Inverter Consumption

[nonitoo]

Just a quick one !

With my 1000w inverter running, just how much power is it draining from my batteries when running, say, the microwave rated at 600w ?

I can just about remember W=VxA from school days but cannot tie the 12v and 240v together.

Is it a straight 600/12=50amp (plus something for the inverter operation - 10%) ?

Is there a rule of thumb I can apply here ?

Thanks

Tom

 

[Chris_d]

Yep the 12V current will be about 20x the 240V current (12/240). A 600W microwave will need about 1000W to actulay work, so thats 1000/240 = 4A at 240V
x20 = 80A at 12V approximately /forums/images/graemlins/frown.gif Don't try cooking baked potatoes!

 

[Andrew_Fanner]

You might want to factor in an efficiency of, say, 85% for your inverter. Most are a bit better than this so you will over spec cables rather than under spec. That makes your 80A a bit more so get 100A cables. Gennies or 240V alternators start to look competitive

 

[Bandit]

A new boat and sockets were wired through inverter although charger fed by shorepower or generator.

Max output through inverter 6amps not enough to run a hoover or an electric kettle and any draw while not on 240v from either source would drain the battery very quickly.

We have foregone the inverter link and rewired sockets to 240volt system from shore or generator.

Unless you have the batteries of a diesel electric submarine I cant see how the inverter makes sense unless you are running a laptop, a cell phone charger or a TV .

 

[Whitelighter]

I am not questioning you, but why does a 600w unit need 1000w to work? Surely then the 600w rating is a misnoma?

 

[andyball]

think is a notional 600W output.... bit like a 25W vhf uses more than 25Watts to produce that much actual vhf power.

 

[mikefleetwood]

Just to correct the misaprehension (If I don't. I'm sure someone else will!) - The 600W rating of microwave is the output power. Like most electronic devices, it is not 100% efficient. The other 400W is lost as heat (that's why it has ventilation slots and a fan).

Edit - look at that - beaten to it again!

 

[fisherman]

[ QUOTE ]


I cant see how the inverter makes sense unless you are running a laptop, a cell phone charger or a TV .

[/ QUOTE ]

I have changed from inverter to 24v psu for my shuttle, couldn't keep the batteries up (too much ticking over while hauling gear). The phone is charged with a car charger on 12v. Many TVs can run on 12v.

I suspect that the inverter uses power even when nothing is drawing from it.
I also suspect that mikef2 will disagree with me!

 

[Chris_d]

A 600W microwave usualy refers to the cooking power, all the transformers, circuitry etc.. use the other 400W converting your 240V to a microwave output. I only plucked that figure off the top of my head, but fairly sure it will be typical. Most appliances will draw a spike of power to start them running, so you need a much larger inverter than your intended load normaly.

Inverters in general are very power hungry, even with nothing connected they will draw around 0.5A, so you need to turn them off when not in use. They are ok for charging the phone or powering a laptop, but if you need 240V reguarly its best to go the gennie route.

 

[nedmin]

The best way of explaining why inverters are so inefficient is, say you put 12volts in and you want 12volts out,the bit you put in is a straight line voltage,the bit you get out is a sine wave so you "lose" the top bit above the curve on the positive cycle as well as the bottom bit on the negative cycle,you then tranform it to 240volts. I know this is not strictly correct but it shows simply whats happening.Ok for about 100watt max but not much good battery wise above that,thats my opinion.

 

[nonitoo]

Thanks anyway everyone, as usual, I have found reassurance and confirmation of my original query.

Tom

 

[Wiggo]

Got to disagree about gennies looking attractive, Andrew. I recently fitted a 2000W inverter (well, two actually, but ine is on SteveE's boat). Ours is there for three reasons: first to run the telly when we are at anchor (sod all load), second to run madam's hairdryer (1500W) before going ashore after being at anchor, and third to run th eimmersion heater (1250W) after a night at anchor to save running the engines.

I added a couple of extra 110Ah batteries to the domestic bank, so we now have 660Ah in total. Total cost was around £400 versus £6k+ for a diesel gennie (I really didn't want petrol on board other than in the tender). On top of that, I added a twin alternator controller and charge splitter, allowing both alternators to recharge the domestic bank, which cost another £500 or so. For me, the inverter is a no brainer.