Homebuilt genset...

[gumpy]

The head I have is a Leroy Somer head. It is rated at 3600 rpm, and 7.5 Kw, if I remember correctly.

[belfert]

I'm guessing you gave up on the Powertech genset like mine.  You did say you thought it would be just a hair too big for your compartment.  I'm sure expense is another big issue.

You should have a good genset and done right it would probably be quieter than the Powertech.

[gumpy]

I'm guessing you gave up on the Powertech genset like mine.  You did say you thought it would be just a hair too big for your compartment.  I'm sure expense is another big issue.

You should have a good genset and done right it would probably be quieter than the Powertech.

Haven't totally given up on it. I just got cheap this spring. Being out of work for a year has tightened my wallet some. And, I have the engine and head sitting in the garage, taking up valuable space, so thought maybe I should go ahead and get it going before it gets warm enough to work outside.

I'm still thinking about that 3Kw Powertech unit. I think I could make it work for my needs, it's less $$$ than the 8Kw, and is smaller footprint. I wish they made a 4Kw or 5Kw unit.

[DrivingMissLazy]

The head I have is a Leroy Somer head. It is rated at 3600 rpm, and 7.5 Kw, if I remember correctly.

The Leroy Somer alternator is manufactured in France. I used to use them occasionally when I needed to build a really Cheap Charlie unit. They are inherently regulated so the output voltage is dependent on both the rpm and the load. OK for an industrial unit for use on a construction site running Skil saws and the like. As i recall the regulation is about +- 5%. The output voltage is typically not adjustable.

Richard

[gumpy]

Well, that's not what I wanted to hear!

I was under the impression these were better units than that, based on the information I got before I purchased it. Maybe
I'd have been better off going with the unit from Northern Tool. I got a good buy on this head, though. It was cheaper
than the NT unit.

So, how does one go about correcting the voltage regulation?  That sounds like it might cause some issues with my Trace
inverter. Although, if it can maintain 120v +/- 5% (6 volts), it might be ok as long as the frequency is stable within about
2 hz.

[DrivingMissLazy]

Well, that's not what I wanted to hear!

I was under the impression these were better units than that, based on the information I got before I purchased it. Maybe
I'd have been better off going with the unit from Northern Tool. I got a good buy on this head, though. It was cheaper
than the NT unit.

So, how does one go about correcting the voltage regulation?  That sounds like it might cause some issues with my Trace
inverter. Although, if it can maintain 120v +/- 5% (6 volts), it might be ok as long as the frequency is stable within about
2 hz.

I suspect that the Northern Lights unit would be similar in quality. I would suggest you try and track down the specs on the head you have. I believe Emerson Electric purchased Leroy Somer several years ago. As I recall, some of their devices had the capability of accepting an input to control the output voltage, but it has been 20 years since I was involved in this product. I did import a large number of the larger 1800 rpm brushless synchronous types for my production and they were very high quality units. I also imported a lot of units from England but the brand name escapes me right now.

Richard

[TomC]

Powertech makes a 5kw for the trucking industry-called an APU-is actually a 5500 watt gen head rated at 5000 watts powered by either a 2 cylinder Kubota or Caterpillar.  Engine runs at about 2200 and the gen is a 3600.  Is mounted in a cabinet that requires the cover to be on since it uses pressurized cooling-meaning the engine fan sucks the air into the cabinet, pressurizes the cabinet then the air seeks the least resistance to get back out which in this case is going through the radiator.  Nice unit, about $4800.  Good Luck, TomC

[Ncbob]

Sorry Craig, have to agree with Richard.  Leroy Somer was a piece of $hit.  Do yourself a favor and find a quality generator to complete your package.

Just a thought.....Machinery's Manual will give you the shortcuts and tables for figuring the size of your pulleys.

Gary has a copy and since he's recuperating from back surgery (it went well for those of you who know Gary
and he'd love the challenge of figuring out the possibilities for you.

Bob

[DrivingMissLazy]

It is not the 3600 RPM or 1800 RPM that is critical. It is the actual design and construction of the alternator.

Most alternators built for the construction trade are built as cheap as possible since many contractors throw them away at the end of a construction project.

To build a cheap alternator there are several steps that can be taken. Since less copper and steel is required for a higher rpm unit, they are typically 3600 RPM. Since out put voltage is typically not critical to run a cutoff say, they are inherently regulated. That means that the output voltage is dependant on speed and load and the amount of capacitive feedback used to control the output. Since the output waveform (harmonic distortion) is not important, then the construction is typically such that the distortion is over 5%.

To get a good alternator, it must be constructed to provide low harmonic distortion and be a brushless synchronous revolving field type to permit precise voltage regulation.

Richard

[donnreeves]

For a really good-cheap generator head, Try looking for an old MH series Onan. I Just mated a 6.5 Onan head to a D600 three cyl. Kubota. All I had to do was have a drive shaft machined that bolts to the flywheel, and fab up a bell housing. I also had the machinist make up a centering disk that slips over the drive shaft to center the bell housing. The tolerances are pretty tight, so alighnment is critical. AS far as engine speed goes, I never heard of hertz. I thought they were a car rental company. Didn't know they did electrical work too. Seriously I just cranked the rpm up untill it read 120V. The governor doesn't seem to keep up with the changes in load very well. I have the voltage set at 124V static and it drops to 114V  at full load. I'm Assuming after reading the above posts that this is the wrong approch. Could one of you electrical gurus please enlighten me. Thanks  Donn

[Stan]

Richard: Please excuse my dumb questions.
1.  When you say 'inherently regulated' are you referring to the type that uses a bridge rectifier to feed some output back into the field, or some other method?
2. In a 'brushless, synchronous revolving field type' how is the voltage regulator connected to the field?
Thanks for the help.

[JackConrad]

   When we had our old (almost antique) Onan, I was told to set the RPM using a frequency meter. I don't remember who explained the procedure to me, but they said to set the RPM to get 62 cycles with no load. When a load was applied, the cycles would be 59 or 60.
   Last year we installed an Energy Management Systems AC monitor on our bus. The EMS monitors both voltage and cycles. If either is out of range it disconnects the bus from the power supply. My understanding (might not be correct) is that cycles are just as important as voltage.  Jack

[Stan]

On good quality gensets with good electronic regulators, output voltage is controlled almost instantaneously by field current. A good regulator will control the voltage so that you see no movement on an analog voltmeter going from no load to full load.

Frequency is a function of speed and there is always some time lag between applying a load and the engine responds to the governor. Just like your bus engine, you have to set the no load speed a little high so that you have the correct speed at full load.

Most things are not particularly sensitive to frequency. The frequency from you utility company varies during the day as the load changes. Their target is a 60 hz average over 24 hours. A 2 hz change in frequency will give you a 3.3% change in motor speed but most electronic equipment has an internal power supply that is not sensitive to input frequency.

[gumpy]

So I looked at the documentation I have on the Leroy Somer head. It's and LSA 35 L9 "E".  It says it's brushless, but
it does indeed indicate a +/- 5% accuracy and <= 5% Telefonic Harmonic Factor (whatever that is).

I guess I don't know what all this is gonna mean in terms of usability. I understand that the frequency needs to be set by
engine RPM, and I know that my Trace SW inverter is sensitive to this. I currently use a jobsite Coleman generator when
we're camping and I have to manually tweak the throttle while watching the inverter frequency display to get it to work.
If I get it set within 1 hz, all is well, but if the engine speed changes and the frequency goes away from 60hz by more than
2 hz, the inverter will kick it out and I have to start all over. It's very touchy. I think I can adjust that tolerance some on the inverter, but really don't want to go too wide. So, I'm hoping my engine will handle load changes well and I won't have that
problem.

As for the voltage, that seems to have a very wide range on the inverter, with limits from 109 v to 132 v. So, if this head is within 5% of it's rated 120 volts, I think it should be ok with my inverter. It seems the frequency is more important to the
inverter than the voltage is.

Does any of this sound logical?

[DrivingMissLazy]

Richard: Please excuse my dumb questions.
1.  When you say 'inherently regulated' are you referring to the type that uses a bridge rectifier to feed some output back into the field, or some other method?
2. In a 'brushless, synchronous revolving field type' how is the voltage regulator connected to the field?
Thanks for the help.

The two types of alternators typically in use today are the inherently regulated, and the revolving field.

You are correct, the inherently regulated uses an internal circuit to control the output voltage, based on current flow and there is no adjustment (generally) available to actually set the voltage.

The revolving field alternator has  separate windings on both the rotor and the stator, in addition to the main power windings. In operation, a variable DC voltage is applied to the exciter stator winding. This voltage is derived from the voltage regulator. This applied DC voltage creates a magnetic field which creates a voltage in the exciter rotor winding. Since the rotor is rotating this is an AC voltage whose frequency is determined by the speed of the rotor and the number of poles on the exciter winding. It is typically significantly higher than the nominal output of the alternator (120 hertz I believe) and is three phase.

This three phase AC voltage is connected thru a set of diodes which converts it  to DC and is connected to the rotating exciter of the main alternator. This DC voltage then induced an AC voltage in the stator (stationary) windings of the main alternator and that is where the output voltage is derived.

The voltage regulator is an electronic device that looks at the AC output of the alternator and creates a DC output that is proportional to the AC input. The DC output is fed to the exciter field as outlined above and the rest is history.

There are some other types of alternators, but they are not in general use in the market today. One I recall is a permanent magnet unit. Permanent magnets, installed in the stator of the exciter create the magnetic field to cause the exciter rotor to generate an AC voltage.

Richard