Inverters - how do they work? Something for nothing?

Beyondhelp said:
Where did it go wrong? I'd rather not make the same mistakes...
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You seem to be suffering unit stew...1320 Watt hours, not 1320 Watts per hour. 1 kW, not 1 kW per hour. Both Watts and Amps already have time incorporated in them (Joules per second and Coulombs per second). If you say x Watts per hour or y Amps per hour, you are very likely to be wrong.

You may think this to be trivial, but if any calculation is going to be meaningful it has to have the units correct. It's a bit like saying the distance between home and your boat is 86 miles per hour. It doesn't make sense.
 
Beyondhelp said:
Why needlessly complicate things for people who don't care to know the difference? Granted I could have made the point clearer, but equally you could have refined it further yourself.

Your mentality intrigues me, your probably about twice my age, and you behave as above? Where did it go wrong? I'd rather not make the same mistakes...
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Watts are units of power not energy. But if that is needlessly complicated and you don't care, that is fine by me.
 
RichardS said:
It can be surprising how quickly the current drain mounts up.

We have a small inverter which plugs into the 12V "cigar" socket on the boat. It's rated at 200W or similar and my wife uses it for her hair tongs but it's not powerful enough for the hairdryer. A couple of years ago she tried to use the tongs whilst one of the boys was running his laptop off the inverter at the same time. It immediately blew the 10 amp fuse in the boat wiring loom!

Lesson learned - tongs always go solo!

Richard
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12V "cigar" sockets are probably the worse kind of DC socket in history. From the outset not designed for any amount of current for long periods of time. You're lucky it had a correctly rated fuse. I've seen people run inverters on laptops drawing around 60-90 watts for long (1hour+) periods of time which whilst below the fuse rating ultimately resulted in melted plugs/sockets. Often the cabling isn't up to it either.
 
awol said:
I know I shouldn't let it get to me but I cringe when I read some of the above. The "1000 watts of usable energy" in the latest missive has pushed me over the edge. Aaaagh!!!!

... and now another "kilowatt of energy" from someone who thinks he's a "physicist". Ye gods!
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leaving aside for the moment that the OP is non technical and doesnt want confusing with technical pedantry, I'd be interested in knowing what is wrong in your view with a "kilowatt of energy". The OP doesnt gain by me adding minutes, hours , years or whatever to the end of it does he?

Thats often the problem with this forum. Someone asks for a simple explanation and instead of getting one he gets posters showing off what they think is their technical prowess in far from simple explanations or alternately technical nit picking.
 
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AngusMcDoon said:
You seem to be suffering unit stew...1320 Watt hours, not 1320 Watts per hour. 1 kW, not 1 kW per hour. Both Watts and Amps already have time incorporated in them (Joules per second and Coulombs per second). If you say x Watts per hour or y Amps per hour, you are very likely to be wrong.

You may think this to be trivial, but if any calculation is going to be meaningful it has to have the units correct. It's a bit like saying the distance between home and your boat is 86 miles per hour. It doesn't make sense.
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That will teach me not to proof read I suppose. I forgot to take into account the fact that I would be judged by my 'peers' in commenting on such a topic, whilst trying to help others who may know even less than myself...
 
wotayottie said:
leaving aside for the moment that the OP is non technical and doesnt want confusing with technical pedantry, I'd be interested in knowing what is wrong in your view with a "kilowatt of energy".
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Technically it does need to be 1000Wh. Energy is power x time. So "kilowatt of energy" doesn't really make sense.

All appliances/devices are rates in Watts (power), but more clearly it really means if this light bulb is on for an hour it uses 100Wh of energy. As I was corrected on above, it does help to get the units right, but didn't feel the need to really be that fussed given the topics intentions - this as you can see is easy bait for those who like to pick up on this, but I can also see you got the idea of what I was trying to get across anyway.
 
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Well yes, Beyondhelp. I am, or at least was some 40 years ago, as well equipped as most to pick technical nits but like you I wanted to help the OP without getting involved in anything more than very broad brush. It doesnt help the OP when posters arguing technical trivialities.

As AWOL said before he decided to get snotty
awol said:
Watts are units of power not energy. But if that is needlessly complicated and you don't care, that is fine by me.
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Beyondhelp said:
That will teach me not to proof read I suppose. I forgot to take into account the fact that I would be judged by my 'peers' in commenting on such a topic, whilst trying to help others who may know even less than myself...
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I didn't intend to be judgmental or nit-pick, but I thought you had simply asked where you had gone wrong. As Awol said, if you want to use watts per hour, that's fine by me.
 
This discussion has gone a bit ugly. Yes often on this forum we see people describe a battery as "100A" when really they mean 100Amp hour. Likewise watts describe power at that instant whereas energy is watts per hour. It seems our language often allows for dropping important detail from common usage which is bad when we are describing technical detail. Play nicely now children.
Re how an inverter works. Yes early inverters used power transistors to switch the battery12v DC 50 times per second.
Indeed I used to have an old vibrator inverter where a coil and break contact made a reed vibrate 50 times per second which had contacts for switching the 12v DC. This approach needs a transformer then to transform this AC to 240vac. The transformer being a great lump of iron and copper.
However inverters came onto common shop shelves when the newer form was developed. Here the 12v DC is switched again into a transformer but the frequency is more like 500 000 hertz. This allows a very small transformer for the same power. The high voltage of the transformer output is rectified and appears as a Dc voltage around 240vdc. Actually a lot more but that complicates description. This DC is simply switched and reversed by high voltage transistors to give 240VAC. This is essentially a square wave not sine wave. The actual voltage is adjusted to give the power of a 240vAC sine wave but in square wave form. Which is fine for a lot of applications.
However a sine wave close approximation can be "assembled" from the DC using a microprocessor. It provides a little burst of power for increasingly long and then shorter periods 20 or so bursts assembling a half of a 50 hertz sine wave. The bursts are then applied in opposite direction to produce the other half of the sine wave. A lot more complicated but when smoothed out can give a true sine wave which is a lot better for many devices. especially induction motors.

Note for the OP any device which produces heat will generally need a lot of power at 240v so should not be used on an inverter. so no electric kettles hair dryers radiators etc. good luck olewill
 
William_H said:
This is essentially a square wave not sine wave.
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Yup, This is what a cheapo inverter output looks like...:eek:

IMAGE020.jpg
 
It's an internet forum.

Truth be told this whole energy/power topic is elementary electronics at best. I'm not about to prove what I do or don't know on such subjects, but as it happens I did build myself a 250w mains inverter when I was about 13 - so 1993/4 ish, as far as I know long before any cheap modified sine wave ones appeared on the market. It used to occasionally fry the TO-3 Darlington drivers under heavy load :)
 
Well then, Forumites. That's been an illuminating (if not somewhat confusing) wee spat!! Thank you, one and all.
As some of you have accepted or pointed out I am very inexperienced in electronics, electrics, physics etc (it's a long time since GCE "O" Levels !!) and so my original question was for a basic "does it or doesn't it work" sort of answer.
But I've enjoyed the technical spat, and actually learnt something. Or perhaps I should say re-learnt something from 1964.

As for the thread drift, I find myself guilty of the crime myself at times, so I forgive you "drifters". Perhaps the Forum should have a facility/button to run drifts in parallel (or should that be "in series";) ) so that the OP is maintained while the technical/subjective opinions are aired. Just a thought.

Anyway, my original question has been answered, thank you, but please feel free to continue with the technical stuff. I'm actually enjoying the drift - but I would ask that the emotions are kept within gentlemanly/ladylike limits :)

P.S. I feel so sorry for the fried Darlington drivers.
I ran a transport company in Darlington in the 70s and often wondered what happened to my absentee drivers....................
 
I am going to support the so called 'pedants' here.

Electricity is not that hard and if you get the units right, then how to calculate them becomes obvious.

Imagine asking a schoolboy:

Birmingham is 90 miles per hour away. You drive at a speed of 45 miles. How long would you take?

Obvious rubbish and totally confusing !

Yes?

Well the same is true for electricity.
 
Robert Wilson said:
As some of you have accepted or pointed out I am very inexperienced in electronics, electrics, physics etc (it's a long time since GCE "O" Levels !!) and so my original question was for a basic "does it or doesn't it work" sort of answer.
But I've enjoyed the technical spat, and actually learnt something. Or perhaps I should say re-learnt something from 1964.
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1964? Ah, those were the days with ergs, dynes, poundals, slugs, etc. with the perennial question - to "g" or not to "g"? It was a wonder anyone understood them.

The yoof of today with only 7 basic SI units to shuffle to cover everything really have no excuse. Almost all calculations (or explanations) involving these units have a "right" answer and that includes getting the nomenclature of any derived units correct. Any other answer is wrong - and if that is pedantic, so be it.

I have always liked the water analogy for elektrickety (as expounded by wotayottie) - at least it ends up with the right units!
 
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