FAQ Page

This is a living document, expect content to be added ongoing. What's posted here reflects the kind of questions we receive.

Answer: I have come across outfits that are selling generator heads and sending their customers all the way to China for warranty and repair work. I'm sure you won't be happy with that arrangement (if something goes wrong). Make sure the folks that sell you the product are going to be involved in the repair and warranty work, if they aren't; you should expect to be on your own. You might ask... who do I call if it doesn't work properly? If they tell you to look in the box for the warranty, you should suspect that you're going to be calling a number in Shanghai...and it isn't going to be a 1-800 number.... you can bet your donkey on that.

Question: How much does it normally cost to ship a head?

Answer:   Between $50 and $400, use the following weights for quotes.

Size        Weight in lbs.        

3kw=         150             32mm shaft size

5kw=          205            38mm            

7.5kw=       285            38mm            

10kw=        305            42mm          

12kw=        340            42mm            

15kw=         420           48mm            

20kw=         440                         

30kw=         560                         

40kw= (3phase)  620                       

50kw= (3phase)   760   


Question: Are there any downsides to the slower speed 4 pole heads in the ST class?

Answer: Yes, these heads have a very high rotor mass, and the diameter is larger than the modern turbine type rotors. High RPMs generate considerable centrifugal force that could deform the windings, and even throw a bobin (winding)  off the rotor! When the RPM goes far above the rated speed, the voltage and thus the current go higher in the harmonic winding, and the field. I have not tested these heads to see where they come flying apart, and I don't know if the current and voltage get high enough to smoke the harmonic or field winding, but it is possible. If the throttle rack sticks on your engine, and RPMs get real high, it may not be economical to fix the head id it scatters parts or smokes. One could calculate the amperage in the field. and put a fuse in series with the AC side of the rectifier, this would offer some protection in over speed, and if the generator has a load on it, the field fuse might pop before the appliances and generator head does. Experience from the field is helpful in tuning this Q and A, and I have not collected much in the way of overspeed experiences, most people know how to avoid this, if you have an engine with no governor, or a faulty governor, beware!         



Question: Does it matter which direction I rotate the generator head ?   

Answer:    No, you may turn it clockwise, or counter clockwise.


Question: Is there any penalty when running a 3 phase head versus a single phase head?

Answer:  Yes! Without adding special equipment, you can only direct 1/3 of the total output to any single 120 volt load. You can only direct 2/3 of the total output of the generator to any single 220 volt load. Since some folks don't understand this statement, we'll continue, "stop reading when you get it". ... Lets' say you have a 20KW 3 Phase generator, and you have three 5000 watt 120 volt loads, you can run them all by plugging each one into one of the three phases. If you had a single 120 volt 15KW load, you wouldn't be able to power it with this generator, but where would you find a single load this big?   When you get into high wattage loads, they usually become 240 volt appliances because this exact condition exists in your home. You can only use 1/2 of the total power coming into your house for a SINGLE 120 volt appliance. This QA was really placed here for readers to grasp the concept of 3 phase, not to suggest there's a problem with them.  Volts times Amps equals Watts, do the math, you'll have no problem running your toaster on most 3 phase heads.


Question:  How much horse power do I need to produce the full rated output of my generator?

Answer:    Use the following continuous ratings. make sure you deduct 3 percent per 1000 feet of elevation for any  normally aspirated engine.  Example: my Cowiche cabin is at 4500 foot elevation, I should expect to get 8.65 horsepower out of my 10 horsepower engine. another consideration, if you are under running the rpm of an engine, estimate how much horse power it will be making at that RPM. If you direct drive at 1800, and the engines HP rating is at a higher RPM, you must factor what the engine will be making at it's working rpm, and keep your expectations realistic. Remember that elevation thing, and always size up. In the case of the 1115, it is making 20-22 hp at 2200 RPM, if we lower the rpm to 18, we should expect 18.

Size-Horsepower (approximate)

3kw= 6.5

5kw= 12

7.5kw= 15

10kw = 18

12kw = 20

15kw = 23

20kw = 31

30kw = 46

40kw = 60

50kw = 75


Question:  Does the ST come with a twist Lock plug and other plug ins ?

Answer:  No,  these heads are for DIY people who would go to the hardware store and round up these pieces if required.  If you are not comfortable doing this, you should seek some help locally.  Generally, you can pick up these items inexpensively at a big box hardware store.

Question: How much chrome plate does the ST have? Does it have enough bells and whistles to impress my friends?

Answer: The ST generator looks like it came out of the 1950s. It's basic and sturdy. It's everything it needs to be for emergency power with none of the plastic, impressive art work and stuff kids like. If you order one, you better like, painted cast iron, and sheet metal.  If you're looking for fancy plated Allen head fasteners, lots of flashing lights, digital read outs, perfect sine waves, do buy a different head.

Question: My friends tell me to be careful running a computer off a generator. They explain that computer power supplies are highly sensitive and will blow up at the drop of a hat; is this true?

Answer: Computer power supplies like the IBM PC Clones, and Apples are "switching" type power supplies, they were designed to provide nice clean power to the computer even when the AC power is not the best. Computer power supplies are often the most tolerant of them all. They survive on inexpensive UPS power that often looks far worse than any generator could make, I think the computer power supply will do well on the ST head, but I have not run one for days at a time...

  Sept 16, 2002 

I am still looking for a generator that is designed so badly that I can't watch TV, listen to the radio, or run my computer on the power it develops. I've owned some real junk, and the worst generator I've found still runs my DSS receiver an allows me to watch several hundred channels of flawless programming without ANY problems.

Some of you will allow the marketing guys to convince you that a high degree of voltage regulation is necessary, they might even tell you your generator needs to run at 60.00000 HZ to watch TV. Fact is, it's just not that critical, even the power company accepts plus or minus 10% for being acceptable in the voltage department.

Please send me examples of any generator you find that makes lousy AC. For the most part, the difference you'll notice is the ability to carry loads, longevity, and efficiency; not whether it's going to run your common household appliances.

Question: How do I produce the charging voltage necessary for my start batteries, my engine doesn't have an alternator.

Answer: Simply buy an off the shelf battery charger and plug it in as you would at home.

Question: I think I have the wrong voltage coming out of my generator, what do I do to correct it?

See the voltage REG page for additional info.

There are a number of generator configurations, so I'll try and address this problem in a general way. If you consider that you have no voltage coming out of a generator that is not turning, we can safely say that the voltage is affected by the speed in most all generators no matter who made the darned thing.

We can safely start with the fact that 60HZ generator heads are usually 2 or 4 pole heads, the 4 pole ST heads need to turn at 1800 RPMs to produce exactly 60HZ. Some people get caught up with a need to run at 60.00000000 HZ, I believe you're fine at 59-61 for all the things I want to do. The days of using the sine wave for a timing reference is over.. you may have an old oscilloscope or something that demands it, but let's be honest... most of us won't be using our generator to run an antique oscilloscope.

Start by getting your generator set up to put out 120 volts, then plug in a frequency meter, and set the speed for 60HZ, watch the voltage as you adjust the speed..  if it gets higher than 130 volts (on the 115 volt leg), or 260 volts (on the 230 volt leg)  while you're increasing the speed, STOP... suspect that something is wrong. It is far better to run the correct voltage and be off on the frequency, than run too high a voltage and the correct frequency... you'll fry fewer test loads this way.

There's a great and inexpensive device called the 'KILL A WATT', do a basic search and you'll find it for as little as $29 dollars. This device plugs in like an appliance and gives you Power factor, frequency, voltage, and total KWH usage into loads up to 15 amps! This is a must have tool for a person who is going to us a generator more than once or twice. Just don't plug it in when the voltage is too high!

Plug the Kill A Watt  in, or a frequency meter, and adjust the frequency to achieve 60hz, check your as you go. if it's 110-125, you have something useful. This may be a time to tell you how much the power companies voltage varies... I see about 126 volts in my shop, I've been on farms in the Midwest, where it's barely 110 volts. so don't get too excited if your output isn't text book perfect, the power company isn't perfect either.

For those of you who think you have too high of voltage, you may have purchased a head that needs the field voltage adjusted, this is fairly easy to do. Identify the source of field excitation voltage, place a rheostat in series with this output and 'tune' in a little resistance to cool off 'reduce' the voltage. This will in turn lower the current in the field of your generator and and lower it's output. As of 10/2003, we will be stocking rheostats to do this for our customers. In my observations, it's better to run a a cycle less in frequency, and set your max voltage in that way.. I can't tell you how many generators out there are a few cycles off and the owner hasn't known the difference for the last 10 years....  

We have received a few calls from folks that have ST heads that produce around 150 volts at 60 Hz (as they measure it), I would guess that a 5 ohm resistor would be all that is required to lower the voltage to an acceptable range if one thinks it's all important to maintain that speed. using a rheostat will allow you to tune it.  

Following are emails that might answer questions, names have been altered

> -----Original Message-----
> From: lealon [mailto:lealon@coco.net]
> Sent: Friday, March 05, 2004 7:29 AM
> To: gbrecke@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxvircom.net
> Subject: Re: brush Vs non brush heads
> Have been doing reading about generator heads... Considering putting
> together a gen set to power up a battery bank and also to run my power
> tools in my woodwork shop.
> I see the ST heads have two brushes on slip rings.
> I am confused a little. Can understand how these are used to provide
> excitation to the coils... but don't have a clue what makes them
> different from brushless. eg.. have not seen anything about how
> brushless work. Have also read in many places that brushless are more
> reliable and give a cleaner power. This too does not make sense.
> Hopefully you can get me straightened out a bit on the two ...
> Thanks
> Steve Tailet

Hi Steve,

The Alternator in your car uses a single brush per ring.

MOST alternators employ single brush per rotor designs, Honda's well received 5KW construction generators like the EM5000 use a single brush per ring. Dual brushes are considered quieter and can increase reliability.

In nearly 40 years the automotive industry has NOT found enough incentive to move away from brushes in their alternators.

Brushes in the ST design carry a small amount of current, they last a long time, they should not be confused with brushes in series wound motors like your shop Vac, or Chop saw that have short lives and often fail and make a mess of your commutator.

I like things you can fix when they break. ST Brush heads are simple and you can reach all parts from the outside.

A brushless head has electrical components on the rotor. A 'capacitor' for a minimum. This cap must survive the G forces and vibration, sometimes they don't. Replacing this cap is not as quick as reaching in and replacing a brush.

As I mention elsewhere, the ST is a 'third world' head that was designed to function with simplicity. The AC output is good enough for anything I have to run including computers, and all the shop and household gear I have.

There is absolutely nothing wrong with a brushless design, but if the cap or other part fails on the rotor fail, you may have further appreciation for the brush type head. I do receive emails from folks that have had failures. Lots of places charge $60 an hour to work on Generators, learn to replace that cap yourself, some brushless designs allow you to get at this part without pulling the rotor, others need to be disassembled.

As for noise, how much is there? What's the difference between the two? Why is it my TV, radio, and direct TV box are not displaying any sign of noise on the brush head? What does this improved noise reduction buy the DIYer?

If it isn't part of the design, it can't fail in service. Anyone can replace a brush in a minute or two, brushes are cheap, and have an infinite shelf life.

ST Generators are NOT the best, just as anything less than a hydro turbine or jet turbine is not the best prime mover for a generator head. But somehow we get along with less and enjoy more independence through our thoughtful selection.


From: Bart A [mailto:bain@skylinknetworks.com]
Sent: Wednesday, May 04, 2005 11:20 AM
To: George Breckenridge
Subject: ST12 Output problems

 Dear George,

 Today I fired up my ST12 for the first time and have voltage but no output

current and the voltage output on U1 acts strangely when a load is applied

as you can see from the measurements below.  Here are the measurements I


 No Load Stator Voltages @1800 RPM

1.  U1 to Case Ground = 117.8 volts

2.  U2 to Case Ground = 114.8 volts

3.  U1 to U2 = 237.1 volts


 Loaded Stator Voltages @1800 RPM (100 watt light bulb attached)

1.  U1 to Ground = 235.4 volts ??? (light bulb will not light)

2.  U2 to Ground = 2.55 volts  ???  (light bulb will not light)

3.  U1 to U2 = 237.5 volts  (did not place any load across U1 and U2)

Other Measurements @0  RPM: (circuits isolated)

1.  F1 to F2 = 17.1 ohms (field)

2.  F1 to Case Ground = infinite

3.  F2 to Case Ground = infinite

 4.  Z1 to Z2 = 6.4 Ohms (harmonic winding) (circuits isolated)

5.  Z1 to Case Ground = infinite

6.  Z2 to Case Ground = infinite

 7.  U1 to U5 = 0 ohms (stator) (circuits isolated)

8.  U2 to U6 = 0 ohms

9.  U1 to Case Ground = infinite

10.  U2 to Case Ground = infinite

11.  U5 to Case Ground = infinite

12. U6 to Case Ground = infinite

 Other Measurements @1800 RPM (No load)

 Z1 to Z2 = 64.0 volts AC (harmonic winding)

F1 to F2 = 55.8 volts DC (field winding)

What do you think?


There are two ways to wire the head

I will assume you are wired for 120/240 operation


|                         put 120 volt loads across here
|                         Put more 120 volt loads across here


U5/U6 become the neutral, the gen case is NOT the neutral, although people do bond the neutral and case together..

 DO NOT connect loads to the CASE!

 Let me know if this helps..

 All the best,

 George B.






Thank You,


Bart A. Austin










All the best,

George B.