Lister Engine Forum
How to / DIY => Generators => Topic started by: BruceM on August 24, 2016, 02:09:32 AM
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Dear friends,
We recently had a open circuit failure of one rotor coil winding of an ST-3 head from Tom at CGG. Since he didn't have a replacement coil, we ordered the matching 19 awg magnet wire and after winding it found the resistance didn't match, and it was much heavier. Checked closely and found that the windings in this year old ST head are ALUMINUM.
I'd also like to add that the windings were not redesigned for aluminum; they are the same 19 gauge as the copper in my older ST-3. The copper windings are 4.3 ohms per coil, these are almost 7 ohms. I'll be checking the stator windings later today, but I expect the same was done there. Visually they look identical, which was not doubt the intent.
I'm now looking for an all copper ST head replacement. Does anyone know of a reputable importer of all copper ST heads? If I'd known this thing was aluminum I would never have recommended it.
Thanks,
BruceM
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I modified the earlier post to include the facts that the windings were not redesigned for aluminum- they are exactly the same gauge as the older copper (and same length/number of turns). They are indistinguishable visually. This means the rating of these heads is seriously bogus. Do we believe the unsolderable crimp connectors are really special for aluminum? I doubt it.
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Have you contacted CGG to see about the possibility of warranty replacement? They might stand behind it and make good.
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Oh man that stinks. I am looking around for a smaller head for another project at the moment and am considering an ST3 or an ST2 if I can track one down. Thanks for the info and please keep us updated on what else you find.
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We have one of the older ST3s (new old stock) from Joel Koch still in stock. Location is in Alaska though, so shipping is a little higher than normal.
Our manufacturer in China claims unequivocally that all of their windings are of copper. I suppose that only dismantling and testing resistance will show for certain what the Chinese have done behind the scenes.
Has anyone else here seen this problem with aluminum windings?
dieselgman
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Thanks very much for the copper confirmation Gary. There seem to be several manufacturers of ST heads and quality is not the same from them all, as others have reported in the past. I'd only recommend DES as a source for them now.
Someone recently mentioned having high resistance connections at the field coil interconnects- if you find crimp tubes, I'd suspect aluminum. They look like they have solder, which they may, but those tubes were used on Jeff's aluminum head so be warned. Both the copper units I have just twisted and soldered field coil interconnects. It's easy to find an accessible wire and carefully scrape off a tiny spot of the red insulation. Then touch up with red electrical varnish or fingernail varnish.
We put together my backup ST-3 generator head (rotor and stator) yesterday. It was purchased about 15 years ago and rotor and stator were shipped separately to allow UPS delivery. Alas, upon inspection of the stator housing casting, we found a crack that ran almost full length near one foot that had been puttied and painted over. I bent and cut some angle iron to fit, and JB welded and bolted it in place. to re-secure the case. Put it all together, hooked up power and a horrible noise is made...the rotor is rubbing on the stator when powered. Visible scratching on rotor and stator. We find that the stator laminate assembly is loose in the case. Drove it back in place, tight, and put it all back together and it still screams when powered. Eventually had to take out the rotor, chuck it in my wood lathe, and true the rotor with an angle grinder while spinning the rotor. Quite a project but it came out very nice. I also smoothed the stator laminates with a 3" drum sander in a drill. After shimming the end bell to center the rotor within the bore, I now have 0.017 inches clearance all the way around (tested via tape strip on rotor). No more binding under power but and then find the harmonic output is pathetic; I can't get over 170 volts with no load though can get 230V on a 12V battery for excitement. I finally tried the 240V AVR I got from china for $25 using the 240V output as harmonic input. That works well and now Jeff is finally back with power again. I'm not very happy with my backup head as my current homebrew AVR requires the harmonic for startup. I'm now very happy to have gotten lucky on my 1st ST-3 which had only the usual and expected bearing and diode bridge failures almost immediately.
Tom at CGG is using Jeff's dead head end bell casting to restore a broken returned unit for Jeff's replacement. Good of him to make good on this troubled unit Jeff had.
It's history:
1 Broken end bell casting which I repaired via steel/bolts and JB Weld.
2 Broken foot casting broke due to uneven casting/machining, repaired by steel/bolts and JB Weld, reground all feet to flat on bottom.
3 "New improved'' bearings failed (groaning) in less than 10 hours of run time.
4 CGG supplied AVR failed in about 30 hours.
5 Field coil failed open at perhaps 60 hrs of run time, eventually found to be wound with 19 gauge aluminum instead of copper so rewinding expense and time utterly wasted.
6 Harmonic output no longer adequate after field coil failure, even with rotor replacement (loaner rotor from my backup unit). It can't handle more than a 1500 watt load.
I do wish there was a smaller Stamford style head available, as I'm getting fed up with ST troubles. I'm going to be kinder and more grateful to my older ST-3 which has been quite reliable. Knock on wood.
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Wow Bruce, that stinks. I am going to pet my 5 and 15KW ST heads too. I have had no problems except lost a rectifier. Probably 500 hours on them guessing. I have a 15 in crate from Gary's latest shippment, I will check it ASAP.
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38ac- My neighbor also checked with Gary's China ST head supplier; they claim they only use copper windings, so you should be good. But I do now think that a full inspection and test running a spare head is good idea with the ST's.
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as much meat as is in the windings, a simple weight check should tell if they are copper or aluminum. Copper, I doubt, units would vary more than a pound from 5K to 5K. If it's more than a pound light, bet on it being aluminum.
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We only have the manufacturer's shipping weights at hand... but we could do some finer weight measurements on our own if it seems practical at some point. Who can tell about the varying thicknesses on the iron castings though?
I would much prefer to stay with the supplier's guarantee about construction materials and testing and hope that they are able to maintain some level of integrity. Of course it is likely a fools errand to hope that we could control the manufacturing process from beginning to end. There are middle-men involved that may not be accountable at every juncture.
dieselgman
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After Jeff shipped his end bell and CGG got it, Tom found that his returned head with broken end bell casting also had a cracked stator housing. I think these castings are too thin or the quality of iron being used is too poor.
As a side note- the $25 Chinese 220V AVR failed on my backup ST-3 with bad harmonic when a 5A slow blow fuse I installed to protect the rotor windings failed under a full load motor start. I may try again once we get a replacement, but I think I'll add a cap across the rotor DC, and a transient voltage suppressor (and increase the fuse to an 8 amp slow blow).
I use a step down transformer to reduce the excitation voltage for my homebrew AVR to 120VAC. That works OK, though it doesn't have quite as much motor starting power as the stock harmonic. I've measured a maximum of 400V peak voltage from the harmonic on starting my 1/2hp well pump, so in theory an AVR which can handle the stock harmonic output should be able to handle 240VAC direct excitation (360v peak). Alas, some much higher voltage head room is needed when the inductive kick back from the rotor is considered, in case of a failed fuse!
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Jeff got a parts (busted case casting) ST-3 and bought a new ST-3 from CGG at a discount as a replacement for his failed aluminum rotor unit. These units are being shipped bolted to 3/4 ply base with no fork lift base or cushioning of any kind. This plus the tension on the cast case from the force fit stator would account for the broken castings in shipping.
The new unit was in good shape, has sealed bearings, and works but was suprising- 350v output (no load) connected on harmonic alone. It will need a heck of large dropping resistor to work on straight harmonic. It was sent with an 120V AVR connected. We hooked that up and as usual, for a 240V setup it is a very poor arrangement. There is some vibration and noise from the ST-3 from just the tiny imbalance of load this causes. All the ST-3's I've tried are completely intolerant of unbalanced loads. I know others do this with ST-5s without too much complaint. It also regulated poorly- 12 volts difference between no load and a 1200 watt load. The ST-3's are quiet as can be on a 240V AVR, which are available from China direct on ebay for $25. incl. shipping. I suggest that if you MUST use a 120V AVR, put it on a tiny 240-120 step down transformer. It will then regulate properly and won't imbalance the load.
We were able to drive out the stator from the parts head quite easily due to the broken case. We drove out his old stator with the bad harmonic from it's case with quite a bit more force required and drove the new parts stator into that casting without any trouble. We ran out of daylight so haven't tested this backup unit yet.
One very interesting observation: We had 3 ST-3 stators sitting on my workbench that were all grossly different; the newest ones from CGG had a lamination that was 3.5" deep. Jeff's prior CGG unit was 4.75" deep, and my 12+ year old unit was 4'' deep. This helps explain why people have reported so much variation in the quality of the waveform from the ST heads. There is a great variation in everything except the castings, which were all interchangeable. It may be another Rajkot type situation, where components are made by small shops, and assembled by others, and sold by others...
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Glad I took the time to read this thread as I was thinking of replacing my 2500 watt Root and Kurtz head with an ST3. When I finally get to that point I'll be very careful and ask some questions.
The sellers of these heads need to contact the manufacturers and make them aware that American buyers aren't stupid....and very demanding when it comes to quality. If one manufacturer gets away with this is won't be long before they're ALL junk.
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I really appreciate this thread. I have an ST15 that has always underperformed. It makes 109 volts unloaded and 104 volts with a 4000W load. Ugh. Drops to the 90's under heavy load.
Not once did I suspect aluminum windings. It's time to disassemble and check.
I did install a voltage regulator from Tom at CGG, wired to use the 115V leg to power the field. That's got the voltage up to 128 max! Nice.
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Chris, my ST 15 can from the same shipment as yours about 10 years ago. I also had the low voltage issue but solved it with a 220 voltage regulator from Tom Osbone and a series of CAPs on the DC side. Now it is also hot in the 240s and 120s. Interesting on the Al windings, I also wonder.
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I have less experience with the Chinese stuff, but have long worked with the (once) American made Marathon heads and others. We have had quite a number of them repaired and rewound over the years, usually by specialty winding shops with all the tricks/tools/and expertise. The LIMA MAC variety is one that is brushless and "inherently regulated"... does not require anything other than its own residual magnetism and very precise winding specs to maintain its voltage within 5% under almost all conditions including minor overloads. We have seen occasional rewind failures due to off-spec wire where the output voltages would be off significantly with only a slight, almost imperceptible, change in the wiring used. We have also seen struggles with some of the Italian heads which apparently used a metric wire size and correct outputs could not be achieved nor properly maintained when rewound with conventional North American available wiring stocks. This is from work done by well seasoned winding professionals who were quite well versed with all the technicalities and nuances.
More recently we have received a large quantity of Chinese ST heads specified, marked, (and supposedly pre-tested) for 60Hz 120/240 operation. Unregulated these heads are producing closer to 300vac at 1800rpm. Tom at CGG confirms that many of his do exactly the same thing out of the box and need a regulator or rheostat to bring them into spec. This may just be the norm with the ST variety of Chinese heads in current production.
With the reported under-voltage stuff and our recent experiences with the ST overvoltage, I am led to believe that manufacturing expertise and conformance to precise specifications may be quite lacking in much of the Chinese stuff. This may have nothing at all to do with the one noted case of sub-standard aluminum windings but rather be more to do with loose or variable manufacturing tolerances. Sound familiar? Like something out of Rajkot? I think it is the same syndrome of immediate money vs quality control - very shortsighted and foolish in my own worldview.
dieselgman
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With the reported under-voltage stuff and our recent experiences with the ST overvoltage, I am led to believe that manufacturing expertise and conformance to precise specifications may be quite lacking in much of the Chinese stuff. This may have nothing at all to do with the one noted case of sub-standard aluminum windings but rather be more to do with loose or variable manufacturing tolerances. Sound familiar? Like something out of Rajkot? I think it is the same syndrome of immediate money vs quality control - very shortsighted and foolish in my own worldview.
dieselgman
Bumping up an old thread, to agree with Dieselgman. I work on some of the finest aircraft mankind has ever produced (The Gulfstream G650ER) and the Listeroid/ST situation is an exercise in frustration. I think they can be viable methods of making power. But it does take some effort and know-how.
My ST head seems to have copper wire.
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I have 3kw st head as well....
Today I found it has aluminum wire... oh joy..
I had redone the rotor winding connections last year.. and ran it for ~10 hours after a winter power outage... all good.
A month ago, I started up the 6/1 to test things.. and no power on the st head.
Wish I had picked up on the aluminum last year.. not too swift...
Next step... get a 2 pole for power backup... rewind the rotor with copper at leisure..? or go for a pricey 4 pole head with better reliability?
this is a hobby ... right..
regards,
steve
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Check your resistance on the rotor windings from the slip rings. If it's open circuit, then check/recrimp the connections again.
My neighbor's ST-3 had one rotor wiring go open within a couple hundred hours of use- and it was not at the connectors. It appeared to be an invisible flaw in the aluminum wire internally; there was no break.
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I did have a look a the resistance at the slip rings... per Utter Power's trouble shooting guide... I saw something in the range of 20Mohm's .... way over the suggested 17ohm.
Proceeded to open the individual connections, to see where the problem was... and noticed white powder coming out of one of my crimp connections... that's when I tweaked on the aluminum windings. This wire is very soft/brittle.. getting shorter so will have to splice in some pieces to make future connections/repairs.
This is a learning experience, but part of the fun... electricity is kinda magic stuff
thanks for the advice,
steve
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update...
I soldered up all the connections on the rotor. Used Uniweld 4300 kit... it worked. Aluminum is not nice to work with... especially with the wires getting shorter.. lots of solders.
See how long things last? .. my soldering may not be long term reliable... original wire is fragile...
I am getting ~7 ohms across each coil and ~27 ohms in total.. at the slip rings.
Just re installed the st head and cranked up the 6/1... there is power... tested it to 1500w.
Plan to get a 3600rpm head .. as back up.
onward,
steve
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Thanks for the tip on the Uniweld 4300! While not ideal, sometimes we must cope with aluminum connections. The biggest bugger is making copper to aluminum connections...did you find something for that as well?
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Last year I had the rotor out and used copper "jumpers" to make up for the shortened ends on the aluminum wire.. it breaks very easily.
At that time I had a couple bad crimp joints.... fixed per Utterpowers recommendations....generally.
Sadly... I did not notice that I was working with aluminum ... thought it was poor quality copper. Never entered my head it was not copper.
Same problem this summer... then the aluminum mystery unfolded... or revelation. (white powder at crimps)
I stayed with aluminum for the repair. Picked up a bit of aluminum at Princess Auto.. similar to HF in US. Hard stuff to find in this area.
The aluminum wire was the same gauge, but much stiffer.
It is a tedious repair and I am not a competent solder type.. but learning is part of the fun.
The Uniweld product is supposed to join copper and aluminum.. think it will.. the flux is effective stuff.
I suspect it is not good for copper and aluminum to touch... corrosion and such.. (experts can weigh in on this)
If you want to join copper and aluminum .. suggest try using a butt connector (stainless), with an anti oxygen paste. Again keep copper from touching aluminum.
I did not have much room left for this connection, had to lengthen the wires from the coils anyway.
Have to think a bit about centrifugal force.. with butt connectors, as well... more stuff spinning in there...forces on ~17awg aluminum wire.
I'm not pretending to be a sage, just rambling per my path (so far) on this repair... hope it helps someone.
regards,
steve
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I'm an utter novice on working with aluminum wire myself, thanks for sharing your experience. There are some very spendy special crimp connectors for aluminum-copper, but I've never used them.
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I too, was going to ask about the rewind option vs repairing the repairs. During rewind, can they skew the windings to improve the waveform. or does that require a total redo of the laminations ?? I've only had mine apart far enough to replace the bearings.
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I don't have any experience with an ST head but just priced rewinding a 5 HP 3 phase motor and it was $550. New motor was around $875.
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Typical cost of $500 to rewind a stator... obviously not normally viable on a $500 genhead.
On the issue of dissimilar metals and corrosion... if you can exclude oxygen from the connection, resistance through the connection will usually remain OK. We use a grease-like product in all such connections in building electrical systems. There are sometimes aluminum/copper interfaces to deal with, they will always build up oxidation (and resistance) if left exposed.
dieselgman