ST-3/5 regulator plans available

[BruceM]

Clytle- The 400V peak voltage (400V for a few milliseconds from a 1/2HP motor start with one 1/2 Hp motor already running) out of my ST-3's harmonic was the stock (no cap) configuration, loaded- it was running off of the harmonic at the time.  The harmonic puts out higher voltage as the current increases, and so spikes some impressive voltage when there is a load surge.  This is why an electronic regulator needs much higher than faceplate voltage to have equally good surge capability. 

A flyback or "catch" diode across the field coil is absolutely required for pulsed operation.  The normal harmonic configuration bridge diode serves this function, but if a transistor switch is used after the bridge, a diode must be placed between the field coil and the transistor, else the transistor goes "poof".

I am now going to the driveway site to update the schematic with the latest revision.  There is now a Digikey.com complete parts list also. 

Here's the downloadable schematic in pdf format: 
http://www.driveway.com/mdqde12615

and the Digikey parts list:
http://www.driveway.com/likde03565

Bruce




    

Bruce M

[ronmar]

ronmar- how are you measuring the .5V?  Seems awful good considering the environment,  any attempt on current measurement.

The .5V can be seen two ways.  On an O-scope, the signal appears like a flat line DC, but if you keep expanding the vertical/voltage axis you will eventually start to see the ripple.  You can also put a digital volt meter across the caps and switch it to monitor AC.  This will show the AC component pretty accurately.  I did measure field current current one time on my ST-5 and came up around 2 amps which is where I came up with the 4K uF of capacitance(2K per amp for good filtration).  Because the input waveform from the harmonic is so spikey, more capacitance is better. 

I am using 50V electrolytics, which are a commonly available power supply filter cap.  Bruce is probably right that the peaks on the harmonic pulses may go up quite a ways.  But I don't think this is a real problem for the caps as these spikes are such a short transient and the caps absorb the energy pretty well.  If it was a big honkin wide powerfull pulse, then a higher voltage cap would be needed.  I have about 10 hours on these caps in operation now and they seem to be acting just fine, time will tell.  Now that the field current is filtered DC, I also use it to power my hour meter(10-80VDC at 6W) so whenever the generator spins, the clock counts:).

Ron   

[BruceM]

The schematic file for download listed above have been revised with a caution about signal ground being hot, and a new file has been added which shows a special test configuration which allows the circuit to be tested in a half wave mode.  This allows the circuit signal ground to be tied to neutral, instead of being hot.  A much safer way to test.  In half wave mode there will be poorer performance regarding surge loads and flicker reduction. The change is just a connection on the spade terminal bridge diode, and neutral wire connection.

The circuit can be bench tested out quite well with no excitation or generator connection- just connect the two tiny DC supply transformers to a 120V source, and adjust the trim pot to just barely see short pulses coming out of the op amp every 8ms.  With that simple step all but the power switch section is tested- without having a hot signal ground. My prototype "full bells and whistles" unit was also initially adjusted and tested this way.

Here's the special test configuration schematic for download:

http://www.driveway.com/pghde47493
 

Bruce M

[mike90045]

Any plans for a PCB for this ?  I have a good PCB package I could layout a board with, and a fab house that etches pretty cheap.
p-cad 2006
http://www.pcbexpress.com

[BruceM]

Mike,
No one has started on the PCB yet.  The schematic is available in expresspcb.com's free schematic capture program. (Just send me an email.)  They also have a free layout program.  I would love to see it done in that, as I could help with layout checking.  I have a version that runs on my W98 machine.  But you are sure very welcome to do it on anything you want, and I'll help if I can.

Bruce

[BruceM]

The proposed circuit was breadboarded and tested by CM on his ST5.  He did a great job and I really enjoyed working with him.

Bench Testing:

CM did his bread board bench test with a fixed 120VAC line voltage applied, and a light bulb attached to the field coil connections.

The regulated voltage trim pot (R2) is set so that the bulb barely glows.  This does adequately test the entire circuit, and upon hookup to the generator, only a minor adjustment will be required.

Testing on CM's ST-5:

CM found the circuit worked fine as a harmonic regulator, <1 volt variation with a range of loads.  For this configuration the harmonic winding is connected to the D3 bridge diode instead of L1, N.  This configuration has merit for those who plan on loading their ST head very heavily, especially with poor PF reactive loads.  Voltage will fall off with extreme loads, but the field coil can't be overloaded. (Thanks Bill Rogers for the test results and discussion of this issue via email.)  The down side is less flicker reduction, poorer AC waveform (the "harmonic hump").  If you are using the last 30% of our rated ST output (even if just by poor PF loads), you should use this configuration with the basic regulator as shown.  However, you should change to a 600volt IGBT transistor and a good sized heatsink, as it does get hotter using this configuration, since the switching time isn't synch'd to the the low voltage time, and harmonic peak voltages are higher.

With the circuit using line voltage (L1, N) as excitation source, the unit will have better flicker reduction, tighter regulation, and a much nicer looking AC waveform.  The slow blow fuse, F,  should be carefully chosen and tested to protect the field windings in case of a protracted overload.

An interesting oscillation:

We had to reduce the capacitance of the AC to DC filter greatly to eliminate an LCR oscillation of his ST5 regulator-field coil which caused a very noticeable flicker. I'm guessing this is pretty much the same situation that Jeff M saw on his original (non digital) regulator/ST-5.  To detune the oscillator, we reduced the capacitance at C8, C7. Ultimately, less proved best for lowest flicker, and instead of the original 200uF we are now at 10uF.  Regulation tightness did not suffer. With this change, flicker is now noticeably better than on the stock harmonic setup, instead of worse. The schematic has been updated for this change.  Stay tuned for some measurements.

Other Changes:
A hysteresis resistor shown in the original schematic as 1M has been corrected to 10M. CM caught that in the bench test stage.

The optional small pcb mount AC relay to cut out the start button as AC voltage rises is now not optional.  It's too easy to get an over voltage situation without it. R7 is now not critical, 20 to 50 ohms, 10 watt, is a good choice.  The schematic shows 50 ohms, 10 watts. (Edit- both the AC relay and resistor can be eliminated for harmonic regulation.)

Here's the updated schematic in pdf:
http://www.driveway.com/mdqde12615

Here's the udated Digikey parts list (.txt)
http://www.driveway.com/likde03565

Here's the schematic in the .sch format of the free schematic editor of Expresspcb.com:
http://www.driveway.com/mfhdw58912

CM may design a PCB, too! Hat's off to him for his great work!

Bruce

[mobile_bob]

Bruce:

very good work indeed, i have been following your progress and am amazed at how it is coming together
your having a clear set of goals to start with looks to have paid off quite well in testing.

the only thing i have a question about is....

who is CB?  its driving me nuts!

the first name that came to mind was charlie brown,,, and now i can't think of anyone else

bob g

[ronmar]

CM?

[mobile_bob]

see how confused i am?

CM?



bob g

[mike90045]

who is CB?  its driving me nuts!

C.M, I have no idea

CB  Circuit Board or PCB (printed circuit board)

[BruceM]

Update:

CM will be receiving the first set of 3 PCB's to check out on monday.  The board is the PCBexpress experimenters miniboard- so as few as 3 for $50 can be ordered.  He says he wants to just release his layout files to the pubic.  So anyone can order some, do a group by, sell them, whatever.

He did a beautiful job on the layout.  Both tiny transformers are on the board, only the big bridge diode is off board (for heat sink mounting purposes).  It's really a lovely pcb design, and my hat's off to him.

Best Wishes,
Bruce M

[Doug]

Cool:

We all need to get behind this once the Beta units are done....

Good job guys!
 

[BruceM]

Hi Folks.

Our own forum member Cliff Myers (aka Copybell) has completed the ST5/3 120V regulator PCB and checkout.  He did a fantastic job. It's compact, but easy to build if you're good with a fine soldering iron and runs nice and cool.

I put Cliff's Expresspcb.com format PCB file up for public download on Driveway.com.  This board can be ordered by downloading their free pcb layout software, loading the file in it, and pressing order.  The board is their "mini board" format, $51 plus shipping for three boards.  Much cheaper ordered as a standard board in quantity, and then you can have nice things such as silk screen and solder mask.

This design is just for 120V output ST3/5 generator heads.

For 240V ouput, stay tuned for Cliff's next creation.  I modified the design for a higher voltage IGBT transistor and driver to handle up to and ST15, and Cliff is working on this new PCB for his ST15, so you will all benefit from his talents and generosity. The 240V design will drive an ST5 with 120V excitation or an ST-15 with 240V excitation, by changing the wiring of the external bridge Diode, D3.

Here are the Driveway files for the ST5/3 120V AVR:

Multipage PDF file with schematic, parts list, PCB art, assembly notes, photo:
http://www.driveway.com/x8o5j5b8p1

PCB file for ordering boards from ExpressPCB.com:
http://www.driveway.com/q3f8s7s7y5

Best Wishes,
Bruce McCreary
Metro 6/1
Snowflake, AZ

[rbodell]

2. with a simple transformer and rectifier the ST Head could be a high power battery charger with I-U Characteristics.


Christian

I have a 120+ amp arc welder built from microwave transformers. I used to have a 200 amp one but never needed that much and somebody needed one so I gave it to them. Just rewind the secondary. I also have a golf cart charger I removed some turns on the transformers secondary and use that as a 12 volt charger.

[BruceM]

Let's keep this thread for the posted topic, please.  Thanks!