# Microwave Oven - any suggestions?



## 97022 (Dec 22, 2005)

Hi everyone

We hope to take delivery of our new motorhome soon - a Knaus Sun Ti 650MF - can't wait!!!

Has anyone fitted a microwave to one?

If so, what make/model/size/power/supplier please and also was it 12v or 240v?

Just in case no one has fitted one in the Knaus any other suggestions along the same lines would be greatly appreciated.

Many thanks, david


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## 88724 (May 9, 2005)

Hi

I went for a 240v, reason cheaper by far than the straight 12v Version.

Asda are doing a 700W version now under £30, 1000w Invertor from Maplins and thats still three times less than the 12v Version.


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## C7KEN (May 27, 2005)

George surely a 1000watt invertor won't be enough to power a 700watt microwave, I have an 800watt and a much larger 4000watt invertor bought of ebay thro firm in high wycombe for £150 use it all the time for bacon sarnies or quicky meals if I am pushed for time no probs whatsoever


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## Raine (May 10, 2005)

we got a 700w one from comet, or was it curries, for 25 pounds


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## Fatalhud (Mar 3, 2006)

found this info on microwave power consumption

Microwave ovens are often referred to by their cooking power, which on average is only HALF their actual operating power consumption. However, switching on the oven consumes an extra 25% power as the capacitor is energised. Thus, a normal 600 watt oven actually needs 1500 watts to operate it.

this makes 1000watt to small you need between 1500 - 2000 watt

Alan H


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## 88724 (May 9, 2005)

Hi Al

That information is incorrect.

1000w Maplins invertor will run a 700 watt Asda Microwave, the Microwave is rated at 1080 watts *input power.*

here is something I wrote up 2 years ago (its not 100% accurate I have found out more and measured/tested stuff since, but its pretty damn close to right.

Mains Microwave through invertor

Modern 240v Microwaves are getting more efficient (most are anyway) so for 700w cooking power they require about 50% more input ampage so a 700w microwave would need 1050w of power in.

1050w thru an invertor would cost about 10% extra to allow for invertor efficiency so thats 1155w so the ampage required would be in the order of 96 amps. Microwaves tend not to run at 100% efficiency on quasi invertors so allowing for this we get 630 cooking watts costing 96 A

So an Invertor fed mains microwave gives roughly 6.56 watts per Amp

Direct 12v microwave

12v microwaves have not advanced as much efficiency wise, a 450 watt Samsung uses 750w, 750w at 12v = 62.5 Amps

So a 12v Microwave gives 7.2 watts per Amp

Overall a 12v microwave is only slightly more efficient.

Other Factors

Price a 240v Microwave can be had for as little as £25, with a brand and good guarantee £40. A 12v version costs up to 10 times more than the average entry level mains version

Size Mains microwaves tend to be 25% bigger capacity

Speed mains will cook quicker (having 630w, against the 450w of the 12v version)

Battery bank size , to maximise the life of your battery bank no current draw should exceed 10% of the amp hour rating of the battery bank, so for a 12v the battery bank "officially" should be greater than 650 ah, for the mains version 1,000 ah is the "reccomended" size.

Another effect of this is that taking say 5 amps per 100 ah battery bank is the 20 Hour rate which allows 5 amps to be withdrawn for 20 hours before flattening battery completely at 10A draw the battery will not last 10 hours as expected. This is just to show that the amp hour draw will cost you more amp hours than the consumption suggests, this would apply to either microwave.

In practice most take the performance "hit" in terms of longivety and actual ah usage.

In the end its all down to what is important to you, cost £, performance (cooking), efficiency (watts per amp used), actual amps used, size of cooking area and ease of replacement out in the cuds (will always be easier to replace a mains microwave)

Ah Comparison figures for a 5 minute warm (not allowing for battery bank size)

12v 5 mins @ 62.5 amps = 5.21 Ah

240v 3.57 mins @ 96.25 amps = 5.73 Ah (the mains will cook quicker 630w against 450w)

End old Quote

In most circumstances I would be more worried that the terminal voltage of the batteries dropped due to Peukerts and thus caused the invertor to cut out, ie woulod expect 2 good batteries to be minimum and that they be well charged.


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## sallytrafic (Jan 17, 2006)

A careful scrutiny of the instructions or data plate is required. I did a quick walk round Comet and looked at those on display a few weeks ago when this topic was aired before, there were still some whose input power was 1.5 times the microwave output power.

Regard Frank


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## 88724 (May 9, 2005)

Hi Frank

That seems to be where they have stopped (at 1.5 Times cooking power) I wrote the quote in my last post 2 years ago and at the time people were still saying "it takes twice as much power and the start up surge is double the cooking power"

It never ceases to amaze me is that people just accept this "Received wisdom" and never actually bother checking and so the myths perpetuate.


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## 96523 (Oct 14, 2005)

*Microwaves*

George
You actually add to the dilemma with your last remarks as, with great respect, how do we know that you know what you are talking about? Most 'experts' give the impression of knowing far more than the rest of us but as you say, how can we tell. I don't disagree at all with your comments but I hope you see our problem?
Pamalan


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## 88724 (May 9, 2005)

Hi Pam (Alan?)



> how do we know that you know what you are talking about?


That question is impossible to answer without apearing big headed.

But with Microwaves, I have tested them on invertors, accurately measured the Ampage at 12v Level and the power consumed at 240 Volts.

If you are not going to believe anyone then the whole point of forums is lost. There are a few people whose posts I trust, but even then I think it through and check it out for myself.


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## sallytrafic (Jan 17, 2006)

*Re: Microwaves*



pamal said:


> George
> You actually add to the dilemma with your last remarks as, with great respect, how do we know that you know what you are talking about? Most 'experts' give the impression of knowing far more than the rest of us but as you say, how can we tell. I don't disagree at all with your comments but I hope you see our problem?
> Pamalan


In this case its easy you don't have to believe George or me just read 'what it says on the tin'. In large letters it will tell you what the microwave output is say 650W and in small print it will tell you the power input say 1100W.

To George. Never mind George, he only said 'with great respect' if he really didn't believe you he would have said 'with the very greatest respect' :lol:

Regards Frank


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## 97022 (Dec 22, 2005)

*Microwave Ovens*

Thanks everyone

Have had an e-mail back from the dealer and it looks like the overhead locker I had intended to use for a microwave will not be big enough so we may just see how we get on before doing anything else - but all the advice is appreciated.

david


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## Scotjimland (May 23, 2005)

My suggestion.. use it as a bread bin, it's all ours has ever been used for.. :roll:


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