Generator voltage control repair

Discussion in 'The Projects Forum' started by Monolith, May 14, 2010.

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  1. Monolith

    Thread Starter Member

    Jun 21, 2008
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    In this country we have now an acute shortage of generator voltage control regulators.
    The government makes it impossible to import spares and the manufacturers seem to build the generators with an intended short life span.

    The national Electricity network is collapsed due to lack of maintenance.
    I have 4 different generators that are broken and there is no way to get spare parts.

    The generator in use now (we have not had public electricity for one month now) is a Toyama 6500W. The load are 2 fridges a Freezer and the computer. Total of about 1KW. The original AVR burned out, the new replacement lasted 3 weeks. Now it does not regulate anymore.

    There are no new ones available. The repair shop askes me to "Invent something"

    I have the means to draw a PCB, etch it and populate it, what I need is a basic circuit that I can adapt.

    Could somebody please help me to find a suitable circuit?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Looking at the original thread - http://forum.allaboutcircuits.com/showthread.php?t=34596 - I moved both to the Projects section.

    You have your own thread now, as the problem is somewhat different from the original.

    Can you supply some information about the generators? Manufacturer, model number, any details about the regulators? All we have is your one Toyama mentioned.

    Are these generators properly fused/have good circuit breakers?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    It sounds like you are in a real predicament.

    First, it would help us to help you if you put your general location in your profile. Use the "User CP" link on the menu bar of each page to get to your profile.
    Then click the "Edit Your Details" link. Location box is about 2/3 of the way down that page.

    Secondly, can you post as much of the circuit as you have, as it now exists?

    Thirdly, do you have access to microcontrollers? For example, can you buy PIC microcontrollers or Atmel microcontrollers and the equipment to program them with?

    Failing that, do you have some kind of inventory list of the things that you CAN get?

    It will do you no good to get a circuit that uses parts that you cannot obtain.
     
  4. Monolith

    Thread Starter Member

    Jun 21, 2008
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    Thank you for the answers.

    2 or 3 years ago with the boom in the oil prices, a large amount of small generators (mostly below 10KW) of many different makes, mostly Chinese, were imported. To us who live out in the countryside, where electric power was always unreliable, this was a great help.

    In the meantime, the government went bankrupt. In January we had a devaluation of 50% overnight. The inflation is over 100%. The government does only release about 10% of the foreign currency needed for imports.

    After 11 years of this government, where no maintenance was made on anything, the roads are full of holes, the electrical net is collapsed, electricity and food are rationed.
    The only good thing we still have, is the cheap gasoline and diesel, at about 0.01 Euro per liter. No complaints there.

    The first thing to go on the generators (120V mono phase or 240V two phases with 60Hz) is the voltage regulator. No replacements can be found on the market.
    The regulators are usually cast in Epoxy resin. No access.

    I know a little bit about electronics. I have a big box with parts since this has been my hobby for years. I have a PICkit2 programmer but am only learning about programming. I also have an oscilloscope.

    I can get electronic parts sent in by courier, Fedex, DLH etc. Maximum 100US$ value at a time, maximum 1Kg. Cost of shipping is 100US$.
    I can order from Digikey, Mouser etc.
    With a lot of paperwork involved, the government allows us US$400 per year for email orders.

    As I understand it, the tricky part with an automatic voltage regulator is to make it so it does not go hunting. The engine has it's mechanical speed control that keeps the RPM at the level needed for 60Hz.
    When the load increases, the mechanical governor injects more fuel to keep the RPM right (3600RPM usually, sometimes 1800RPM)
    With a step load, like when the freezer start' up, the engine speed wobbles a bit and then stabilizes.

    Then there is the voltage control of the generator. With a step load, the regulator needs to respond fast enough so that the voltage does not drop below the cutout level of the voltage protector of the equipment. About 100V.
    Then there must not be much overshoot otherwise the regulator starts "hunting", getting into oscillations.
    There is usually a fairly large capacitor that helps stabilizing.

    I am looking for a circuit that could be adapted for 3 different ranges of generators. 2 to 5KWA. 5 to 10KWA, 10 to 15KWA. All 120-240V 60Hz, single and 2 phases.

    I would mount the regulator externally. A good heat sink is needed.

    My suspicion is that the regulators fail because they were designed for colder climates. Here the temperature is quite steady at 30 degrees Celsius, day and night. The regulators are mounted inside the generator housing and cooled by the hot air of the engine and generator cooling.

    Thanks for your help

    Monolith
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    One suggestion is to use acetone (with good ventilation) to dissolve the epoxy and try to determine the components in the controller as well as the failed part.

    Acetone is not a lot of fun - it has explosive vapors. It also eats the epoxy out of PC boards, so it will be a pain to do the first ones. If it's always the same part that fails, though, then a lasting fix may be possible.

    And someone may have a better way of removing that epoxy.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Sorry that you have not actually received any answers as of yet; merely more requests for information from you. However, please be aware of our dilemmas; we would like to help you, but have no knowledge of where you are (Greece, perhaps?) and have almost no knowledge of the generators that you currently have, besides the one make and capacity that you have supplied. I understand all languages except Greek, and "Toyama 6500W" is half-Greek to me.

    I can only imagine.

    I'm afraid this is becoming a rampant problem.
    Quite understandable; they wish to stimulate production within the country itself. Every purchase made from abroad only makes the economic situation worse. Frankly, I wish our government would do something similar; but this is not a political forum.

    Times are difficult in many places.

    A bargain, indeed. I have never seen prices that low for either fuels you mention; not even close.

    You might try slowly chipping away at the epoxy using something resembling tools that a dentist uses.

    In the States, we have Dremel (tm) motorized tools, to which one can affix a wide variety of sanding, cutting, drilling, shaping, sawing, etc. bits to remove small amounts of material at a time. If you have a number of the same type of regulators that are no longer functioning, you may completely destroy several of them while trying to grind/sand/cut/chop away the epoxy, but if you are patient and persistent enough, learning from each encounter, you may be able to successfully determine what is underneath that epoxy.

    Do you have some PICs on hand? If so, which ones?

    For future reference, you should only order those PIC uC's that have a -E part number suffix. They are rated for higher temperatures than the -I suffix parts.

    Your shipping costs are far beyond absurd, bordering on the obscene. It's not like you were shipping plutonium-235.

    That goes back to the "make it here" type of mentality. That's rather difficult to argue with.

    There's more to it than that. The regulator needs to respond rapidly to transients like "load dumps" where an existing load is discontinued/turned off, but also able to respond to sudden loads like your fridge compressor motor being turned on under load (stall current), which (at least momentarily) appears like a dead short to the generator.

    A heavier flywheel will help to keep the engine speed even more stable. Balancing a flywheel (or any rotating mass as a dynamic load) is a rather daunting task, particularly if you don't have somewhat sophisticated instrumentation to indicate where the weight needs to be added or removed.

    My grandfather was a master machinist and a foreman at the General Electric Steam Turbine Works in Albany, NY (USA) - definitely no slouch at such things. He was also an avid boater and fisherman. He spent many hours devising ways to better balance the propeller for his 18hp Evinrude outboard motor, but he never was completely satisfied with his efforts.

    He then bought a bronze propeller from a company named "Michigan Wheel" that claimed he would get better performance for his particular situation. When the propeller arrived, he immediately checked the balance of the propeller using his test fixtures, and was amazed to find that the propeller was perfectly balance in every respect that he could determine, besides being a work of art.

    I'm digressing from your original topic, but it is definitely related. Adding weight to the flywheel will help a great deal to stabilize the RPM; but at the same time, unless the flywheel is perfectly balanced, the load on the bearings and resultant vibrations will tear the motor apart.

    Understood - but we don't have a good idea of what the value of that capacitor might be, nor what the existing wiring of the genset might look like, nor where the regulator is connected into that wiring.

    We don't even know what the 1st one is.

    Are you going to help us help you, or are we just going to have an ongoing puzzle here? Since you can only make a few orders per year, you better give us as much information as you can. Otherwise, you will have a very long, hot summer/winter/spring/fall.

    More than a good heat sink. You may need water cooling.

    That's quite likely the basic problem.

    Water is one of the least expensive and most efficient means of transferring heat. Problems associated with water cooling should be rather obvious, so I won't go into them unless you feel that you need to.

    Right now, you have multiple broken generators of which you have only given very general information about one of them.

    Don't expect to put such a general request for information out and expect to somehow magically receive a schematic and parts listing that will fix all of your problems. It really is not that simple, otherwise you would not have this problem to begin with.
     
  7. Monolith

    Thread Starter Member

    Jun 21, 2008
    13
    0
    I did fill in Venezuela in the user CP as you asked. So again, the country is Venezuela.
    Acetone is a forbidden substance here and I doubt if a part number would be readable on a burned out transistor, once it is dug out of the epoxy.

    Toyama, Changfa, Changdong, Zejiang, China Andi, Taizhou, Changzhou are some of the makes of the generators. Mostly air cooled gazoline or diesel powered.

    What I need is a basic circuit of a AVR, an Automatic Voltage Regulator. Once I have a basic circuit, I can scale it for the size of the generator.

    Water cooling a heat sink of a transistor or SCR, on a 5HP aircooled gas engine?? Changing the flywheel???

    Thanks for the help

    Monolith
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    OK, perhaps you did not see the "Save Changes" button at the bottom of the "Edit Your Details" page. If you move off of that page without clicking the "Save Changes" button, any changes you make are lost.

    Very curious - you can't get nail polish remover?
    How about isopropyl alcohol?

    Burned-out resistors are not nearly as likely as burned-out semiconductors.
    However, if a schematic could be created from several similar regulators, the burned up components could likely be figured out. Right now, we don't have much to go on.

    Well basically, the regulator needs to control the field current while sampling the output voltage. At this point, I have no idea how much field current your gen sets might require.

    If your basic problem is that the regulator circuit is overheating, you need a more efficient way to remove the heat from the components.

    Water is 1.4 times as efficient at conducting heat than copper is.
    Aluminum is only about 59% as efficient as copper.

    If the frequency of the output is unstable under load, increasing the mass of the flywheel will help a great deal to stabilize the frequency.

    As I've already suggested, balancing such a device is quite tricky.
     
  9. ifixit

    Distinguished Member

    Nov 20, 2008
    639
    108
    Hi Monolith,

    I've been down this road before. See if you can find out how many wires are going to that sealed module in order to get a clue of how things work. Most small gens work the same way, but there are some variations.


    Look for...
    • 2 wires for the field winding (FW).
    • 2 or 3 for the excitter winding (AW).
    • 2 wires thar bring in a sample of the output winding (OW).
    • 1 wire for a ground.
    • others?
    In the mean time, checkout this tread...
    http://forum.allaboutcircuits.com/showthread.php?t=18074

    The attached pictures are from that tread. The 'avr schematic' is not of the Honda, but a no-name gen. If your gen is similar, we will have a good place to start on an external control board.

    Good Luck,
    Ifixit
     
  10. Monolith

    Thread Starter Member

    Jun 21, 2008
    13
    0
    Ifixit, thanks a lot for the schematic and the link.

    Today we have mains electricity again, so I will look at the generator and see what more information I can get out of it.

    The original regulator had 4 wires going in to it and 2 wires going to the brushes.
    The brush holder is made of plastic. It got hot, probably because of the brushes making bad contact and sparking.
    At one time the brush housing melted and the current was suddenly interrupted. I suspect that the high flyback at the sudden cutoff under load, zapped the regulator.

    The replacement regulator, the only and last one available had 4 more wires, but fit perfectly into the slot of the old one. There also happened to be a connector plug for the extra wires. It worked for some time, but now does not regulate anymore. It looks very similar to the original, except the transistors that are sticking out of the epoxy, look smaller.
    So I think it was meant for a generator of the same make but lower power.

    With the regulator not regulating the load, I boost the voltage to 133 under no load, (with the small pot on the regulator on max) then start connecting the loads one by one. With the fridges and freezer, fan and computer working, the voltage is down at 108V.

    Thanks for the help
     
  11. Monolith

    Thread Starter Member

    Jun 21, 2008
    13
    0
    OK, I got a few numbers, cost me about 2 pint of sweat. It is hot and the hot air of the air cooled diesel engine blows over the generator.
    There are 2 sets of wires from the AVR.
    + and – for the field, going to the brushes. The brushes are OK
    The voltage is 46VDC with no load, drops to 44V with load. Current is 0,78A, peaks briefly to 0.9A when switching on the load.
    2 wires named Z4 and Z8 going into the AVR. 36VAC, drops to 35VAC under load.
    Plug with 4 wires:
    Z8, green color
    Z7, Voltage between Z7 and Z8 is 20VAC
    Z5 and Z6, voltage between Z5,6,7,8 starts at about 25, but drops slowly down to below 10V, when measuring.
     
  12. ifixit

    Distinguished Member

    Nov 20, 2008
    639
    108
    Hi Monolith,

    First, take 2 pints of cold beer to replace that sweat.:)


    We need to verify the function of those connections.
    • The Z4 - Z8 voltage of 36VAC might be the exciter voltage, which will be present even with no field current. To verify, you could run with the field connection off. There should be no 120VAC output, but there should be a voltage still coming in somewhere which the regulator uses to 'excite' the field winding.
    • Two other pins must supply a sample of the output, which might be the 20VAC. Check if it is porportional to the 120VAC output. With the brushes disconnected it will be 0V, same as the output.
    Have Fun,
    Ifixit
     
  13. Monolith

    Thread Starter Member

    Jun 21, 2008
    13
    0
    thanks for the answer and help.
    Yes, the Z4-Z8 is the exciter voltage that gets rectified for the field.

    The other 2 pins I can not really measure, because the voltage starts dropping as soon as I touch the pins with the probes, with the generator running and generating.
    Could it be that this is an initial voltage generated from stray induction in the not connected wires?

    I did not check with 240V.
    Cheers,
     
    Last edited: May 18, 2010
  14. ifixit

    Distinguished Member

    Nov 20, 2008
    639
    108
    Hi Monolith,

    Those “floating” measurements don’t make sense. Perhaps the problem with this generator is a bad connection, or broken wire in that circuit. The regulator may be okay. Can you troubleshoot with an ohmmeter? Be sure the generator is off of course.

    I have attached a sketch of how I think it might be connected. The connection form the output might be direct from L1 or L2, or from a tap off the winding in between.

    Good Luck,
    Ifixit
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Documentation is everything.

    May I suggest that you document where you are referencing your probes when you are taking your voltage measurements.

    It's possible that you are measuring using a point that is isolated from anywhere else in the circuit; in that case your readings would not be valid.
     
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