Wow,
I have been working on my Kohler 4.5 CM 21 RV generator, and found that the magic smoke has been let out of the voltage regulator....then when I looked up part #233833 I found that it sells for $368 dollars....
(rant rant rant)
So I have determined that it is indeed time I learned how to build voltage regulators...
I am still trying to figure out how the one on the Kohler works...but I know from the PDF...
http://campkahler.com/files/kohler-7cm21-rv-service-manual.pdf
that a bridge rectifier is involved...Mouser has one for $3.05 that will pass 35 amps...I also determined from the manual that a test of the voltage regulater involves an AC voltage of up to 120vac. The manual says the brushes pass no more then 2amps, so I am thinking the rotor power is less then 250 watts. This makes me think the Mouser rectifier part will work...but, but, but,
I don't have a clue how the voltage regulator works yet...It has the stator AC input wires, and the dc output to the rotor...only four wires. There is an additional dc field flash input wire, but that is inconsequential to regulator operation....
The knee jerk reaction here, is that the stator winding that powers the rotor, puts out power proportionally to the other stator windings making generator output power. So I it makes me think that the voltage regulator doesn't directly control generator out put...like it has some preset parameters that it works in, but no real link to the actual output voltage...
So what do youse know about all this?
For me, this is a perfect problem...the rest of the generator is really simple...so much so that I feel confident I could make this run for a while...
DF
www.centralgagenerator.com
carries a much cheaper regulator than could be substituted. They may be able to help you re: your specific application. Almost any regulator that takes your AC input will do the job.
There is much more to the regulator than what is shown in their diagram. It is NOT just a bridge diode. The rotor field is fed DC in pulses, with the pulse width or duty cycle determined by the output AC voltage.
Best Wishes,
Bruce
A friend of mine had a problem with the generator on his boat taking a long time to get up to power.
A guy that came out to look at it quoted him something ridiculous for an AVR like $500 PLUS installation.
I got him to get the old one off and found one on fleabay for under $20 and fitted that.
Saw him on the weekend and the thing has been perfect for over 12 months now.
He said he was going to buy a couple more just in case and put them away for that price.
You may be able to find something on Fleabay for yours as well.
Bruce is right, the schematic on page 5 is not really a schematic, it is a simple representation of some of the function of the circuit to help describe sequence of operation.
The more telling schematic is the one found on page 39. That schematic tells me a few things. The first thing it tells me is that the regulator function is tied to the solid state control board. The second thing it tells me is that the generator probably has a harmonic winding which generates the energy used by the regulator to excite the field IE: Energy coming from terminals 42 and 43 instead of sampling the main AC output... It also appears that same energy is fed back to the control board, either to provide it with power, or as some sort of monitored feedback used for control.
This appears to be an analog regulator as it sends regulator field current right to the brushes. I believe most of central GA generators solid state regulators are pulsed type and are designed for brushless generators. They send a large pulse each cycle and on a brushed generator this can distort the AC output. Also since the excitation energy and regulator are tied to the control board, bypassing it with a standalone regulator might cause the control board to do unplanned operations as it may need to interact with the regulator...
I know it sucks, but sometime there is no substitute for the OEM part. I would however make absolutely certain that that part is needed. I only skimmed the manual, but there appears to be a regulator test procedure.
Good luck...
Well, I sure appreciate all the help. I especially like it when the folks who know about regulators and electronics share what they know...
In this instance, if I have to buy a $368 voltage regulator...to be able to continue diagnosing why the generator isn't working...well, it means that I would probably just scrap the generator part and use the engine parts to keep a different Kohler 341 running.
Fortunately, my ignorance is a blessing this time...I am willing to learn how the system works, and try to build or adapt some other parts to make the generator operate again....
The harmonic circuit, must be what I thought of as proportional to the regular AC output...so it seems the harmonic is about one tenth the wattage of the other two stator windings.
So it would be possible for me to series wire ten 12volt batteries, and feed the rotor that way. Then I could see what the regular AC out put would be. From there, I could add or subtract cells to vary the DC voltage to the rotor, and record the AC out put voltage. Of course, I have to limit the current, but these little UPS batteries don't give up much.
Ronmar, I am ignoring your statement, about the regulator depending on input from the "Decision Maker" controller, for two reasons, 1. I don't think there is any interaction between the voltage regulator and the controller. 2. If there is, and the controller is bad, as well, then we are talking unobtanium, and I will have to bypass that as well.
As it stands, the generator worked only after it was pulled from the RV. So I do believe there was a problem with the interlock or controller. When I set the engine ignition up to stand alone, then the generator began working. Also when the unit was in the RV, it would not crank or have spark. This led me to rewire the engine, and suggested to me that the interlock circuit was faulty. Once the engine was running on its own, then, the generator worked fine. Then something heinous happened, a squall blew the tarp off the unit and it got wet. After that, it doesn't generate anymore. So....I can only assume, that I have to learn what kind of generator circuit it has, and then try to duplicate or invent a way to regulate its voltage....
I will see if I can find out about harmonic generator circuits....
BPJ
My only concern on page 39 is the ''ac interlock circuit board'' which feeds the ''solid state control board''. If the engine will still start and run at present, this may not be a show stopper. I'd leave the "ac interlock circuit board" connected as shown.
Genhead terminals 44 and 33 do seem to be a harmonic winding, which could be used or the terminals 2 and 4 (line L1 and L2) could be used for excitation.
All the modern design AVRs are pulsing, and would be OK for the brushed generator head. The rotor coil is such a huge inductor that the pulses don't cause significant problems.
I don't see any problems with using a "standard" AVR on this brushed genhead. The mysterious functions of the "solid state control board" should still be functional, if that board is still operative.
You can use either the line voltage output for excitation source to the AVR or the terminals 44 and 33 which seem to be a harmonic winding.
You can evaluate the generator head by connecting a variac to the L1, L2, through a bridge diode to the brushes. Flash the field with +12VDC to positive brush from the diode bridge. Start the engine. You have to initially crank up the voltage on the variac all the way to get it to start generating, then immediately dial it down to get the desired voltage at L1 and L2. Have an analog volt meter on L1, L2. You can adjust the variac to suit a fixed load, confirming that all is well with the genset except for the regulator.
Just my 2 cents worth.
Oh Boy! this is great news!
I working on a video right now to show you what actually have. I want to simplfy this machine down to the bare essentials...thx for the tips. I would like to read more about harmonic windings...any suggestions?
BPJ
http://www.youtube.com/watch?v=26uEzkJSagY&feature=youtu.be
This is a video, I made describing the generator problem....please reply with any comments or ideas...BPJ
Well that line running from the control board with a 2A fuse right into the middle of the regulator isn't there just for show:)
You don't need a whole string of batteries to excite this thing. A single 12V gellcell applied to the field will be more than sufficient to provide enough excitation current to run the output to full voltage and then some...
Ronmar, Yes, I saw the high current line from the controller to the regulator. That's enough current to drive the field coil. It seems unlikely to be a control signal back from the regulator, so I would just clip it and cap it and see what still works.
Dualfuel- As Ronmar says, the field coil will likely need a fairly low voltage, like 24V maximum. It will need MUCH higher voltage (like 120V) for a surge load, like starting a motor. The field coil always takes only DC, thus the bridge diode is always before it. The field coil is a huge inductor, so feeding it pulsed DC is fine, it will filter out those pulses.
Ronmar's suggestion of just hooking up 12V dc to the field coil brushes to confirm that the rotor and main windings are OK is a good one. Just hook your AC voltmeter to the L1 L2 outputs and see if she "lights up". Just a note- you can fry the rotor if you leave 12V applied for too long without the cooling fan operating, so just apply the 12V once it's already spinning. With no load it will go well over the rated voltage. No bridge is needed for this test.
After that test you could also check the AC voltage on what we think is the harmonic winding. It won't be much with no load- just a few volts on an RMS volt meter. It's not a sine wave so a cheap non-RMS meter won't tell you the voltage reliably.
Dear Bruce and Ron, and anybody else with facts or an opinion,
I am still trying to identify what more is in the field circuit. The regulator test asks that you hook up two 120VAC incandescent light bulbs and feed the regulator 2amps from a variable transformer. Various things are supposed to happen, during the test, when one changes the voltage in. Would this indicate another component was part of the regulator, besides the bridge rectifier? You mentioned this earlier. It must be very tiny, because the regulator doesn't look like it has room for more then the five diodes....four for the bridge, and I assume one more for the 12volt flash.
The other thing that is bothering me...there is an open feedback loop between the engine and generator. All the engine is concerned with, is turning at 1800rpm, as per the mechanical governor. So, I am trying to come to grips with how the generator makes the load appear...bear with me here. For example, I turn on the iron or microwave, and a big hole appears in the circuit, down which all the electrons pour. Is it because all these electrons are pouring in (amperage), that a magnetic field opposing the rotation of the engine, is created? This would be going on, on the stator side of things....but what about the rotor side of things? As the rpms fall, so would the power created in the harmonic stator winding. Is that what the regulator is trying to do? Up the voltage during the momentary fall of rpms? I get it that the engine doesn't care about anything other then the rpm, and a good flywheel/governor/clean carburetor setup, can make that fall of rpm, very temporary indeed.
I get it that you need more power at the rotor, during a load. I think I get it, that the power is created by upping the voltage at the rotor. Is it because, the rotor, as an inductor, is surrounded by an powerful opposing magnetic field, that is resisting the flow of electrons through the rotor windings?
Ok so I am missing some component that, at 1800rpm, and no load on the stator, passes 2amps of Xvac, to give 120 vac at the stator side. Then when it "sees" that this X voltage is falling, it loses some resistance and ups the voltage from the harmonic winding to the rotor brushes.
Wow, does this imply that the rotor always runs on less voltage then the harmonic winding is supplying? Because it would be a feedback spiral, if the rotor used maximum harmonic voltage all the time. As the rpm dropped so would the voltage, rotor power would drop, and it would quit opposing the "hole" and engine rpm would increase. Would this be the point where harmonic voltage increased? I would like to understand this, play by play....yeah yeah, I can go out in the snow, and play with a ups battery, and a meter..wasting time, and precious gasoline on some empirical studies. Its just, if you fellas, already know what is going on, I wish you'd deign to share it, so I could go directly to a solution.
Anyhow, I gotta stop here because the buffer on the machine is too slow for me to type on.
Thanks,
BPJ
You've got the basics right. The harmonic winding is located within the stator windings such that increased load (amps) causes an increase in harmonic voltage. So it tends to provide some degree of self regulation. For stock ST heads, that's all the regulation you get.
If an electronic voltage regulator is to be used, it must limit the current going to the field coil (rotor). You can use either the harmonic ouput or the 120vac output as the input to the voltage regulator. The AVR knows nothing of rpm, but will limit the average current going to the rotor so that the set voltage is achieved. The AVR typically does the limiting by pulse width modulation. The rotor is a big inductor and will smooth those out. If the harmonic winding is used, and does not have sufficient voltage for a given load, the AVR will turn on full and do no limiting, but the AC output voltage will sag.
If you use a variac or variable transformer plus bridge diode to drive the field coil/rotor, you don't need a bulbs in series to reduce the voltage. You can just dial down the voltage via the variac adjustment. I ran my ST-3 head like this for a test, off of the AC (line) output. It's a good way to confirm that your rotor and stator windings are all in good condition. An AVR can then simply replace your manual adjustment, by "chopping" or limiting the duty cycle of the excitation to the rotor.
Morning, and I might add in - looking over the manual link you provided, the regulator you currently have is somewhat simple. All it does is two things:
1) Decide of the AC output voltage level is too high or too low
2) If too low, drive the Field. If too high, cut back on the Field.
Of course the devil is in the details, but from a fundamental standpoint that is all it does..
It has 5 connecting wires. Two go to the rotor to drive the Field - this is how it is able to control the final output voltage - buy doing a PWM drive on the field per above.
Another two wires are connected to the AC output of the generator. These two wires serve a dual purpose. The 1st is to sample the generators output voltage and decide step #1 above, the other purpose is they pull current from the output, rectify it (aka, the Bridge Rectifier that is crudely shown) and use that as a power source to drive the Field per step #2.
The last wire ("B") is connected to the "decision Maker", which actually connects it to the starter solenoid. This wire is used to give an initial 'boost start' to the regulator for field current in the case there is insufficient residual magnetism inside the core of the generator. Aka, 'flashing the core'.
Going back to the starting point: If your generator is not working and you suspect the regulator, I would do the tests on page 6-7 of the manual you linked to. Best if you can find someone with a variac to be able to change test voltage into the regulator and see how it behaves. You should be able to see the test light bulbs go from full on, to flickering, to full off as you raise the input voltage over a range of say 80 to 150Vac. But even if you can not find a variac, the test as described should give you a basic go/no go insight.
Assuming the regulator is bad (have you checked that 10A B fuse inside the 'decision maker'??), then I would think a low cost 3rd party AVR should be able to be easily connected up - at a much lower cost than the Kohler replacement part.
Hope this helps, and best of luck getting it working!
-al-
Ok, a friend and I talked through the regulator function yesterday. I came up with this plan. I am going to use the harmonic winding leads by plugging them into the AC side of a small old school battery charger...then I will take the DC side of the battery charger and feed the relay of a mechanical voltage regulator (think Delcotron). This relay could feed the rotor pulsed DC...
Yes folks, our "crazy ideas" department is working over time....unfortunately I still have a few more hours work to do on the producer fueling the generator's engine, and cannot implement the battery charger plan.
Good concepts but some technical problems, dualfuel. The old style transformer type battery charger steps down the voltage from 120VAC to 16VDC, as well as doing rectification.
You could confirm operation of the generator head by just attaching a 12VDC battery to the field coil brushes, but no load voltage will likely be much higher than normal.
You also can't use a mechanical relay type voltage regulator for this, as it requires a faster response and tighter voltage range than they are capable of.
You need an aftermarket AVR. Forget the harmonic windings, just use the line AC to the AVR.
I can give you a schematic and PCB design for a simple AVR that is proven if you'd like, but without some more electronics background, I think you're much better off buying one.
Best Wishes,
Bruce
Thank you Bruce,
Unfortunately, I am unable to purchase anything at this time. I would be very curious about what an AVR circuit looked like.
I have lots of junk. I am hoping to be able to learn how a voltage regulator operates and adapt the junk I have, to the application. I am by no means fanatic or crazed but am busy learning how this works. I am enjoying thinking about the magnetic fields and what the feed back loops would have to do.
thx BPJ
Bruce - I'd like to see that schematic and PC design for the regulator. Do you know what it would cost for the parts for it, roughly?
Thanks.
Quote from: Dualfuel on November 01, 2013, 10:52:25 AM
Thank you Bruce,
Unfortunately, I am unable to purchase anything at this time. I would be very curious about what an AVR circuit looked like.
I have lots of junk. I am hoping to be able to learn how a voltage regulator operates and adapt the junk I have, to the application. I am by no means fanatic or crazed but am busy learning how this works. I am enjoying thinking about the magnetic fields and what the feed back loops would have to do.
thx BPJ
Hi, so some background questions...
First, have you confirmed the AVR you have is the problem? Doing the quick go/no go test in the shop manual link you posted early on? Did you check the fuse? (If only I could say the times I overlooked something simple were few...)
Assuming it is bad, what load are you driving with the generator? And specifically, how sensitive it is to 'over voltage'? Is it pumps and such, or just a heating element? My 'creative thinking' is: If you are driving a load that is really not too fussy about the voltage / frequency given to it, you might be able to do something quick-n-dirty. Like, just use a bridge rectifier to get a high voltage DC, then run it through a series of auto light bulbs - maybe start out with 6 or so, to cut the Field voltage down to something usable. Play with adding and remove light bulbs until the produced AC voltage is close to what you need. But also know, ANY change in the load will through this all out the door. So, if you are driving a heater element that is cutting in and out - wow.. But if it is a constant load, and one that would not mind being over or under voltage say 20%, perhaps this will get you going?
If all you are trying to do is 'get the Hay in', and will fix things right over the winter - - - Tell us a bit more about what you are using the AC generator to drive...
-al-
Thank you for reading my earlier posts....I will review the diagnosis of the generator
Originally it was in a motor home, and the engine would not run. I removed it from the motor home, and built an ignition circuit for the engine. I got the engine running, and then noticed that the generator worked...
I forgot about it and it rained on it. Then I noticed the generator was not making electric power anymore...testing led to the discovery that there was no current or voltage at the rotor.
I hooked up a 12volt dc wire to "flash" the rotor...the engine gave a grunt, and I heard a pop. I smelled the magic smoke. I couldn't see what had happened until I shut off the engine, looked at the .pdf manual and went looking for the voltage regulator....sadly, it was this component that exploded. Not sure why, as I put the 12vdc on the wire that it was supposed be on, to flash, or "build up" the rotor magnetic field. Regardless, I know that the regulator is a useless blob of melted plastic...but the underlying problem must have been in the decision maker.
These Kohler parts are very very expensive and cannot be purchased...yet the engine is superb..very quiet at 1800rpm. Also, the more I learn about the generator, the simpler it actually seems.
OK, I'll look up my schematic and post it somewhere with a link here. Maybe by tomorrow...
Bruce
Here's a PDF file with schematic, instructions, parts list, etc.
https://www.dropbox.com/s/8s60dog9ifskre6/ST5%20120V%20AVR%20Multi%20PDF.pdf?n=149234369
I have the schematic and layout in Expresspcb.com's free program form if someone that wants that. The board is their standard experimenters board size, last I checked it was $60 for three boards.
Not much interest in this since affordable AVRs became available.
How it works: The regulator rectifies the 120VAC into DC, with the positive lead connected to the brushes. The negative side is switched through a logic level gate, N-channel Mosfet, whenever the AC voltage drops too low. A single op amp comparator drives the Mosfet gate. Since the rectified and R-C averaged AC voltage is lowest during zero cross time, the unit will tend to switch on during lower voltage times. This is easy on the AC waveform shape, and easier on the Mosfet. The circuit does NOT do an RMS conversion of AC voltage so if you apply very poor power factor loads, the voltage regulation will be crap. I tried doing a true RMS version, but the analog RMS conversion chip introduces too much lag and the flicker correction is much worse, so I went back to the original circuit as shown.
Let me know if you have trouble accessing the file.
Bruce
Bruce - I was able to get the PDF from dropbox. Thanks for sharing the circuit. It looks like I could build it on a perfboard with no problems. I wasn't able to find the transformers on digikey, they must not carry them anymore. I might have to do some substi-tootin. But then their web site is really slow for some reason.
Thanks!
You're very welcome, Thob. The Mosfet MUST be an N-channel logic level gate type comparable to the one on the parts list, or it will fail during the start up.
PM me for any assistance and my phone number you need if you do decide to build one. I know of at least two others that did it on perf boards. This was designed as the simplest AVR possible.
I'm still running my own perf board prototype, which also does high/low voltage detection, field polarity reversing via DPDT switch, flash field, allows "manual reversion" to the harmonic winding only, and does not require pushing on a start button. I meant to upgrade it to a PCB but haven't gotten the "round toit". Starting over now, I would not bother to support the stock harmonic setup, and instead would just make a backup board. On my prototype, I used a couple Darlington power transitors (BU924 I think) to switch the low side, and slow the rise/fall time to reduce EMI on the AC power. (fast switched Mosfets do cause some high frequency ringing) This plus 0.1 uF metal film capacitors parallel to each diode in the bridge makes for pretty clean AC.
Dear Bruce,
Thank you for posting the regulator circuit. I find it absolutely fascinating what can be done with Mosfets and modern electronics...
Would I be out of place, here, on this thread, if I asked to explore other ways to regulate voltage? I promise, sometime tonight I am going to go dig out my Stockel's and review the mechanical voltage regulator used on alternators. Also, I will dig for my GM service manual that gave the step by step build up of the solid state regulator in the 10si series. Til, then, something you wrote, that a mechanical regulator would be too slow...has me puzzled. The four pole alternator on the Kohler turns at 1800 rpm...its 60hrz. Are you saying that a regulator that operates on a much higher frequency and three phase, would be too slow to react to 60hrz?
Look, if these questions are inappropriate, I sure understand. I don't waste my time teaching people how to make cold weather biodiesel either...its just in this case, I sense there is a fundamental problem that I am missing and I better get a grip on it, so I can head in the right direction.
The problem as I define it right now, is that I have to take a signal from either the harmonic winding or the stator winding proper, convert it to a signal that the regulator is designed for, then convert the signal from the regulator to a signal the rotor can use.
What I know so far is the rotor is flashed with 12vdc. The original regulator was tested with 120vac, and so it stands to reason that that is the operating voltage of the harmonic winding. I have been repeatedly told the the rotor is using pulsed dc. I cannot prove the pulse is anything other then 60hrz, @ 120vdc or there abouts as its adjusted.
Anyhow, I am still very excited about this problem...and after walking around the place, I found another generator that is a four pole Kohler powered, and a two pole without regulation as well. So its readily apparent that I have got to get "up" on how this stuff works. So thanks for reading this, and thanks for any comments that you thiink will help.
BPJ
My AVR typically gives the rotor a little piece of the full wave rectified AC (think back to back humps of 120V peak) during the lower voltage portion. If you try to do that every 8.3 milliseconds with a relay, it won't work, because of the lag in mechanical relay response, and because even if you had a "miracle relay" the contacts will fail very quickly. In addition, the deadband for on/off on a relay is just too broad to be useful for this.
Alternately as someone suggested, you could connect the harmonic to a bridge diode, and put an adjustable resistor in line with the output. Guess at 20 ohm, 200 watts. If the harmonic winding regulates fairly well, this might be barely adequate.
Perhaps you can find an AVR off of a scrapped generator head.
8 cyl engine turning 3600rpm cycles its breaker points at 240hrz. I have several of these engines whose hour meters have clocked over 4000 hours.
Sorry, I just couldn't help it.
I won't bug you about this anymore...BPJ
Okay, I have been having a blast studying up on voltage regulators. This morning I was enjoying reading about Diactor regulators...they seemed super simple. The drawback is that they are from the last century, and I don't have any of them laying around.
I did manage to find my...Auto Mechanics Fundamentals by Stockel. and my Delco Remy Training Manual DR5133S. On page 390 and 391, of Stockel, he describes a single unit mechanical voltage regulator...whose operation is as follows: At start up, the lower contact set is engaged offering the field 2amps @battery voltage. Rising voltage creates a stronger magnetic field in the pole piece drawing the lower contacts apart. This sends 3/4amp to the field. As the alternator speeds up even more the pole piece engages the top set of points. This grounds the field and no current flow is offered to the field. Three positions, 2amp, 3/4amp, and no amps. What I found fascinating is the amperage offered the rotor of a Delcotron is the same as that offered to the rotor of the Kohler. Hmmmm.
I thought about the difference in stator outputs, less then 1200watts for the Delcotron and 4500 watts for the Kohler. I suppose the difference is how long the field is offered the two amps before stator voltage rises enough to need regulation. Its probably very quick in the Delcotron. In fact, the training manual says the regulator can switch between 10hrz and 7000hrz.
The training manual gives the build up of a 10SI voltage regulator...which is basically two transistors and a zener diode, with an accompanying group of resistors and a capacitor. The manual suggested that the zener breakdown voltage was 8vdc.
Another remarkable thing about both these regulators was that both can regulate the current offered them.
The one major difference between these two types of alternators is, the automotive alternator operates at varying high frequencys while the Kohler's is fixed. Not sure what it means to the regulator....
So this research is allowing me to design the test I want to perform on the Kohler...if I can find out what the harmonic winding offers in the way of voltage and power, I think I can adapt it to either a single unit mechanical or a 10SI regulator. The other test is to see what the harmonic winding output is compared to the stator winding's output.
DF