Inverters: Discussion here.

Map Monkey · Post by **Map Monkey** » 30 December 04 8:53 pm

Riblit,

Most electrical devices have efficiencies which vary in relation to their loading......however assuming this does not change over the load range...

The device will use the same current - the 550w rating is the maximum rating of the device, after which the overload protection may activate or the regulated voltage output may vary outside the accepted range.

Regards

Agsmky

Kerry · Post by **Kerry** » 30 December 04 9:02 pm

riblit wrote:
Let me ask you another question..

I had a computer with a 230 WATT power supply. Marked on it is 115/230V~1/0.5A. Output rating is marked as +5V/23A, +12V/9.5A, -5V/0.5A, -12V/0.5A

Assuming it powers the computer correctly, if I replace it with a 550 WATT power supply with the same efficiency will it draw more input current?

More questions? Always more questions? I thought we were discussing inverters and notebook adapters, really what has a power supply got to do with what's been discussed? So how about we resolve the issue (confusion) with inverter output and adapter input/output first, then we could move onto power supplies if you want to.

Cheers, Kerry.

Kerry · Post by **Kerry** » 30 December 04 9:07 pm

Mind Socket wrote:I hope you're both talking about the input power of the same thing (110/230V adapter or the 19V laptop) after all that.

Lets hope there's no confusion between the 150 watt inverter OUTPUT and the 70 watt (or 90 or 120 or whatever) OUTPUT of a laptop adapter.

Cheers, Kerry.

Geof · Post by **Geof** » 30 December 04 9:49 pm

<*of topic*> (well kind of)
Then theres the 300 watt car stereo (or rather mono) from china ($24.95 from your autojunk shop). Should that be 300 whats? Or may be it's 300 watts of heat when you grind it up and ignite the powder in a jar of pure oxygen

<*of topic/*>

Let me ask you another question..

I had a computer with a 230 WATT power supply. Marked on it is 115/230V~1/0.5A. Output rating is marked as +5V/23A, +12V/9.5A, -5V/0.5A, -12V/0.5A

Assuming it powers the computer correctly, if I replace it with a 550 WATT power supply with the same efficiency will it draw more input current?

NO

I think the bottom line here is the less conversions the better as each one has it's losses.

I know of one person that ran his clock radio of one of those cheap inverters and wondered why time was flying and another person who took his clock on the boat to tassie and was very early for breakfast

.

The accepted method of adjusting the output voltage of them (cheap inverters) is to run an incandesent lamp of them and adjust for the same brightness as the mains. There is no garantee that if fed into a product that rectifys the mains like a smps that the performance will be the same however smpss can mostly cover a wide input voltage. As for the poor bridge rectifier in the smps (primary), most arn't fast switching so modified sine wave (or modified square wave depending on how you look at it) can be a bit hard on them.

riblit · Post by **riblit** » 30 December 04 10:11 pm

Kerry wrote:
More questions? Always more questions? I thought we were discussing inverters and notebook adapters, really what has a power supply got to do with what's been discussed? So how about we resolve the issue (confusion) with inverter output and adapter input/output first, then we could move onto power supplies if you want to.

Cheers, Kerry.

What does it have to do with the question - quite a lot as they are both switch mode power supplies.
agsmky has the right answer - the device will use the same current, notwithstanding the fact that it has a higher rating. The input power has nothing to do with what is written on it, rather it is a function of the output power and the conversion efficiency of the device.
In order to work out the input power required by the laptop power supply you need to know the output power required and and the efficiency of the power supply. You said the laptop draws 3.5A max at 19 volts. This is 66.5W (your figure is 65 Watts from the label you read so you won't get 3.5A). The input figure does not mean it draws 2A, in fact its inrush current from cold will be a lot more than 2A, but that's another story. A 2A, 240V fuse will be sufficient to protect the device.
If the power supply consumed 460W to supply 65W what happens to the other 395W? Seems to me it would make a good heater. think how hot a light bulb gets and thats usually not more than 100W. Does your power supply get that hot?
Switchmode power supplies these days are 85% to 90% efficient - check some specs on the web.

An 85% efficiency means that 85% of the input power is converted to useful energy - in this case low voltage DC, and 15% is converted to heat energy. The input power will be 15% more than the output power, so we need 76.47 Watts input to get 66.5 Watts of electrical power and 9.97 watts of Heat.

As previously stated, the 150W 'pure sinewave' output inverter will supply sufficient power to drive the laptop power supply..

Kerry · Post by **Kerry** » 30 December 04 10:49 pm

You said the laptop draws 3.5A max at 19 volts. This is 66.5W (your figure is 65 Watts from the label you read so you won't get 3.5A).

Do we need to get to the Nth decimal place or does "around" 3.5A @ 19V get the meaning across. If it's pedantic you want then pedantic it will be

If the power supply consumed 460W to supply 65W what happens to the other 395W?

You do realize there is a difference between 240 volts and 12 volts

You know that might be the reason why it takes less power to run a DC/DC adpater than an AC/DC adpater eventhough the 12 volt input requires a higher amperage, funny that hey.

Here's a question for ya, same battery, same amount of charge (all things equal), same AC/DC notebook adapter, which mode will run the longer? Powering the adapter in AC mode through an inverter or powering the adpater via 12 volt

As previously stated, the 150W 'pure sinewave' output inverter will supply sufficient power to drive the laptop power supply..

It's your laptop, feel free to use whatever you like but then a DC/DC laptop adapter actually makes a lot more sense than any inverter.

Cheers, Kerry.

riblit · Post by **riblit** » 31 December 04 12:15 am

Kerry wrote:
If the power supply consumed 460W to supply 65W what happens to the other 395W?
You do realize there is a difference between 240 volts and 12 volts You know that might be the reason why it takes less power to run a DC/DC adpater than an AC/DC adpater eventhough the 12 volt input requires a higher amperage, funny that hey.

Cheers, Kerry.

If you read back through the thread you made the assertion that the laptop power supply would not work as it required more power than the inverter would supply. I have not seen anything in your remarks that offers any proof to that assertion or that disproves the points I have made. If any of my electronic students had offered an argument similiar to yours I would have failed them.

Geof · Post by **Geof** » 31 December 04 8:07 am

A smps has very different rules of operation than a series regulated power supply. They are a lot less waistfull and thats why they are widely used. Who wants 400 watts of heat coming from their power supply? If you intruduced 400 watts of heat (round figures OK) into one of those little laptop smps boxes you would end up with a smoking melted mess.

100 watts at 240 volts is 435 mA right. To use some of the above logic you would need 13.8 volts at 435 mA to power an inverter to produce that right

. Wrong Make that happen and you have a possable perpetual motion device and a Nobel Prize coming you way

riblit · Post by **riblit** » 31 December 04 9:29 am

Geof wrote:A smps has very different rules of operation than a series regulated power supply. They are a lot less waistfull and thats why they are widely used. Who wants 400 watts of heat coming from their power supply? If you intruduced 400 watts of heat (round figures OK) into one of those little laptop smps boxes you would end up with a smoking melted mess.

100 watts at 240 volts is 435 mA right. To use some of the above logic you would need 13.8 volts at 435 mA to power an inverter to produce that right . Wrong Make that happen and you have a possable perpetual motion device and a Nobel Prize coming you way

You can't take the 'above logic' and twist it around to say something like that Geof. The source of the 240V has not been mentioned apart from EcoDave's point that it would be sufficient to drive the laptop power supply and Kerry's assertion that it would not, because of what is written on the Laptop power supply tag. I have been concentrating on the Laptop power supply to show that its input current is a lot less than that stated on the tag. Ohms law and the conservation of energy hold irrespective of the power supply design. This can be proven very simply with the Laptop and Power Supply, a meter and 10 Ohm resister.

Your 13.8 Volt supply will need to deliver around 10A to get 100W at 240V from the inverter output (assuming 80% efficiency)

Now I'm going to look for a Kangaroo..

EcoTeam · Post by **EcoTeam** » 31 December 04 10:13 am

riblit wrote:
Kerry wrote:
A 150W "pure sinewave" inverter will work fine with a 70W switch mode converter
150W relates to the 230V output and the 70W relates generally to the 15-24 volt output of the adpater, both relates to OUTPUT. So how can an adpater the requires 230V ~2A input, that is requiring 506 watts work fine with a 150W inverter of any type?

Cheers, Kerry.
...and why do you think you need 506 Watts input power?

Huh?
I've just come back to this thread and haven't read it all, so please forgive me if I'm not with the program...

A "150W" inverter *should* supply just that, 150W of continous output power.
The laptop takes 70W max, so a 150W sine wave inverter should have plenty of reserve to power that. There is no need to calculate voltage or current here, power is power.

Going back to the orginal question. The 150W cheap square wave inverter didn't work because of the load being used (the SMPS laptop adapter). This is why I made the comment that a 150W sine wave version would work, because that's what the SMPS laptop adapter is designed to work with, and hence the efficiences would be reasonably high.

EcoDave

Geof · Post by **Geof** » 31 December 04 10:16 am

Your 13.8 Volt supply will need to deliver around 10A to get 100W at 240V from the inverter output (assuming 80% efficiency)

Yes that is the point I was making.

To use some of the above logic

"some" is the operative word here. I didn't specify how far above (it not from your post riblit).

The point I'm making is based on those cheap Inverters being nothing more than a stepup (voltage) smps with a mosfet h bridge on the out put to make so called modified sine wave.

The source of the 240V has not been mentioned apart from EcoDave's point that it would be sufficient to drive the laptop power supply and Kerry's assertion that it would not, because of what is written on the Laptop power supply tag.

Thats what My comments were all about. I thought if we looked at it from another angle it may all become clear.

Kerry · Post by **Kerry** » 31 December 04 10:42 am

Really in all of this it's becoming amazing how manufacturers specifications, apart from being a legal requirment are basically ignored although one of the purposes that manufacturers actually label input/output requirements of their power devices is so that users can determine the power they require to drive the thing and the power they expect it to deliver.

Maybe manufacturers are wasting their time putting specifications on devices as many appear to be quite prepared to ignore the spec and plug things together anyway. So why do you think manufactuers put specifications on devices? And if one ignores those spec then what does say about the user?

You know gen sets are quite interesting also, people generally go out and buy a gen set to provide enough power based on the loads they want to drive, end up with a 7kVa set and THEN use a 15 amp lead? People actually do this yet the simple laws of electricity states that 15 amps @ 230V can only handle 3600watts.

Finally can someone tell me how many amps can be delivered from a 150W output @ 230V

Cheers, Kerry.

Geof · Post by **Geof** » 31 December 04 11:17 am

Finally can someone tell me how many amps can be delivered from a 150W output @ 230V

652 mA - plenty of "I" to run your input name plate rated smps with a 19 volt 3.5 amp output rating. If I had a $ for every over rated name plate I would have more dough than Bill Gates

. I think a lot of these manufactures put the mains fuse rating on there product so as when the user replaces the fuse they won't overdo it. Sure the inrush current may be 100 amps or more for a nano second but not much longer. As for name plate ratings there are so many phone chargers etc out there that the name plate rating (out put this time) is of little relavance as the output voltage / current can change widly depending on what mode they are in. Thankfully laptop smpss are fixed voltage output and the current drawen from them is totaly dependent on the requirments of the laptop.

Gee may be the moderator should cut this thread and rename it the smps debate as we are waffling on

now of to find a cache... remember them

Map Monkey · Post by **Map Monkey** » 31 December 04 11:41 am

Hi all,

It seems to me, as an former electrician

, that many people are having problems coming to terms with the difference between true power and apparent power.

Let us move on somewhat from this discussion and solve some simple fundamentals.....check out http://www.pcguide.com/ref/power/ext/basicsPower-c.html for some good information......and don't forget to click through the various pages.

If people have problems with understanding this information, by all means ask away (someone else may be able to help

) . BTW this is by no means an attack on anyones knowledge, just a means to get all geocachers better educated

Regards

Agsmky

EcoTeam · Post by **EcoTeam** » 31 December 04 11:49 am

Kerry,
I'm afraid that you have missed the whole point of this, you are applying ohms law without actually understanding what is going on.

No current or voltage maths is required. Everthing can (and should) be calculated with the RMS power and the efficiency figures.

Here is the deal, ignoring any efficiency losses for the moment.
An inverter (or any power supply) which is specified at (for arguments sake) 150W (RMS), is capable of *supplying* 150W continuously to the load. If the load only takes 10W then that is all that is drawn from the inverter. If there is no load then the inverter draws nothing. (this is what Riblit was getting at)

That's it. It has nothing to do with the nominal mains input voltage or current, nor with the output voltage or current. There is no need to calculate these, and unless you know *exactly* what you are calculating, you will be wrong.

In the case of the said laptop, it is specified as drawing 70W *maximum*. The laptop will draw 70W regardless of what is used to power it.
The SMPS laptop converter is expecting a sinusoidal input waveform, the cheap square wave inverters do not produce this, so the SMPS is *much* more inefficient at producing it's output power.
Assuming 80% efficency of the SMPS (a typical figure), the inverter needs to be able to supply 87.5W. So in theory an 87.5W RMS rated sine wave inverter could power that laptop. The inverter also has some inefficiency, so it may be taking say 100W from the car battery total.

In the case of the square wave converter, things can get very complicated. But to make it easy to understand, basically, the SMPS will now be grossly inefficent, say only 25% efficent. Thus needing a 280W capable inverter. But as I said, this is grossly simplified. In reality, high frequency peak currents are more likely to play a major part.

Easy?

EcoDave