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Solid State AVR on an ST-3 Head - Any need for it ?

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These voltage regulators are available all over EBay and Amazon for anywhere between $10 and $30.
Are they any good?
Are they even necessary?
I would think that sine wave conditioning would be a better product to push for the ST heads.
In any case, If any users found a benefit from installing a solid state AVR on an ST heat, please pipe in.
I have an ST-3 and I'm wondering if I should add an AVR ?

By the way ... what currenty controls the voltage on my ST head ? just the engine rpm?

GB160 AVR Automatic Voltage Regulator for Brush Single Phase ST Alternator
Product description
100% brand new and high quality.
GB-160 AVR(Automatic voltage regulator) is applicable to harmonic excitation, 1 phase brush generator.
It is suitable for ST series single phase110/220VACgenerator.
Made with flame retardant and heat resisting material, stable and reliable to use.
High precision, long service life.
Voltage regulation rate:;1.0%
Exciting voltage: 20-100VDC
Shunt current: 10A
Package weight: 274g (approx.)
Package List:
1 * Automatic Voltage Regulator

My neighbor has one on his ST-3.  His is using the harmonic for excitation, regulated by the AVR, as the stock unit voltage so high that there is no choice but to use it, which is common with some of the CGG units.  He gets about 2-3 years per unit, with heavy use.   

FYI- these do NOT regulate to RMS voltage so won't work well with a nasty PF load like a cheap high current , switch mode batttery charger.  Output voltage will be too low for a very bad PF load.

One of the issues regarding longevity is that even in the ST-3 with a normal harmonic, the voltage peak is over 400V, while RMS voltage is much lower. 

The standard harmonic system of the ST3 sorta regulates output voltage by sensing load current via the harmonic winding, so for a big load spike, like starting a motor, it really works well.  I have a dual mode setup, my own design AVR for normal running, but I can switch to harmonic only for running a small switch mode type MIG welder.  I have an adjustable resistor to limit harmonic current to get the desired voltage. 

For cleaning up the output waveform several methods have been reported depending on what the problem is.  The cheapest digital o-scope or usb scope will let you see what needs to be done.  The common methods are- adding motor run capacitors on the line output (for some ratcheting and spike distortions),  running an AVR on the line voltage instead of the harmonic (if you have "harmonic hump" distortion.  Some found adding capacitance after the bridge diodes helped with harmonic hump distortion.  If the ratcheting and spikes are really bad, I'd add two 200-400 uH chokes plus capacttance on the line output.  A surplus line reactor plus motor run capacitor will also help but is pretty spendy. Putting massive amounts of capacitance (> 60uF) of motor run capacitors starts to affect your peak motor starting capability and starts to show a little in fuel consumption. 

For the high frequency EMI on the AC line,  I found that adding 0.1 uF snubber capacitors parallel to each diode in the bridge (4 total) made a world  of difference.  With these small caps (240VAC rated) the EMI went from detectable across much of the AM band from 8 feet away from AC wiring to 8 inches in just a few spots.  A standard dual common mode choke filter will also be helpful but I found the snubbers got it good enough for me and only cost me a few bucks.

That's my pitch on ST heads-  I envy the guys with Stamford clones who just belt them and forget about it!  The variation  in different ST heads is huge, in terms of waveform quality.  At one point I had 3 different ST-3 rotors and stators on my bench- and none were physicially identical to the others.  I"ve seen lots of waveform screen shots from ST-5's also, and they also vary dramatically.  The best thing I can say about ST heads is they are cheap, and simple. If you get copper windings and put in good bearings, and a modern bridge rectifier, they are reliable in creating a high THD waveform for thousands of hours.  My custom low EMI inverter with a 5 step sine has lower measured THD (measured THD of 12%) than my ST-3 (measured THD of 15%), even when running on mains excitation instead of harmonic.  Either runs everything I need just fine, but the timer motor on my washer makes some noise on the generator.

Interesting, Bruce

I have an ST-clone Chinese head I bought for a few hundred $$ years ago - basically thinking "copper windings + solid cast-iron construction = good bones"

I guess time will tell - but it's awfully rough:

Both bearings growled and grumbled from new so I replaced them with Timken/SKF ones.  One of the shafts was only about 70% machined as it was made uneven, out-of-round & partly undersized.

The brushes are "crumbly" and one just broke in half.  The springs behind them are the nastiest folded-tin I have seen anywhere.  They might work?

The fasteners right across the unit are just rusty muck-metal with heads so thin a spanner slips off them - so I have replaced them all

Normal stuff, really, I guess; and probably analogous to Indian Listeroid export units

But the electrics.  My god . . .

There was an isolator/on-off switch on the side.  The positive wire attached to it had no clearance at the bottom and a half-inch or so of bare wire was jammed against the tin base of the dog-box.  I don't know if the unit will generate power - but if it did, the casing would have been livened-up nicely.  I took it out, joined some good wire onto its terminals and ran the wire out through the outside of the box, using a gland and some insulated sleeves.  I guess I'll find a better isolator & mount it somewhere else.  Maybe something with some fuses  . . .

There's an output-box thingie with a couple of screw-on-knob terminals - but the phase & neutral wire terminations inside it were just made of folded thin copper plate.  I took them off, took the rusty steel terminal bolts out of the terminal holes and extended the wires, adding some shrink & insulation and running them out - I guess they'll end up on the terminal block for initial trials

Inside, everything was just floating around loose - I guess the big alloy thing does some sort of regulating job?  I'd be interested in suggestions as to what to do with it?

Once it's spinning - if it makes power, I guess I'll mount a tidy enclosure somewhere and block off the hole in the top where the dog-box sat

Apart from the fact the body was "live", I don't think you would have got ten hours out of either of those bearings?

I guess we'll see.  I have a nice Markon unit as Plan "B"; but I figure this unit has to be a good one for someone who knows nothing at all about gen heads to make mistakes on

When Bruce talks generators the authority has spoken! ;)
I was very lucky on my 2 STs. After belting them up to confirm they worked and check voltages all I had to do is replace the junk connection boxes and the diodes. Neither get very many hours, maybe 200 on the 15KW and 50 on the 5 but both have worked well for my needs, stand by home power and portable generator.

Ha, thanks Butch, my experience with the ST's is just one of practical necessity.   It was an educational "opportunity". 

MikeNash, good point on the need for removing the doghouse, I forgot to mention that abomination.  Adequate heat sinking of a modern, metal cased bridge rectifier is also essential. 

It really is a shame that the ST's aren't made in a more reliable and consistent manner with decent QC.  The best ones have acceptable waveform and voltage regulation by the stock harmonic system, though I expect THD is still about 15%.
For a smooth sine, you really need skewed rotor windings, it seems.


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