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Author Topic: 3k st alternator just stopped mid work  (Read 35870 times)

tyssniffen

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Re: 3k st alternator just stopped mid work
« Reply #60 on: October 30, 2015, 10:51:59 PM »
"So if the avr is fed 48vdc from an external source it should have enough voltage.."
 -- Well, I don't have another external source I could get 48v from, especially out at the gen shed. 

I can bypass the AVR by following the Z1 and Z2 parts of the diagram in this manual: http://cgg1.com/index_htm_files/ST%20Manual-42013.pdf

I will also set up easy swap out connectors for my other AVR - the old one I swapped out at the start of all this.

I've gone full blow out on the wires now, and set up a working, labeled table, inside the gen shed: 
http://1.bp.blogspot.com/-z_MFhWot0hE/VjPz6s-A7vI/AAAAAAAAGoM/m2xVHjmpH_U/s1600/altblowout.png

feel free to tell me I'm doing something wrong.
6/1 with 2 tank for WVO.  pushing power into off-grid house battery bank, in winter.

Tom

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Re: 3k st alternator just stopped mid work
« Reply #61 on: October 31, 2015, 02:35:29 AM »
Bruce, The diagram in the attached photo shows it's input coming from the z windings.

Tys, Since the voltage you measured is at 23 and the field windings require 48, this is why it's only generating 55vac output. I would guess that the output voltage will be the same without the AVR. That is unless you have two bad AVR's.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

tyssniffen

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Re: 3k st alternator just stopped mid work
« Reply #62 on: October 31, 2015, 03:46:37 AM »
I did the test of removing the AVR.   same 55 or so volts.

Tom writes, "the voltage you measured is at 23 and the field windings require 48, this is why it's only generating 55vac output."     

yes, but why aren't the field windings getting/creating 48?  something not connected?  something broken?
6/1 with 2 tank for WVO.  pushing power into off-grid house battery bank, in winter.

carlb23

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Re: 3k st alternator just stopped mid work
« Reply #63 on: October 31, 2015, 10:48:03 AM »
i looked at your wiring diagram and while i am by no means an electrical expert i just went through a similar problem with a 2 pole 8kw head.  It turned out that my head had a bad Z or Harmonic winding and i was getting little to no voltage out of it.   Someone on here I can't remember who suggested i contact tom @ CGG as he has a AVR that will work off  L1 and L2 bypassing the Z / harmonic winding. I installed this avr on my non working gen head and now it works fine.  It also has a voltage adjustment.   

The only issue i had  (this was not the avr's fault )was that when i tried to start my 3.5ton central air the A/C would pull down the main windings voltage  too far for it to recover to correct voltage and would not start the A/C.   I have pulled over 7kw of resistive load on this genhead with this avr and it has worked very well it just didn't like the huge inrush current necessary to start the 3.5 ton A/C.   I have since installed a quality THREE WIRE hard start kit on the A/C and now the generator will start it without any problem as the hard start has lowered the starting current required by over 50%.


Here is a link to his Ebay store but i would call him and tell him you are a member of the lister engine group and ask for a price  Call CGG at 478-457-5524 (Cell) or 478-453-9358 ask for tom

http://www.ebay.com/itm/ST-115-Volt-Automatic-Voltage-Regulator-Brush-type-AVR-/151018637383



BruceM

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Re: 3k st alternator just stopped mid work
« Reply #64 on: October 31, 2015, 04:18:52 PM »
My apologies, Tom, CarlB, Tysniffen.  I confused the issue by not looking closely; I didn't notice that the AVR was also hooked to the Z windings.  If the Z winding output is insufficient, it would explain why swapping AVR and bridge diodes, did nothing. Connected as shown on the AVR diagram, this AVR can only LIMIT the output of the Z winding. If the Z winding is bad, output will be too low even though the AVR ouput will be full on.  

 It does look like a case of bad harmonic windings, as CarlB suggested.The AVR you currently have, Tysniffen, MIGHT work if the 120V stator output was directed through the AVR where the Z windings normally go.  One leg of the stator's 120V out  should go straight to the bridge, the other through the AVR as your Z winding does now.  Under a peak load, the Z winding will put out peak voltages higher than the 120VAC, so it should not fry your AVR.

The CGG regulator that I suggested to CarlB does work in this manner IF the problem is indeed the AVR, as it appears to be.  If you will read CarlB's previous thread, you'll see that I suggested using a Variac as input to the bridge diode to confirm that the field and stator windings were all working fine.   You don't need external AC power with the variac, as you can set it to the highest output voltage initially to get it started using just the stator AC input, then dial it back once the voltage comes up.  Bill Rogers kindly told me of this method when I was troubleshooting my own ST-3 problems.

Again, sorry I confused things.
Bruce






tyssniffen

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Re: 3k st alternator just stopped mid work
« Reply #65 on: October 31, 2015, 04:48:28 PM »
again, thank you all for the continued discussion. 

I just want to be clear - I removed the AVR completely, still only gett 55v.  swapped out the 'old' AVR, still got 55v. 

it would seem that the above conversation is saying my Z *windings* - inside the case somewhere - are screwed up.   it's not the connections? it's not how it's connected?


BruceM:
"The AVR you currently have, Tysniffen, MIGHT work if the 120V stator output was directed through the AVR where the Z windings normally go.  One leg of the stator's 120V out  should go straight to the bridge, the other through the AVR as your Z winding does now."

to restate for clarification:  you are suggesting I wire the stator wires (the little thing that goes through that switch and light?) and hook them instead of the Z winding?  can you give me more specific based on my blown out photo? which where?  (I added numbers to the image for easier reference-- http://1.bp.blogspot.com/-twTt2OGOP6c/VjTwrg2y6MI/AAAAAAAAGoc/SGieKPi8hwU/s1600/altblowout.png )

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BruceM

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Re: 3k st alternator just stopped mid work
« Reply #66 on: October 31, 2015, 05:37:38 PM »
The "AC out"wires  in your picture are connected to the Stator- the windings that are stationary (thus "stator") around the outside of the Rotor (the part that rotates).   The one that is grounded (the "neutral") should be connected directly to the bridge, where you currently have the Z winding connected.   The other of the "AC out" wires should be connected (instead of the Z winding input) to the Z winding AVR input (the terminal that does not go to the brushes).  This will result in the Z windings being disconnected completely from the AVR and bridge.  The "AC out" is now providing the excitation going through the bridge diode and brushes, making the Rotor into an electromagnet.  The AVR will limit the current going to the bridge by chopping the "AC out" as presented to it as if it was the Z winding output. 

I can't guarantee that this will work with your AVR, but it probably will. 

If it isn't clear what you are doing, you should study some basic brushed generator head diagrams on the web so that you have a feel for how these beasts work.  It will help you greatly should you have to do some troubleshooting in the future.  Ask questions if you don't follow, please.


tyssniffen

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Re: 3k st alternator just stopped mid work
« Reply #67 on: November 01, 2015, 07:30:47 PM »
" The one that is grounded (the "neutral") should be connected directly to the bridge, where you currently have the Z winding connected.   The other of the "AC out" wires should be connected (instead of the Z winding input) to the Z winding AVR input (the terminal that does not go to the brushes)."

you mean run an ADDITIONAL connection from the AC outputs (coming off of U6 and U1) in the way you describe... right? I would keep the output connected to something that would put out power...  and is this suggestion for a test, or as a solution?  that is, would I keep it that way?
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BruceM

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Re: 3k st alternator just stopped mid work
« Reply #68 on: November 02, 2015, 01:10:32 AM »
Yes, it would be an additional connection of the AC output to the AVR, where it currently has the Z winding in and out.   

Yes, it would be a permanent fix, assuming your AVR will work that way.  The Z winding is not needed when an AVR is used with the AC output as the source for not just regulation sensing but also for power to drive the field coil (through bridge and brushes).

This is how CarlB solved his bad Z winding generator head problem.

I use this method on my ST-3 as well, as I don't like the waveform distortion that the Z winding makes on my particular unit.


Tom

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Re: 3k st alternator just stopped mid work
« Reply #69 on: November 02, 2015, 03:47:06 AM »
I have a concern that tys's AVR is probably only designed for 48vdc and that connecting 120vac to the rectifier may fry the AVR. Is there an input label on the AVR somewhere?
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

tyssniffen

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Re: 3k st alternator just stopped mid work
« Reply #70 on: November 02, 2015, 04:48:15 AM »
there does NOT appear to be any input markings on the AVR I have.  If this fries it, well, we'll know something else.

one thing I've picked up from this discussion is that AVR isn't all that great anyway.
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dieselgman

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Re: 3k st alternator just stopped mid work
« Reply #71 on: November 02, 2015, 05:09:27 AM »
I have not heard of too many problems with the Chinese AVR controls... but, prefer the British Stamford in SX460 flavor. In my experience, they are very robust and reliable.

Our next shipment of ST heads will be so equipped.

dieselgman
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BruceM

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Re: 3k st alternator just stopped mid work
« Reply #72 on: November 02, 2015, 06:22:35 PM »
The ST-3 Z winding will put out peak surge load volts of over +-400 volts!  I confirmed this on mine via digital scope capture, while starting only my 1/2 HP deep well pump. I expect the peak would be even higher starting a bigger motor.  My homebrew AVR on 48VAC was a pathetic dog which couldn't start even a single 1/2hp motor.  At 120VAC, is is not quite as good as the stock Z-harmonic setup for big motor starts, but it's adequate for my needs.

 The normal ST-3 Z winding output is very NOT sine, but rather, 4 brief spikes per rotation.  So the RMS (true) voltage may be only 24volts for a normal running load, but is in excess of 120V RMS for surge loads.  That's why you can't beat the Z-harmonic for starting motors, and CarlB had to put a soft start kit on his compressor motor when he changed over to an AVR off of 120VAC.

So there is no concern regarding peak voltage switching an AVR to 120VAC for excitation source if the unit has worked for some time on the Z winding.  There may be other design issues for an AVR, and without seeing the schematic for the specific unit in question, I can't give assurances; but it should work.







BruceM

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Re: 3k st alternator just stopped mid work
« Reply #73 on: November 02, 2015, 06:31:30 PM »
 post to wrong thread, deleted.
« Last Edit: November 02, 2015, 06:36:43 PM by BruceM »

tyssniffen

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Re: 3k st alternator just stopped mid work
« Reply #74 on: November 02, 2015, 10:31:41 PM »
sorry, looking for more clarification on this fix. (it's raining today, so I'm skipping working on wiring anyway)

I've posted another photo here:
http://4.bp.blogspot.com/-Mw48cgB_xEI/Vjfi54CUAPI/AAAAAAAAGow/G7sumGCr_tw/s1600/altblowoutwithdrawnlines.png

with GREEN DRAWN on lines of what I think is the suggested change. 

Connecting on AC out (#1) to the bridge retifier  and connectig the other AC out (#2) to the Z winding going into the AVR (#6)   Does that all look correct?

Also, I'm unclear on whether I UNHOOK the Z windings, or leave them connected.  my green slash marks are on the Z wires - do I cut those or leave them connected?
6/1 with 2 tank for WVO.  pushing power into off-grid house battery bank, in winter.