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12 volt DC -> 240 volt AC inverters

 
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richard333



Joined: 02 Nov 2005
Posts: 6
Location: Midlands
PostPosted: Mon Nov 21, 05 8:01 pm    Post subject: 12 volt DC -> 240 volt AC inverters  Reply with quote    

Hi,

Are these inverters any good?

For example, can you drive economy eco-bulbs from them?

How about TVs, radios & computers?

Or is the square wave / modified sine wave they seem to give out totally useless for most equipment?

Thanks!

Richard

hardworkinghippy



Joined: 01 Jan 2005
Posts: 1110
Location: Bourrou South West France
PostPosted: Mon Nov 21, 05 10:00 pm    Post subject: Reply with quote    

Hello Richard,

Why don't you buy economy bulbs that operate directly from your DC source rather than changing the current to AC ?

I've just been experimenting with 12v LED lights, I've posted pics in the "cheap lighting" thread a few days ago. We've spent this evening wiring up more, it's really exciting. (Well, it's my idea of fun anyway )

I'm typing this now with a laptop powered by solar connected to a tiny little car inverter which I bought about four years ago.

I've never had any problems with either this or the larger (600 watt) inverter that we use in the house.

We use all our 220 equipment - hand tools, shearers, rechargables stuff etc with the inverter and have never had any....



BOOM !

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Tue Nov 22, 05 12:03 am    Post subject: Reply with quote    

Hi Richard!

Generalisations!
An inverter is at best 90% efficient. So at least 10% of your power is going to go as heat.
So using low voltage kit will be a more efficient solution.
Computers - a "mobile" (rather than "desktop replacement") laptop will use a fraction of the power of a "mains" machine. You can probably find one whose (mains) battery charger outputs 12v. There would then be no need to go up to 240 and down again to 12... (My iBook charger outputs 24.5v... how tricky would that be?)

TV's and radios may suffer "interference" from the 'rough' power from a "modified sine wave" inverter. But you can find tv's and radios that run off 12v - they are sold for use in cars and caravans... My Sagem Digital Terrestrial TV box wants a nominal 13v input from its fat plug 'transformer'... !

If you must run 240v equipment (which is rarely designed with energy efficiency as a prime consideration), then a true sine wave inverter should run anything (as long as it can handle the load - including any starting transients.

Have a look here
http://www.windandsun.demon.co.uk/inverters_standalone.htm
you'll find similar stories across the web...


A good reason for using an inverter is to cut your powerline losses -
Power is volts x current
But losses are proportional to the current *squared*,
so using a higher voltage to transmit the same generated power (lower current) would dramatically reduce the losses - and your investment in thick copper cables...

Jonnyboy



Joined: 29 Oct 2004
Posts: 23924
Location: under some rain.
PostPosted: Tue Nov 22, 05 10:39 am    Post subject: Reply with quote    

Can't remember much about my 'o level physics but IIRC the main problem with inverters is poor supply quality under load.

From compariative pricing if you want to supply to devices that require high loads then go for a generator. If it's eco bulbs at 11w each or laptops, portable tv etc, then you should be OK.

dpack



Joined: 02 Jul 2005
Posts: 34459
Location: yes
PostPosted: Tue Nov 22, 05 6:19 pm    Post subject: Reply with quote    

malcome would be yr man but i dont know how to sort that ,sorry .

dpack



Joined: 02 Jul 2005
Posts: 34459
Location: yes
PostPosted: Tue Nov 22, 05 6:23 pm    Post subject: Reply with quote    

new reality , new physics . i do know some things but not this one . as i say he knows plenty .

Last edited by dpack on Tue Nov 22, 05 6:25 pm; edited 1 time in total

dpack



Joined: 02 Jul 2005
Posts: 34459
Location: yes
PostPosted: Tue Nov 22, 05 6:24 pm    Post subject: Reply with quote    

pps make it work

richard333



Joined: 02 Nov 2005
Posts: 6
Location: Midlands
PostPosted: Tue Nov 22, 05 7:52 pm    Post subject: Reply with quote    

I've had a think about this. I really want an emergency supply rather than a long term eco power system.

The cost of charger+battery+inverter [or 12-volt lighting] is non-trivial ... for me anyway.

The battery life is not good either, with any size of load.

I have found a 2-stroke generator for under 100 all-in :
http://www.worldofpower.co.uk/acatalog/SIP_04515_Suitcase_Generator.html

Whilst not exactly eco, it seems the overall cheapest solution to power cuts of say 4 hours a day for a couple of weeks, as might result from very cold or very violent weather, or if support staff got the dreaded [not yet existent] bird flu.

Almost a "plug & play" solution.

Any comments anyone?

Richard

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Tue Nov 22, 05 8:53 pm    Post subject: Reply with quote    

Well, its less than 1kw max.
And I'll bet it wouldn't last long if you ran it mainly near peak power...
That should be enough to supply the electric needs of a conventional central heating system (don't forget to allow for high startup currents for pumps) and a few lights.
Don't forget that you would not connect such a device to your mains.
You connect specific the item(s) to the genny.
And most ch systems are not wired through a 13amp plug. So you may have some tampering to do.
Then there's safe fuel storage. And petrol doesn't 'keep' indefinitely.

Note that it would need to be 3x more powerful to run an electric kettle...

Personally, I think there should be little risk of a (domestic) power shortage - leaving aside other risks to civilisation. But that's an entirely different matter.

It could provide insurance against that sort of risk though. But is pretty unlikely to have any other justification or use.
Maybe something a little more powerful - capable of running a power tool far from the mains - might be more generally useful?

Jonnyboy



Joined: 29 Oct 2004
Posts: 23924
Location: under some rain.
PostPosted: Wed Nov 23, 05 12:01 pm    Post subject: Reply with quote    

richard333 wrote:
I've had a think about this. I really want an emergency supply rather than a long term eco power system.

The cost of charger+battery+inverter [or 12-volt lighting] is non-trivial ... for me anyway.

The battery life is not good either, with any size of load.

I have found a 2-stroke generator for under 100 all-in :
http://www.worldofpower.co.uk/acatalog/SIP_04515_Suitcase_Generator.html

Whilst not exactly eco, it seems the overall cheapest solution to power cuts of say 4 hours a day for a couple of weeks, as might result from very cold or very violent weather, or if support staff got the dreaded [not yet existent] bird flu.

Almost a "plug & play" solution.

Any comments anyone?

Richard


I wouldn't recommend it (obviously)

But I connected my house to a 3kva 4 stroke transformer when we were waiting on the supply. I gave enough to light the house (eco bulbs) run the central heating pump and a fridge.

The big problem is connecting it to the supply and what do do when the power comes on. I can't see you finding a safe way around that.

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Wed Nov 23, 05 12:32 pm    Post subject: Reply with quote    

Jonnyboy wrote:
... The big problem is connecting it to the supply and what do do when the power comes on. I can't see you finding a safe way around that.


PLEASE Don't anyone think of connecting such a genny to their house mains during a power cut.

Jonnyboy had an unusual situation where his house was internally wired but not physically connected to the mains.


Plug any specific items into the genny. Use a socketstrip. As previously remarked in a thread of Jonnyboy's, be careful with earthing, and don't rely on ELCB protection...
Don't even think about hooking the genny to the ordinary house wiring. (Unless you have a professionally designed fully synchronised and mains intertied "alternative energy" setup, when you wouldn't be thinking about a 1kw petrol emergency generator...)

For emergency use, fuel cost hardly matters.
But for more routine use, it would.
It's effectively impossible to buy petrol without paying Road Fuel Duty - a waste for a genny.
Diesel generators should be able to run legally (if they physically will) on alternative fuels, like biodiesel, veg oil, paraffin mixtures, heating oil...

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