Matching microwave and inverter

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Sid52

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I'm thinking of getting a microwave for the motorhome and am looking for recommendations for a small microwave and the inverter to run it, bearing in mind the high start-up current. Would I need a pure sinewave or would a modified sinewave be ok?
I have 2x 100watt batteries and solar for charging.
Cheers
Sid
 
Your batteries are rated in Amps and your Microwave will be rated in Watts. The bigger the wattage of your Microwave the bigger your inverter will need to be, and consequently your batteries are then not man enough to drive the inverter. You also have to consider that the inverter itself uses power to convert DC to AC. Ask yourself do you really need a microwave?
 
Whoops, meant amps!
Assuming a low powered microwave of 700 watts, that would mean c 60 amp draw, and assuming a couple of minutes to do say scrambled eggs, then that shouldn't be too much of a drain on fully charged batteries. I would anticipate switching the inverter off when not in use.
Not decided as yet, and have to find space as well!
 
We decided that, to be able to use Aires, we need an inverter for the microwave and to charge laptops and smart phones. We consulted RoadPro and settled for a 1500 watt pure sine wave model which would have no problem with our already fitted 800 watt microwave.
I find any issue such as this divides opinion: we are also having “steadies” fitted by Alko next month as I want to be level when parked up and many will say the cost is not worth the gain.
I would heed advice from this forum and ask the expert professions
- RoadPro and Eddie from VanBitz for two.
If you search this site for “inverter” posts you will quickly receive a lot of information.
Conal
 
I think you’ll find that a microwave of 700 w will draw double that as the published wattage is not what it draws.

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Microwaves are l think power hungry. The advertised watts are the output cooking power, the input power is higher. For example the small one I have at home is 700 watts cooking power but 1200 watts input. By my calculation that is less than 60% efficient. By the time you have allowed for inverter losses, say another 5 to 10%, you are going to be using a lot of battery watts to run a microwave.
 
We have a cheap domestic microwave don't know how many watts but I think it says 1200 on the back, we have a 2kw pure sine inverter and used to run from 2x110ah GEL batteries after 2 or 3 minutes the battery volts would say 12.2 ish but came back up once the cooking was done, we now have 4x110 GEL and the volts dont go much below 12.6 after 4 minutes use and then back to 12.9 so happy with that. We have 320watts of solar that can have it all back in in a couple of hours.

Works for us(y)

Martin
 
I would suggest you need pure sine wave to correctly operate a microwave. When running our microwave on the inverter, our battery monitor reads a draw of around 100 amps, this is obviously not sustainable for a huge amount of time, but fine for small amounts of time.
 
I've had a camper for 8 years, and never needed a microwave. Just need to plan ahead :)
 
Our 900w microwave pulls about 80amps throu a 3000w invertor, as you are only using for minutes at a time don’t think it’s much of a problem for a battery bank as long as cables are short enough and thick enough to handle the current

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Yorick said:
I've had a camper for 8 years, and never needed a microwave. Just need to plan ahead :)
Click to expand...
Sorry, we had a microwave for 240v usage for 3 years, but never used it, so binned it.
 
Yorick said:
I've had a camper for 8 years, and never needed a microwave. Just need to plan ahead :)
Click to expand...
No, it's true. However for some things it's much more convenient, less messy and saves gas. Probably not so much as I would ever get round to fitting one though :sleep:
 
Sid52 said:
No, it's true. However for some things it's much more convenient, less messy and saves gas. Probably not so much as I would ever get round to fitting one though :sleep:
Click to expand...
It's the least important thing I can think of. If you need something to defrost, put it in the sink through the day.

If you're travelling, why freeze anything to defrost later ?????
 
manda3000gt said:
Our 900w microwave pulls about 80amps throu a 3000w invertor, as you are only using for minutes at a time don’t think it’s much of a problem for a battery bank as long as cables are short enough and thick enough to handle the current
Click to expand...
Is that a pure sine wave inverter? I've heard that a modified sine wave will work although it makes the microwave buzz and may shorten its life.
Actually, that 80 amps is a lot less than the starter load when starting a diesel engine, so as you say it shouldn't be an issue for short periods.
 
Yorick said:
It's the least important thing I can think of. If you need something to defrost, put it in the sink through the day.

If you're travelling, why freeze anything to defrost later ?????
Click to expand...
I never mentioned defrosting, although it may be handy if we've forgotten to take it out in the morning.
Actually, we nearly always take food we've cooked at home and then frozen, for use many days later.

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We were on an aire a couple of years ago, the family with a young baby needed a bottle warmed to feed aforementioned baby. We happily switched on our inverter and let her use our microwave. To be honest, it was that or listen to the baby screaming! :D
 
Sid52 said:
Is that a pure sine wave inverter? I've heard that a modified sine wave will work although it makes the microwave buzz and may shorten its life.
Actually, that 80 amps is a lot less than the starter load when starting a diesel engine, so as you say it shouldn't be an issue for short periods.
Click to expand...

‘You can’t get a quart into a pint pot’ - you haven’t got a large battery bank and unless you’re on EHU then you won’t be able to achieve what you’re asking. Get a pan on the stove.
 
I used to have a mini samsung microwave 550w and ran it on a 1000w Ring Modified sinewave inverter.
It ran perfectly which was very surprising to me.
We found it wasn't worth wasting the space for the few times it was used.
 
Better answer if you have the spare payload is a small Honda 2. gennie , for the short periods a micro operates . Easier than having to uprate your whole 12v system to handle m/wave. you also have the benefit of a emergency power supply :) I find a micro real handy , esp porridge :)

PS also handy for popcorn !!
 
tacr2man said:
Better answer if you have the spare payload is a small Honda 2. gennie , for the short periods a micro operates . Easier than having to uprate your whole 12v system to handle m/wave. you also have the benefit of a emergency power supply :) I find a micro real handy , esp porridge :)

PS also handy for popcorn !!
Click to expand...

Don’t think people on site will appreciate you firing up a genny to warm your porridge early in a morning :)

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Sid52 said:
Is that a pure sine wave inverter? I've heard that a modified sine wave will work although it makes the microwave buzz and may shorten its life.
Actually, that 80 amps is a lot less than the starter load when starting a diesel engine, so as you say it shouldn't be an issue for short periods.
Click to expand...

Quasi Sine Wave
Only found one thing it would not run so far and that’s a Tassimo coffee maker, well under the power rating just the electronics don’t seem to like it
 
People might find the following interesting
How to compare model ratings with other Combis:
Watts vs VA : the truth
The most significant issue to be aware of is how output ratings are massaged to appear better than the competition. You might be excused for thinking that a unit with ‘3000’ written on it, for example, means that it will deliver 3000W continuously. This is not necessarily the case if you look at the small print.

Have you ever found it strange that the product you want to run (i.e. the hair dryer, washing machine, TV, etc), has the power consumption shown in watts, yet the inverter/ generator companies give you the rating in VA, and when you put your 1000W product on a 1000 VA inverter it does not work. In the small print you find out that the 1000 VA inverter is only 700 watts for 10 mins then it over heats- this simply cannot be right.

In the eyes of the unknowing consumer, rating a power product in VA is a simple way of using meaningless figures to confuse and make performance appear better than it really is. Unfortunately this practice is still allowed in Europe (European standards committees are looking into this practice) unlike the USA where there are recognised standards (eg ABYC) and you can be sued for publishing misleading information and incorrect ratings. The only true rating, without confusion, is in watts, using a simple resistive load with unity power factor, such as an electric heater / standard light bulb, etc. This method gives a lower correct figure, however, it is not what the marketing teams involved in promoting power products want to see.

Take, for example, a 3000 Victron Multi that is perceived by the public to be 3000W continuously rated. If, however, you read the Victron specification for watts at 40 degC the actual power is 2200W.The Sterling 2500W Combi delivers 2300W which in fact makes it a more powerful unit. This distortion is not limited to Victron, unfortunately most, if not all, the European manufacturers push model figures to the realms of fantasy in spiralling competitiveness and in order to confuse and impress the public who believe that these figures are actual continuous power rating.

Furthermore, the effects of temperature and the duration of duty (i.e. how long a load is maintained) can also be used to manipulate ratings. It is much harder for a unit working in 40 degC ambient temperature than in 25 degC, just as it is harder to run at a higher load for extended periods. Therefore, a unit rated for short periods at a cooler temperature will also appear more powerful.
To illustrate, taking data published by Victron Energy and Mastervolt, the following comparison can be made

To see the rest look here
https://sterling-power.com/products/pro-combi-s-pure-sine-wave-inverter

I am not endorsing any particular product , have no connection
but informative ?
 
Sid52 said:
Is that a pure sine wave inverter? I've heard that a modified sine wave will work although it makes the microwave buzz and may shorten its life.
Click to expand...
I have a Bestek 2000W modified sine wave inverter, cheap and cheerful. It struggles to run the low-end microwave, about 700 watts output, 1200 watts input. When on EHU, the microwave works better.
The Nespresso coffee machine simply will not even start to run, even though it is only 1200 watts.

I'm looking for an excuse to scrap this inverter and buy a PSW one. It's definitely a 'buy cheap, buy twice' situation. It's not the power. As a test I ran three 500watt heaters from it, no problem. It's just the modified sine wave waveform that's the problem.

Anyway, microwaves are quick and convenient. Everything that makes them good at home makes even more sense when camping. Definitely feasible with two 100Ah batteries.
 
Sid52 said:
I'm thinking of getting a microwave for the motorhome and am looking for recommendations for a small microwave and the inverter to run it, bearing in mind the high start-up current. Would I need a pure sinewave or would a modified sinewave be ok?
I have 2x 100watt batteries and solar for charging.
Cheers
Sid
Click to expand...
When I had a big battery bank and ran (1000W) microwaves I managed perfectly well with modified sinewave inverters. They were good quality and rated at 1800W. I’d get a PSW inverter, just in case I needed to run something more sensitive (like hair straighteners). Good inverters should cope with a much higher initial load than their rated one, but I’d still like to get one that had 20% more output than the rated input power of my microwave.

Microwaves and batteries are heavy. I’d review what you’re intending to use one for and look for alternative methods, rather than trying to be ‘home from home’. That payload might be more usefully used for things like beer or wine.

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Seems a lot of hassle

Scrambled eggs = pot
Warming baby bottle = pot of hot water and a few minutes
Heating up frozen food = pot

Pot wins
Cheaper than a microwave an inverter and a generator.

I'd spend the money on refillable gas instead
 
Microwave will run fine on a modified square wave inverter,, however if I was buying now I would get a pure sine wave as they are useful to run anything. Most things I use our microwave for only take a couple of minutes so current draw not really a problem if you have adequate solar.
 
tacr2man said:
People might find the following interesting
How to compare model ratings with other Combis:
Watts vs VA : the truth
The most significant issue to be aware of is how output ratings are massaged to appear better than the competition. You might be excused for thinking that a unit with ‘3000’ written on it, for example, means that it will deliver 3000W continuously. This is not necessarily the case if you look at the small print.

Have you ever found it strange that the product you want to run (i.e. the hair dryer, washing machine, TV, etc), has the power consumption shown in watts, yet the inverter/ generator companies give you the rating in VA, and when you put your 1000W product on a 1000 VA inverter it does not work. In the small print you find out that the 1000 VA inverter is only 700 watts for 10 mins then it over heats- this simply cannot be right.

In the eyes of the unknowing consumer, rating a power product in VA is a simple way of using meaningless figures to confuse and make performance appear better than it really is. Unfortunately this practice is still allowed in Europe (European standards committees are looking into this practice) unlike the USA where there are recognised standards (eg ABYC) and you can be sued for publishing misleading information and incorrect ratings. The only true rating, without confusion, is in watts, using a simple resistive load with unity power factor, such as an electric heater / standard light bulb, etc. This method gives a lower correct figure, however, it is not what the marketing teams involved in promoting power products want to see.

Take, for example, a 3000 Victron Multi that is perceived by the public to be 3000W continuously rated. If, however, you read the Victron specification for watts at 40 degC the actual power is 2200W.The Sterling 2500W Combi delivers 2300W which in fact makes it a more powerful unit. This distortion is not limited to Victron, unfortunately most, if not all, the European manufacturers push model figures to the realms of fantasy in spiralling competitiveness and in order to confuse and impress the public who believe that these figures are actual continuous power rating.

Furthermore, the effects of temperature and the duration of duty (i.e. how long a load is maintained) can also be used to manipulate ratings. It is much harder for a unit working in 40 degC ambient temperature than in 25 degC, just as it is harder to run at a higher load for extended periods. Therefore, a unit rated for short periods at a cooler temperature will also appear more powerful.
To illustrate, taking data published by Victron Energy and Mastervolt, the following comparison can be made

To see the rest look here
https://sterling-power.com/products/pro-combi-s-pure-sine-wave-inverter

I am not endorsing any particular product , have no connection
but informative ?
Click to expand...

Thats why good brand inverters say their wattage as continuous. I have a Ring inverter that is rated at its full output for 12hrs continuous. BTW I have a spare 600w pure sinewave inverter for sale if any one is interested just message me.
 
Reallyretired said:
Microwave will run fine on a modified square wave inverter,, however if I was buying now I would get a pure sine wave as they are useful to run anything. Most things I use our microwave for only take a couple of minutes so current draw not really a problem if you have adequate solar.
Click to expand...
I am not convinced that all microwaves will run on all modified wave inverters because ours wouldn't OK it made the right noises but nothing got warm, swapped it out for a PSW and all was good.

Martin
 
funflair said:
I am not convinced that all microwaves will run on all modified wave inverters because ours wouldn't OK it made the right noises but nothing got warm, swapped it out for a PSW and all was good.

Martin
Click to expand...

Theres a big difference between different models of modified sine wave. Some are less modified and more square wave.

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