlimited' book (available on their website) and directed at cruising recreational vessels: "The benchmark for energy consumption is standard household equipment, which now has excellent insulation........If permanent AC power from an inverter is available anyway, it is certainly advisable to install a standard household refrigerator and freezer'.
We have two fridges installed: an Isotherm marine fridge/freezer that was auto-sensing and is now direct-connected to the battery and so DC-only; and as described previously, is boosted by a computer fan in hot weather; and a domestic under-counter 'bar fridge', used mainly for keeping drinks cold, that is AC-driven and supplied by the inverter when we are offshore. Both work well and I think what works best for a given vessel is mainly about battery bank size and inverter quality. I also agree it has to look good !...so no velcro strips to secure doors !!
We have two fridges installed: an Isotherm marine fridge/freezer that was auto-sensing and is now direct-connected to the battery and so DC-only; and as described previously, is boosted by a computer fan in hot weather; and a domestic under-counter 'bar fridge', used mainly for keeping drinks cold, that is AC-driven and supplied by the inverter when we are offshore. Both work well and I think what works best for a given vessel is mainly about battery bank size and inverter quality. I also agree it has to look good !...so no velcro strips to secure doors !!
