Generator Information
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Some tips on the purchase, installation and use of Petrol Generators.Generator information on a plumbing site? Why you may ask? Well we use generators pretty often ourselves and many of our customers do too. The purpose of this page is to give some basic practical advise on the selection, installation and operation of (smaller) petrol generators. If you are looking at a big diesel unit then you really need specialised information from the supplier - this page is not for you. Note that I do not favour any particular type or make - I don't sell or install these things - but I do repair them now. Its worth noting "up front" however that many are not viable candidates for repair. I can help you with circuit problems, faulty AVR's and engine problems. Burnt out alternators and broken engines are not worth fixing. The most common repair request is for generators that have been left standing and wont start. These I can fix! Selection. Not so easy. There are hundreds of models available on the SA market. By far the majority of these come from China. This is not nessesarily a bad thing - we use Honda's, Briggs & Stratton and China specials at BBDC. You need to decide if you want to take the chance given the huge difference in price between say a Honda and a Chinese. If you think it's worth going for the Chinese make sure you buy it from a big company that can support the warranty. The quality of these Chinese Generators is generally OK. Note that I said "generally" and "OK". Most smaller Chinese generators use a fairly standard power plant - a CLONE Honda GX200 6.5 HP and others in the GX series are typical. This is tried and tested technology - it really depends on the individual build quality, which has in recent years been getting better and better. These engines are also used on a variety of other machines - water pumps, pressure washers, go-karts and lawn mowers. These engines can sometimes be identified by a cube shaped muffler and air filter with a silly little red on/off switch. Sometimes the low oil system in close proximity. They are all "overhead valve" configuration. It is said that Honda GX parts all fit perfectly! Size? You must decide how you want to use the generator. Do you want to drive your whole house including geysers and heaters with an auto transfer so that you don't notice the switch over? If you do then you are looking at a smaller (a big one being 500-1000KVA) diesel genset of maybe 50-80KVA. If you just want to power your lights and TV then a 2.5 KVA may be enough for you. Work out what you need in terms of appliances. Add up the combined wattage and that gives you the total wattage required. Watch out for things with motors - fridges, air con, vacume etc. These place an inductive load on the generator and draw up to 3x their rated wattage on start up. They also draw more if they are loaded heavily - like an angle grinder. so you need to make provision for this. I generally tell people to try and stay away from this kind of load if they can - stick to resistive loads like lights, TV's, small heaters etc. Don't buy a 4000 Watt Generator if you think you need 3800 Watts! - I would suggest that you go for something of 4500 Watts or bigger. At the end of the day many people buy what they can afford and then connect appliances until the generator almost stops. They then back off one or two lights and leave it to sort itself out. This is a sure way to burn it out! Don't overload them! Stay within 80% of their rated load. Rating - Here in Gauteng you have a nasty thing called "altitude". We are 1.8 Km in the air! In other words 1.8km higher than the guys in Durban. Generators (and cars) are rated at sea level. So - your 4500 Watt generator is actually only maybe a 3800 Watt generator at 1600 metres. Also be aware of two distinct ratings - Maximum Continuous and Maximum (surge). Maximum continuous is where the generator can run all day and maximum surge is only valid for a couple of seconds. You need to buy according to the maximum continuous rating. You then need to de-rate this number further because of altitude. There is another issue that many are not aware of in terms of output rating - frequency. Generators built for the US market are designed for use at 60 Hertz. In SA we use 50 Hertz. Now in order to produce the slightly lower frequency our generators are slowed down by 600 rpm. In other words they run at 3000 rpm rather than 3600 rpm for 60 Hertz. What does this mean? First it means that you have slightly less wattage (electrical power) available at the lower frequency and second it means that the engine is probably not developing maximum power. Small air cooled engines are designed to produce maximum power at 3600 rpm in most cases. This is a problem when the gennie gets bogged down by a momentary overload - it bogs down when the governor cracks open the gas because its just off its power band. In other words the throttle response is much slower than it should be. Many manufacturers do not factor this into their rated output specification. Output Type. We are discussing single phase 220/240 VAC units here - the type that would supply your house when the mains power goes away. There is a further consideration - actually 3 further considerations. The first is voltage control. I suggest that you get one with AVR (Automatic Voltage Control). The AVR does not always work as advertised but I guess some control is better than none. Also be aware that generators produce AC (Alternating Current) as do Eskom. The difference is that Eskom produce a very nice clean sine wave that alternates at exactly 50 times per second. Most little petrol generators produce a very grubby looking (ragged) sine wave that varies around 45-55 Hertz. There are some appliances that really don't like this "dirty" AC power. Computers and other switched mode power supplies are generally ok - they convert it to DC anyway. Some transformer based chargers cook fast! The problem is that you cannot "see" this unless you happen to have an oscilloscope. It's a fairly safe bet that your generator will put out the "grubby" wave - if an appliance bleats about it then don't use it with the generator! Better still - don't even try it! As mentioned the frequency should be 50 Hertz. This usually happens when the engine is doing exactly 3000 rpm. As you load the generator and significantly drop the rpm so too you decrease the frequency of the AC. The voltage also drops as does the output power with the frequency reduction. Not a good situation because the appliance will draw more current as the voltage drops and you get a sort of cascade effect which will either trip the generator or just stop it. Very bad situation either way. Don't overload your generator! The other big problem is one of voltage and load regulation. The generator basically regulates its voltage by changing it's speed - it's a bit more complicated than that, but good enough for the purpose of this discussion. This works via a governor coupling to the carburetor. AVR tries to stabilize the voltage but it can only work within a fairly tight range of minimum and maximum. As you load the generator the throttle is opened to increase the speed (more power). This also maintains the correct frequency. If you should now suddenly "switch off" the heavy load, the governor will only react to an "overspeed" after it has already happened. It closes the throttle and the engine will slow down - but this process takes time! If you look at the voltage output while this is going on you will notice a huge voltage spike as the load is switched off - some due to inductance and some due to overspeed. I have measured spikes up to 600 volts on my scope. Now if you have a sensitive appliance connected to the generator during this spike you are going to have to get someone to try and put the smoke back! Remember that this situation is much, much worse without AVR! If you must run a small sensitive appliance of a small generator then you can stabilize it a bit with a couple of incandescent light bulbs. Say 100 Watts or so will slightly load the generator and stabilize the output. Then you connect your laptop charger. Don't connect high current devices at the same time. Ideal output voltage in South Africa. There is no magic number. It should be in the region between 220 and 240 I guess. Spot on 230 would be good, but more importantly its the voltage under load that is important. It should maintain a nice steady output between 0 and about 90% of its rating. Problems arise when it is only pushing out 180 volts at 80% of its rating or 255 volts at 10% of its rated load. Connection to the house. Unless you really know what you are doing you MUST get an electrician with wiremans ticket to make a semi permanent connection into your house wiring. If you don't do this then you are stuck with extension cords. See "Dangers". Operation. When you buy your generator I suggest that you read the manual before you even think of starting it. If you don't have time to read the manual or your manual is in Chinese then at least confirm that the generator has oil in it. Most are shipped dry! You need between about .6 to 1.5 litres of monograde of the recommended viscosity. See "OIL". I further suggest that you run it for the first hour under varying loads up to 70% of full load in other words - run it in! Let it warm up a little before you load it. A minute or five would be nice! Don't run it in with no load at all. Change the oil after an hour or two. One important point - always try to stop the generator/pump/pressure washer etc by letting it run out of fuel - turn off the fuel tap and let it burn the remaining fuel in the carb until it stops. Why? Two reasons. First you reduce the amount of fuel in the carb so that if it dries out it is less likely to clog up the carb and second (more important) you don't "rinse" the inside of the cylinder with a rich fuel mix when you switch off the spark. A governor controlled engine (4 stroke) will crack open the throttle the moment it feels the speed drop. The result of this is a high volume of fuel being sucked into the engine as it comes to a stop. This dilutes the oil coating on the parts inside the engine - particularly the rings and cylinder. Next time you start the engine there is no (reduced) coating of oil (its been washed off) and the coating takes a short time to build up again. Wear happens in this short time. This lubrication issue does not apply to two strokes but the premix fuel may be more prone to gelling. Maintenance. With a Honda or Yamaha I may change the oil after the first 20 hours as suggested. With a Chinese engine I will definitely change the oil after only one hour of use. Why? Have a look at all the steel and aluminium in the oil when you drain it for the first time! Drain the oil again at 6-10 hours. The only other two major items that you need to watch is the air filter and spark plug. OIL. I have a slightly different approach to the type of oil I use on all our small engines - generators, pumps, compactors etc. These things are expensive to buy and they don't actually need lots of oil. Because of this I use premium synthetic oil in all our engines. The first two changes I use Castrol SAE 30. The third change (after 6 hours) I use Castrol Edge 10W-40 Synthetic. I then follow the 25 hour oil change periods with synthetic oil thereafter. Most small engine manufacturers (including Briggs and Stratton) now recommend synthetic oils in their engines. I am a total convert :-). The other VITAL issue is the oil level. These little air cooled engines work hard for extended periods. Oil keeps them alive. If you keep the oil clean and topped up your generator will last for many years. If you neglect the oil it will die in hours! Air Filter - a clean filter is important. Clean it as recommended in the manual or every 50 hours. Less in dusty conditions. Buy a new one if it's not cleanable. A clean air filter makes the engine run better. Make sure you oil the oil bath types. Air filters are less critical in most domestic situations. There is not that much dust to be ingested. Spark plugs get dirty and wear out. Change them as recommended or when they look tired. Some engines (few) have oil filters. Change them every time you change the oil. Finally, some thoughts on the little two stroke generators that are very popular in SA at the moment. These are copies of an old Yamaha design (ET 950, still available in SA!) and are made in China. They come under a variety of badges - Ryobi, Tiger, Tasmiya etc. Output is from 550 Watts to 1000 Watts. They run on 50:1 premix and a full tank looks like it can last up to 6 hours. The engine uses a cast iron cylinder and is of a fairly high quality. The fittings and alternator's quality seems to vary quite a bit, but for the price you pay these are generally a very good buy - BUT you can be unlucky and get a lemon. We use two of these generators - primarily to run small drills (650 Watts) on sites with no mains supply. The older one cost me R900 about 10 years ago. It's still running like an old Singer sewing machine. The newer one I traded on a job (cost would have been R500) works fine but uses slightly lower quality parts than my old one. But it works exactly as expected. The joy with these little generators is that you can carry them around with one hand and they are easy to use except that they smoke a bit. Also they take up very little space on your truck. I would not use them for laptops etc - voltage regulation is not very good :-). They are fine with small power tools though. - They use 50:1 premix. Dont stray far from this. Err on the side of more oil BUT If you add too much oil you will cause the engine to run lean - hotter. This is not good for a two stroke! - They fire on every stroke thus putting out almost double the HP for a given displacement when compared to a 4 stroke. They are quick to adjust their speed - up or down and they are remarkably quiet when running at only 3000 rpm! - Change the plug that is supplied. NGK BP6ES works. Keep it clean. - Use premium quality 2 stroke oil - it causes less carbon buildup. RUN THE GENERATOR OUTDOORS ONLY. Internal combustion engines release large amounts of Carbon Monoxide. Carbon Monoxide will kill you and everyone else in a confined space. Do not allow the exhaust to discharge under a window in a door or into a basement or cellar. The petrol fumes are also not very healthy but the Carbon Monoxide will kill you first. Running your generator in a inhabited room or house is as efficient as gassing yourself in a car. In other words it is a recognized way of committing suicide. I cannot state this in a more explicit fashion. The generator must be run away from your house or garage. Other Dangers.
Please email me on info@blockbusterdrain.co.za if you need any other info or if you strongly disagree with anything I have written :-))
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