I have a '98 h450 with the Grunert 110v refer/freezer with holding plates. Per Grunert, It should draw aboutu 7.5 amps AC including the water pump while running, although it sometimes draws as "little" as 6. I have a balmar 80 amp alternator and two 8d gel cell house banks, which I always run together (battery combiner switches "on). They, and I assume the starter battery, are charged through a Freedom 100 amp, 2000 Watt charger/inverter. What I can't figure out is why the compressor draws down my batteries when I am steeming at 2800 RPMs. I thought the fridge would run off the charger/inverter, which should be drawing power from the alternator while the motor is running. Any thoughts would be appreciated. Thanks, Jim
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Isn't also 12vdc?
Jim: Isn't you unit also 12vdc? Why arent' you running it off the DC all the time. I have never understood the value of a unit that ran off of 110vac for a boat. Assuming that you have a battery charger that is plugged into shore power, it will keep your batteries charged and keep you beer cold too!
Jim: Isn't you unit also 12vdc? Why arent' you running it off the DC all the time. I have never understood the value of a unit that ran off of 110vac for a boat. Assuming that you have a battery charger that is plugged into shore power, it will keep your batteries charged and keep you beer cold too!
The Alternator is .....
charging the starting battery. When the motor is running the voltage of that battery should be over 13.8 volts. If the combiner is working properly the voltage of the house bank should be up well over 13 volts. Check it with a voltmeter. If it is below 13v check the wiring or replace the combiner. The inverter charger only charges when you are connected to shore power. Your hose bank need to be tied to the starter battery through a switch or combiner to have the diesel alternator charge them and keep the beer cold
charging the starting battery. When the motor is running the voltage of that battery should be over 13.8 volts. If the combiner is working properly the voltage of the house bank should be up well over 13 volts. Check it with a voltmeter. If it is below 13v check the wiring or replace the combiner. The inverter charger only charges when you are connected to shore power. Your hose bank need to be tied to the starter battery through a switch or combiner to have the diesel alternator charge them and keep the beer cold
DC vs AC
You need to realize that 7.5 amps at 120volts AC is the equivalent th 75 amps at 12 volts. Factor in the effeciency of an inverter at about 90% and your fridge is drawing more power than your alternator can produce. Also the freedom inverter is a modified sine wave, not a true sinewave inverter. Therefore, electric motor effeciency goes down even more. Probably down around to 70-75% effeciency when running on the inverter. Single phase AC is not a very effecient power source for an electric motor. Alternators don't like to run at maximum output all the time. Choices, Install a bigger alternator, convert to DC, or better yet, run another compressor off the engine in parallel with the existing compressor. That way you have reefer when at dock, and when the engine is running.
You need to realize that 7.5 amps at 120volts AC is the equivalent th 75 amps at 12 volts. Factor in the effeciency of an inverter at about 90% and your fridge is drawing more power than your alternator can produce. Also the freedom inverter is a modified sine wave, not a true sinewave inverter. Therefore, electric motor effeciency goes down even more. Probably down around to 70-75% effeciency when running on the inverter. Single phase AC is not a very effecient power source for an electric motor. Alternators don't like to run at maximum output all the time. Choices, Install a bigger alternator, convert to DC, or better yet, run another compressor off the engine in parallel with the existing compressor. That way you have reefer when at dock, and when the engine is running.
Thanks for Replies
Steve - The unit is 110 only. Couldn't agree more that Hunter had their heads someplace dark when they made that decision on a "cruising" or any other type of boat meant to leave the dock. Daryl - Someone suggested that I need to turn off the starter battery while underway because once that is topped off, charging power to all three banks will be decreased to a trickle regardless of the needs of the house batteries. Don't know if this is true. Either way a voltage test seems to be in order. Ruedi - I didn't realize the efficiency loss was so great. However that still should provide a 55-amp output, leaving a substantial battery bank to cover the other 30-or-so DC amps needed to make up the difference. Again, sounds like it's time for the multimeter and possibly a largere alternator. Thanks for your input! Jim
Steve - The unit is 110 only. Couldn't agree more that Hunter had their heads someplace dark when they made that decision on a "cruising" or any other type of boat meant to leave the dock. Daryl - Someone suggested that I need to turn off the starter battery while underway because once that is topped off, charging power to all three banks will be decreased to a trickle regardless of the needs of the house batteries. Don't know if this is true. Either way a voltage test seems to be in order. Ruedi - I didn't realize the efficiency loss was so great. However that still should provide a 55-amp output, leaving a substantial battery bank to cover the other 30-or-so DC amps needed to make up the difference. Again, sounds like it's time for the multimeter and possibly a largere alternator. Thanks for your input! Jim
Opt for replacement.
Personally I would replace the refrigeration. I have both, an AC dorm fridge and a 12 volt A/B in my original H37C icebox. But my dorm fridge only draws one amp, about 9 amps DC. And I can easily run both, all the time, with my 300 amp-hours and 55 amp alternator. I also have the Freedom 20 inverter/charger. I think that you can keep the waterpump and add a 12 volt Adler/Barbour water-cooled unit. You could also install a Link 2000. It is absolutely the best way to keep tabs on the batteries and charging.
Personally I would replace the refrigeration. I have both, an AC dorm fridge and a 12 volt A/B in my original H37C icebox. But my dorm fridge only draws one amp, about 9 amps DC. And I can easily run both, all the time, with my 300 amp-hours and 55 amp alternator. I also have the Freedom 20 inverter/charger. I think that you can keep the waterpump and add a 12 volt Adler/Barbour water-cooled unit. You could also install a Link 2000. It is absolutely the best way to keep tabs on the batteries and charging.
jim,
It's not that the inverter is that ineffecient, its simple electric math. What remains constant is how many watts you are using. Watts is how you measure electrical power, not amps. Amps is simply the rate of current flow. Watts = amps x volts. So your fridge uses 900 watts of power 900 =7.5amps x 120volts. 900 = 75amps x 12 volts
It's not that the inverter is that ineffecient, its simple electric math. What remains constant is how many watts you are using. Watts is how you measure electrical power, not amps. Amps is simply the rate of current flow. Watts = amps x volts. So your fridge uses 900 watts of power 900 =7.5amps x 120volts. 900 = 75amps x 12 volts
Too much power for fridge
I don't know if a fridge/freezer would draw 7.5A from 110VAC power. It's more than one horse power. Compare to household fridge/freezer it is almost draw nearly twice more current. To turn off start battery during underway otherwise charging current would drop to trickle is totally false.
I don't know if a fridge/freezer would draw 7.5A from 110VAC power. It's more than one horse power. Compare to household fridge/freezer it is almost draw nearly twice more current. To turn off start battery during underway otherwise charging current would drop to trickle is totally false.
Amps in and out
If your unit is pulling 75 amps at 12 volts, and the compressor runs 50% of the time, you should not be having a discharge problem over time. The inverter would pull an average of 37.5 amps from the batteries in an hour while your alternator should supply more than that to the batterries. You may see a discharge condition when the compressor is actually running, but the your bank is being charged when it is not, assuming your alternator is putting out somwhere its rated capacity.
If your unit is pulling 75 amps at 12 volts, and the compressor runs 50% of the time, you should not be having a discharge problem over time. The inverter would pull an average of 37.5 amps from the batteries in an hour while your alternator should supply more than that to the batterries. You may see a discharge condition when the compressor is actually running, but the your bank is being charged when it is not, assuming your alternator is putting out somwhere its rated capacity.
Doesn't make sense...
when out power went out during the hurricane(s) here in Fort Lauderdale, we ran a power cord to our home fridge from our boat in the canal to power it enough to keep everything from spoiling.. the Link monitor only showed about 20amps.... which is about 240 watts... I can't imagine that a much smaller fridge without an icemaker etc is using 750 watts or better... Brian
when out power went out during the hurricane(s) here in Fort Lauderdale, we ran a power cord to our home fridge from our boat in the canal to power it enough to keep everything from spoiling.. the Link monitor only showed about 20amps.... which is about 240 watts... I can't imagine that a much smaller fridge without an icemaker etc is using 750 watts or better... Brian
Grunert is a great system
We have a 460 with the same Grunert and its a great system. However, we have the optional 135 Amp Alternator which may solve your problems. I would check your batteries, and alternator. Also make sure the house battery selector switch for the Inverter (rotary switch) is on Both.
We have a 460 with the same Grunert and its a great system. However, we have the optional 135 Amp Alternator which may solve your problems. I would check your batteries, and alternator. Also make sure the house battery selector switch for the Inverter (rotary switch) is on Both.
Need More Umph (Amps)
Periodically when cruising I am forced to run my Grunert on the inverter when the generator craps out and I also see decreasing amps from the batteries. I have the standard alternator but have also installed 550w of solar power on the hard top bimini and that helped. Previous poster was very correct on the decrease in efficiency when running off the inverter (loss through inverter and loss due to modified sine wave which the compressor doesn't particularly like). Suggest you add some solar or a large alternator. Remember, though, that those alternators decrease output with increase in temperature.
Periodically when cruising I am forced to run my Grunert on the inverter when the generator craps out and I also see decreasing amps from the batteries. I have the standard alternator but have also installed 550w of solar power on the hard top bimini and that helped. Previous poster was very correct on the decrease in efficiency when running off the inverter (loss through inverter and loss due to modified sine wave which the compressor doesn't particularly like). Suggest you add some solar or a large alternator. Remember, though, that those alternators decrease output with increase in temperature.
a few questions/answers
There's no way your fridge is pulling 75 amps, ,so let's get rid of that notion right now. No boat system, other than maybe your anchor windlass and starting system are pulling anyting close to this. If it were true, you'd need #2 guage or lower wiring just to handle the amperage. I'm guessing you don't. I'd agree that your rep was close to accurate, around 20 amps max. Forget about wattage. ALthough it's important for some calculations, it irrelevant here. Wattage is a measure of work, or "horsepower." The real concern is draw on your batteries, which is a function of amperage. There is no REAL constant in your system, as everything varies depending on the other. As voltage goes down, amps reduce, reducing effective work, or wattage. We make assumptions based on a constant 12v or 24v DC and 110vAC(sometimes 120vAC). So let's ask a few questions here..... What happens if you increase the RPM? If your batteries hold longer, than your alternator is not putting out enough amps to replenish your system under load... look for a bigger alternator, or more efficient fridge. It is possible that your starting battery is shutting down your charger. If you haven't installed one, look at a multi bank regulator for your alternator, and verify your chargers programming. It may be possible to change settings to charge longer before reverting to "trickle". I don't know your charging system, and would consult with the manufacturer. I did notice that you run starting and house batteries together. this is not necessarily the best option. A combiner would put the two banks together for charging, then separate for non charging use. I'm sure this will spark some discussion into electrical theory, but remember that there are exceptions to the basic rules depending on the application. For example and solar panel is rated in watts, or the ability of the unit to perform work. This is because the applications vary. The amount of usefulness is determined by the system is used in, example a 12V DC system can expect, on a perfect day, with perfect connections, and perfectly maintained batteries,that a 500watt solar panel will provide 41 Amps over a set period of time. Not all at once, nor will you get the full amount in a day. We make assumptions for camparisons and estimates. Don't fall into this trap. Consult your mfg reps for details on your fridge, answer the question of RPM affecting your charging, and go from there. Good luck
There's no way your fridge is pulling 75 amps, ,so let's get rid of that notion right now. No boat system, other than maybe your anchor windlass and starting system are pulling anyting close to this. If it were true, you'd need #2 guage or lower wiring just to handle the amperage. I'm guessing you don't. I'd agree that your rep was close to accurate, around 20 amps max. Forget about wattage. ALthough it's important for some calculations, it irrelevant here. Wattage is a measure of work, or "horsepower." The real concern is draw on your batteries, which is a function of amperage. There is no REAL constant in your system, as everything varies depending on the other. As voltage goes down, amps reduce, reducing effective work, or wattage. We make assumptions based on a constant 12v or 24v DC and 110vAC(sometimes 120vAC). So let's ask a few questions here..... What happens if you increase the RPM? If your batteries hold longer, than your alternator is not putting out enough amps to replenish your system under load... look for a bigger alternator, or more efficient fridge. It is possible that your starting battery is shutting down your charger. If you haven't installed one, look at a multi bank regulator for your alternator, and verify your chargers programming. It may be possible to change settings to charge longer before reverting to "trickle". I don't know your charging system, and would consult with the manufacturer. I did notice that you run starting and house batteries together. this is not necessarily the best option. A combiner would put the two banks together for charging, then separate for non charging use. I'm sure this will spark some discussion into electrical theory, but remember that there are exceptions to the basic rules depending on the application. For example and solar panel is rated in watts, or the ability of the unit to perform work. This is because the applications vary. The amount of usefulness is determined by the system is used in, example a 12V DC system can expect, on a perfect day, with perfect connections, and perfectly maintained batteries,that a 500watt solar panel will provide 41 Amps over a set period of time. Not all at once, nor will you get the full amount in a day. We make assumptions for camparisons and estimates. Don't fall into this trap. Consult your mfg reps for details on your fridge, answer the question of RPM affecting your charging, and go from there. Good luck
It does draw 80 amps per hour
millham39 of South Portland wrote in reply #12 " a few questions/answers There's no way your fridge is pulling 75 amps, ,so let's get rid of that notion right now. No boat system, other than maybe your anchor windlass and starting system are pulling anyting close to this." I don't like telling someone that they are absolutely wrong, beyond the shadow of a doubt.... etc. etc. but this time you are. So, face that fact. I had the same refridgeration system on my hunter 460 for 5 years. I hated the fridge. Whenever it was on, it would draw at the consistent rate of 80 - 90 amphrs per hour. If a search on the 450 460 refridgeration is done in the archives, I think that many hits will show up. I certainly contributed to some of them. A refridgeration technitian also confirmed the 75- 80 amp per hour draw of this system. The freezer might run the better part of an hour just to cool the plate. The fridge flat evaporator plate would run only a few minutes every hour. The total DC draw from this fridge, as I recall it, was in excess of 300amps in a 24 hour period. When we took delivery of the boat, the sensing tube was not properly attached to the freezer holdover plate. The freezer was running about 75% of the time. We did a 10 hour engine run through the welland canal at about 2000 rmp and could not keep our batteries charged even with the high output alternator option. The only way we kept the batteries charged was by running the generator. We eventually overrode the freezer thermostat so that we could control when that section came on. The freezer is the hardest draw on the system. By controlling its running time, we would always run the freezer side, while the generator was running. I could not imagine running this refridgeration unit without having a generator on board. This year we finally ripped out the AC system and replaced it with a DC system. The plates and water pumps were both replaced. Good luck. Sorry for starting off on such an offensive note, but this was the absolute worst part of owning our boat. Warren
millham39 of South Portland wrote in reply #12 " a few questions/answers There's no way your fridge is pulling 75 amps, ,so let's get rid of that notion right now. No boat system, other than maybe your anchor windlass and starting system are pulling anyting close to this." I don't like telling someone that they are absolutely wrong, beyond the shadow of a doubt.... etc. etc. but this time you are. So, face that fact. I had the same refridgeration system on my hunter 460 for 5 years. I hated the fridge. Whenever it was on, it would draw at the consistent rate of 80 - 90 amphrs per hour. If a search on the 450 460 refridgeration is done in the archives, I think that many hits will show up. I certainly contributed to some of them. A refridgeration technitian also confirmed the 75- 80 amp per hour draw of this system. The freezer might run the better part of an hour just to cool the plate. The fridge flat evaporator plate would run only a few minutes every hour. The total DC draw from this fridge, as I recall it, was in excess of 300amps in a 24 hour period. When we took delivery of the boat, the sensing tube was not properly attached to the freezer holdover plate. The freezer was running about 75% of the time. We did a 10 hour engine run through the welland canal at about 2000 rmp and could not keep our batteries charged even with the high output alternator option. The only way we kept the batteries charged was by running the generator. We eventually overrode the freezer thermostat so that we could control when that section came on. The freezer is the hardest draw on the system. By controlling its running time, we would always run the freezer side, while the generator was running. I could not imagine running this refridgeration unit without having a generator on board. This year we finally ripped out the AC system and replaced it with a DC system. The plates and water pumps were both replaced. Good luck. Sorry for starting off on such an offensive note, but this was the absolute worst part of owning our boat. Warren
DC experience
The DC unit was installed at the end of the season. Unfortunately, at this time, I only have expectations. No real experience. I need to get through a warm summer first. What I can say however, is that the DC system has 2 separate compressors and water pumps. They are switchable as to water and or air cooled. Each compressor draws about 4 - 5 amps dc. There are now 2 holdover plates. One in the fridge and the other in the freezer. Assuming that they each run 50% of the time, then, we should consume about 5 amps per hour in total, or about 120 amps per day. Part of the difference in the experience will occur, because at no time will we be drawing 80+ amps per hour from a 400 amp bank. Over the course of 1 hour, almost 1/2 of our useable battery bank would be gone. Until we got control of the freezer and ran it with the genny only, we were afraid to leave the boat at anchor for fear of having no power upon return. However, some have stated that their AC systems have worked well. Ed Shank is not the only one. I was initally advised to look for leaks in the ice box etc. to improve the overall efficiency. This was done and did not help much. Next season, I can report back on real world results. Warren
The DC unit was installed at the end of the season. Unfortunately, at this time, I only have expectations. No real experience. I need to get through a warm summer first. What I can say however, is that the DC system has 2 separate compressors and water pumps. They are switchable as to water and or air cooled. Each compressor draws about 4 - 5 amps dc. There are now 2 holdover plates. One in the fridge and the other in the freezer. Assuming that they each run 50% of the time, then, we should consume about 5 amps per hour in total, or about 120 amps per day. Part of the difference in the experience will occur, because at no time will we be drawing 80+ amps per hour from a 400 amp bank. Over the course of 1 hour, almost 1/2 of our useable battery bank would be gone. Until we got control of the freezer and ran it with the genny only, we were afraid to leave the boat at anchor for fear of having no power upon return. However, some have stated that their AC systems have worked well. Ed Shank is not the only one. I was initally advised to look for leaks in the ice box etc. to improve the overall efficiency. This was done and did not help much. Next season, I can report back on real world results. Warren
Another advantage to going DC
We no longer have to leave the inverter on. The inverter was a freedom 25. It was usually warm and consumed power even when the fridge was not running. Because the new system is DC, we probably save 20 +/- amps per day here too.
We no longer have to leave the inverter on. The inverter was a freedom 25. It was usually warm and consumed power even when the fridge was not running. Because the new system is DC, we probably save 20 +/- amps per day here too.
lets get our facts straight
I apologise if I mis understood the posts here, but lets clarify. 75-80 amp-hours is different than what was being talked about in previous posts, which was 75-80 AMPS. Yes I can beleive 75-80 amp-hours, which is apx 6-7 amps...more in line with what I would expect, and within allowable tolerance for most wiring situations This is why the topic is difficult to talk about, as there are many terms out there that are used incorrectly. I have 18 years as a marine and aircraft electrician/electronics tech. If you feel I have nothing to offer here, so be it. Anyway, I agree with installing a DC, or AC/DC fridge. It solves some of the problems, but I'm still curious about the RPM question.
I apologise if I mis understood the posts here, but lets clarify. 75-80 amp-hours is different than what was being talked about in previous posts, which was 75-80 AMPS. Yes I can beleive 75-80 amp-hours, which is apx 6-7 amps...more in line with what I would expect, and within allowable tolerance for most wiring situations This is why the topic is difficult to talk about, as there are many terms out there that are used incorrectly. I have 18 years as a marine and aircraft electrician/electronics tech. If you feel I have nothing to offer here, so be it. Anyway, I agree with installing a DC, or AC/DC fridge. It solves some of the problems, but I'm still curious about the RPM question.
no offense intended
I did not intend to show disrespect for your experience. It just that the issue is one that I am very sensitive too. Every point of view, right or wrong helps the discussion move along. If you found the earlier posts confusing, I am sure that others did too. Warren
I did not intend to show disrespect for your experience. It just that the issue is one that I am very sensitive too. Every point of view, right or wrong helps the discussion move along. If you found the earlier posts confusing, I am sure that others did too. Warren
Thanks again everyone
Thanks for the additional input everyone. Here are the manufacturer's specs for the Grunert unit in question: Model AC450 w/R404-A refrigerant .5 hp compressor rated at 875 watts 7.7 amp draw combined at 120v for compressor & water pump, which equates to (sorry Millham) in excess of 75 amps DC. I always have both of my house battery banks engaged but I will try turning off the starting battery this weekend to see if that makes a difference. After reading all the sage (and sometimes conflicting) advice you've all been so nice to share, the only thing that makes sense to me is that the starter battery is shutting down the charger (thanks Millham). That would also explain why Warren couldn't keep up with the draw with (I assume) the 135-amp alternator. If that were not the case, even 75% of rated output from my alternator should take enough of the load to keep the batteries from being drawn down so quickly. And I believe 2800 RPMs (80% of max) is what that engine should cruise at so I would hope max alternator output would be at or near that speed. I'll also test the batteries to make sure they are up to spec. If shutting off the start battery doesn't work, the next step is a larger alternator and larger battery bank. the $3k-plus it would take to switch to DC is too rich for my blood at the moment although I'd love to hear what Warren put in his 450 and at what cost. Thanks again for all of your input. Jim
Thanks for the additional input everyone. Here are the manufacturer's specs for the Grunert unit in question: Model AC450 w/R404-A refrigerant .5 hp compressor rated at 875 watts 7.7 amp draw combined at 120v for compressor & water pump, which equates to (sorry Millham) in excess of 75 amps DC. I always have both of my house battery banks engaged but I will try turning off the starting battery this weekend to see if that makes a difference. After reading all the sage (and sometimes conflicting) advice you've all been so nice to share, the only thing that makes sense to me is that the starter battery is shutting down the charger (thanks Millham). That would also explain why Warren couldn't keep up with the draw with (I assume) the 135-amp alternator. If that were not the case, even 75% of rated output from my alternator should take enough of the load to keep the batteries from being drawn down so quickly. And I believe 2800 RPMs (80% of max) is what that engine should cruise at so I would hope max alternator output would be at or near that speed. I'll also test the batteries to make sure they are up to spec. If shutting off the start battery doesn't work, the next step is a larger alternator and larger battery bank. the $3k-plus it would take to switch to DC is too rich for my blood at the moment although I'd love to hear what Warren put in his 450 and at what cost. Thanks again for all of your input. Jim
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