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Old 03-27-2011, 04:08 PM
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Default Microwave and inverter

Thinking about carrying a small microwave aboard our ocean boat with an inverter to power it. Boat has duel Sears AGM batteries.

Microwave will be stored in a cabinet until needed then set on the counter and used for heating small items such as sandwiches, coffee, soup, burritoes, etc.

Am looking for ideas for an 1,000 watt inverter and am wondering if I can just clip the inverter to a battery and then run the main motor while using the microwave so I do not drain the battery.

Any suggestions for an inexpensive inverter? Does the idea sound reasonable?
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Old 03-27-2011, 04:14 PM
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My brother runs his microwave and refrigerator on his inverter, refrigerator full time when we cruise long distances. You just have to make sure to size the system correctly. A clip on connection won't do it, you need good cables with the right connections properly fastened.
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Old 03-27-2011, 04:23 PM
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First try and find a pure mechanical microwave (timer and power level), it will work better with a MSW inverter (cheaper than pure sine wave). I have used a number of microwaves and inverters. With the Modified Sine Wave, they make more noise and don't heat quite as fast as with a pure sine wave inverter. The two batteries may not be enough. For a 800 watt mechanical microwave and a 1000 watt inverter, I have two group 31's which are dedicated to that and a refrigration system. The microwave will draw down that battery pretty fast--you only have as little as 20 minutes use total of many batteries such as a group 24. You want solid cables and crimped on fittings with heavy cables, (size depends on round trip battery to inverter and ******. Yes it is "doable".
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Old 03-27-2011, 05:16 PM
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Originally Posted by Snowwolfe View Post
Thinking about carrying a small microwave aboard our ocean boat with an inverter to power it. Boat has duel Sears AGM batteries.

Microwave will be stored in a cabinet until needed then set on the counter and used for heating small items such as sandwiches, coffee, soup, burritoes, etc.

Am looking for ideas for an 1,000 watt inverter and am wondering if I can just clip the inverter to a battery and then run the main motor while using the microwave so I do not drain the battery.

Any suggestions for an inexpensive inverter? Does the idea sound reasonable?
Powering a microwave oven from batteries and an inverter is certainly reasonable. I do it on my boat and did it on my previous boat. As for your plan:

The "1,000 watt" rating is cooking power, not power consumption. Look on the label on the back near the power cord. You will find that that 1,000 watt inverter consumes about 1,500 watts so you need at least that much power from your inverter.

An inverter capable of supplying 1,500 watts is going to need a decent sized bank of batteries and the cable to the inverter cannot be "clipped" to the batteries. The inverter must be installed close to the battery bank but it can't be installed in the engine compartment because it is not ignition protected. The cables will be very large and you will need to provide circuit protection to ABYC guidelines.

So - It can be done and is a great convenience on a boat. But, you need to have it done by someone qualified to do marine electrical work. Have that person pick out the inverter and other materials, don't hand him something from Harbor Freight and tell him to install it.
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Old 03-27-2011, 05:50 PM
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Guess it will not be worth the effort but have one last idea.

What about connecting 8 gauge battery jumper cables from one battery to the inverter? And only using the microwave for 5 minutes at a time while the main motor is running and charging the battery?
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Old 03-27-2011, 05:57 PM
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Guess it will not be worth the effort but have one last idea.

What about connecting 8 gauge battery jumper cables from one battery to the inverter? And only using the microwave for 5 minutes at a time while the main motor is running and charging the battery?
For the cost of a good inverter you could get a Honda generator, that would run the micro and charge your batteries at the same time.
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Old 03-27-2011, 06:18 PM
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Originally Posted by Snowwolfe View Post
Guess it will not be worth the effort but have one last idea.

What about connecting 8 gauge battery jumper cables from one battery to the inverter? And only using the microwave for 5 minutes at a time while the main motor is running and charging the battery?
Most likely there will be enough voltage drop that the inverter will shut down.

Before you buy or do anything, look up the inverter installation instructions on the manufacturer's website.
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Old 03-27-2011, 07:02 PM
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For the cost of a good inverter you could get a Honda generator, that would run the micro and charge your batteries at the same time.
I thought of that as well. Own a Yamaha 1000 watt generator we use on the RV when we just want to watch movies. It will power up and run our home microwave so might just take it on a fishing trip and see if it gets in our way or not. It might be the easiest thing to do.

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Old 03-27-2011, 07:21 PM
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1000 watt microwave uses 1500w. At 120v nominal voltage, that appliance uses 12.5amps. Convert that through an inverter, with a 10% power loss(not sure what they actually consume as an inverter), and you are roughly pulling 140 amps out of that battery. With your standard group 24 deep cycle, that will likely only give you about 15 min. of usable juice. At that, using a 10% voltage drop, on a non-critical load, assuming that it is 16' of conductor(8 ft jumper cables, doubled for amperage return to the battery), you need a 1/0 conductor, which will be costly, and very heavy. As it is, 8awg cable only has an ampacity of 100 amps, and if for more than a few seconds, the insulation will go up in smoke, and could catch fire.
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Old 03-27-2011, 07:58 PM
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My brother runs his microwave and refrigerator on his inverter, refrigerator full time when we cruise long distances. You just have to make sure to size the system correctly. A clip on connection won't do it, you need good cables with the right connections properly fastened.
If that refrigerator is a 120/12 volt fridge he would be better off running it on 12 volt and saving his inverter.
My house battery system consist of four six volt battery 210 amp hrs each for a total of 840 amp hrs and I only run my fridge on 120v when I am on shore power,( 3000 watt xantrex inverter), twin 150 amp alternators one dedicated to charging my house the other my starting (two 31series agm).
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Old 03-28-2011, 04:27 AM
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If that refrigerator is a 120/12 volt fridge he would be better off running it on 12 volt and saving his inverter...
Yes, I agree. His refrigerator is 120 volts only. Mine luckily is dual voltage. We have the same boats, his refrigerator failed and the cost for the dual voltage unit was quite a bit more.
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Old 03-28-2011, 06:05 AM
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............ his refrigerator failed and the cost for the dual voltage unit was quite a bit more.
Well yes, it's more complicated. In the end though, on a typical boat that doesn't have a generator running full time, a dual voltage refrigerator is the best solution. Set it and forget it.
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Old 03-28-2011, 07:02 AM
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We have a 26' Glacier Bay Renegade. We intalled a microwave in the head compartment. We purchased a Xantrex Pro Watt 2000 Watt Inverter from West Marine. We ran "00" battery cables about 15' to the battery switch.
It works well. We noticed if we don't have the engines running, we sometimes get the low power "chirp" from the inverter. Especially if we are pulling from one battery only. With the battery selector on "both" we usually are fine. If we need to run the microwave for a while, heating several dishes of food, we run the engines and no problems at all. We also installed an outlet (GFCI protected) next to the rear console for ease of plugging in other appliances.
We installed the inverter ourselves and I believe the cost including the inverter and all wiring and terminals was around $700.00.
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Old 03-28-2011, 07:11 AM
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8 gauge will not cut it. For a 1500 watt inverter I wouldn't go any less than 1/0.

If it draws 10 amps on a 120 AC circuit, it is going to draw at least 100 amps on a 12 volt circut, not counting effeciency losses.
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Old 03-28-2011, 07:21 AM
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We have a 26' Glacier Bay Renegade. We intalled a microwave in the head compartment. We purchased a Xantrex Pro Watt 2000 Watt Inverter from West Marine. We ran "00" battery cables about 15' to the battery switch.
I think the instructions call for no more than 5 feet or so. You may have left this out of your description, but you must have circuit protection within seven inches of the source (in this case, the switch).

There is very little voltage drop in a length of 120 volt wiring. There is a significant drop on the 12 volt side.
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Old 03-28-2011, 07:26 AM
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I don't see where he's looking at a 1,000 watt microwave. He was looking at a 1,000 watt inverter. That would limit him.. if lucky.. to a 700 watt oven.
Also, mount your inverter as close to the batteries as possible. Run the AC cord long but keep the DC cords short. Amperage demands large cables (the DC side) while AC doesn't.
I just bought this 2000/4000watt inverter for $150. It's not rated for marine use and low efficiency but if you're really just wanting it for a microwave. It's more for power outages for me but since I have about a a dozen inverters this one was a cheap add on.



If you just want to do a microwave why not just buy a 12v microwave? Trucker use them or microwaves plus inverters all the time. You can buy them at bigger truck stops. You aren't doing anything novel, it's a normal item.

http://www.microwavewizard.com/12vol...waveovens.html
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Old 03-28-2011, 07:38 AM
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I don't see where he's looking at a 1,000 watt microwave. He was looking at a 1,000 watt inverter. That would limit him.. if lucky.. to a 700 watt oven.
Right, but it's important to be aware of the difference between "cooking power" and power consumption.
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Old 03-28-2011, 07:58 AM
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Yes you are correct. I installed an inline circuit breaker just before the connection to the battery switch. I don't remember the size of the circuit breaker off hand but it was adequate for the load.
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Old 03-28-2011, 08:15 AM
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What about connecting 8 gauge battery jumper cables from one battery to the inverter? And only using the microwave for 5 minutes at a time while the main motor is running and charging the battery?

Here's the problem - 1,500 watts of power from an inverter, means 1,900 watts at 12v, which is 160 amps - an 8 guage cable is rated for 40 amps - the minimu size cable for what you are doing is 1/0, which is what is uses to start small diesel engines.

A microwave is a lot of power for a short period of time. You will need a 2000w inverter to accomplish what you want to do.
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Old 03-28-2011, 07:27 PM
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Some of you guys are just nuts. First a 1000W Honda will NOT run even the smallest microwaves. I have tried. It barks and shits and shuts down even with a little 800 watt microwave. I use a cheap Costco inverter rated at 1700 watts. It will run any 1000-1200watt microwave.
Good luck with your 1000 watt yamaha. It must be a much way better then those hondas.
I have no issues running my microwave with a group 31 battery. Sometimes I run it on a group 27 for soups, coffee and popcorn.
Please bare in mind you must use very short cables from batter to inverter. My power connection is two 4 gauge cables crimped together for each lead two feet long. I would have used 2 gauge if I had it laying around. It is ok to use an extension cord fom the inverter to the microwave. Your huge power loss is on the 12 volt side.
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