Guest David Posted July 4, 2005 Share Posted July 4, 2005 Clive can you help please. How much power do's a small inverter use, ie,drain onbattery. I am thinking of one to power a lap top 16v 3.36a using its mains power lead, to supplement the battery life. David Link to comment Share on other sites More sharing options...
Guest Clive Posted July 4, 2005 Share Posted July 4, 2005 Hello David, Modern Inverters are quite efficicnt, normally in excess of 90%. 16 volts X 3.36A = nearly 54 watts. Add 10% for the inverter losses and the maximum wattage your inverter will require will be about 60 watts. 60 devided by 12 volts = 5 amps from the battery. But the Laptop will only require this power when all disk drives are running and the processor is very busy processing fast moving graphics. Most of the time it will be a lot less. Allowing for the ineficiencies I would say allow an average of 2.5 to 3 amps to run your Laptop off the inverter. Hope that helps Good luck Clive Link to comment Share on other sites More sharing options...
Guest David Posted July 4, 2005 Share Posted July 4, 2005 Hi Clive, Thanks that sounds OK to me think I will get one. Some long time ago I asked about running GPS on laptop, not decided yet. But someone answered and said that their Lap Top kept crashing whilst on the move, not liking the bumps etc. I have tried mine running a programme whilst on the move and it was OK. I did put a pad of foam underneath it, making sure all vents were clear, I think this ironed out the bumps. Thanks again. David Link to comment Share on other sites More sharing options...
Guest Neal Posted July 4, 2005 Share Posted July 4, 2005 David Having up-graded to a 1000W inverter I have a British-made 250W modified sine wave inverter surplus to my requirements. If your interested respond with your email address and I'll contact you. Don't mention this to Clive!! (only joking) Regards Neal Link to comment Share on other sites More sharing options...
Guest Clive Posted July 4, 2005 Share Posted July 4, 2005 I have found a problem with AC from inverters and have tried all inverter types, pure sine wave, modified sine wave and my home made square(ish) wave. They ALL generate lots of electrical noise that wipes out HF radio reception on most ham bands unless the incomming signal is stonking. Real mains is OK. Even pure sine wave inverters generate it with with lots of little rectangular waves of different magnitudes put together and the radio can hear them all! You can't beat rotating machinery for a real pure sinewave. I notice that our local largish caravan shop at Woolhampton sells inverters of the same type as Maplin do but at twice the price! Maplin £29.99 for 600 watts. £19.99 for 300 watts. Link to comment Share on other sites More sharing options...
Guest Bill Posted July 5, 2005 Share Posted July 5, 2005 Clive Given the advantages of “rotating machinery”, why doesn’t anybody build a 220v alternator driven by a 12v motor? Wouldn’t this also be cheaper - at least for the higher wattages - than the solid-state contraptions we use? (Not to mention quieter than a petrol generator. I suppose we could imagine a generator with a selectable choice of petrol or 12v motors.) Link to comment Share on other sites More sharing options...
Guest Clive Posted July 5, 2005 Share Posted July 5, 2005 A 230v 50 Hz alternator capable of producing say 1.5 Kw will be about10 inches diameter and about 14 inches long. It must have its speed carefully controlled to 3000 RPM. It will be bl...y heavy and quite expensive. The driving motor will be of a similar size and weight. It will also make a noise. I am afraid that these solid state contraptions do have quite a few advantages re size, weight, cost etc but they sure screw up HF radio reception. I have a 3 KW alternator connected to a Petter diesel in my garage. It would far exceed the residual weight capacity of most motorhomes. I will just run my Laptop from a BIG battery that will last. Link to comment Share on other sites More sharing options...
Guest Bill Posted July 6, 2005 Share Posted July 6, 2005 Clive Many thanks for your reply, but I’m still puzzled. You can buy off the shelf a 2.5kw 220v petrol generator that is nowhere near as big, heavy and as you describe, and cheaper than a 1.5kw inverter. Given that petrol motors usually weigh more than electric motors of similar capability, how do they do it? And why couldn’t our hypothetical converter do likewise? Link to comment Share on other sites More sharing options...
Guest Clive Posted July 6, 2005 Share Posted July 6, 2005 I think Bill is trying to keep this one going! Some of the later petrol powered generators actually have an alternator running at greater speeds than conventional that produce a multi phase output which is then rectified into DC This DC is used within the contraption to feed an inverter that produces the 50 Hz near sinewave output. Quite clever but also likely to upset my HF radio! The aproximate sizes I proffered were based on some old squirrel cage single phase AC motors I have on equipment in my garage. A motor and an alternator are quite similar in many respects. I think you are mistaken with your 2.5 Kw generator and 1.5 Kw inverter cost comparison. The inverter should cost less. Electric Motors and Alternators operating at 50Hz are likely to weigh more that a light weight petrol engine, especially if this engine is running at a greater speed than the alternator. On the other hand a directly coupled diesel plodder will be a heavy old lump. I have two, one iron engine which runs at 1500 RPM and the other an aluminium engine that runs at 3000 RPM. Both drive alternators to produce 50Hz but one alternator is single pole and the other double pole. By now most should have nodded off! Link to comment Share on other sites More sharing options...
Guest Bill Posted July 8, 2005 Share Posted July 8, 2005 Clive No, this is not a wind-up! I am genuinely seeking after having an apparent anomaly cleared up. I was not aware that there was gearing involved – though it makes sense. In the July issue of MMM, a 1.5kw inverter is advertised on page 207. It is second-hand, but the advertiser says the new price was £300. On page 357 a company called Quadpower advertises a 2.5kw petrol generator for £299. If you have ever bought a petrol lawnmower you will know that they are a good deal more expensive than the electric equivalent – and I can only assume that the difference must be because petrol motors cost more than electric motors. Why not replace the petrol motor in the Quadpower by a 12vDC one? For me at least, at this sort of level the questions are academic, because you would need a battery the size of the one in a U-boat to sustain a 2.5kw output for any worthwhile length of time. Link to comment Share on other sites More sharing options...
Guest Clive Posted July 8, 2005 Share Posted July 8, 2005 Hi Bill, Well there are always exceptions. I use a Hayter Harrier mower for my grass and these are over £500 new. I have recently been told I can purchase a petrol mower of the same size for under £100 from B&Q. But on digging deeper into the detail you only get what you pay for. Hayter has a Briggs and Stratton 4 HP engine and powered roller the B&Q version doesnt have this or Honda (the other reliable motor) Traditionaly motor-generator sets have the two units coupled directly on the same shaft. But to get more power out of the same set of engine bits you use gearing or belts to enable the engine to run faster. Another detail, with directly driven sets the engine speed must be accurately controlled to achieve 50 Hz. With those modern units that generate DC and have within them an inverter the engine speed is not that important. I suggest you look carefully at your 12 volt loading, perhaps invest in a solar panel and leave generators alone. I purchased a 800 watt Yanmar 4 stroke generator, loverly little job like a small briefcase and quite quiet, carried it around for 3 years and never used it. So sold it and got an 80 watt BP Solar Panel. Link to comment Share on other sites More sharing options...
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