Inverter

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ontheplane

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Hi there,

Asked about this earlier but more questions:-

I want to run a kettle, a microwave and a vacuum off an inverter (not all at the same time of course - only one at a time!)

Do any of these need a pure sine wave or will a cheaper modified sine wave work for these?

Does anyone know where I can get a 2200w + (The kettle is the highest user at 2.2kw) inverter - prefer to pick up rather than online as would like one for the weekend. Oh - and not more than a couple of hundred pounds please!

Thanks
 
A couple of hundred pounds !?!?!?!? You'll be lucky...

I doubt you'll find a 2-2.5kw. inverter for much less than 500 squids. There's one here, for instance. (5kw. max, 2.5kw. continuous).

Why not buy a 1kw. kettle, 500 watt microwave (still needs about 1kw.) and a smaller vacuum ? It'll cost you much less.

I use one of these, but I've never tried to boil my (1kw.) kettle on it. Although it will run an 850 watt water heater for half an hour from 2 x 110 Ah. batteries.
 
Is a possible - however the lower powered microwaves, kettles etc seem to perform a lot worse, and cost enormously more than just the boggo standard ones. The vacuum is also a wet-vac and a blower that can inflate the tender (don't ask, the usual 12v inflators don't work on it!)

I may actually re-think on this - the kettle is the only thing that needs more than about 1200w - and we currently only use this when plugged into shore - if we want to boil some water for tea while afloat I guess we could use the microwave??

If I didn't get one to power the kettle, I can get away with a 1500W model - i'll see if they are much cheaper.

I have been looking at these - but the problem is that although cheap - still more than I wanted to pay in an ideal world.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=110384535600

Drop below 2500w and the prices drop enormously....

http://cgi.ebay.co.uk/1000W-INVERTER-200...%3A1%7C294%3A50

for example is only £60 - and soooo close to the power I need, but I'd like a few hundred watts spare over what it says I need.

Do all microwaves need pure sine wave then?
 
What battery power do you have available? There's a formula for calculating your requirements, but I'm too thick to remember what it is. Perhaps someone else could suggest it?
 
2 x 12v batteries - one 72AH the other 110AH

If I was running any of the above loads however I would have the engine ticking over to provide some charge to it at the same time.
 
I'm reasonably confident you'll suck the life blood out of those batteries in short order with a 2.2kw. draw - and your alternator will be ploughing its gonads off to replace the current taken.

You need someone to chip in with the calculation formulae.
 
Yep, I know this.

That's why I'm considering abandoning the Kettle - then I will only need 1300W - say 1500W to be on the safe side... not only are these a lot cheaper, but the batteries will stand a chance!

To be fair I run a 700W inverter on the car regularly and that's never a problem - I always run the engine whilst using it.

I am just concerned from the above comment that to run a microwave I might need a pure sine wave inverter - which are a LOT more expensive!

Darn it!
 
More info here , but it does say...
[ QUOTE ]
All inductive loads - fridges, pumps, many power tools and so on - must be powered by a pure sinewave inverter.

[/ QUOTE ]

...and I've powered my 550 watt drill from mine, so mine must be a pure sine-wave....I think. /forums/images/graemlins/confused.gif
 
WE have a little inverter, that plugs in to the cigar socket. Great for phones and even the TV. WE also have a Honda generator, which will run the whole boat, but not the hot water or microwave. Not a big deal, even in the depths of winter.

Humm. We have an oven for heating food. /forums/images/graemlins/confused.gif
 
That's interesting Carlton - that 500W microwave is EXACTLY the model we have (although mine hasn't been adjusted down to 500W) - I wonder if they have just turned off full power! Therefore I could just only go up to 75% of full power.

Is a Microwave an inducted load then?? If so, it would suggest I'll need a pure sine wave type. I will chat to this guy at the yacht place and see what he says.
 
Watts = Volts x Amps so to get 1200 Watts from 12 Volts you will need 100 Amps (1200/12). However an inverter will struggle to be 90% efficient and there's also voltage drop in the cables so 100A per KW is probably not a bad measure to work to.

Assuming you have separate engine start batteries so that both batteries can be used for domestic without leaving you unable to fire up the engine you've got approx 180AH theoretically available. 100Amps would therefore (again theoretically) be available for 1.8 hours or 108 minutes.

In practice you don't want to discharge lead-acid batteries regularly much less than 30 or 40% max. 20% is even better at that rate of discharge. That gets you say 20% of 1.8 hours, which is 22 minutes. Remember your kettle takes nearly double that.

Formula is: Output KW (e.g. kettle) / Input Volts (i.e. 12V battery) x percentage efficiency (80-90% for a good inverter) = Amps drawn from battery.

Time battery lasts = AmpHours available / Current drawn x percentage discharge acceptable (20-40% IMO).

Doing the sums 2200/12 x 85% means your drawing 216 Amps. 182/216 x 20% x 60 (to get from hours to minutes) means you've got 10 mins to boil the kettle. After that you should think about recharging your batteries.
 
It is an inductance load but not a straight-forward inductive load - the power supply for the magnetron probably wouldn't like anything except a pure sine wave. If it did work with a chopped wave form you'd probably see big decrease in efficiency as well I suspect.

Microwaves are pretty notorious for being fussy about their power input.
 
[ QUOTE ]
Doing the sums 2200/12 x 85% means your drawing 216 Amps. 182/216 x 20% x 60 (to get from hours to minutes) means you've got 10 mins to boil the kettle. After that you should think about recharging your batteries.


[/ QUOTE ]

Thanks Grumpy - I suspected as much, which is why I said
'you'll suck the life blood out of those batteries in short order with a 2.2kw. draw '...

Much better to use less power-hungry appliances in the first place, IMHO.
 
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