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Old 10-19-2015, 07:17 PM   #1
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inverter installation

Gentlemen, I have a 99 HR 32' Admiral which I have converted to 50 amp. I wish to supply current to a 18 cf Sears refrigerator that I have installed. It draws 6 amps at startup and runs on3 amps. according to the Sears Tech. I have a large (1) battery, largest cranking amp I could find at Walmart. I have two inverters, a 750/1500 watt and a 2000/4000 watt. Can I run the fridge on the one battery, can I use the small inverter. My idea is to connect to the battery with proper size cables,inline fuse, mount the converter in the storage unit adjacent to the battery location (separate) and use a heavy extension to the refrigerator. I would only use when traveling without generator and for a period of 6-7 hours. Thanks for any input

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Old 10-19-2015, 08:16 PM   #2
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Are your inverters modified sine - or pure sine ? Pure sine is better, motors don't like modified sine and usually run hot or not at all.....

1 battery won't run your fridge for long. In addition it sounds like you bought an automotive starting battery- instead of a deep cycle type. Starting batteries are not made for the use you intend. They will not be able to deliver current as long, and will be permanently damaged by the repeated deep discharge/charge cycles.

You should purchase 2 golf cart 6 volt batteries, and wire them in series to deliver 12 volts to the inverter. Golf cart batteries are made for heavy duty service, and will perform best with an inverter.

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Old 10-19-2015, 08:24 PM   #3
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If I read your post correctly your only going to run the inverter while driving from park to park. If this is the case your alternator will take care of the current draw of the inverter. Battery won't really be doing much. So no worried about it not being deep cycle. Lots of freg motor running on MSW inverters as long as it's not a cheap one.
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Old 10-19-2015, 08:27 PM   #4
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Wellll - - It will work but you will not have much cushion of time. Your 12V drain is 10 times the 3amp 120VAC drain or 30amps DC. This should not be a problem while traveling since I assume that your engine alternator should be able to supply that amount of current. However without the engine running it's a different story. I would be reluctant to run at night with the additional drain of headlights and other drains unless you have a high capacity alternator.

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Old 10-19-2015, 08:31 PM   #5
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Yeah, my thinking was the current draw was small enough that the battery would not be greatly affected. Will the 750/1500 watt be enough to get the compressor going?
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Old 10-19-2015, 08:35 PM   #6
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Deep cycle batteries last longest if you don't discharge them below 50% capacity but they can be used down to 20% but it shortens the battery life. Going below 20% guarantees very short battery life. Your refrigerator application will use 3 Amp-hours per hour worst case. So for the fridge part of the load you don't need huge 200 Amp Hour golf cart batteries, like the big motor coaches have. Even two 35 or 36 Amp Hour batteries would cover it. That size costs about $ 75 each. Or you could go with one 100 Amp Hour Marine Battery, that costs about $ 100, and your connections will be simpler. Note that with your 2nd Inverter, depending on what you are going to do with it, you may need a lot more than 100 Amp Hours ( of which only 50 AH is usable for longest battery life ) of power storage.

Also note that somewhere below 50% of power storage remaining your inverters will hit low voltage shutdown, so designing your system to only use the top 50% of battery stored powered is good for that reason, too.
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Old 10-19-2015, 08:46 PM   #7
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Yes, you can use the 750 watt inverter.

3 amps 120 volts = 360 watts.

The inverter will be drawing 36 amps, 12 volts DC.

If it runs 1/2 the time, it will use 18 Amp Hours.

Your alternator should keep up with the draw.

Guessing a 120 AH battery, (1/2 usable) it should be able to run the fridge for 3 or 4 hours, without any charging source.

As others have suggested, get a deep cycle 12 volt or a pair of GC2, 6 volt batteries.
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Old 10-19-2015, 08:51 PM   #8
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Your refrigerator probably has a few issues. Make sure the auto defrost is turned off when traveling or the power drain can go a lot higher.

At 6 Amp 120 VAC your power budget is 720 watts for the refrigerator. That does not need big wire on the refrigerator side. One the inverter input you have a bit of a different story, 30 amps or so going in takes bigger wire. You also need a pure sine inverter for a motor driven compressor or you are asking for a failure. I would use a dedicated inverter for the fridge so I could use it by itself. YMMV.

As people pointed out, really wrong battery. You can run it if you want then replace it when it dies or try to do something else. NEVER buy a battery rated in Cold Cranking Amps for a deep cycle application no matter how much the salesman lies. Your question is how many amp hours are you storing. At 30 Amp draw for the refrigerator you will need 30 x how ever many hours = amp hour capacity or watts. Same thing in this application so it is a question of how the battery is rated. Then figure in 50% maximum discharge if you want reasonable battery life so double what you computed. In your case 30 amp x 6 hours x 2 = 360 watts or amp hours rating on the battery. Forget CCA, that's maximum short term current.

Your alternator will help assuming that you have a system for charging the house battery while driving. I would not assume it will do the whole job as it also has other loads to supply. You might get away with what you have for a while depending on how much you travel. Years if you only move twice a year. Maybe months if you move every 3 days. If you do not have the right inverter and need to buy a new one a 1000 watt will run the refer and tv with a bit of margin for cell phone charging, etc. Forget the microwave, coffee pot or hair dryer on the inverter. Good luck. ;-)
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Old 10-19-2015, 09:02 PM   #9
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Thanks to each of you for your insight. Appears to be a little more than i envisioned. Back to the drawing board
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Old 10-19-2015, 09:24 PM   #10
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Originally Posted by powercat_ras View Post
Your refrigerator application will use 3 Amp-hours per hour worst case. So for the fridge part of the load you don't need huge 200 Amp Hour golf cart batteries, like the big motor coaches have .
Your calculation leaves out the conversion of 120 volts to 12 volts. That increases the amp draw 10 times. 3 amps 120 volts becomes 30 amps 12 volts.
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Old 10-20-2015, 09:37 PM   #11
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You can go down the road with no power to the refer for your 7-8 hours as long as you don't open and close the refer. I have gone 20 hours without power because of a transfer switch fault. The freezer portion was still below freezing and the box portion was in the high 30's

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