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Forum Index : Electronics : Sine Waves
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| Susan Newbie  Joined: 28/05/2015 Location: AustraliaPosts: 3 |
Hello I was wondering if you are able to help me? We have a pure sine wave inverter/charger and an old generator which is a modified sine wave. We got told that there is a possibility that the generator could harm the charger because of the different wave form. Is this correct? If so, is there a converter that converts modified sine wave to pure sine wave that we could install between that generator and charger? Thank you for your help. |
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Downwind Guru  Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Your question may seem clear to yourself, but not so clear to myself. You need to give a little more information to make the situation more clear to be able to give you information that is helpful. For example what is the generator actually being used for? If its only battery charging via the inverter than i see no problem. If its supplying power with the inverter off line, than again no problem. More important is some data to work with, like what inverter you have and what generator you have. Pete. Sometimes it just works |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Unfortunately there is no inline device that I know of to easily convert a modified sine wave to a true sine wave. There are ways it can be done, but results can vary and it would be cheaper and easier to buy a sinewave generator. Can you tell us makes/models of the charger and generator, might help. If the charger has a big beefy transformer inside, then its probably OK. Some devices are OK on modified sine wave, some not. My mother lived off grid for a few years, all her appliances were fine except pedestal fans, they would only last a few weeks in summer. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Glenn I have used a 1 to 1 transformer with a .22 cap across the input and output windings one on each with the two other ends soldered together with 1 meg resistor to earth. different size caps give a better result so some experiment is necessary. I tends to round out the wave and stopped a lot of the buzzing in the motors it drives, it uses a bit of power but not enough to worry about. All the best Bob Foolin Around |
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| Susan Newbie Joined: 28/05/2015 Location: AustraliaPosts: 3 |
Hello Thank you for your answers. Here is some more information which hopefully help a little more. We are completely off-grid and on a 12 volt system. We have solar panels which keep the batteries charged up most of the time. If they are not completely charged we charge them with the generator which is a Lister-Petter, 10kva, Single phase, 240 volts, 50 Hz and rated 0.8 PF (this is the information that is displayed on the generator). Our inverter/charger is from Giant Power and is 12v/3000w. Set up: The generator is connected to a junction box, from the junction box goes a cable to the inverter/charger which is then connected to the batteries. We also run the generator to run the washing machine which is a twin tub at the moment but I would like to buy a front loader which needs pure sine wave. Which also brings me back to my problem that the generator is a modified sine wave. The charger on the inverter/charger unit broke already twice and the guy from the place where we bought it said that it could be because of the modified sine wave on the generator. So if this is really the case we don't want it to happen again. Susan |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Susan I suspect the generator would be pure sine wave, giving its a Lister and especially its capacity. Seams odd that a 10kW generator would be nothing but sinewave, but I could be wrong and other forum members might know more. I also suspect the output voltage of the generator may have drifted off spec and may be the cause of the charger failures. My neighbour recently had a similar problem, he has moved into a removal house and has to wait 6 months to get the power connected, so until then has been running a old diesel 8kw generator. His plumber fitted a new on demand water pressure pump, with the electronic controller. He blew 3 pumps in a week, and eventually ditched the electronic controller and fitted a old school pressure switch and tank, which has worked faultlessly. He also took his generator into a service center and they discovered it was running a little fast and the output voltage was about 280 volts, so they adjusted it back to 240v. The 280v would be been the cause of his electonics pump controller failures. It may pay to test the generator output. See if you cn find someone who can test the output for voltage and see if its a sinewave, and make adjustments if needed. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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rustyrod Senior Member  Joined: 08/11/2014 Location: AustraliaPosts: 121 |
Suggestion, There are plenty of meter on eBay And cheep Small rectangular There are pretty digital units too. Combined with AC amps Then if you need to check the 50 Hertz there are some like this. Anyone, Would the hertz meter measure modified sine wave and indicate it was 50 Hz, if so this type of meter would not differentuate ? Would a person need an oscilloscope? or is there a "black box" to tell a person if any unit produces pure sine or modified ? Ooh, I like the look of the 2.9 inch ones, I wonder how I could justify getting some to play with. Always Thinking |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
I tend to agree with Glenn, as a standard generator needs to run at 3000 RPM and if outside that RPM then the Hertz and voltage changes, i would be more suggesting the investment in a good RPM meter rather than volt meters. The problem with older generators on average is the govenor dont always maintain constant RPM at 3000, so the output fluctuates above and below what is required to maintain a constant output voltage. If below 3000 then the Herts will be low and most likely the voltage low, and then vice versa if the rpm is too high. The 3000 RPM is equated from 3000 / 60 (seconds) = 50 Hz (hertz). The first thing to check is the RPM of the motor. Pete. Sometimes it just works |
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| dwyer Guru Joined: 19/09/2005 Location: AustraliaPosts: 574 |
Hi Susan Lister-Petter, 10kva, Single phase, 240 volts, 50 Hz and rated 0.8 PF running on 1500 rpm nor 3000 rpm ? 
dwyer |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Ok, my bad, a diesel generator is normally 1500 RPM which in checking yours is, but the same principles applies, just a 1500 Rpm and not 3000 Rpm, also the web site suggests your generator may have a Rpm meter as standard, so check it. Pete. Sometimes it just works |
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| Susan Newbie Joined: 28/05/2015 Location: AustraliaPosts: 3 |
Hello Guys Thank you very much for all your input. Looks like we have to do some testing. Our generator is about 20 years old and is diesel run. Thats why we think it is a modified sine wave. We also think it has 1500RPM. The inverter/charger (before it broke down) showed that the generator was putting out 50 Hz and between 238-245 volts. Info: the inverter/charger is one unit. So when we charge we can't turn the unit off as we wouldn't be able to charge the batteries then. So would it be possible for the generator to break the charger? Susan |
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| rustyrod Senior Member Joined: 08/11/2014 Location: AustraliaPosts: 121 |
When AC power was invented I think it was sine wave. I think the nature of magnetism generation creates sine. Only when transistors were invented and could be on or off, they invented half on/off, the modified sine wave for inverters. With snazzy electronics these days they can make electronics do anything, even pump blood! Is the genny itself connected to the diesel, a DUNLITE? most of them were brushless. If yours has brushes they could be worn and making "spikes" on the power. Then there could be filter capacitors under the genny covers that could be dud. RE Breaking the charger, We went through tvs and light bulbs when we moved here on grid power yonks ago then the lightning took out the transformer out front and the computers,microwave telephone,fuse box. we are the only one hooked to it. The men came to replace the transformer, mate this is a 285 volt tranny! I think it was 480 three phase. The new one is 240/ 315 3phase. OK. Now, bulbs last forever, tv has spiders, oh, but the welder is not so hot anymore. So Yes, if your genny is a bit high it could damage sensitive electronics. How many units have burnt out? Will the charger work? or the inverter work? Is it dead? Has a repairer inspected it? maybe something simple. Then, do you switch the power off from the genny first, before stopping the motor? A Funny bedtime story, A lot of the Dunlight units were self starting, when a light was switched on and stopped when the last bedlamp was turned off. Had a job once, the 12volt starting battery was failing quite often. A thousand tests later.........the lady did a lot of sewing, need i say more!!!!! Poor engine, hot starter, and a battery that barely got charged The station boy would be sent to crank start it some nights. How did I find the problem? I was sitting on my toolbox looking at the silent engine passing the time. running up the hourly rate? it started up, Ok, something came on up at the house. I had almost run the thought through my head and it stopped??? what? that was quick. now its starting again, run seconds and chug chug stop. and again. what is wrong with the control board ? dirty connection? touch a wire it starts. touch something it stops, touch nothing. I spent ages cleaning every connection. SAME! damm and stone the crows. Then I got summoned to the garden for a cup of tea and a dainty cuccumba sandwich, Greasy servants were not let in the house. Any place will do me, I was starving by now. I'm sure my stomach thought my throat was cut. The lady mentions something is wrong with her sewing machine. This morning it was working then it wasn't. Some days it works for a while then stops. She would get a governess/girl to bring it out. GIANT light bulb moment. Patient lady, press foot, waiting, waiting, machine sews, lift foot, adjust cloth, press foot, waiting.... Leave it inside. Just turn a light on lady! But my husband says that wastes power Ok, roll your eyes. Ok people you can stop rolling on the floor laughing your A off. Did she never mention the failure of the sewing machine to hubby. maybe domestic matters were not to be mentioned. hubby runs the station, lady runs the house and domestic staff. (They had children, Oh, You don't need talk about that) 6 hour job. Hit em $20 and travelling. well she did give me 4 tiny little sandwiches and a big mug of black tea. fair is fair. Always Thinking |
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