Just installed A.C. powered refrigerator components to convert my ice box. works great at the dock, but my inverter trips off when I try to run it from 12 volts. The refrigerator plate says it draws only 70 watts, and I figure the start up current might be 3 or 4 times that. My inverter is a Heart Interface with a capacity of 300 watts continuous and 600 watt surge capacity. Heart has been no help. Anyone have a similar problem using an inverter?
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Amp tester!
Ed: Electricians have these testers that they can put around a wire to test the amount of draw on a line. Maybe you can beg, borrow or steal one to test your setup at the dock. This may give you a better idea of what is really happening with the power that you are going to required. To be honest a 300 watt inverter sounds a little wimpy. If this is not direct wired (not a cigarette lighter plug), I doubt that you are getting the full rated power either.
Ed: Electricians have these testers that they can put around a wire to test the amount of draw on a line. Maybe you can beg, borrow or steal one to test your setup at the dock. This may give you a better idea of what is really happening with the power that you are going to required. To be honest a 300 watt inverter sounds a little wimpy. If this is not direct wired (not a cigarette lighter plug), I doubt that you are getting the full rated power either.
E
ED
Steve D
Steve - I tried hard wiring it in, but it made no difference. I used a meter with a 2 amp max at 120 volts and blew the fuse at start-up on AC current, so all I know is that the load is over 240 watts, which does not tell me much. I am going to try to meter the load, but I can't believe that the little compressor draws 600 watts at start up - but maybe it does.
Steve - I tried hard wiring it in, but it made no difference. I used a meter with a 2 amp max at 120 volts and blew the fuse at start-up on AC current, so all I know is that the load is over 240 watts, which does not tell me much. I am going to try to meter the load, but I can't believe that the little compressor draws 600 watts at start up - but maybe it does.
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Yves Langlois
Peak current draw
Anytime you have a motor in an electrical circuit, you have to be very careful about the amperage capacity of the circuit. Any electric motor ( as you have with a compressor) will draw on startup an incredible amperage for a few micro seconds, your calculation are base on 3 to 4 time the running AMPs, you better double that figure and then add some. In a standard electrical circuit, you could use a slow blow fuse or breaker. With and inverter it's just that the power is not there. Yves S/V OPIUM
Anytime you have a motor in an electrical circuit, you have to be very careful about the amperage capacity of the circuit. Any electric motor ( as you have with a compressor) will draw on startup an incredible amperage for a few micro seconds, your calculation are base on 3 to 4 time the running AMPs, you better double that figure and then add some. In a standard electrical circuit, you could use a slow blow fuse or breaker. With and inverter it's just that the power is not there. Yves S/V OPIUM
Ed, now I'd try a larger inverter.
Ed: I think I'd try to get ahold of a larger inverter just to try it. Most os these bar reefers are made overseas and the QC may not be as good as we would like to believe. If you use a 1000 watt inverter and it does not wrk then you probably should get an electrician. If you find that a 1000 watt inverter handles it, then you need to decide is you really can carry enough battery power on board to run it this way.
Ed: I think I'd try to get ahold of a larger inverter just to try it. Most os these bar reefers are made overseas and the QC may not be as good as we would like to believe. If you use a 1000 watt inverter and it does not wrk then you probably should get an electrician. If you find that a 1000 watt inverter handles it, then you need to decide is you really can carry enough battery power on board to run it this way.
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Richard Owen
The numbers don't work
From my experience, the math doesn't work when you are dealing with the stated ratings for inverters. For example, we have a DC fridge which draws 70-80 amps (DC) when running, so a max of 960 watts, right? When the batteries were fully charged, it would start and run sometimes on a 2000 watt inverter. Even with the engine running, it would sometimes not start and sometimes start and then shut down the inverter. We changed to a 2500 and have had no problems. I think the answer is a larger inverter because I believe that the usable power in real life conditions is much less than what they are rated at. IMHO
From my experience, the math doesn't work when you are dealing with the stated ratings for inverters. For example, we have a DC fridge which draws 70-80 amps (DC) when running, so a max of 960 watts, right? When the batteries were fully charged, it would start and run sometimes on a 2000 watt inverter. Even with the engine running, it would sometimes not start and sometimes start and then shut down the inverter. We changed to a 2500 and have had no problems. I think the answer is a larger inverter because I believe that the usable power in real life conditions is much less than what they are rated at. IMHO
K
ken
to richard on fridge
richard drawing 70-80 amps for a total of 960 watts does not add up ,I think you mean 7-8 amps draw and total of 960 watts. KEN
richard drawing 70-80 amps for a total of 960 watts does not add up ,I think you mean 7-8 amps draw and total of 960 watts. KEN
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Stirling Hasen
don't give an amp
Electric Motors draw infinite amperage at the nanosecond of starting up (dead short), and taper off from there as they come up to speed. That is why they put Capacitors in the circuit to help out the physics of it. (Big AC Motors like on a Air compressor etc.) Volts * Amps = Watts 1 amp at 12 Volts = 12 Watts 1 Amp at 120 Volts = 120 Watts etc. 80 Amps at 12 volts = 960 Wats (previous post was fine in the math dept.) Anyways 70 watts seems a little low for a Fridge? Here's an Idea Why can't Marine Air Conditioner and Refrig manufactures manufacture a centripetal clutch to unload the compressor motor and give it a chance to come up to speed before kicking in the load (which increases the amperage) If they did that, the startup power required would be alot less!!! (but it would be more complex and prone to mechanical breakdown. (Catch 22)
Electric Motors draw infinite amperage at the nanosecond of starting up (dead short), and taper off from there as they come up to speed. That is why they put Capacitors in the circuit to help out the physics of it. (Big AC Motors like on a Air compressor etc.) Volts * Amps = Watts 1 amp at 12 Volts = 12 Watts 1 Amp at 120 Volts = 120 Watts etc. 80 Amps at 12 volts = 960 Wats (previous post was fine in the math dept.) Anyways 70 watts seems a little low for a Fridge? Here's an Idea Why can't Marine Air Conditioner and Refrig manufactures manufacture a centripetal clutch to unload the compressor motor and give it a chance to come up to speed before kicking in the load (which increases the amperage) If they did that, the startup power required would be alot less!!! (but it would be more complex and prone to mechanical breakdown. (Catch 22)
E
ED
Stirling amps
I agree that 70 watts sounds low - the nameplate also says 1 amp at 115 volts, so whichever is right, I would still not be drawing very much . In regard to the post with a refrigerator pulling 960 watts, seems to me to be way too high - the typical boat battery would only feed the thing for an hour or so. That wattage is that of a 1-1/4 HP motor - the size used in a small air conditioner. Thanks to all for the responses.
I agree that 70 watts sounds low - the nameplate also says 1 amp at 115 volts, so whichever is right, I would still not be drawing very much . In regard to the post with a refrigerator pulling 960 watts, seems to me to be way too high - the typical boat battery would only feed the thing for an hour or so. That wattage is that of a 1-1/4 HP motor - the size used in a small air conditioner. Thanks to all for the responses.
R
Richard Owen
Answer to Ed and Ken re: 960 watts
First, as Stirling Hansen said, the math is right. 80 amps at 12 volts is 960 watts. At 120 volts it is 7-8 amps, but the significant number on a 12 volt system is 960. Second, it is a big draw, but with approximately 800 A/HRS of battery (400 useable) I can actually run that fridge for 5 hours before having to re-charge. The fact is the fridge runs about every 3 hours for about 15 minutes, so the daily draw is about 2 hours running, or 140-160 A/HRS. We will usually re-charge once a day - if the sailing is good that means we run the genset for an hour and when that's added to the usual bit of diesel power, we will get to somewhere around -50 A/HRS. the next day's use will run it to somewhere around -200. On the last trip, I found that we could run the genset with the diesel and get a full 130 amps into the battery bank. Of course, if we decide that we want to conserve more, we can do it quite easily by adding a bit more ice and watching the other power draws close (like, no movies). It works very well. We were out for 16 days last trip and never hooked up to shore power once. Sorry for the ramblings. ROwen
First, as Stirling Hansen said, the math is right. 80 amps at 12 volts is 960 watts. At 120 volts it is 7-8 amps, but the significant number on a 12 volt system is 960. Second, it is a big draw, but with approximately 800 A/HRS of battery (400 useable) I can actually run that fridge for 5 hours before having to re-charge. The fact is the fridge runs about every 3 hours for about 15 minutes, so the daily draw is about 2 hours running, or 140-160 A/HRS. We will usually re-charge once a day - if the sailing is good that means we run the genset for an hour and when that's added to the usual bit of diesel power, we will get to somewhere around -50 A/HRS. the next day's use will run it to somewhere around -200. On the last trip, I found that we could run the genset with the diesel and get a full 130 amps into the battery bank. Of course, if we decide that we want to conserve more, we can do it quite easily by adding a bit more ice and watching the other power draws close (like, no movies). It works very well. We were out for 16 days last trip and never hooked up to shore power once. Sorry for the ramblings. ROwen
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