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George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308
Posted: 11:39am 16 Dec 2017
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I'm looking at buying an AC single phase generator on a listeroid twin engine.
I'd like to know if there is any problem running the generator output through a suitable sized rectifier and then feeding the DC into a solar Inverter and into the mains?
The gen head will be 6KW and the inverter 5kw so should be no problem with supplying enough power or being a 240V gen head, the rectified voltage should be in the sweet spot for the inverter. I want to be able to do this so I can sync the gen head to the mains in order to backfeed.
Any problems with doing this as far as the gen head and Inverter are concerned?
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678
Posted: 09:08pm 16 Dec 2017
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I can't answer your question, however, I am curious as to why you want to do it. If the intention is to reduce your electricity bill you may find after doing the sums that buying the petrol to run the generator may cost more than the savings from the bill. Unless you are getting fuel free or very low cost. What calculations have you done? If that worked out economical it would be great.Cheers Caveman Mark Off grid eastern Melb
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 09:22pm 16 Dec 2017
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This has been done and I am planning to do it also, however my reason is as a backup power source for off-grid when there is little sun. It has also has been done by using a large induction motor with capacitors added to it, this makes it into a generator. Mark is correct that you can't buy fuel to run a generator and save money compared to the cost of grid power. Using waste vegetable oil or similar would change that equation. But doing this to run your meters backwards opens a big can of worms that I don't want to get into.There are only 10 types of people in the world: those who understand binary, and those who don't.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:35pm 16 Dec 2017
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I looked at doing something similar using low cost natural gas as fuel. Petrol or diesel would cost much more.
Natural gas in Melbourne is roughly about 2.2 cents per Megajoule. Thats 1,000,000 watt seconds or 0.28 Kwh for 2.2 cents.
Roughly 7.8 cents per Kwh for total heat energy. But the engine is only going to convert about 20% of that to mechanical energy, and the alternator maybe 85% back into electrical power.
An even rougher estimate might be 46 cents per Kwh to generate power from natural gas. And you have to include wear and tear on the engine which might require fairly frequent rebuilds.
Cheers, Tony.
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 09:56pm 16 Dec 2017
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I have an 8KW Lister generator, this is a direct injection model which is more efficient but won't run on waste vegetable oil unless it is converted to biodiesel. It uses 3 litres per hour at full power so the current $1.36 per litre would cost $0.40 per kWh just for fuel.There are only 10 types of people in the world: those who understand binary, and those who don't.
George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308
Posted: 12:23am 17 Dec 2017
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With respect, it wasn't a cost question but an electrical one.
I have been running Veg oil in my Vehicles, the Lister and all the other diesel engines I have for 15 years now. I have made thousands of liters of bio as well so I'm pretty comfortable with the whole veg fuels thing. I built a very simple processor many years ago that takes me longer to fill up by hand ( for exercise) and empty than it does for the thing to clean the oil and I can go out, go to bed or whatever and leave it running if I want. Don't have to stand there watching it. When it's done I have clean, DRY oil that is in fact cleaner than pump fuel.
I don't even think that running free fuel makes the equation for making ones own power that worth while when one looks at the over all picture of maintence etc. If one could use the heat for warming the house in a co-gen situation which is also something I'll look at for winter, the numbers usually change but for power only, not usually viable when grid power and especially solar is available.
If free fuel made it economical to go Off grid, I'd already be there because to blow my own trumpet, there aren't a lot of people around that know more than I do about this veg oil caper. There is a lot more to being power self sufficient however than free fuel for a generator as many knowledgeable people here whom are off grid would well know.
I have also done the Induction motor as generator thing and it's a pain in the arse for someone like me that cannot make up automatic controllers. I had the 3 phase motor running through a big bridge rectifier then into the inverter. Because the inverter kept trying to find the sweet spot of the power output, it caused the voltage and engine to constantly ramp up and down. Also trying to get the best power from the motor gave high voltage problems as the harder you drive it to get the watts the higher the voltage also goes. Rectify it and it's real easy to go above the voltage the caps and the inverter is happy with which is what happened and I blew one side of the inverter.
I came to the conclusion that in order for it to work the motor providing the power should be over rated for the inverter. This way the inverter could just max itself out applying a constant load to the motor and could then be tuned RPM and capacitance wise to give a steady output and safe voltages. To do this one would need a motor about triple the nameplate output as what they were trying to get out. A 15KW Induction motor is a substantial beast for a 5 Kw output and I could never find one at the right price.
A normal generator is much more useful IMHO as I can use it for varying loads that will be switched in and out that an IMAG has trouble with.
Looks like I'm going to be able to get this new engine and 6KW Gen head so I would like to use it for balancing the backfeed on my solar panels. This is one more step I want to practice with a view to one day going off grid. Trying to learn as I go in small steps and learn different aspects. It seems to me with a good size ganny, one need never have to worry about bad weather or the level in the batteries. Fire up the Veg fueled genny ( which I would like to get a controller for to automatically start and stop the thing) and all is good.
I don't know what can of worms backfeeding opens up but without trying to be rude, don't really care as long as it does not cause problems electrically. I would assume the electrical input source to the inverter is irrelevant as long as it is DC and clean enough not to cause issues. What comes out would be the same if it was input by solar or anything else.... I hope.
To create a safe and usable input for the grid tie solar inverter, is there anything different I need to do to the setup with the IMAG? Just trying to check with the more knowledgeable in case there is something I am missing?
Rectify the output to get DC and feed it in? As long as the voltage is within the limits of the inverter I can't see any problems but what I am really wondering about is if I need some caps or some thing to smooth the output from the rectifier or if it will be OK to feed into the inverter as a DC source as is?
What I did before with the IMAG and inverter was playing around. The IMAG was pretty much indestructible in that setup and the inverter was in essence disposable but this would be lifting the game somewhat and I do not want to stuff up either the gen head, it's AVR or the inverter I want to couple it to. I'm not an expert but I was hoping to get the feedback from those that are or have done this before I make a mistake that everyone else knew about.
Any input on the electrical side of things being if this is OK or anything else I need to do would be appreciated.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 12:47am 17 Dec 2017
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I have not personally done this myself, but I can maybe throw a bit of light onto some potential problems.
First of all solar panels are a high impedance current source, and the grid tie inverter (or any inverter) draws a heavily pulsing current. The inverter load falls to almost zero at the zero crossings, and rises to a very high peak at the crests of the mains cycles. To cope with that, the grid tie inverter will have some high voltage electrolytic capacitors to provide an energy reservoir.
The guys that designed the grid tie inverter used the minimum sized capacitors they thought necessary for cost saving reasons. There will still be some ripple voltage at the input when driven from solar panels, and that should not be too much of a problem.
Now looking at the alternator and the rectifier side of things. To produce a steady dc output voltage, again a capacitor bank will be required to supply the load while the alternator goes through its zero crossings. What is less obvious is that the windings in the alternator only supply current during the rectifier conduction time. When the diodes are off, the current through the alternator will be zero.
The less ripple voltage there is, the shorter the diode conduction time. But that produces some very high but short current peaks in the alternator. That dramatically raises the temperature of the windings way beyond normal operating temperature.
The solution is to fit a large dc choke between the rectifier and the alternator capacitor bank. That choke (if its sufficiently large) will keep an almost constant current through the alternator windings which will run much cooler. It will also reduce the ripple voltage on the capacitor bank.
Another related problem is that the alternator is putting current pulses into the capacitor bank, and the inverter is drawing current pulses from the capacitor bank that might be close in frequency, but not exactly in frequency lock.
That can cause a strobing effect, where the capacitor voltage undulates at the frequency difference. The effect may be small, or it may be dramatic. The grid tie inverter may not be able to cope with high cyclic changes of input voltage. It may require adding a lot of extra capacitors to reduce the voltage fluctuations.
It will all probably work fine. I am just playing Devil's advocate here alerting you to some potential problems and how to fix them if they do materialize.Cheers, Tony.
George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308
Posted: 01:16am 17 Dec 2017
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What model engine is it? Sounds like one of the newer rebranded high speed/ low weight types rather than the old style 600/1000/ 1500 genuine lister/ clone types. The one I have now is a CS 6/1 Roid and the one I hope to get is a 12/2. Engine alone weighs in at a mere half ton.
All of those old style types including the multi Cylinders JP's etc ran mechanical pumps and being Direct or indirect is irrelevant to the fuel use. The determining factor is in the pump. As long as it is the mechanical plunger type, you CAN run Veg.
If you are worried about the much talked about and completely blown out of proportion coking issues, water injection is the answer. I run that on my 4WD and the lister as a preventative of any problems. Does not have to be some expensive set up with mega high pressure pumps and all the rest of the cap the retailers of WI systems scaremonger with, A steady drip into the intake is all that is required. Have a Chinese Horizontal set up like this and it's done maybe a couple of hundred hours on veg which they are known to clag up on and the thing is BETTER than when I got it new.
The Yamnar clones conveniently have a little plug at the top of the engine which goes into the intake for priming with a bit of oil or your favorite starting fluid without taking the air cleaner off. Makes great place to screw in a small fitting to drip the water into.
For CLEANING, the water is better to go in as droplets rather than a fine, evaporating spray. The water will not only keep the engine internals such as ring lands and valves, ports etc clean but will also keep buildup occurring in the exhaust. Had a problem with that on my old mercedes where the exhaust would carbon up and then when I'd be towing something or driving the thing hard on the highway it would get hot enough to catch alight and I'd have the effect of 2 Kg of Charcoal being fanned by a strong blower taking place.
The sparks out the exhaust were pretty cool but the brightly glowing Muffler DID set the underneath of the car on fire once which was a bit of excitement. Shaken up softdrink bottles can make very useful Fire extinguisher's.
As an aside, You should be able to make Bio Currently for around .35C/L depending on how much you have to pay for Meth and Koh. The price of those seems to vary quite a bit. Lucky I always had the cheapest prices I heard of near me. Mate and I would go get up to 4 Drums of meth at a time to make the trip as worth while as possible and as we did 1000L batches, we used a drum and a bag of Koh every time.
George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308
Posted: 01:22am 17 Dec 2017
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Thank You very much for the input. I suspected it would not be as straight forward as just hooking it up.
Could you suggest where the best place to put the caps would be and what amount you think would be needed to alleviate the problems?
Thanks again!
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 01:33am 17 Dec 2017
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Just try it first and see what the problems may be. There may not be any.
If the dc voltage has a lot of ripple, or slowly cycles up and down, try adding more capacitors.
Cheers, Tony.
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 01:53am 17 Dec 2017
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The engine is a Genuine Lister Petter TR2 1500 RPM, these engines have been used to drive generators in radio transmitters where they run nonstop for 6 months and only get stopped to service them and then off they go again. They will go for 40,000 hours before requiring a rebuild, I am not sure an indian rip off of a Lister would come near that.
It is not a high speed engine, 1500 RPM is classed as low speed and it has 2 simple mechanical injection pumps, if anything it is simpler than the Lister CS engines.
Direct injection engines do not run well with waste vegetable oil, the pre-combustion chamber of a indirect injection is much better for that type of fuel. It will run fine on bio Diesel though, the difference is not in the pump but in the injector and combustion chamber.
Because it won't run on WVO I plan to sell it and use an Onan 10KW I have instead, it has indirect injection.Edited by Madness 2017-12-18There are only 10 types of people in the world: those who understand binary, and those who don't.
George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308
Posted: 03:17am 17 Dec 2017
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Direct injection should not be that big of a deal. I have run plenty of direct injected engines on veg and had no problems at all. There are a lot of variables however from the quality of the oil you use to the individual engine.
The internet legend is that indirect engines are best but having run both types I say it is more an individual thing than a type rule.
it would be interesting to see how it went with 5-10% unleaded mixed in. Yes, heard all the fear mongering about that too but 15 winters and a lot of othe blending in a range of different vehicles and with different engines has proven what poppycock that is as well as is most veg folklore. Only problem I found with blending is 15% in summer is not a good idea especialy with E10 as it causes vapor issues when you shut the car off for a short time allowing it to heat soak then try to restart. Don't need that much over 20oc anyway.
5% ULP i believe brings the fuel burn timing back to that of diesel pretty much and as most people don't adjust their injection timing, this makes a significant difference on some engines.
Is the onan a complete Gen set?
If so, watch the gen head and make sure the slip ring assembly is secure. I have seen 4 of these things where something there comes adrift from the screws to the whole carrier thing and destroys the gen head.
I also discovered there are a lot of onan engines only around particularly in marine circles where this has happened. It seems to happen quietly as no one hears anything just the machine stops generating. Open them up and you find things floating round inside that should be. Always the same thing and they are known for it.
Replacement Rotor is a bit over $800 from onan as a reco unit. Seems to be the cheapest option to get them going again. The ones I have seen were all under 10 Kw, mainly 6's but I don't know if the problem is confined to those models or not.
If you haven't checked or had the thing apart to have a look, I'd strongly suggest it.
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 04:41am 17 Dec 2017
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The Onan is a converted Marine generator set, it is not one of the toy ones sold more recently. It has no slip rings as it is a brushless alternator. The engine is a 4 cylinder 1.9 Litre 1500 RPM Diesel rated at 10KW electricity output and like the Lister I have, it will do that all day every day.
I would rather run on straight WVO apart from startup and shut down than add petrol or make it into biodiesel at 35 cents a litre. The generator will only need to run a handful of days per year anyway. If I was confident with my car running it I might be tempted to make Biodiesel but I am not going to risk it with common rail injection.Edited by Madness 2017-12-18There are only 10 types of people in the world: those who understand binary, and those who don't.
George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308
Posted: 09:42am 17 Dec 2017
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If the oil is liquid, IE, above say 5oC to err on the side of caution, the start up and shut down on Diesel/ bio is a crock as well. I run my vehicle on WVO even in winter and don't have any problems starting and it does not lead to coking of the rings either.
If the engine won't start on oil and it's not near freezing, there is something wrong with the engine.
So much of these " rules" are based on what someone said who repeated what the guy before him said who is repeating what her read someone else say who..... and NONE of them have ever put it to the test ( go forbid we do something to our 30 YO worn out POS engine!) and if you ask, can't even explain the physics or processes behind the need to do the thing they are preaching.
You mentioned a DC choke. Could you give an idea of the size you think would be needed and where a person may get one. Looked them up on fleabay but they seem to be pretty exy things.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 12:53pm 17 Dec 2017
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I don't know if you even need a choke. A lot depends on how heavily loaded the alternator is, and if overheating of the alternator windings is a problem.
If it is, then we can look at the specifics. Cheers, Tony.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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