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View Full Version : How much watt for a pure sine wave converter?



Flo-w
13th July 2012, 09:28 AM
Just add up the watts of the devices you want to use, right? Sounds easy enough.
But for example my Macbook Pro which I'd like to run on the go (I take a lot of photos and need to back them up on longer trips) has a 85W power supply. At the same time it say's 1.5A :confused: Isn't 1.5A at 240V 360W? And even at 110V (US) it would still be 165W.

Winnie
13th July 2012, 09:59 AM
Except your laptop doesn't use 240V, look on the transformer and it will say the output of it.

threedogs
13th July 2012, 10:29 AM
1000 watt inverter will run microwave oven , small colour TV, power tools , flouro lights, buy larger than you need cheap as now less than $500. isnt it volts divided by watts equals amps or something like that, brain fade at the moment

Flo-w
13th July 2012, 12:17 PM
I'm referring to the transformer KRISTOFFA: input 100-240V, 1.5A; output 18.5V, 4.6A; output 16.5V, 3.6A. At the same time it's called a "85W Portable Power Adapter". That would be 18.5V * 4.6A. But how do the 85W output go together with the 150W-360W input?
Should be Watts/Volts = Amps threedogs

macca
13th July 2012, 02:04 PM
Mate bigger is better,
1000w will cover everything and some and have little or no surges when stuff starts and stops.
Something to check is how many amps they draw on the 12vdc side under load and with no load, some will surprise you idling at 5amps!!!! More than your fridge.
Ours has an anderson plug and is totally disconnected when not in use.
Cheers Macca

Flo-w
13th July 2012, 04:30 PM
And I thought I would just need a small and affordable sine wave inverter. Hm... :-/
I'll be able to disconnect it via a circuit breaker with reset button.

the evil twin
13th July 2012, 06:42 PM
Hiya Flo-w

What goes in isn't what comes out and most lappy 240 volt power adapters are very inefficient and can have some interesting inrush currents when first turned on.

The 240 Volt spec is actually for 100 to 240 volts input and the 1.5 amps is the max spec... sooo... at 100 volts (not 240) if you want to work that to Watts it will be approx 150 Watts. When connected to 240 Volts the input current should be a max of maybe .6 amps

The output spec is a maximum continuous rated for the power adapter and in your case is 85 watts which the Lappy should never get close to unless the batteries are dead flat as the battery charging is by far the highest drain of supply current.

That translates as using a max of 150 watts (240) A.C. to convert and produce a max of 85 watts (15 Volts usually for lappies) D.C.

Bottom line?... a 300 watt inverter will do the job easily and will not need the heavy gauge wiring on the 12 Volt side like the 600 and 1000 watters.

Macca is also correct about the Inverter Idle current. Some of them are awful hungry and you can easily flatten a vehicle battery with the bugger just turned on and nothing running of it. Another reason to stick to a smaller one IF it suits your need. A 1000 watt Inverter idling at 5 amps is very common in the cheaper to mid range units.

the evil twin
13th July 2012, 06:48 PM
Also, if only for a Laptop... should have asked,

Have you considered an up-converter readily available from Dicks, Jaycar etc? They will use 12 Volt DC to produce 15 to 18 Volt DC and plug directly into your lappy from a Ciggy Plug or other Aux source. You don't need the 240 Volt Power pack at all then.

Yendor
13th July 2012, 07:39 PM
If it's just to charge your MacBook pro you can get a 12 volt DC car charger.

http://www.ebay.com.au/itm/GPK-CAR-CHARGER-APPLE-MACBOOK-PRO-15-17-LAPTOP-12V-DC-POWER-ADAPTER-CORD-/270905080780?pt=Laptop_Adapters_Chargers&hash=item3f13337bcc#ht_1882wt_1114

Flo-w
13th July 2012, 07:40 PM
Thanks evil twin. I will also need to recharge batteries for camera which again requires 240V. Otherwise good idea with the up-converter.
I'll probably just go for something in the middle like a 600W inverter. They seem to be able to peak at 1200W for short times. And it gives me a bit of reserves as mecca and threedogs have pointed out.

Cheers everyone.