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Re: 3000W Chinese Gensets Info.
Err….. points and condenser….. I just put a set in a dump truck about a week ago. Have a couple extra sets for different things in the storage bin around here. And a snubbing capacitor is far from ideal. If it is a low value cap then it will have the same effect as a cap/condenser in an ignition. It will hold off the voltage spike long enough for the points to open (not arc) but the peak voltage spike will potentially damage the insulation on the inductor the contacts are driving. If you use a large capacitor to absorb the energy and prevent the large voltage spike, then your contacts will be subjected to a very large current spike when they engage. The cap is completely discharged. So it is almost like closing on a dead short. It doesn’t do the contacts any good. And from real world experience, a diode is far more reliable than a capacitor is under server conditions and with old age. More electronic equipment dies from failing capacitors, than from semiconductor problems. When I have a piece of equipment that is starting to act fritzy the first thing I do a thorough check of….. is the capacitors in the unit. More often than not, changing a couple flaky ones will bring it back to life. I usually switch out all the critical ones anyway. As a mater of fact, I have a DSL modem right behind me that I have changed a few bad caps on. It had a couple low ESR capacitors in it’s switching power supply that were taking a dirt nap..419Views0likes0CommentsRe: 3000W Chinese Gensets Info.
I will stick my nose in…… Try a new spark plug. I have seen spark plugs break down when they heat up. Make sure everything is disconnected from the kill wire on the ignition coil. Disconnect the kill wire where it leaves the fan shroud. Anything on the kill switch line could cause it. If that doesn’t do it………. the only things that come to mind are……… Ignition coil breaking down. Or valve sticking when the valve train heats up as the engine is loaded. As soon as the engine comes to a stop, and the valve cools, then it unsticks. That could be caused by deposit build up on the valve cause by infrequent usage, or bad fuel.349Views0likes0CommentsRe: 3000W Chinese Gensets Info.
And I have also run across a little difference in how briggs and Honda rate their engines. When I seen that a 11hp OHV Honda has 337cc and a 11 hp OHV Briggs has 391cc, I decided to dig a little bit more. I found out that Honda rates their engines in some form of gross horsepower measurement. On a few sites I found the actual net ratings for the normal line of Honda engines. The 11HP Honda is actually 9.5HP. If you do the math……… (9.5hp/337cc)391cc=11.022. That closely correlates with the Briggs rated horsepower, which means they are rating theirs in net HP. So…….. Honda engines….. real horsepower…… Model, rated HP, real HP. GX100 3HP 2.5HP GX120 4HP 3.5HP GX160 5.5HP 4.8HP GX200 6.5HP 5.5HP GX240 8HP 7.1HP GX270 9HP 8HP GX340 11HP 9.5HP GX390 13HP 11HP GX610 18HP 16.6HP GX620 20HP 18.1HP GX670 24HP 20.5HP So…….If you had a10HP briggs engine, and you wanted to buy a Honda engine that will be guarantied to have at least the same continuous capacity as the briggs, you need to buy a 13HP Honda engine. Conversely, a Briggs generator with a 5.5HP engine should be able to handle the same items as a Honda with a 6.5HP engine. Some of the china clone engines are using the net horsepower, and some are using the gross horsepower. That is why some have the 98cc engine listed as 2.5HP and some have it listed as 3HP.349Views0likes0CommentsRe: 3000W Chinese Gensets Info.
The response of a generator to load application as a function of the voltage regulation method. That little 2000W peak generator that I complained about in the other thread did prove to be a benefit to my knowledge base after all. Something seems strange about how it responded to the application of a load. Something that was different from all the others I owned. The instruction booklet showed that it was a non regulated capacitive feedback excitation generator head. But…….. When I took the end cap off, it had an AVR!!!!!!!!! It provided an unmatched look at how an AVR style system responded to load transits. The generators small rotating mass amplified how it responded to small load changes. And it proved to be the answer as to why the generator could not handle the application of a 1200W resistive load. When I done thorough power test with a variac controlled load, I could smoothly test the outer limits of it’s operation and I found the answer to the problem. The torque curve of a gasoline engine drops off when you move away from the optimal RPM range. The function of the AVR will naturally increase excitation in response to a load increase to counteract output winding resistance. The function of the AVR will also naturally increase excitation in response to a decrease in prime mover RPM. That is because…… With a constant excitation field, a generator output voltage will drop as the RPM drops. So, to maintain voltage, it increases excitation as the RPM drops. The drive torque of a generator is the function of the RPM and the output wattage. Or roughly, TQ=W/RPM On a resistive load, the wattage it pulls is constant as long as the RMS voltage stays the same, irrelevant of line frequency. When RPM falls, The voltage stays the same. The wattage pulled by the load stays the same. That results in a dramatic increase in driving torque required to drive the generator head. While, at the same time, the engine’s torque output capability drops with the falling RPM. It should be obvious that that creates a positive feedback situation. Dropping RPM, more load torque, less supply torque, which results in even less RPM. Final result, a stall. On a non regulated head, the voltage drops when the RPM drops. That results in a reduced load, and a reduced drive torque. That is because the wattage of a resistive load drops or increases at the square of voltage. While the voltage output of a generator drops in direct relation to the RPM. So, an unregulated generator running at half rated RPM driving a resistive load, will require one half the torque it would require if it was running at rated RPM. A regulated generator running at half rated RPM will require twice the torque as it would if it was running at rated RPM. So, how does that cause a problem with my generator? When you apply a block load to it. It takes time for the governor to catch up. The speed that the engine drops to will be the determining factor as to the question of it’s ability to handle the load application. If the speed drops to a point where the required torque is greater than what the engine can deliver at that RPM, then the engine speed will drop to the point that it stalls. Even if it can easily handle the load when it is slowly applied. On my generator in question. If I used a variac to slowly apply a 2KW resistive load. I could manage to load it to 1.4kw before it reached the ledge and fell into the feedback loop that results in a total stall. When it is sitting at that knife edge, all it takes is the littlest disturbance to stall it. When I apply a load all at once, the generator can only handle about 800 watts without stalling. I can apply 1200W of load if I apply the first 1kw in blocks of 500 and allow the generator to catch up. Then apply the last block of 200W. When the generator goes over that knife edge and starts dropping into a stall, the only way I can avoid the stall is quickly dropping the load to 500 to 600 watts. Then the generator will recover and I can reapply the load. If I remove the AVR and apply a regulated DC supply to the excitation field to manually control the output voltage. The disposition of the generator improves greatly. I can drop a 1.2KW load on it with ease and it won’t stall out. The voltage drops at first, but it comes back when the RPM comes up. I can even drop a 1.5kw load, on it and it will handle it. The output voltage drops some, which means I have to up the current to get 1.5kw, but it can handle it. When I used the variac controlled 2kw load, I could push it past 1.5kw but the engine slowly drops in speed as you apply more load. The engine is obviously at full throttle. It also seams to handle starting motors a lot easier when it is operating unregulated…. Well…. I was kind of expecting this result. The reactive current that a motor pulls will go up as the line frequency decreases, so long as the voltage stays the same. So, as the generator slows, the motor will start pulling more current, which piled on top of the other things going on with the generator, makes the positive feedback even worse. A non AVR generator will reduce it’s voltage as the speed drops. That prevents the motor from drawing more reactive current as the line frequency drops. Remember. The metal in an electric motor’s armature is designed to operate at just below saturation. Reducing the line frequency in an inductive circuit caused a greater field to build up in the metal of that inductor. That is why you can not use an American 60hz transformer/motor in the UK 50hz. It will overheat from saturation. In a non regulated generator, the armature is designed to operate at saturation. That is what regulates it’s voltage. The generator head will always saturate before the motor that it runs will. No mater what the operating speed. In a regulated generator, the head is not even close to saturation. When the speed drops, and the voltage stays the same, the motors it runs will saturate before it does. That saturation will cause an increased load on the generator system and contribute to the stalling of the generator. The regulated generator in question can output 190v before it saturates. That means that it can put out 120V all the way down to 37HZ which will cause saturation in almost any inductive motor load or transformer if the engine RPM drops off. It is not as pronounced on larger generators because they have a larger rotating mass which gives the governor time to catch up. A small generator with an AVR of this size with it’s low rotating mass is basically useful for running electronics and nothing else because it can not maintain speed with the application of a load over half it’s rated capacity (1500W). When it looses RPM it will avalanche into a complete stall. So it will stall if you apply a block load greater than half it’s rated capacity. The stall is a result of the AVR action compounding the problem of a drop in RPM upon the application of the load. Now, if I could just find a way to convert it over to a non regulated head. The easiest way would be to build a regulated DC supply and set it to maintain a generator output voltage of 125V when it is unloaded. That will give me something to think about……….349Views0likes0CommentsRe: 3000W Chinese Gensets Info.
Some other products I thought would be worth mentioning. A two stroke digital battery charger. Up to 55 amps charge current at 12V. http://www.diytrade.com/china/4/products/5521655/YK55A_12V_Digital_Battery_Charger.html The inverter generator version of the two stroke generator. http://www.diytrade.com/china/4/products/4519588/YK950i_Digital_Inverter_Generator.html A four stroke version of the digital battery charger. Up to 50 amps charge current. http://www.bikudo.com/product_search/details/13976/yk50a_digital_battery_charger.html For people that mainly run the generator to charge the batteries. They are the answer to a prayer. If you used them to charge a battery bank that runs a sine wave inverter. You would have a true to life series hybrid generator.:B381Views0likes0CommentsRe: 3000W Chinese Gensets Info.
Brushes are just chunks of carbon. Nothing will really bother them. The only contact surface that will suffer degradation is the slip ring that they run on. It’s copper or brass and will suffer oxidation with contact with the elements. The green sheen as you would call it. On slip rings on a rotating field generator, the oxidation isn’t really much of a problem. The field coil is relatively low current, so nothing will be damaged by a little bit of poor contact until the brushes run on the rings long enough to clean them by normal friction. Now I have books covering the prepping and maintenance of brushes and commutators. But that is mainly for high current brush systems. Where poor contact will result in burning and scorching of contact surfaces. Not a problem in your champion.382Views0likes0CommentsRe: 3000W Chinese Gensets Info.
Here is a new type of generator head for china gens. http://www.made-in-china.com/china-products/productviewyGYnxkmvOJsN/Permanent-Magnet-Generator-Sets.html Rare Earth Permanent Magnet Generator: 1, Compact Structure, Small Bulk, The weight is 30% lighter than the regular. 2, Without Field Winding, Exciter, AVR, brush. etc. High reliability. Maintenance-free, without Electromagnetism disturn. simply to operate. it's the main advantage than the regular generator. 3, With the same power, double efficiency than the regulars. 4, power factor. can reach 0.98. 5, Can save gasoline more than 20% than the regular. which has more important meaning in nowaday's world. 6, Almost perfect Waveform. 7, Life time can reach ten years. HS Code: 85013200 Trademark: Rano Origin: China Packing: CTN Min. Order: NEG Transportation: FOB/CFR/CIF Company: Shanghai Roco Magnetics Co., Ltd. Yes you heard that right. Permanent magnet setup. Of course it can’t have an AVR. But it doesn’t have any field coils or anything. So there is nothing to break in that department. Being PM, it should be able to stand capacitive reactance with no problem, unlike electrically powered excitation systems. Pure sine wave without brushes. There is one type of excitation system I haven’t seen on any china generators. Brush type, non AVR. The type with rotating field, and a LV DC winding on the stator that feeds a rectifier and capacitor to feed DC to the field. It puts out a high enough voltage for the head to reach magnetic saturation, which is It’s normal operating point. It is a relatively common system with colemans and the like. I have seen capacitor excited brushless, and AVR brush type, but never any non AVR brush type generator heads on china genneys. It’s exactly like an AVR head but with just a simple diode and capacitor to feed DC to the field, and the proper number of turns to achieve the right voltage output. The design has the benefit of pure sine wave output like the AVR gensets. No suppressed voltage peaks resulting from capacitive pumping causing stator saturation, at 90 and 270 degrees on brushless gensets. And with no problems from AVRs. It is a design that was common on American gensets but I haven’t seen a single Chinese unit with that setup. The voltage regulation is similar to the brushles units. It operates at saturation so voltage is determined by number of turns in the output windings. Voltage will go up or down proportionally with speed. So an engine with tighter govern control will produce a more stable output voltage. And now comes a some modification ideas. You could turn an AVR head into a non AVR saturation limited head by taking the AVR out and putting in a simple bridge diode/capacitor setup to feed the field coil. You would have to play with the number of stator turns on the winding that supplies it to get the field to the saturation level, but not push the voltage high enough that it melts the field windings. Then you would have to pull a specific number of turns off the 120V output windings to get the proper 120V. You will have basically turned an AVR head, into a brush type, non AVR head. Another interesting idea that has accrued to me. Wind the stator with a heavy gauge three phase winding, with enough turns to get 15 VDC out of a proper 3 phase rectifier. Have a low current single phase winding to power the field coil at 40 to 60VDC and use the 15VDC high current output to charge batteries. If you modified the generator properly, you could get around 200A of battery charging ability out of a 3KW generator. If you was real fancy, you could rewind the field (armature) with heaver wire so it would be able to obtain full output voltage with a field drive a little under 12V. That would allow you to use a normal automotive regulator to regulate the voltage output of the generator. The only type of gen head I am sure I won’t see on a cheap china genny is like the ones on the winco and old homelite that I have worked with. The type with the output windings on the armature. With the solid cast stator with big pole pieces. They are built like a tank.397Views0likes0CommentsRe: 3000W Chinese Gensets Info.
BTW, if you should want to know what can happen with a catastrophic AVR failure, disconnect one of the two yellow wires from the AVR on the Champ and give the rope a pull. Umm. That would be in the open failure mode. (ie) no stator current/low output condition. What you have to do to find out how much it will put out when the regulator shorts and puts too much current into the exciter coils is….. Hook a DC source across the brushes. Slowly increase the DC voltage. You will know when you have reached magnetic saturation of the generator head when an increase in exciting voltage no longer achieves a similar increase in output voltage. That is the point where it comes to a stop when the AVR fails in a high output state. Hmm… you could change an AVR head to a non AVR head by using a DC source to excite the generator into the saturation range, then take enough turns off the armature to bring the output voltage down to the desired operating range. Which would be using armature saturation to regulate the output voltage.204Views0likes0CommentsRe: 3000W Chinese Gensets Info.
It is found that when the AVR fails, most generally the Q windings will burn I will “assume” that the tech is referring to the exciter/stator windings when he mentions the Q windings. As far as I know. For that statement to be correct, here is what has to be true. The AVR has to fail in the high output state. (Applying full excitation current to the stator) The Stator windings and the maximum AVR voltage output have to be designed in such a way that the maximum voltage output will exceed the stators maximum power dissipating capability. (ie) It can put out enough voltage to generate enough power dissipation in the stator to cook it. It must operate in the high output state long enough for the pre-stated situation to play out. (ie) long enough for the stator to heat up and cook. While it’s running in that state, It’s output is in a continuous overvolt condition. For all the above to be true, they would have to design the exciting system in such a way that the maximum output voltage of the regulator is far and above the normal excitation voltage, and thus current to drive the stator coils. And at the same time, the generator is operating close enough to magnetic saturation that the output voltage doesn’t go high enough to make the operator shut the generator down as fast as he can. That would mean that the regulator is dropping most of the voltage in the regulator chain. And since it is a series circuit. That would mean that it is dissipating most of the wattage. That would mean that the AVR is dissipating orders of magnitude more power than it actually needs to for that generator head. Basically the generator head excitation system would have to be a horribly inefficient design. My electronics professor would chew me out for coming up with something like that. If you drop available exciting voltage. (voltage going to the AVR) Get the voltage just above the maximum exciting voltage you will need for the stator coil. You will drop the dissipation across the AVR. That will reduce the robustness needed for (and the cost of) the series regulating element. Make it easier to cool the circuitry. And if it fails, it will not drive the stator voltage into the danger zone. Thus, the failure will start and stop with the AVR circuit, and won’t spread down stream. Considering the fact that most companies try to make things as cheep as possible, I don’t consider his idea likely. The more likely scenario I see is the stator coil is overheated from capacitive feedback till the varnish melts on the coils. When the coils short out, they act as a short across the output of the AVR and cause the regulating element in the AVR to blow. For that statement to be correct, here is what must be true. The normal regulated output voltage of the generator is close to saturation. That way, when the capacitive load is put on the generator, and generator overexcites. The output voltage doesn’t clime high enough to make the problem evident. When the above situation is in place the stator melts, shorts out, and blows the AVR. A lot simpler failure path! Given both possibilities, it is much more likely for the latter to be true. Basically I think the melting stator is blowing the AVR instead of the bad AVR melting the stator. Just the opposite of what the tech stated. Normally when you get an AVR failure the generator will just operate with a high output voltage, or no output, until someone detects the problem and shuts it down. That is because the maximum output of the AVR into the exciting coil is just above the normal exciting voltage feeding the coil. That allows for an efficient exciter circuit design. When it fails into the high output state, there isn’t enough AVR output voltage to drive the stator coil into the danger area.204Views0likes0CommentsRe: 3000W Chinese Gensets Info.
A non AVR generator may be the answer up to a point…. The problem is even with a non AVR unit, if you get enough capacitive feedback, then it will melt the stator on a non AVR generator too. It won’t make the voltage jump around because the design of the generator prevents it, but the stator is still soaking up that capacitive reactive power. It won’t over volt and destroy anything connected to the generator, it will just kill the generator. It will tolerate capacitive loading better, but it will still only take so much. The easy answer for a situation where you have to run large capacitive reactive loads is… Get an inverter generator. The H bridge in an inverter can tolerate +90 to -90 degree power factor. (fully capacitive to fully inductive) The capacitors on the power buss store the circulating charge, instead of it being dumped into the stator, and overexciting it. It basically shields the generator from the load. Now the not so simple answer. It may be cheaper to replace find and replace the appliance that is causing the problem, instead of buying an inverter generator. But an inverter generator would be able to run anything you get in the future without worrying about capacitive loading ever again.204Views0likes0Comments
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