Author Topic: Why ST heads?  (Read 7542 times)

AdeV

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Re: Why ST heads?
« Reply #15 on: September 16, 2017, 07:58:31 PM »
The Chinese have also invented a way to copper plate aluminium...

Ick! Please don't do that for quoting again... my eyes are bad enough as it is, I could barely read it!

You can insert a quote in any number of ways; simplest is to click "Insert Quote" - RHS of each post underneath the reply box. This is ideal as it preserves quotes-in-quotes(-in-quotes etc.). Just be careful when you edit (trimming is always good) that you are closing the correct {quote} block! Preview is your friend here!

Second easiest way is to cut'n'paste the bit you want, highlight it in the reply box and hit the "quotes" button - looks like a speech bubble (kinda), next to the "#" button, just under "Font size" on the toolbar. That won't attribute the quote, but it will indent it & put it in a box.

Third way, hardest but best control, is to write the tags yourself: Open square bracket, the word quote, close square bracket, anything after that tag will be in quote format. To finish it, the same again but add a forward slash (/) straight after the square bracket. Kinda hard to show, but it should look a bit like this:

Code: [Select]
[quote]your quote here[/quote]
So no more shadow text OK? That's not a rule, but trust me, if I go cross-eyed trying to read a post, I ain't gonna read it...
Cheers!
Ade.
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1x Lister CS Start-o-Matic (complete, runs)
0x Lister JP4 :( - Sold to go in a canal boat.

BruceM

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Re: Why ST heads?
« Reply #16 on: September 16, 2017, 08:34:33 PM »
No, I'm not forgetting fundamentals of EMC, but it's good that you did a little thinking so as to attempt to redeem yourself.  This response shows signs of life. 

If you check again, you will notice that I listed specifically high frequency EMI as a potential problem for all electronics. I listed only one practical example from a specific thread here.  Alas you are incorrect again regarding relative EMI of square wave and MSW inverters.  The rise/fall times of output waveforms are typically controlled for Square wave and MSW inverters and they do not generally have high frequency EMI worse than sine inverters, as the latter often have switching rates internally that tend to be much faster, and many sine designs are now transformerless.  All inverters typically have very strong common mode higher harmonics in the 500K to 50MHz range; they vary dramatically depending on the designer's EMC skills. 

Yes, in fact I have designed, built and tested a specialized ultra low EMF/EMI inverter.  Low radiated and conducted emissions was the primary design goal. I selected a low frequency design based on the old Trace Engineering SW Sine series,  but mine  is a 5 step modified sine for 1500 watt continuous with 3500 watt surge load. The extra step allows for low enough THD to keep motors cool and happy, and the low number of transitions per wave allows relatively low losses using semi-linear, slow rise/fall times.  It starts and runs 1.5 HP motors (which is was the other design goal) and has measured THD of 8% and 92% power efficiency.  It uses two 1100 watt toroidal transformers and also has very low ELF magnetic fields. It was designed with low emissions as the primary design issue and an improved MSW was selected on purpose for that goal.  With NO passive filtration on the transformer(s) output, it has no audible emissions via AM radio within 3/4 inch of the output AC line. (Distortions via spectrum analysis are below 10KHz.)  I am still working on the prototype; I'm considering variable speed operation and soft starts for solar well pump application; much as Franklin now does on their single phase solar pump controllers.  I'm also adding passive ELF filtering of the DC supply side so that 60Hz doesn't show up on my clean DC.  Alas, the project has been delayed due to unavoidable home maintenance projects the last couple months. I'm saving up for a high performance spectrum analyzer to more fully tune the design for lower emissions.

To do a full, true sine wave with relatively high efficiency and ultra low EMI would be a hell of a design challenge, much more so than the design I have done so far. I compromised on a 5 step MSW (1st prototype was a 7 step) based on a couple academic papers proposing such an approach for better THD; though to the best of my research no one had actually implemented this before. 

So in short, square or MSW inverters are NOT inherently higher EMI,  I believe my multistep MSW likely is the lowest EMI of any ever built. (Not externally shielded and filtered.) There are many internal sources of high frequency EMI (500K to 50Mhz) that show up on the output waveform, primarily as common mode emissions.  You can easily confirm this via AM radio. Many inverters will wipe out much or all of the AM band within 8 feet of any connected above ground wiring.  Variations in good EMC design are far more significant that sine vs MSW or square or internal PWM rate.

I have some videos showing the 1st prototype design and some testing with an air compressor motor for anyone who is actually interested. It is non-edited and is only semi-technical for a very smart but non-EE friend.








I have also worked on  a few projects adding passive filtration to existing inverter systems.  This is problematic as most facility type, high performance filter have fairly high levels of capacitance to earth.  For many inverter designs, including Magnum's and mine, reactive loads drain the batteries just as well as linear loads.  I've worked with Magnum and Genisco engineers to come up with a specialized high performance filter that only draws 15 watts 24/7.  Many facility filters draw 100 watts or more, which is hell on a smaller off grid power system.

I don't typically talk about my electronics projects here because it is not the emphasis of this forum. We do have a couple other outstanding EEs here doing professional level designs for embedded MCU controllers. I'm really a EE/CS type but have taken graduate training in EMC 27 years ago and do advanced "hobbyist" level designs.



















starfire

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Re: Why ST heads?
« Reply #17 on: September 16, 2017, 10:53:03 PM »
Adev, it looked very different on the preview, I will try harder...... :)
BruceM has pretty much reiterated what I was saying, so all good....
I try not to get too techy with the electronics side of things as its not the primary focus here, but sometimes............ :o

cujet

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Re: Why ST heads?
« Reply #18 on: September 23, 2017, 09:40:54 PM »

How many hours of brush life are you folks getting with these ST heads?

 

I have an ST15 head, about 11-12 years old. I don't want to claim outrageous hours.  However, it's been used after multiple power outages and storms for many, many weeks of running. AND many, many weekends of "off grid" operation. Of course, it's stored outside in less than ideal conditions. Just this last storm racked up 125 hours of use.

So, let's say it now has at least many hundreds of hours, at least 500, and 11 years.

The brushes don't have any noticeable wear. Come to think of it, that's the first "good" thing I've ever said about my ST15 generator head. As the power quality certainly is not great, nor was the chronic low voltage. (fixed with a CGG VR running off the main winding)

Just a guess, I'd say the brushes have an extremely long lifespan.
« Last Edit: September 23, 2017, 09:43:02 PM by cujet »
People who count on their fingers should maintain a discreet silence

mike90045

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Re: Why ST heads?
« Reply #19 on: September 24, 2017, 06:49:43 AM »
>  Flicker shows up only in  cheap LED/CFL designs where there isn't true regulation. 

Uh, it also shows on my incandescent bulbs.

mikenash

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Re: Why ST heads?
« Reply #20 on: September 24, 2017, 08:18:47 AM »
>  Flicker shows up only in  cheap LED/CFL designs where there isn't true regulation. 

Uh, it also shows on my incandescent bulbs.

FWIW I have six generators in various service vehicles and other situations.  All of them have done duty at my off-grid site where I hope the 6/1 will some day serve.  There's a 2.2 kVa Honda which is six months old and probably has twenty hours on it.  There's a 5 kVa Honda/Dunlite which died last year at ten years old.  There's a 7kVa Honda-engined unit with a Chinese alternator which i bought new and is used almost exclusively to run the arc welder, there's a 2.2kVa Chinese Honda-clone the brand of which escapes me which has been the working genset in my service vehicle - I don't know how many hours it has done but it's on its third starter assembly and second AVR, and there's a 6kVa Chinese Honda clone mostly used by my neighbour which I bought last year at six or seven years old but with only ten hours and a lot of dust on it,  and there's a 2.5kVa Honda Dunlite now 14 years old and still going strong as a backup on another site  . . .

What I'm getting around to here is that I have spent a lot of time in my house/shed/workshop there, in the dark, with the lighting running of whichever one of these is in service - and they all flicker just the same as each other, as far as I can tell.

Just my $0.02

BruceM

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Re: Why ST heads?
« Reply #21 on: September 24, 2017, 04:57:02 PM »
We would expect only modest perceived flicker on incandescent bulbs or non-regulated CFLs and LED bulbs from 3600 rpm driven generator heads.  Some will see some 30 Hz flicker as the engine slows between power pulses.  It is likely that none of the cheaper AVRs will do anything other than provide an average voltage that is correct.  The marketplace is a race to the bottom, and for most sales, flicker is a non-issue. 

It is very different than with slow speed engines...where the flicker rate goes down into the human biological range (brain wave frequencies).  This can be profoundly disturbing for some.

Perception of flicker varies significantly between individuals, and other conditions.

Truly regulated bulbs are the simplest solution, and the inverter-generators are also a good solution. 






mike90045

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Re: Why ST heads?
« Reply #22 on: September 24, 2017, 08:43:34 PM »
....and the inverter-generators are also a good solution.

there's an idea, find a gen end from a honda euxxxx and belt that onto the listeroid

BruceM

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Re: Why ST heads?
« Reply #23 on: September 27, 2017, 11:52:44 PM »
The variation in ratcheting/ spikes on the waveform is the big problem. On bad ones, it makes some electronics a problem.

Will the vendor specify THD of 7% or better and/or show you a waveform image?  If not, run away.

Do you have a way to measure THD and look at waveform of the one you get? What will the vendor do for you when you find you got something grossly out of spec???