[kd883]

Hi guys,

I'm looking at setting up dual batteries and an inverter to power some lights and various 240V chargers around camp. I've done some homework on the dual battery set up, but I'm just not sure of where to start with the inverter. A mate recommended a 1500W pure sine wave inverter from ebay, whatever that is?

http://www.ebay.com.au/itm/Pure-Sine-Wave-Power-Inverter-1500w-3000w-12v-240v-Caravan-Boat-Car-/390475449313?pt=AU_Boat_Parts_Accessories&hash=item5aea2683e1

I'm not sure of a couple of things:

1) What power I would need

2) What the difference is between "pure sine wave" and "modified sine wave" and

3) What the go is with the peak rating.

Any help would be greatly appreciated.

Cheers,

KD.

[Trypt]

Dont know the ins and outs of sine vs square wave but here goes.
sine wave the ac wave form is actually a wave where as square wave just cuts from one polarity to the other. as far as i know.
this is fine for lights and tools and fridges and stuff but isnt ok for delicate electronics like computers and phones etc.

as for output. peak power is the power the inverter can handle at peak load, eg. spike when switching on a tool or a light.
rated output is what it can handle constantly for long periods

2400w will give you enough power to run anything thats 10 amp.
oven, microwave, welder, big stereo etc

1500w should be adequate for a camp.

ive got a 600w for odd things, runs a grinder ok and corded drill. charges phones etc no problems

[Bugsta]

KD, only you can really work out how much power you 'need'. Add up the combined power requirements of all the devices you plan to run at most at any given time. Of course, you may have 10 devices but will never have all 10 on at once. eg. Never lights during the day, and never power tools at night.

You will also need to take into acount the total amount of power (AmpHours) you need over a period without the batteries being charged, and still be able to start your vehicle in the morning. AH = Current draw x Time

Some useful equations...
P = VI. Remember Power remains the same regardless of voltage (ie, before and after the inverter), so if you divide the voltage, you multiply the current
To use Trypt's example of 600W:
V=240v
P=600watts.
Therefore I=600/240=2.5amps
And at 12v,
I=600/12=50amps.
If you are wanting to use 50 amps for 2 hours, thats 100AH. 2 very decent batteries would be required for this.

A sine wave is a very smooth curve that oscillates about a central value (0volts in this case) from one extreme to another. Equipment to create this costs money, so cheap inverters use a crude method by producing a 'modified sine wave', as trypt said - is a sqare wave that changes polarity. It is usually smoothed to some degree but will never be as good as pure sine wave. And yes, if you have electronic equipment, even a TV, very good idea to choose pure over modified square.

[Blakey]

modified square or triangle wave creates noise lots of it. any transformers will hum like crazy as the huge loss in eddy currents. most TV's should be fine unless they are a CRT they it will be crap. most speakers will have an undertoned hum if the amp is powered from the modified wave.

if your wanting to use power tools IE things that have motors you will need a large then what is required inverter or the power tool will never fully start up as all motors have a huge power draw at start up. and if your inverter cannot power that it most likely wont fully start up the motor.

there is a lot more losses from a modified square wave inverter so what it says it can output isnt a true figure it will be less.

pure sine wave inverters are a lot more expensive because of the needed circuitry to create the sine wave and sustain it. its way more efficient and doesn't create noise in AC appliances.

but if your just want something cheap to run some lights and if you have enough output power tools a modified wave inverter will be fine.

also on bustas advice. Power in to something never equals power out. this is not an ideal world there are losses in everything power in will always be larger then power out. unless you live in a place that is 0Kelvin where there is no Resistance and no loss from heat etc. yes it can work for simple calculations but in the real world power out is always less especially in something that needs a voltage transformation in this case 12V to 230V.

[fordem]

An inverter to power lights & 240V chargers...

My suggestion would be to use LED lights and wherever possible 12V chargers - for most of today's electronics, the chargers are switch mode power supplies that reduce the AC utility voltage down to a much lower DC voltage, so you would be wasting energy stepping 12V DC up to 240V AC and then back down to whatever DC voltage your particular device uses.

Much of today's electronics can be charged from a 5V USB source, 12V cigarette lighter to USB adapters are readily available from as low as 500mA, up to 2000 mA (required by iPads and tablets) and for laptops, car adapters are aslo available.

Oh - switch mode power supplies will run on either pure sine, modified sine or square wave inverters - they only draw current on the peak of the wave and don't care about the waveshape, older "linear" pwer supplies, as mentioned previously, will buzz.

[Bugsta]

All agreed Blakey. Was just keeping it reasonably simple.

[got_bar_work]

Anything over 600w and u will want the car to be running at the time or its going to kill ur batt quick