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Old 16-04-2009, 21:24   #1
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Microwave, Solar Panels, Batteries

Hi,
I hope somebody has been there before and has a quick - should work or forget it answer
Hanging out in La Paz now with 4 X 130 Watt Kyocera Solar panels on my amas and 4 Trojan 105 (parallel/series) - 440 AmpHours which my Xantex C60 Solar Charge Controller keeps happy all the time.

So I'd like to use my 700 Watt Micorwave via an inverter, just to heat up some food plates. So maybe 10 minutes max.

Some people told me I'll toast my batteries if I discarge with 60 amps some say I should be fine. Bit confuesed so I hope for somebody who has a similar setup and can well, confirm first hand if it works or not.

thanks in advance,
Olaf
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Old 16-04-2009, 21:42   #2
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I have much less in the solar department but more in batterys. 6 of the same as yours. I fired up the microwave while under power once and could easily tell the alternator didn't like it. I could hear the engine load up. That was enough to tell me to save it for when I'm in a slip.

Where are you in La Paz? I'm in Singlar.
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Old 16-04-2009, 21:53   #3
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Hi Mingat,
heard you name a couple of times when I was listening to the network at 8 am.
I'm in Marina de La Paz.
beer ?
cheerio,
Olaf
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Old 16-04-2009, 22:04   #4
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700 W microwave typically draws 2x that amount in real life (check the back for amperage and multiply by 120 to get watts). Is your inverter 1500 W or greater?

Now 1500 W / 12 volts / 0.90 efficiency = actually 138 A.

138 A x (10 minutes / 60 minutes per hour) = 23 A.hours.

It's a fair bit, but nothing a decent size battery bank or inverter will have trouble with.
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Old 16-04-2009, 22:21   #5
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We have 450 watts of solar panels, 660 amp-hour bank, 2500 watt inverter. We use the microwave on the inverter frequently and have for years without any issues. We never use it for more than 2 minutes at a stretch though, usually for popcorn. I don't think I would try it for 10 minutes straight. Our microwave draws over 100 amps.
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Old 16-04-2009, 23:47   #6
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Thanks for the replies - guess I have to install the inverter now and give it a try.
Thought I'd ask though because I have flooded batteries and people told me that they would start to boil if I draw that much amps.

thanks again,
I'll brew some coffee
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Old 17-04-2009, 05:54   #7
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You also may have some wattage being contributed by the solar array. Could be as much as 400 watts maybe. This is well within a reasonable discharge rate for deep cycle batteries. You will however note that it will result in fewer amp/hours available from the battery pack due to the higher than 20 hour discharge rate.
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Old 17-04-2009, 10:53   #8
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Love the microwave

One reason that modern marine power inverters proliferate is because they will drive microwave ovens. I've been doing just that since 1985 when I got my first inverter/charger. A 1200 W inverter will drive the largest microwave on the market because a good 1200W unit will deliver peak power around 3kW.

A 440 Amp-hour rated battery bank should be quite sufficient to drive that load. I often microwave two large potatos for 8-10 minutes with a microwave that draws 1200W. Not much later I microwave other items to heat them up...no problem. Been doing that for years. The only caveat is that the battery resistance (not capacity, although related) must be suffidiently low so that the inverter input voltgage equals or exceeds 11 Volts at the end of the cooking time. With a good battery bank the Voltage will be 12V under load even after 15min of continuous ON microwaving. If the voltage is not high enough the cook times get longer and longer.

It is normal when driving an alternator while using an inverter for the engine to load down, after all, that is what is called a supported system and the energy is coming from the engine. With a good system no harm is done. Same thing would happen if the engine is working while you use the windlass to get the anchor up with a minimum retreival time due to higher operating voltgage.
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Old 17-04-2009, 11:19   #9
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Quality of life afloat

Although I am not the originator of this thread, I want to also say thanx for that. My batterys are near the end of their life and you just gave me reason to go for the low resistance batterys. Now I just need to qualify for the loan to buy them.
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