ST3 Generator Head output half voltage

[BruceM]

My ST3 generator head has been in service about 12 hours, running a 230VAC 1/2HP submersible well pump. It was running fine this morning.  Alas, when I went to start it up again this afternoon for a few hours, the output voltage is only 115VAC (no load).  This puts my off grid shop/home site grading project at a standstill.

I checked all the connections, brushes, etc. Everything looks fine. I had no oscilliscope at my remote property, just a VOM.

The half voltage output seemed like a possible field coil diode bridge failure, so I took apart the stock bridge and checked each diode. Alas, they check out OK, but one had a cold solder/loose connection to the heat sink after I moved the wire so I will attempt to resolder it this PM.  I don't have confidence that this was  loose before I moved the wire, though it was a bad solder joint.

Any suggestions for what might be wrong and/or where I could get a replacement diode bridge quick?
I have a battery powered oscilliscope I can bring out tomorrow.

Thanks,
Bruce M

[Tom]

My ST5 did something similar. If you measure the field voltage it should show around 48VDC. I replaced the Chinese unit with a standard bridge rectifier from Radio Shack. I believe these are better units.

[dkwflight]

Hi How about a part number from Radio shack. I have a 20K head so it probably won't be heavy enough, but
Thanks
Dennis

[rsnapper]

I picked up a couple of bridge rectifiers from a locally owned electronics shop. NTE brand part # NTE5344 rated at 1000 volts and 40 amps. George told me to triple the data plate exciter voltage and amperage. I may have overdone it a little (I tend to do that) but it still works. I did away with the original dog house and mounted the rectifier on the inside of the end housing. I bought a standard 4" X 4" x 12" electrical trough for the electrical connections.

Rick

[BruceM]

Thanks Tom, Rick.  I also decided to just replace the stock bridge. I had a moderate size bridge diode in my parts bin and will see if that will get me going today until I get something better suited. For today I'm just going to bolt it to the "dog house" with and extra piece of copper sheet for a heat spreader/heatsink and some heat conducting goop.

I also found that the Utterpower web site has a very nice article on ST gen head troubleshooting.  With this, 12v soldering iron and my ST manual in hand, I'm off to my remote property this morning.

Bruce M

[cujet]

I generally make full wave bridge rectifiers by using 4 choice diodes. This way, I can control the type of diode used. I can also replace one diode if necessary. I use quality crimp connectors (aviation spec) and this eliminates the vibration related failures of a hard solder joint.

For whatever stupid reason, I find I can build exactly what I want easier than I can find it locally.

Chris

[listeroidsusa]

Cujet, you got that right! I went to my local hardware store and asked for a 3/4" drill bit and they told me "they don't make drill bits that big", oh really?, I took one of my 4" morse taper drills over just to show them "they" DO make drill bits that big! I usually have to improvise on parts if I don't have time to order from out of town. Here in Rutherfordton all you get is dumb looks when you ask about tools, parts, or information. BTW, size your replacement diodes by the PIV (peak inverse voltage) AND the amp rating. Trippling the PIV is good insurance. I had all my ST heads equipped with heat sink type diodes when I ordered them. If you replace a bridge rectifier be sure to use a good heat sink. This alone will add years to the life of electronic components.

Mike

[sid]

 Mike////talk about dumb looks/after we were talking at denton  last sat./ I left early that evening for brevard n.c. took htw 74 south toward rutherfordton // talking on the phone with the wife and took a wrong road/ stopped in your town when I saw the police.. 3 police in the car and another pulls up/simple question //how do I get back to 74 west.. they look at me and point 3 different direction//I knew I was in trouble/ out of the 4 only 3 answered/ the 4 th did not know where she was at//good thing you live in a small town//  sid

[BruceM]

Finished checking the ST-3 this AM.  Alas, the problem was not the bridge diodes.

I'd be very grateful for some help interpreting my findings:

The Field coil measured 15.2 ohms, greater than 2 megaohms to case.
The Harmonic coil measured 9.9 ohms, greater than 2 megaohms to case.

The harmonic coil output when connected looks like two positive spikes/pulses of about 1.5ms width, followed by two negative spikes/pulses of 1.5ms width, with an overall period of 16.67ms.  The pulses are evenly spaced over the period.  The first pulse of each (positive or negative) is less than half the amplitude of the second pulse, which is 106 volts.  The total peak to peak voltage is 212 volts.

My replacement bridge diode (15A, 450V) is faithfully turning this obviously faulty AC waveform into a pulsed/spiked DC. 

With no load hooked to the harmonic coil, I saw a 27 volts mostly sine wave peak to peak AC waveform, after flashing the field coil with 12VDC just to be safe. 

The generator is now on my bench and I'm ready to pull the rotor and stare like a newbie at the stator coils- how do I find the harmonic??  What do I do now???

Thanks,
Bruce

[dkwflight]

Hi thanks for the info
My next question is "What is the light bulb and switch for?

It seems to me the switch turns the small light bulb on!
I tried the switch under load. The gen kept right on making power at the same rate.
Dennis

[BruceM]

Yes, Dennis, the switch just turns on/off the neon bulb. A baffling piece of China tech.

[Doug]

Bruce:

2 Meg to case sounds bad( is that with a DMM), this isn't an old head is it?
Open it up look for obvious burned coils and such.
Maybe the harmonic winding is shorting in on itself.

I've only seen pictures but it looks like the Harmonic winding was laid into the stator first under the main winding. I have no idea what the span on the coils should be in relation to the main winding but my gut feeling is it will be half that of the main winding.

WHAT EVER YOU DO, don't cut any connection on the winding to take things apart. The right way to strip a core is with a blow torch and a little heat to soften up the varnish and gently spread things open to see how it was connected and record. To removed the winding cut the knuckle opposit side of the stator from the connection and gently heat the coils to soften things up so you can pull out the coil group intact to disect them later to find the number of turns pole coil.

Never heat a stator so much that you turn iron red!!!!!
Stand up wind, don't inhale the fumes.
Record the wire size with a micrometer.
Draw a picture of what the winding would look like if you could cut the stator in half and lay it out flat like so you can be sure of how the coils lay and the sequence for connection the coil groups.

Last but not least I don't think you want to be stripping and winding this yoursel and its probably cheaper the buy a new head than have one wound but I would look at prices for both options. A REAL winder could probably improve the performance of the head by removing the 50 hz tap and making some adjustments to wire size and possibly turns, but I can't realy say much on that without seeing the coil data. Its a dying art most guys won't want to tinker wityh winding data unless they have a computer spread sheet to do the math for them. Old guys who know the formulas and do it on paper are few and far between.

Dennis the Z winding connected to the neon tube and switch probably served a purpose at one time. Who knows it might be usefull for a battery charger or something....

I'm not saying you need to start ripping it apart! Just trying to let you know what your getting yourself into should you decide to try and rewind it yourself. Now that I have re read your post I see this is only a 12 hour old unit. There must be a simpler reason for the trouble your having other than a winding failure unless it was over loaded and fried.

Doug

[BruceM]

Thanks Doug,
No overload- the unit has only run a new (17 hrs) 3 wire 230VAC 1/2hp well pump.  Was pumping fine at shut down, next time I started it up the voltage didn't come up to norm BEFORE any load.  Load is fused, also.
 
I pulled the rotor to look at the stator windings.  Everything looks fine, no smell of arcing/burnt varnish.  It does look like the harmonic winding is integral to the stator winding, so "replace harmonic winding" per the manual means a complete stator rewind.  Not something I can handle.

I haven't had good luck with this ST-3, first bad bearings right out of the box, now this at 12 hrs. Discouraging and hard on the budget.

Bruce M

[Doug]

Yes thats got to be a real disapointment.
Who manufactureed the head? Maybe we can "convince" them to replace it as a good will gesture....

Doug

[BruceM]

I don't know who the manufacturer is, but it's labled Power Solutions.

I wonder if anyone else has any experiece with the ST3 heads?  I could convert my mount and ribbed pulley bushing for an ST5 if they were truely much more reliable.  My typical load is 1000 to 2000 watts.

Bruce M