Don’t agree with the Expert

[Jcorstorphine]

In the December edition of PBO it was mentioned that cheap generators will produce a square wave rather than the pure sine wave associated with normal mains.

Now, I may be totally wrong but I cannot see how a rotating winding within a magnetic field can produce anything other than a sinusoidal waveform. It is true that the cheaper solid state inverters produce a square wave and they are not suitable for many types of electronic equipment but I have used my TPG 950 from B& Q (£65) to power my Hi Fi with no problems. Just to check my theory I will attach an oscilloscope to the output via a Voltage dropper and look at the waveform.


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[Talbot]

I'm with you on this, expect to see a nice sine curve.
Cheap inverter is a different matter!

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[macd]

Suspect you're dead right. Can't see how a gennie can easily produce anything but a sine wave. But a journo confusing generator with inverter in the heat of deadlines...that seems well within Faraday's laws.

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[HenryB]

Your theory is OK as far as it goes, but I'm fairly certain that my small generator uses a built in inverter to produce the 220 volts, hence the square waves. It needs some bit of electronics otherwise it would have to be run at a constant speed in order to maintain the 50 cps frequency.

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[Viking]

Re: Watt???

Thought generators produced electricity not waves????

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[fireball]

Re: Watt???

it was sat in the puddle ... the vibration caused all the waves.

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[William_H]

Thats an interesting concept for an AC generator. (A bit unexpected) can you confirm that you get 50 hz at any engine speed? Most generators (AC) must be run at a constant speed. It is interesting that on jet engines driving alternators they use a very complex constant speed drive gearbox to produce correct alternator rotation speed over arange of engine speeds to get a correct AC frequency. Regarding journalists it is really off puting to be treated like imbeciles by journalist and even more off puting when you know they are way out of their depth yet still try to appear to be an expert. (Only buy PBO for the pictures) regards will

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[ccscott49]

You are partially right! Cheap generators will produce sine wave leccy, but cheap inverter gennys do in fact produce modified sine wave, which is just a double square wave. But as you say, my modified sqyuare wave inverter, powers all my fancy lectronics, without trouble.

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[andyball]

http://store.advancedmart.com/si4diinelge3.html as one example


many generators use inverters inside, not just cheap ones. Probably reely cheap ones will be square wavey..Mind you, Honda say ...

"Honda also offers Inverter Generators. Inverter generators are smaller and lighter as power is created electronically and not through a conventional alternator. Inverter power offers the cleanest power output, ideal for sensitive electronic devices.



Also, even non-inverter cheap gen's can't manage a proper sine wave, esp under full load.

 

[HenryB]

William,
I can't check it now because the genny is on my boat. It's a Honda 350 watt unit and has 2 speed settings for 175 and 350 watt output. The motor runs at approximately double speed at the higher setting. It powers all sorts of electronics at either speed, but it won't run a battery charger - I've tried several but none works. I'm sure that the frequency stays fairly constant and assume that it's the square waveform that stops the chargers working. The electronics are sealed in potting compound so I'm not sure what goes on inside.

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[Robin]

I would suggest that unless you have a small output 12v charger the reason your generator will not run it is lack of oomph or va va voom. Most chargers are not 100% efficient at converting AC amps to DC amps and even those that are have another problem (power factor I think it is called) that reduces it too. I'm no expert except that we had a 750w Kwasaki generator on our old boat and it would not run a modern 30A 'smart' charger. We had a real expert, in fact the charger designer, (Poweramp Hawk) come on board with a huge dummy load set-up so he could simulate ultra flat batteries and call for max charger output, he then detuned it so the Kawasaki could just run it without tripping the trips, about 25A at 14.4v DC.

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[HenryB]

Robin,
Overloading isn't the problem. If I try to run the boats main charger (a 2x20A smart unit) the generator throws the overload switch. If I try using chargers (as low as 4A) the generator runs OK but the chargers just don't output anything, hence my guess that it's the waveform that's just not compatible with the transformers in the chargers.
Any other ideas most welcome.

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[Robin]

Ah but something is trying to happen since your 20A unit throws the trip on the genny. Maybe the actual output from a tiddly 4A charger (I bet that it will never do that 4A, probably 2A max) is too small to register? On our current boat we have just fitted a Sterling 40A 'Pro' which has a separate remote controller and can switch down the output from 100% to 75%, 50% or 25% so hopefully cutting it to an acceptable level for the genset but it isn't on board and I haven't tried it yet.

Hopefully someone really in the know will pop up soon!

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[computertech]

Correct

that is exactly what is happening
stu

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