ST head question

[tdale4]

I am in the planning stages of puting together a lister powered genset. I'm pretty much sold on the 16/2. I also plan on getting a 15KW st head. I noticed that it comes in two flavors from one supplier i found. One is "AVR" and one says "transformer", what is the difference? I want a genset that keeps to the KISS principal, one that I can work on in a pinch, which gen head is better for my application? If I read his site correctly, George on utterpower runs without any VR, So perhaps I need to find a thired type of ST head I havn't seen yet?

Thanks,
Tim

[Doug]

Buy an Onan if you need reliable power.....

These are hobby engines....

16 hp don't try and go over10 kva

St heads are junk, simple junk is easiert to fix than complicated junk.....

[Stan]

Actually Tim...the rule is 2hp /kw, and for continuous use that's pretty much it!  You might get a second of two of "excess" kw if your engine has big flywheels, but anything over an 8kw machine is a waste.  I know, I'm going to get flamed for saying this     You also have to consider if your machine will be giving you 16hp!  It'll lose hp for every thousand feet above sea level, then there's wear and tear, carbonning up etc. etc. etc.
Stan

[tdale4]

I understand that it will not give more then 10KW continous, but with the flywheels I figure it could put out more for a few seconds to start a heavy load, like a well pump, etc. I might just go with a 10KW head, but I'm still trying to figure out if I need one with AVR or not.

Tim

[adhall]

Tim:

I'm still learning about generator heads myself, but I'm happy to share what little I know. (Just ask anyone who knows me.  )

To the best of my knowledge, this is what the various catch words mean:
   "AVR" = Automatic Voltage Regulator
   "VR" = Voltage Regulator

As nearly as I can tell, these two acronyms mean the same thing. They refer to an electronic device that monitors the output of the generator and adjusts the field current so as to maintain a constant output voltage. The main advantage of these devices is that the generator voltage does not change much with load changes or with engine speed. A secondary advantage is that the output power from the generator is "cleaner" (i.e. less distortion and noise). The primary disadvantage to these devices is that being electronic, they are more easily damaged than the other parts of the generator. Another disadvantage is they are more difficult to troubleshoot, and when you do discover the failed part, you may have trouble finding a replacement.

I am a little unclear about the meaning of "transformer type". Your post was the first time I had seen the phrase. I believe this refers to the type of excitation that is used on a ST head which is also called "harmonic excitation". This involves a special winding on the stator that powers the field through a recitifier. This winding is designed to increase the field current as the load increases. (How this happens is black magic to me at this point.) The main advantages to this method are simplicity and rugidness. The disavantages are that the generator output voltage varies with engine speed and, to a lesser extent, with load. Also, the generator output power is dirtier. I have seen some reports on this forum where people had trouble getting a UPS to operate when powered by an ST head. For non-electronic devices (like lights, motors, and heaters), this isn't a problem.

By the way, you don't necessarily have to choose exclusively between one or the other. You can install an AVR on a standard ST head. That way, if (or when  ) the AVR fails, you can disconnect it and return the head to "transformer" excitation.

I hope this helps you some with your decision.

Best regards,
Andy Hall

[tdale4]

Andy,

Thanks for the reply. Sounds like an AVR on a standard head will be the route for me. I want a gen set that is simple and most of all reliable. I'd like to be able to repair it myself, which rules out most commercial gen sets like Onan. I'm still in the planning stages.

The system I'm designing will power a small "get away" my wife and I are building out in the country on 27 acres. Power company is $20,000 away so I think we will be off grid for a while. We'll only be out there a few times a month for 1-2 days at a time, so a system shouldn't be to hard to develope that will give us power, for when we're there. For the water well I'm thinking about a dedicated 24 volt solar pannel powered pump that will fill a large cistern when we are away, if it's possible it shouldn't tax the gen set at all, so the largest load will be a 2 ton ac unit.

Tim

[mobile_bob]

Doug:

"St heads are junk, simple junk is easiert to fix than complicated junk....."

most curious, how do you arrive at this conclusion?
junk by what standards?  what other alternatives are there at the price point?
what other alternatives are available in any price point that do the job without sophisticated VR?
What other alternatives are there that are user friendly to the point that one could rewind it in his garage
with some preperation?

personally i find them to be exactly what the DIY'er needs for 99% of users.

did you have a bad experience with an st head from a less than scrupulous supplier? bad experience with more than one head?

seriously i would like to know what you see as the alternative to an st head that doesn't cost 4 to 5 times the price

bob g

[Stan]

I don't have any hands on experience with them but I seem to remember many people describing "grease that wouldn't melt in hell", " inferior bearings",  "doghouses that shake themselves apart",  "melting diodes",  "missaligned brushes",  I know you put the qualifyer in your posting to allow you to attack anyone by saying "they're cheap" but still, doesn't that sound like junk to you??
Stan

remember the difference between low price and good value.

[mobile_bob]

Stan:

""grease that wouldn't melt in hell", " inferior bearings",  "doghouses that shake themselves apart",  "melting diodes",  "missaligned brushes",  I know you put the qualifyer in your posting to allow you to attack anyone by saying "they're cheap" but still, doesn't that sound like junk to you??"


lets take a look at each of the faults you refer to and the seriousness of each

1. grease that won't melt in hell, thats easy enough, clean and repack

2. inferior brgs, here again repack will take care of most, replace with a higher grade of brg that is commonly available everywhere brgs are sold

3. dog houses.... , remove them! if you are building a serious home power system you want the electronics and guages up on a panel anyway.

4. melting diodes, a bridge that you can replace with one from radio shack for peanuts? not really an issue

5. misaligned brushes,  align them! that is certainly not a problem for a DIY'er

what we do have is a nice heavy unit, that works, and for a price that is within reason for what you get.
there are no other alternatives to the ST head for the money, ease of repair, simplicity, and availability.

without the ST head, we are back to converting car alternators, or finding the ellusive surplus head which is not an easy thing to find, locateing and rebuilding
an antique head, converting a motor, all of which have as many or more faults.... or....

spending some serious bucks on modern heads, which require additional electronics  as well.

for the money i am unaware of anything that comes close to the value of an ST head, warts and all.

btw,,, i am not attacking anyone.
i simply asked why Doug saw them as junk.

bob g

disclaimer:
i do not sell st heads, i do not receive financial consideration for defending st heads, and all that stuff.
but i do own a few of them, and will likely own a few more.
i do want a 3 phase st head though!

[Doug]

Well maybe thats a stronger word than I should have used.

Lets say they are frugaly challenged, DIY friendly, field servicable.

I've noted a pattern of failure on the ST heads, they way some of the Indian heads are built is actualy a little scary. From a long term reliability POV I think a low level blue print of a new ST head might be a good idea.

Doug

That hasn't stopped me from buying one myself. Friday I had a long discussion with a fellow that sells imports from China who has agreed to import one for me ( for considerably less than Ebay Canada or other listed ).
I have no illusions that a 250 USD ST head will be significantly better or worse than the engine that is going to drive it. I don't think it fair to give people the impression that the heads are premium quality or that they even measure up from a mechanical stand point to anything you can buy localy regardless of who sells it or what thye claim. It may well be a bit of a hit and miss thing....