Power Factor

[Ian]

carlb23, Yep, the thought of driving a DC motor had crossed my mind but the ST head is known to be bomb proof and would also allow me to isolate my house from the grid and drive the house totally from the ST if the grid power were to go off for a long time (because the grid tie inverter automatically shuts down when there is no grid). Besides, my warped mind thought that DC rectification was a more elegant solution!

Keep the suggestions coming!

Regards,
Ian

[Ian]

Jim Mc, many, many thanks for your considered reply - this is precisely the kind of knowledgable feedback that I was looking for along with the "University of Life" feedback that others have kindly given. This is a great forum with people trying to help each other rather than give the 101 reasons why you shouldn't do something.

I have access to a couple of 3 phase ST heads and this is my fall-back solution. I guess, from your response, that this is no longer a fallback but probably my next step!

Do you have any other pointers or tips ?
What kind of ripple should I be seeing if I full wave rectify a 3 phase alternator (would it be in the region of <10%) ?

Regards,
Ian

[Holter]

SMA Is offering their Inverters with Trafo (also the SMC6000) in another version as Windy boy. The technician did not recommend you this? Those Inverters are here often used for cogeneration. they are often connected to the rectified power of a 3~ PM Generator.
The Windy Boys are technically similar (if not the same) to Sunny Boys, but instead of the MPP Tracking mechanism you can program the evacuated Power in relation to the DC voltage to match the Power output of a wind generator at different wind speeds, but of course you can also let it operate at a fixed DC Voltage or constant Power for cogeneration.
But here also: 3 Phase or smoothing the DC with Capacitors (with fixed voltage operation even the use of a small battery bank may be possible)

Christian

[Ian]

Christian (Holter), you are correct, the technician(s) did not recommend the Windy Boy.

As has been mentioned previously, product liability must be drummed into the tech support guys and the summaried answer they must give when someone like me asks the questions is ..."SMA make inverters for PV and wind turbines, we do not have an inverter for what you are doing"

Now, I hope I do not sound like I am advertisng SMA products here but I chose the Sunny Mini Central 6000A because it is very versatile. SMA do not really advertise the fact, but, if you have the installer password (and a piggy back connector), you can configure it for the following "modes" - PV (MPPT), Turbine (MPPT), Constant voltage, Constant current, Off grid.

In my limited experimentation so far, I have found that the PV (MPPT) mode extracts more power than I have managed to do with either the Turbine mode or Constant voltage - but, hey, there is a lot still to play with.

Is there anyone else out there rectifying single phase AC and using the rippled DC as the input to a grid tie inverter and if so, what are your observations and thoughts please ?

Is there anyone else out there using an SMA inverter in a similar way ?

Regards,
Ian

[Ian]

Hibbo - No, the capacitors are kind of "ringfenced". I think a photo would be best but I do not have one to hand right at the moment.

If I remember correctly....
The DC inputs go into a monitoring area of the PCB where, I guess, voltage is determined and reverse polarity taken care of. This is also the section that SMA call their ESS switch - it is quite a neat device to electronically cut the DC circuit before disconnecting a DC cable (it attempts to stop the potentially very large and alarming arc that may ensue if the DC cable is disconnected whilst still under load). Other cicuits here include "ground fault monitoring" and "then overvoltage protection", monitored by some varisters. The power for the rest of the inverter is also taken around here.

Then, I think we get to the capacitors - 20 massive PCB mounted jobbies!

Why do you ask and what can you tell ?

Regards,
Ian

[Doug]

"the ST head is known to be bomb proof"

No thats a stretch.....

The ST is Bomb, dirt cheap and known to be made workable.

What brands are your ST and heads and from whom did you purchase them?

[Ian]

Doug,

ST brands and sourcing:
One of them is branded "Shanghai Yangke Engine Co Ltd" which I obtained from Volvox here in UK before it went out of business or ceased to trade or whatever (no answer to calls or e-mails and a disaster I would not want to repeat). This unit has done 200 hours and the front bearing neded replacement due to noise plus the "soft, dull, non metallic knock sound". It takes longer than most ST heads to self excite (even after cleaning up the slip rings and brushes). The bridge rectifier was a good quality unit and it came with an AVR (that really works) and a doghouse mounted two pole breaker. The doghouse is larger than most with a hinged front panel door. One of the interesting features is a couple of doghouse front door panel mounted LED lamps. There is a red lamp which illuminates almost as soon as the voltmeter shows any output voltage and stays illuminted whilst there is voltage upon the output. the second lamp is green and only illuminates when the voltage on the output gets above about 200V. I think it is interesting because both of these lamps are wired across the mains output (actually across the voltmeter) and they must have their own built in resistors, diodes and zener diodes and the brightness does not vary with voltage. If I remember correctly there are 3 or 4 surface mounted LEDs under the front lenses and are quite bright. I like these lamps so much I would like to fit them to my other ST head but I cannot find any more like this - so if anyone knows where I can get a couple from - please let me know.

The second ST head comes from "Stationary Engine Parts" in UK. Whilst the doghouse and innards is different, the main machine appears to have exactly the same components, materials and assembly techniques as the "Yangke" machine. The doghouse is smaller, had a discrete component bridge rectifier (really crappy), a single pole breaker and the stupid "tell tale" lamp and switch. To his real credit, Steve Perks at Stationary Engine Parts supplied an AVR and a decent bridge rectiifer which have now been fitted. In addition, I have also installed a 10,000 microfarad capacitor across the field to ensure I could get the highest voltages at the lowest revolutions.
I decided that I would take this machine apart before I even ran it and replace the bearings and fix the issues that needed fixing. This has now been done and it is the primary generator in my system.

I have had dealings with Stationary Engine Parts for about a year now and I have to say I would have no hesitation in recommending them for service, honesty, and integrity.

I hope this helps.

Regards,
Ian

[Doug]

Well thats very interesting and thank you for the current information.

I am troubled to hear Volvox has gone under.
I thought they might be a company with legs

[GuyFawkes]

Well thats very interesting and thank you for the current information.

I am troubled to hear Volvox has gone under.
I thought they might be a company with legs

can't say I'm surprised, to the best of my knowledge they had no real engineering experience to call on, and the first thing they did was jump on the marketing bandwagon, selling listeroids while claiming / talking about genuine lister longevity and quality.

I'm reminded of the line from the film Christine, "Boy, you can't polish a turd."

[Doug]

As I recall they were an " Utterpower Associat " company. From what I under stand they were trying to work together for the best parts and prices. Its a real pity it didn't pan.

You can't polish a turd eh?

Is this a turd?
We haven't seen everything yet....
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180149370884

[mobile_bob]

i would expect a three phase st head could be under your 10 percent ripple, and at the very least easier to clean up.

as for buck converters, boost converters, or buck/boost converters, do a google search
there is a ton of info on there theory of operation
and if you have mppt you will have to have one of them included (buck, boost or buck/boost)
wikipedia has a pretty good explanation of there operation as well.

basically a buck converter will "buck" down high voltages and make more amps, a boost converter
will "boost" low voltages and sacrifice amps, and the buck/boost can do both as needed with the same tradeoffs in
amps output.

bob g

[Ian]

Again, many thanks guys.

I will Google / Wiki as suggested.

Regards,
Ian

[jimdunne]

Hello icrowther,
Have ran several PS ST heads for going on six years, and can tell you that the newest one is indeed, better than the older one.

The biggest issue was a brush holder that was not right on the older one (ST 10). When I replaced it, it took care of the problem. Also bought the kit then from utterpower that got ird of the doghouse for the 10 KW, and it worked fine.

Have not tracked the time so carefully, but there is a good 6-8,000 hours on the oldest, and maybe 2,500 hours on the newer one (ST5 with no doghouse).

There is one man in Arizona, and two up here I know that have more hours on their units than I do, with the same good luck. One of them had a noisy bearing and replaced it. I use a needle greaser and add a shot a year in the 10 KW.

They are not bombs, that is garbage talk; they are simple and inexpensive, and do a good job. Have also read that they have been passed by the inspectors in Canada.

I am sure that there are cheap ones out there. Maybe it is like tools, or cheap cars. (or cheap women!)

[jzeeff]

Just to review, you are using standard ST head to generate AC, and then rectifying this into a high DC voltage to be fed into a high voltage grid-tie inverter.  Capacitors are used to take some of the ripple out.   Using an inverter gets the UL approval needed for grid-tie.  This makes perfect sense.

Typical DC power supplies (like this one) tend to have power factor/harmonic  issues - they only draw current near the peak of the AC voltage waveform. 

This low power factor causes short term increases in amps, causing more loss in the wires (as compared to s simple resistance load).  This causes more heat loss in your generator.    You want to reduce this inefficiency. 

I agree that a 3 phase generator would be better in that there would be less inefficiency and ripple that *might* bother the inverter.

Standard power factor correction techniques using inductors and capacitors cannot be used to fix harmonic current.

Standard  high voltage grid-tie inverters are designed to take a wide range of DC input voltages - although the voltage usually varies slowly, not at 60Hz.
I suggest that removing the capacitors would allow the circuitry in the inverter (perhaps a boost/buck) to do what it is intended to do.  I can't say if this would hurt the inverter.

I would be interested in some measurements as to how much more heat is being produced in the generator - ie, a comparison of a plain resistance load to a reactive load.  Ie, is this worth worrying about?

http://en.wikipedia.org/wiki/Power_factor_correction

[Doug]

Not worth worrying about just buy Cap run motors where you can and lighting with built in correction.

Let the VA and VARS Watts looks out for themsleves. If you have a problem you will notice it and quickly stop using the offending apliance.