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Catalina/Capri 25/250 Sailor's Forums

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which kind of inverter for microwave?

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Gloss
Master Marine Consultant

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USA
1916 Posts

Initially Posted - 05/22/2005 : 09:58:55

Hi Folks,
Someone in my club asked me a question which I didn't know the answer, but I did know further questions to ask to get to the correct answer.
What kind of inverter to use with a microwave?
I do know that there are three kinds of inverters, from least to most expensive, you have square wave, modified sine wave, and pure sine wave. Each is used for various levels of electrical/electronic protection. I know that you have "what you can get by with", "what is recommended" and "what is best" to use.

I do know that the absolute best is pure sine wave, but is really expensive.

So what is the answer?
Thanks

Frank Gloss
Formerly 89WK/TR
85 Ericson 32-3 shoal draft "Molto Bene"

Edited by - on

Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 05/22/2005 : 10:55:56

As far as I know microvaves are more appliances than electronics, so they are not picky as to the quality of the 110 supply, unlike computers etc. So, the cheap version will do. Having said that, they are also power hogs, so some serious battery power will be required.

Personally I don't like them, and what they do to my food....so I use the stove for heating things. The microwave that came with Lady Kay is used to keep food from predators, and in thunderstorms I put some electronics in there believing that it is a "cage of Farraday" that might protect them from being zapped......

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 05/22/2005 : 11:21:05

If you have only a low-end square-wave inverter, I would hesitate to use that for anything expensive, or with solid state electronics in it. You probably can't hurt a power tool like a drill with a square-wave, but I would not want to risk damaging something like a micrwave oven, portable TV, or laptop computer. One other thing about microwave ovens is that most of them are not very energy-efficient. If the unit is rated, for example, at 600 watts of cooking power, it's input current draw could be almost 1000 watts. You need a BIG inverter to power even the smallest 400 watt microwave ovens, like the itty-bitty 0.4 cubic foot one I use in Quiet Time if I will be staying in a marina with shore power. Inverters themselves are only about 75% energy-efficient, so if your appliance wants to draw 1000 watts at 120 volts A/C (8.3 amps), the inverter will draw 1333 watts from the battery - that's 111 amps at 12 volts! It doesn't take long to draw down a boat's battery with that kind of load on it, and the inverter would need to be connected to the battery with very heavy cables, 6 ga, or maybe even 4 ga. And an inverter that can supply 1000 watts continuous is going to be very large, and quite expensive.

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Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 05/22/2005 : 12:03:45

So based on what Larry is saying, I should talk my friend out of a microwave. Unless of course it is on shore power.

Myself, I don't want a microwave on board anyways. At home, I use it to reheat leftovers, and cook popcorn.

On board, Jiffy Pop (if you can find it in a store) works well on my Origo stove, but you have to shake it a lot so it won't burn.

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Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 05/22/2005 : 13:53:12

I do believe the wattage listed on the appliance is the draw....not the cooking power. It would be illogical to leave the consumer guessing as to how to wire it....conversely it is "accepted practice" to keep said consumer in the dark as to how much bang he's actually getting for his buck...

My nuker is a 1200 watt unit, the inverter is 1500, and yes the cables is a 2 gauge, and the battery a pair of 4D's (200A ea.)

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John V.
Admiral

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USA
559 Posts

Response Posted - 05/23/2005 : 07:54:53

I have a very small 700 watt microwave on board and use a 2000 watt inverter to power it. Two deep cycle 215 AH batteries provide power and even then the draw is almost too much. I use the microwave to heat leftovers, when I am at my own dock an on shore power. I can use the mw if there is a lot of wind and the airX is putting out more than 15 or 20 amps. It mostly provides a place to store boat papers passports and I68 forms. BTW the inverter also powers tools and the laptop ( a much smaller draw) I know most of you are already in the water but for me things are getting close with splash in Lake Superior in about 4 weeks.

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jkittka
Deckhand

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USA
8 Posts

Response Posted - 05/23/2005 : 10:25:08

In talking with the rigger while my boat was being commisioned he suggested going to Home Depot and purchasing a Husky brand inverter. He uses it on his own boat to run a micro and a dorm style refrig. He stated that he can not run both at once but the Husky has the capacity for initial surge and only cost 80$.

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JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 05/23/2005 : 11:05:07

I have a West Marine cheapo 600 watt inverter. It runs my laptop computer just fine with no damage. Also can run my stereo boom-box but you hear a little hum. Charges cell phone. Can run a small home refridgerator.

I believe a 1000 watt invertor would run a small microwave just fine, especially for the short periods. However, the sine wave is essential for clocks. Breadmachines will not work well on a square wave invertor.

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atgep
Master Marine Consultant

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1009 Posts

Response Posted - 05/23/2005 : 21:32:34

Oscar, didn't you "reheat" your gps in the microwave last year???

Tom.

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Bubba
Admiral

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USA
542 Posts

Response Posted - 05/25/2005 : 22:08:13

I was wondering if anyone else remembered that.

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Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 05/26/2005 : 08:41:26

All the brilliance and genius I have to contribute and you guys remember THAT!!!

No I haven't cooked any electronics in there lately....I hide food in there now, for the risk of rodent invaders has proven higher than that of electronic thieves.....

I guessed you guys missed that story....I'll start a separate thread...

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Sloop Smitten
Master Marine Consultant

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USA
1181 Posts

Response Posted - 05/26/2005 : 13:06:53

Stopped by Costco yesterday. They have a 1500W Inverter for $89 that claims to run a 900W Microwave for 30 minutes on a 78 series battery. I think I have all these numbers right. Committing from memory.

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Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 05/26/2005 : 14:13:07

If that's a 100AH battery you could probably do that...

900W at 12v= 75Apms/2= 37.5 plus, say 10% loss in the inverter is 40ish amps, double it so you don't kill your battery...and don't do anything else.........

I think that's all correct....engineers?

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jlguthri
1st Mate

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USA
93 Posts

Response Posted - 05/26/2005 : 21:55:44

I would think 10% inverter loss would be optomistic...

Shoot, contact the tech support of the people who manufactured the microwave... this way, if it lets the smoke out, it will be someone else's fault... esp about if a cheapo square wave inverter will do... one one hand i tend to think of microwaves as fairly 'dumb' appliance, but on the other hand, i don't know much about how they work either...

I wouldn't worry about using squareish wave inverters on laptops, and the such because it gets rectified back to dc anyway...

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