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#1 RenascentMisanthropy

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Posted 07 September 2017 - 09:20 AM

Can someone explain to me why this doesn't work.

 

I have a 2000/4000w inverter which runs from the alternator in my vehicle.

 

When using the inverter, I increase the idle speed so that the alternator puts out 14.4v, I can run all sorts of power tools, 850w angle grinder, 1800w electric chainsaw, 2000w heat gun to name a few.

 

My 800w microwave however refuses to run. It starts off looking healthy but then it appears to lose interest and slows down and makes a funny noise.

 

Do I need a ballast?


Edited by RenascentMisanthropy, 07 September 2017 - 09:26 AM.

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#2 Master_Scythe

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Posted 07 September 2017 - 09:57 AM

I'd dare say it's a rating thing.

 

I'd wager the 800W is the power the magnetron puts out into the cooking area.

NOT the power it draws from the wall.

 

Now I have no idea how efficient a magnetron is, but if it's less than 50%, you're asking 1600W out of a (probably overrated) 2000W Inverter.

OK, scratch that, I just googled:

 

 

The modern magnetron is a fairly efficient device. In a microwave oven, for instance, a 1.1-kilowatt input will generally create about 700 watts of microwave power, an efficiency of around 65%. (The high-voltage and the properties of the cathode determine the power of a magnetron.)

 

Lets assume this is NOT a brand new microwave.

Lets assume even if it is, it's not usually a luxury product that many people spend a Grand on, so the Magnetron is PROBABLY cheap, regardless.

So my 50% efficiency is probably about right; possibly even less.

 

I'm also not sure how Magnetrons react to Square wave power, as compared to Sine Wave power.

Is it a Sine Wave inverter?

 

It's a power thing.

 

The reality is that most inverters, regardless of brand, in the 'same size package' really hate giving more than 1500W from a 14V source (Roughly 10A), they're just built to a price point, and the thickness of an average circuit board trace starts to be a limit from heat.

 

If you really want to use a microwave on the road, hit up Kmart or Target.

 

First, of all, they have a brand new 700W for under $50.

So instantly, it's a little less power, and MIGHT just get through (hopefully its magnetron is newer also).

 

If that doesn't work, those new ones are digital, and have power levels!

You should be able to make it a 500w microwave or less by turning it down on the menu.


Edited by Master_Scythe, 07 September 2017 - 09:58 AM.

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#3 RenascentMisanthropy

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Posted 07 September 2017 - 11:37 AM

Thanks for that information, that makes a lot of sense.

 

It is a pure sine wave inverter.

 

I have this dream of microwaving a frozen pie when I'm on my adventures.


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#4 Master_Scythe

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Posted 07 September 2017 - 12:14 PM

Yep, grab a chieapie, that's already lower rated, and then microwave below max power :)


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#5 Rybags

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Posted 07 September 2017 - 12:23 PM

2000-4000W sounds like a shitload coming out of a car based invertor - where does it plug in?

 

Generally the cig lighter will be on a 20 or 30 Amp fuse, often shared with another thing or two like the radio.

20 Amps = about 240 Watts, 30 Amps = about 360 Watts.

 

If it's direct from the battery then sustaining 1 kW should be easy.  Fairly sure disability carts have a motor in excess of that (but generally use 2 batteries).

 

I tend to have the feeling though is it a sine wave thing?  Most cheaparsed invertors do the approximation thing.  I've got a $40 can one from SCA and tried a variable speed AC Dremel clone on it and at lower speeds it struggles.

It could be that the magnetron is working fine but the turntable motor has problems.  Also some microwaves have a second motor which drives a stirring device up top to help further spread the waves.



#6 RenascentMisanthropy

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Posted 08 September 2017 - 09:21 AM

2000-4000W sounds like a shitload coming out of a car based invertor - where does it plug in?

 

Alternator/battery positive via 26mm^2 cable (good for 280amps)

 

My inverter was $400.

 

I've been using this as a theoretical indication of my load draw @ 14.4v

https://www.redarc.c...er-current-draw


Edited by RenascentMisanthropy, 08 September 2017 - 09:31 AM.

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#7 Rybags

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Posted 08 September 2017 - 12:00 PM

Should be plenty.  Can you test using the reduced power setting on microwave?

e.g. my one lets you set other ratings from 1-9.  Of course it's not a variable power, it's just a variable duty cycle but if you set it to the lowest it means the magnetron is on maybe 10% of the time.

That might allow you to deduce where it's having problems.



#8 RenascentMisanthropy

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Posted 09 September 2017 - 08:45 AM

I'll give that a go and see what happens :)


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#9 RenascentMisanthropy

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Posted 04 March 2018 - 12:59 AM

"update"

 

I still haven't gotten back to this, but I've been doing some more late Saturday night reading.

 

https://caravanandmo...ven-power-draw/


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