Author Topic: Solid State AVR on an ST-3 Head - Any need for it ?  (Read 632 times)

veggie

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Solid State AVR on an ST-3 Head - Any need for it ?
« on: May 08, 2022, 11:34:00 PM »
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
=================================
Features:
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.
Specification:
Voltage regulation rate:;1.0%
Exciting voltage: 20-100VDC
Shunt current: 10A
Package weight: 274g (approx.)
Package List:
1 * Automatic Voltage Regulator
« Last Edit: May 11, 2022, 03:43:16 AM by veggie »
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BruceM

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #1 on: May 09, 2022, 05:37:12 AM »
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.



« Last Edit: May 09, 2022, 05:50:00 AM by BruceM »

mikenash

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #2 on: May 09, 2022, 07:44:42 AM »
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

38ac

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #3 on: May 09, 2022, 11:19:26 AM »
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.
Collector and horder of about anything diesel

BruceM

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #4 on: May 09, 2022, 03:29:54 PM »
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.








veggie

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #5 on: May 09, 2022, 06:18:57 PM »
"The best ones have acceptable waveform and voltage regulation by the stock harmonic system, though I expect THD is still about 15%."

Thanks BruceM,
Just to be clear, do you suggest not adding and AVR until the unit is installed and the output is evaluated?
If I was lucky enough to win the lottery and get a "good one" then no mods may be required ?
(Other than the usual bearings, Junction Box, and tidying of the wiring)

Veggie
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BruceM

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #6 on: May 09, 2022, 07:37:29 PM »
Yes, you won't know what you've got until you check it out and also take a look at the waveform, and see if you have issues with your various intended loads. (Check your AC voltage using a true RMS voltage mulitmeter at a range of loads.)  Many ST's are being sold that are wildly high voltage, and thus will likely require an AVR or a large dropping resistor in the harmonic to bridge rectifier circuit.   If you intend on using it for non-electronically regulated lighting, you will have less Listerflicker by using an AVR using the AC ouput as excitation instead of the harmonic , and this will also help with "harmonic hump" distortions if present. 

Some LED lights are electronically regulated with a small AC to DC switch mode power supply. They will get rid of the Listerflicker unless it's extremely bad.  The stock harmonic regulation amplifies Listerflicker, and during compression stroke, the harmonic output will drop so low that the AVR won't help, since it only limits the excitation and can't amplify it.


mikenash

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #7 on: May 10, 2022, 08:19:26 PM »
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.

Hi Bruce.  Appreciate the input, thanks.  I know less about electronics than the Queen of England does about the poor . . . so I figure - see pic - the bridge rectifier is the alloy-bodied gizmo in the pic?  I might have a google and see what they do.  But I should replace it with a "good one"?  Cheers

BruceM

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #8 on: May 10, 2022, 08:37:07 PM »
That may be OK, it looks like a modern one.  A picture from the other side would help.
I'd order a new one to have on hand, in case it's crap.  When your output voltage suddenly goes way low, that's the usual culpret (with Chinesium bridge diode).

Here's an example of what you want:
https://www.ebay.com/itm/224811975854?epid=25016784898&_trkparms=ispr%3D1&hash=item3457d684ae:g:LP0AAOSw07hh9D9b&amdata=enc%3AAQAGAAAA4DnkmsOqUD5Je7CXIp1vp20AWgEgoojiNCXA37jPM8BMpvjM1U4Yfupo7yaDHQ%2FWrT%2Fcg4npkrGOlp5z50wf8GCQFT68xqa89gdinHLtlG0vPIZUGluNz0ey9Ioc0pK3Egc8qiRPkpJjqCOqHKNYkftz9cvug0K4JLVudSv8c1EZzaWdRRSb8BoT9diH5euXC1Ihu0SFZuxvdHAKjrf9cCk4jDaSsDU2C8qjhiastbesKQfUKpD7COBS946hkpx6XRc%2FpBP24L9PhzmcE15wZsOrD8Tkccxa%2BJxCaq%2FUaYPc%7Ctkp%3ABFBMssOY95Vg

A bridge rectifier is just four diodes potted in a metal or plastic box.  Two AC inputs, usually opposite corners, and two DC outputs, usually marked + (plus)  and - (minus).  It turns AC (from the harmonic winding on the stator, which is very spikey and non-sine, and turns it into pulsed (spikey) DC for the rotor.  The rotor windings have a huge inductance, so they smooth the input current to create a more constant magnetic field at the 4 rotor poles. 

For this application, the metal body is better for heat sinking to some aluminum. A die cast aluminum case to replace the doghouse comes to mind. Use some thermal paste or a dab of silicone caulk It should be as thin as it can be, to just increase the surface contact area.






38ac

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #9 on: May 10, 2022, 09:56:36 PM »
Mike, My 15KW ST had a rectifier like yours and it failed quickly as they are know to do. Luckily I had ordered a few 5010s per the advice of good people here. They do need to be screwed to a heat sink of some sort. the metal junction box has worked well for me.
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BruceM

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #10 on: May 10, 2022, 11:17:36 PM »
If you're changing the bridge rectifier pre-emptively (a wise suggestion, 38ac), then consider cleaning up your the high frequency EMI by adding 4 capacitors to the bridge. The use of the piggyback spade connectors works well, or you can solder them to the base of each connector.  One on each side. 

This is the type of capacitor you want, with the part number on Digikey:

CMPPAC310V104K10S5

It's a thin film 310VAC rated capacitor, 0.1 uF.  About $0.30 US.  Similar spec parts should be available around the world.

I can't get the page to load or I'd give you link.  Digikey seems to be overloaded this afternoon.

This is highly effective in reducing radio frequency noise from the ST line output.  Check it with an AM radio (old regenerative tuner type with static sound between stations) before and after and you'll agree.




veggie

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #11 on: May 11, 2022, 03:42:36 AM »

BruceM

Excellent tips !

Thanks again,
Veggie
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BruceM

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #12 on: May 11, 2022, 02:54:44 PM »
You're most welcome, Veggie. 
Putting a 0.1 uF capacitor parallel to diodes is what's called a "snubber".  It reduces the bust of high frequency EMI that occurs when diodes start and stop conduction.  Sometimes a resistor and the value are specifically tuned to the circuit, but for many low frequency applications like this one, just 0.1uF works quite well. 

In the case of the stock (no AVR) ST-3, these 4 capacitors (about $1.20) will reduce the high frequency EMI as much or more than a $70 dual common mode choke filter unit.  A demonstration of the cost effectiveness of correcting an EMI problem at it's source (or even better by design) vs a downstream filter.

The fast switching of an AVR can also add high frequency EMI to the AC.  A snubber capacitor across the excitation in/out switch may help with this, but it is best solved by design.  In my own AVR, I intentionally slowed down the switching speed to limit the emissions. This works using either Mosfets or Darlington Bipolar power transistors, but requires the use of a bigger transistor that can handle the slower transistion, and often, an upgrade in heat sinking as well.  In practice, you can often get huge reduction in emissions with very little or no loss of efficiency. 

Most devices will tolerate this EMI on top of the AC without difficulty, but some may have problems.

mikenash

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #13 on: May 11, 2022, 08:12:30 PM »
Hey guys - thanks for the excellent advice - much appreciated

I have few chunks of finned, heat-sink alloy here out of 150kW-sized VSD/VFDs - a piece of one of them will work well.  The lads here try to throw them in the scrap every time we do a clean-up but I keep saying "I'll use these one day . . ." so there we go

I will mull over all this good advice & google a few bits so I understand - especially good explanation-to-lay-idiot of the bridge rectifier, Bruce, thanks

Powdermonkey

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Re: Solid State AVR on an ST-3 Head - Any need for it ?
« Reply #14 on: May 11, 2022, 11:59:05 PM »
Hey guys - thanks for the excellent advice - much appreciated

I have few chunks of finned, heat-sink alloy here out of 150kW-sized VSD/VFDs - a piece of one of them will work well.  The lads here try to throw them in the scrap every time we do a clean-up but I keep saying "I'll use these one day . . ." so there we go

I will mull over all this good advice & google a few bits so I understand - especially good explanation-to-lay-idiot of the bridge rectifier, Bruce, thanks

Bruce- It seems you're a wealth of knowledge regarding power generation.  As for me, I'm a gear head, and reasonably okay with the electrical side.  I've got scopes, and can wrangle some basic stuff.  But your knowledge is unique.  Would you ever consider putting an e-book together?  Drawings?  Instructions?