ST5 differnt voltages blew my bench grinder etc.

[bschwartz]

I finally got my 6/1 Metro up and running with an ST5 head.  I have about 4 hours break in spread out over about 3 days.  I was testing the new exhaust today and had about 1800 watts or so split fairly evenly.  Each leg was showing around 117 volts........ I took a break for a bit and came back to only half of my devices running, and the smell of burnt electronics.  One leg was now reading 95 volts and the other was showing 172 !!! on the Killawatt meter.  Everything on that leg smoked.

Now the question.. WHAT HAPPENED?!?! and what do I do about it.

It was an ST5 purchased off the bay from Tom Osborn with an AVR (I have a variable resistor on the way to replace it).

[Doug]

I suspect if this was a load test with 90 on one leg and 170 on the other the AVR is trying to compensate for something and is increasing the field voltage. It could be a loose connection and unfortuntely it could mean the low voltage leg has developed an internal short and the AVR is trying to boostthe voltage to compensate.

[bschwartz]

I opened up the doghouse, and the AVR is checking voltage across both legs (the meter on the front was showing close to 240V which seems normal).  What could cause one side to jump so high?  Even if the AVR was trying to compensate for another issue, wouldn't both legs go up? 
On a good note, my exhaust is only about 1/10 the volume of my intake!!!!

I took the suggestions of a propane tank for an expansion chamber, then to a 30 gal barrel inside of a 55 gal put into the ground.  I can't believe how QUIET this is!  I'm now awaiting the $3.94 Solberg FS-250 air filter/silencer (I love ebay). 

I've been lurking since December when I first got Horton (6/1) and have been reading all I can (yes I got 'the' CD)  I've had a custom idler gear bolt cut ( dual cam offset !!).  I got the 'must wire wheel every bolt' bug.  Tappet guides have been trued (they rotate now).

This is so much fun.

[bschwartz]

Woo Hoo, I'm an idiot.  Sort of.  A sacrificial CGFI blew protecting the motors and stereo!
The voltage problem still exists, but at least I don't also have to replace other equipment.

[ronmar]

I think that Doug is correct.  If I have my brain correctly around the makup of a 4 pole ST head, each pole has 2 windings. One of each of these windings produces about 30V. One winding from each pole is wired in series with a winding from the other poles(4 windings in series). This gives you two 120V outputs when properly excited by the rotor. If a pair of the rotor windings was shorted, this would drop the voltage on that 120V leg about 60V.  I would guess that your AVR is wired across both 120V legs and is regulating 240V. It dosn't care how it gets 240V or that the 120V legs are not balanced.  If one leg drops 60 volts, the AVR will build the field to get the total back to 240V.  So I am guessing the increased field is pushing the shorted leg to 90V and the good leg to 170V.

I believe the pole windings are tied together around the brush end of the stator.  If you follow the wires on the weak winding, you might get lucky and find a short in an accessible spot where the windings are spliced.

Good luck.

[bschwartz]

Thanks for all the rapid responses.  Tom called me and had me check the grounds etc.  It seems that in fact the AVR was across one leg (not the 240V that I thought), and it failed.  When he had me pull the AVR out of the circuit and run direct, I got 135V on one leg and 140V on the other.  He will be sending a replacement.

For anyone who may have interpreted my mention of Tom in any negative way, PLEASE let me be clear.  I only stated his name as an identifier of the gen head, NOT anything bad about him.  Tom has been the BEST vendor I have ever worked with for any purchase.  I wish I needed something else just to give him more of my business.

[Doug]

Me....
"the AVR is trying to compensate for something and is increasing the field voltage" or should I have said flux....

Make sure your connections are tight and you have things like AVRs connected properly...

The fact one leg should so be much more different from the other troubles me. The iron in one should not have saturated and not the other ( theory ).

So how EXACTLY was this all connected to produce this effect.
Others ( including myself ) can learn from this

[bschwartz]

I used a 4 wire connection.  Ground on generator to ground on transfer switch ( like this one http://www.grainger.com/Grainger/items/2KEP5 )
Center common to common, and two hots to two hots.  Pretty simple.  A one to one relationship.  Leg one feeds A,B,C and leg two feeds D,E,F  C and D are bridged to provide 240 to my compressor.  In the gen head (this is where I get fuzzy with new to me info) the Z (I think) winding goes to one side of the diode bridge, the other goes through the AVR then to the other side of the diode bridge.  From the bridge we go to the brushes.  Did I get this right?  Engine function I understand.  Basic electronics I'm OK with.  Windings on generators are a new animal.

I agree, the different voltages are what troubled me as well. 
Everything was working (as best as I know) for several hours.  I checked brushes (and attachments), wires to output etc.  Nothing jumped out at me as unusual.  I was really hoping someone would have said "Oh yeah, just check out the ......".  I did a search and nothing like this came up.  Tom believes it is the AVR.  He is sending a replacement.  I'll just trust him and go from there. 

[Doug]

Can I see a picture of the AVR connected to the bridge and Z leads?


I can't quite picture this and to be honest I have not seen an AVR on an ST before. I was expecting you to tell me it had 6 leads 2 for the brushes 2 for the Z leads and possibly 2 for the gen output termincals to sence the voltage.

[bschwartz]

The AVR has 4 wires.  Two connect across common and one leg to measure the 120V and the other two (thicker) connect between one of the Z (I think) windings and the bridge rectifier.  Tom told me that the replacement he is sending will measure across the full 240V.  I'm also picking up a 150W 10 ohm rheostat that could be put in its place in a pinch.  It can be used to adjust the voltage, but not regulate it.  If I don't have another job after work today I'll try to get a picture of the setup in the doghouse.  The AVR I have in there is this model http://cgi.ebay.com/ST-Automatic-Voltage-Regulator-AVR-120-240-V-1-Phase_W0QQitemZ160358402087QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item25561b0827&_trksid=p3911.c0.m14

[Doug]

Hmm....

There's a print on the AVR cover that indicates its for a 3 phase unit and I don't see a bridge in it.
But I am not familiar with this unit and the vender knows his product so I assume that his instructions are correct.

150 watt??
I think thats a bit bigger than you need check your ST manual my gut feeling is maybe 15 watt is enough. Try it without the regulator the Z winding's function is to self regulate. Its not perfect and not as good an AVR but it should allow you to run tools and lights ect, but I would not trust the TV or PC with it untill you know its not going to spike at low load on you.

[bschwartz]

I think he sells single and three phase units and that may have been the wrong picture.  The 240v AVR arrived today and after installation and testing, I think I figured out what happened, just not the technical why.  It seems that the 120V AVR was on one leg.  When I was testing, that leg had slightly more load.  The voltage dropped, causing the AVR to raise the current (is that how it works).  That raised the voltage more on the other leg, and seeming to self balance by lowering the voltage on the heavy side, the AVR leg drooped.  That caused the AVR to boost more........ etc.

I decided with Tom's advice to try loading the heck out of the generator tonight for about 2-3 hours after installing the new unit.  I was pulling (according to the kill-a-watt) 1700 watts on one leg and 1250 on the other.  Voltages were more even with the 1700W side about 115 V and the 1250W side about 122 V.  Gentle black puffs of smoke from the exhaust, but chugging away fine.  This is the first major continuous load this high as the engine only has about 5 hours on it now.  Near 3KW seems great to me as the engine isn't broken in yet, and I'm at about 4500 feet.

I think I'm beginning to see the possible negatives to an AVR system.  Time will tell if I keep it inline, or pull it and install a simple rheostat.

[Jim Mc]

...One leg was now reading 95 volts and the other was showing 172 !!! on the Killawatt meter. 

The symptom you describe is typically caused by a bad or intermittent connection between the generator's neutral and your panels' neutral bus bar.  It's a classic symptom of a bad neutral connection - Double check the neutral wiring and make sure there is no way for  it to be switched, disconnected, or otherwise opened.  

[mbryner]

I've been researching the forum, trying to decide whether to install an AVR on my ST7.5.   There are many threads on it and so many opinions.

So, Georgia Generator (Tom, as mentioned above) has multiple AVR's for ST heads.   No offense to anyone intended, especially if Tom is a member of this forum, but I don't have a clue what to buy.   

We all know how the Listeroid is poor at rpm governing, and my machine is no different.   My inverters have occasionally failed to lock onto the ST power to charge the batteries, like yesterday.   When I look back through the inverter error logs, it reads frequency too high/low, voltage too low, etc.   Again, this only happens occasionally, but it would be nice to get cleaner power.  Also, my fluorescent lights flicker like crazy when running on the generator power; seems to be voltage not frequency issue.   The frequency is (relatively) stable for a Lister at ~58-65 Hz, but I notice voltage can get low, like 107 V.

Here are a few I was looking at.   The first has built in meters, etc.:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=150368550392&ssPageName=STRK:MEWAX:IT
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=150355185131&ssPageName=STRK:MEWAX:IT
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160360959289&ssPageName=STRK:MEWAX:IT

Is there any AVR that you guys have a consensus on recommending?   Are the cheap ones any worse than the expensive ones?   Or stay away from AVR's and just install a rheostat, and manually adjust the rheostat and engine governor knob?

Very confused....   

[bschwartz]

From my recent experience, I would go for a 240V AVR over a 110V AVR .  I just got a big (read BIG) rheostat that I plan on trying, but don't have a recommendation yet on that route.  If going the AVR method, Tom is an awesome vendor to deal with.