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Inverter Load for Microwave

Old 04-07-2003, 07:01 AM
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Default Inverter Load for Microwave

i just put a 600 Watt inverter on my boat...to power a 600 watt microwave. i've tried running the microwave off the inverter with the engine running, warmed up with the alternator charging (it's a 60 amp alternator). when i turn on the microwave on low to medium power, it runs for about a minute, and then the inverter "fault" light comes on. when i try to run the microwave on high power, it runs for about 10 seconds. this fault light is supposed to be on when either input voltage is too low or when output requirements are too high. i have a meter across the batteries when i am running the microwave and it holds 13.8 volts most of the time, drops to around 12.4 volts when the microwave kicks in every 20 seconds or so. so i don't think the problem is low power input. would it make sense that a 600 watt microwave on low power would be too much load for a 600 watt inverter? i'm running #8 wire up to the inverter, fused at 70 amp ANL fuse, which should be more than enough load. i am going to have a 105 amp alternator put on the boat also.

any thoughts on what it will take to run the 600 watt microwave would be great. is the bigger alternator the problem? do i need a bigger inverter?

thanks.
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Old 04-07-2003, 08:20 AM
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Default Inverter Load for Microwave

The problem has NOTHING to do with your alternator.

Think of this problem like this:

You have to drive 100 miles into the desert and then turn around and come back. Your vehicle gets 10 miles per gallon. Would you take with you exactly 10 gallons of gas into the desert??


Ok, well likewise, you should be using a 600 watt inverter to run a 600 watt apliance. Keep in mind the 600 watt inverter if you read the fine print is rated probably at 300 watts (ussually half) for sustained ussage, and 600 watts max at peak ussage.

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Old 04-07-2003, 09:40 AM
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Default Inverter Load for Microwave

My experience parallels Birdmans. The fault light and alarm seems to turn on when the load is close to the maximum rating of the inverter. My supplier stated that the max useful rating (except for big expensive units) is about 60 to 75% of the listed rating.

A safe continuous duty cycle is about 50% of the inverter's stated capacity.

Thats my experience.

Miss-Be-Haven
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Old 04-07-2003, 10:00 AM
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Default Inverter Load for Microwave

Three quick points:

1) The rating on your microwave is output power. Since the unit is not 100% efficient, it has a greater input power than output power. (See the note above about driving into the desert).

2) I have a 650watt microwave on my boat. It fully "loads up" a ProWatt 1000 inverter. I have size 2 cables feeding the inverter, and it is less than three feet from the battery bank. Loss of voltage at the inverter input will significantly degrade its ability to make rated output.

3) Your battery bank capacity has to be great enough to provide a high level of DC current to the inverter, without the supply voltage dropping off. I have two banks of two Group 24 batteries, and use all four in parallel (ALL on the battery selector switch) when using the microwave.



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Old 04-07-2003, 11:04 AM
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Default Inverter Load for Microwave

Ocn

Excuse me capt for budding in .. Ocn I am putting together a '95 Islander with twin 200 hpdi and while researching electronics on this forum came across some of your posts on how you have yours rigged ( a/c etc.) I am currently reading up on 12v basics but may have some questions for you in the future on some specifics - I will keep them as brief as possible - mind providing me an email where I might reach you ? Mine is rayos@bellsouth.net ( i.e., one question is where did you put the 4 batteries?) Thanks.. and sorry Capt.
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Old 04-07-2003, 11:43 AM
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Default Inverter Load for Microwave

sounds like my suspicions are confirmed, it's most likely the inverter size...going to try the portawattz 1000 and see how that goes...thanks!
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Old 04-07-2003, 12:52 PM
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Default Inverter Load for Microwave

Your inverter is probably rated at 600 VA and not Watts. If you were driving a bunch of light bulbs (resistive) load of 600 watts, it would probably work fine. Once you get into driving inductive loads like microwave magnitrons, motors, etc, it could easily take 1000VA to produce 600 watts of power. It is kind of what they call power factor, and let's leave it there.
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