What size inverter

Hi all,
What size inverter is needed to charge the batteries on a standard lap top computer? The adapter is a Sony AC 19.5V
The input: 100-240 V ,1.5 A, 50-60 Hz.
Output : 19.5V, 4.7A


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Reply By: Echucan Bob - Sunday, Jun 28, 2015 at 18:01

Sunday, Jun 28, 2015 at 18:01
Something like this would be cheaper, easier and more efficient.


AnswerID: 556456

Follow Up By: Echucan Bob - Sunday, Jun 28, 2015 at 18:30

Sunday, Jun 28, 2015 at 18:30
Actually, you'll need a very long extension lead for the second one!
FollowupID: 842635

Reply By: Allan B (Member, SunCoast) - Sunday, Jun 28, 2015 at 18:26

Sunday, Jun 28, 2015 at 18:26
Bob, If you prefer an inverter rather than a 12v input adaptor then you will need at least one rated at 150 Watts. However, a 300W inverter will cost little more and provide an edge of surety. Be very sure to purchase a "Pure Sinewave" inverter as "Squarewave" or "Modified Sinewave" types are likely to not work properly or even harm your adaptor or computer.

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AnswerID: 556457

Follow Up By: Phil 23 - Monday, Jun 29, 2015 at 08:19

Monday, Jun 29, 2015 at 08:19
Actually, most laptop switch mode supplies are less fussy about Modified sine wave than most people think.

The first thing their circuitry does in feed the AC through a bridge rectifier & feed it into large filter caps to provide around 340 volts DC for the rest of the circuitry.

The diodes in bridges aren't at all phased by the modified sine, or almost square wave AC input.

What is more sensitive though, is wire wound transformers.
Because they rely on rise & fall of magnetic flux, they are very critical of input wave forms.

Earlier UPS units & the more basic models on the market are nowhere near sine wave & happily run computers & monitors with their switch mode supplies with no issues.

What I have learnt over 25 years in IT, is to be very wary of plugging transformer based power packs on the likes modems & smaller network switches into UPS outputs.

Have had many service call after power outages where the story is that the UPS kept things up running, but these other devices have now failed & invariably, their power packs now have open circuit primaries.

All that said, I've recently bought a pure sine wave unit, but still have 150 & 300 watt MSW inverters, that I've still used right up to now.

They don't need totally ruling out of the equation. They have their price & uses in the right situations.

FollowupID: 842659

Follow Up By: Ross M - Tuesday, Jun 30, 2015 at 09:32

Tuesday, Jun 30, 2015 at 09:32
Phil 23
Possibly the crappy square wave caused unusual heating in the primaries and they got too hot and burned out.
Same effect with a crappy square wave on electrical/electronic equipment whose circuitry expects to see a sine wave but gets fed lumps which makes it unsure what to do or just doesn't start oscillating and burns out.
FollowupID: 842711

Follow Up By: Allan B (Member, SunCoast) - Saturday, Jul 04, 2015 at 15:33

Saturday, Jul 04, 2015 at 15:33

All well and good (most times) with your..... "most laptop switch mode supplies are less fussy".... but rather unfortunate if the OP draws the short straw!
Apart from waveform issues with switchmode supplies, harmonics and other artefacts can sometimes be an issue.

The investment in a Pure Sine Wave inverter is good insurance for all conditions.

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FollowupID: 842899

Follow Up By: garrycol - Saturday, Jul 04, 2015 at 16:28

Saturday, Jul 04, 2015 at 16:28
I went to buy a 12v to 19 odd volt (120w) charger for my HP laptop just before my last trip. Average quality ones were about $65 and better were about $80.

I went onto ebay to see if I could do better and came across a 300/600w pure sine wave inverter for $65.90 delivered. I figured that while a 12v charger would be OK it really was limited to the laptop where the inverter with greater output would have greater uses and hence more practical. So I bought it.

Worked great on the trip powering the laptop easily and my rechargable lights.

At home last week we had two days of planned power outages so I brought a spare battery inside and used the inverter to power my 25cm LCD TV, my laptop, my mobile phone which was being used as a WiFi hotspot and at one stage charging my 1200cca starter pack in case I needed it a s a backup.

The inverter handled it all ok with the cooling fan on coming on a few times. The cooling fan on the inverter only came on a few times which means it was drawing over 150w - it never got over its 300w as a red light comes on when it does.

So a small pure sine wave inverter is a good cost effective alternative to the dedicated 12v laptop chargers.

FollowupID: 842902

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