Lawn mowers as generators without taking them apart

Discussion in 'General Electronics Chat' started by Rolland B. Heiss, Feb 20, 2015.

  1. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    I have what may be a basic question and I could probably figure it out with trial and error here or there if time permitted but if one were to crank up a gas powered lawn mower where would you attach the voltmeter to positive and negative in order to ascertain what voltage was available to tap into? Recently I watched a few videos of people who had taken apart a lawn mower and attached a car alternator via a pulley system to the motor which created a generator. Is it possible to merely attach wires to a running lawn mower someplace and attach them to a power inverter in order to generate electricity without dismantling the mower itself so I can mow the lawn again come spring?
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Seriously? o_O

    Do you think you can you hook wires up to an engine that has no electrical system and get power from it?
     
  3. bwilliams60

    Active Member

    Nov 18, 2012
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    Are we talking about your basic everyday 3.5-5.5 HP Briggs and Strattonor Tecumseh engines or something more elaborate? If it is your basic engine with an ignition system and a kill switch, you don't really have any options. The coil is fired by a magnetic pulse from the flywheel and a coil/spark plug wire/spark plug and I highly doubt that will be much use to you. If you are attaching an alternator via a pulley, well, you are already generating power although I do not recommend this either. You have not mentioned what you want to use it for so hard to comment on anything else but these engines are pretty basic electrically speaking. Please elaborate.
     
  4. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    Yes, as a matter of fact I do but I am not as learned as you so tell me if it is possible or not? By the way, if it has no electrical system as you imply then why is there a spark plug and wires and copper and such? I want to know! Don't look down upon me because I am curious. Help me... or don't. I see electrical sparks between the plug and the other side of the gap so how is it not an electrical system despite the fact that it is fueled by gasoline? Why all the wires? I might be an idiot but it seems quite electrical to me.
     
  5. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    I just what to know if it is useable and frankly I don't see why not even if only to light an LED but I'm sure it could do much more so the LED reference was fairly tonge in cheek. The engine in my lawnmower is a Briggs and Stratton of some kind. Haven't the HP rating in front of me but just pretend it is the lowest rating. I must be able to do something with it apart from cutting the grass by tapping into the energy produced by the gasoline and the rotation of the blades.
     
  6. Brownout

    Well-Known Member

    Jan 10, 2012
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    Outside of lighting a neon bulb that indicates a spark, you won't get any useful electric power from your lawnmower. As mentioned, the only electrical system is a magneto that generates high voltage for the spark plug. You'll need to attach a generator. I've seen it done before.
     
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  7. #12

    Expert

    Nov 30, 2010
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    So you want to use a 3 hp gasoline motor to light an LED.
    If you designed cars this way, the average Toyota would come equipped with 5 million horsepower.
    Very inefficient use of gasoline.

    Looking at your curiosity level, I might suggest that you attach a 1k resistor to an LED and walk around touching the wires to trees, door knobs, cats, and fence posts.
     
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  8. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    If your mower has an electric starter and an on-board battery, there is a chance the starter motor is doing double duty as a generator. If your mower is like that, you can get usable current for such things and lights, but I have only seen that in riding mowers. The on-board battery part is important. My small snow blower has electric start, but that depends on being plugged into a wall socket.

    John
     
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  9. darrough

    Member

    Jan 18, 2015
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    If it has a battery, then just take the battery out and use it to power a LED or whatever else. I mean why use a gas engine to make electricity when you already have a battery?

    In regards to the original question, would it work if you put a huge capacitor in parallel with the magneto?
     
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  10. WBahn

    Moderator

    Mar 31, 2012
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    As you may or may not have gathered from feedback thus far (some of which I think has been needlessly abusive -- but then I've been guilty of that myself from time to time), you are very unlikely to get useful energy from a typical lawnmower's electrical system. The thought is not unreasonable and I applaud the curiosity involved -- and also that you are looking for understanding as to why it won't work. The basic problem is that the electrical system on a small engine like this is designed and rather optimized to do one thing -- provide power for the spark plug. It produces high voltage, but very little energy. I found some information from McLaren that indicates that it only takes a few millijoules of energy to ignite the fuel air mixture and that ignition systems typically dump a few dozen millijoules. So say you have a single-piston lawn mower engine running at 3600 rpm, which is 60 Hz. That's only 30 sparks/second. Let's say that the ignition system dumped 33 mJ/spark, that would only be 1W of power.

    If you are designing engines, you don't want to make a magneto that is going to do anything more than provide a healthy spark, which means it is going to be able to deliver that 1W of average power and not much more. Not only is this so that the magneto will be as low cost as possible, but also because you want to rob as little power from the intended application as possible. Furthermore, the whole system is designed to get that very short high voltage pulse to the spark plug at just the right time. You don't have to dink with it much at all before you have either robbed too much energy or reduced the voltage too much or messed up the timing.
     
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  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    If I heat a cup of Instant coffee in a microwave oven, will I move backwards in time a few seconds?
     
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  12. Reloadron

    Active Member

    Jan 15, 2015
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    In a word no it is not possible to connect wires to a lawnmower engine and get any useable electricity from it. Yes, there is a wire for the spark plug but the electricity found there is nothing you can do anything with.

    Yes, as you have seen you can use a lawnmower engine to drive an automotive alternator which in turn can be connected to an inverter and that will give you some useable power. Short of doing that the basic answer to your basic question would be no.

    While off topic I can go to for example Harbor Freight and buy a 4000 Peak/3200 Running Watts, 6.5 HP Generator for less than $340.00 USD. Personally I live up here in the Cleveland, Ohio suburbs and winters can be cold an brutal. An emergency generator is a good thing to have. Even for hose living in warm climates like Florida being without power for a week or more following a hurricane can be a nightmare. I like my creature comforts. :)

    Ron
     
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  13. jpanhalt

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    Jan 18, 2008
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    No, but if you sleep in the basement with the dog, you will age a just little slower. However, the radon might get you before you notice the difference. ;)

    John
     
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  14. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Been a while since you worked on a riding mower, John? :) Since the riding mower boom in the late 60's early 70's the engines use an extra set of alternator coils and the flywheel magnets to generate the electricity for battery charging and lights. Maybe there are some of the garden tractors with a vertical cylinder engine(like the old Simplex) that still use a starter/generator system, but all of the Briggs, Kawasaki type engine starters have a Bendix type drive on them.
     
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  15. shortbus

    AAC Fanatic!

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    If the O/P really wanted to do this, you could get another ignition coil from a similar mower, take the secondary off of the coil and mount it opposite of the engine magneto coil. You would get ~6Volts AC from it at an unknown amperage.
    But it would be a last ditch, life or death , end of the world way of getting power, IMHO.
     
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  16. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    @shortbus
    My Case 444 w/14HP cast iron Kohler (circa 1971) uses the generator as the starter. I guess you are right. It has been a few years. John
     
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  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Of course if you have the Randy Quaid V8 version then it is a whole different story.....!

    Max.
     
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  18. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Not looking down on you. Just not sure what you are going for being the power levels you are referencing don't exist on a lawn mower engine by themselves.

    Typically the magneto type ignition system is not really considered an electrical system being it only does one thing and has no real built in options to supply power for anything else.

    When you say hooking up a power inverter you are talking about having a power source that is capable of at least a few hundred watts but as others have pointed out the ignition coil on a lawn mower engine is a pretty poor power source and even if modified they are not good for more than a few watts at best.

    As far as putting a generator system on a lawn mower engine there are two options. On larger mowers there are dedicated system that mount under the flywheel that can produce a few tens of watts on the largest ones and on the small push mower engines there is an auxiliary coil that bolts on to the side of the magnetos coil that will give you a few watts at best.

    If you need any more power than that you have to run mechanical power to a dedicated generator or alternator system. Personally if you want to go that route I recomend using a large truck alternator being they are usually rated to put out their full power at ~3600 RPM so they are perfect for a direct shaft to shaft drive system which will, if the alternator is large enough, give you the most efficient conversion of your engines HP into electrical power.

    BTW the conversion for horsepower to kilowatts is 1 HP equals 746 watts which means that you 3.5 HP B & S engine would be able to run a ~2600 watt load. Ideally factoring in efficiency losses figure about 1500 - 2000 watts electrical power at peak.
     
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  19. wayneh

    Expert

    Sep 9, 2010
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    For what it's worth, my Seadoo boat has a magneto-powered charging system that is, in principle, a lot like what the TS wants to do. A big difference is that my boat engines (yes, there are two) run up 7000rpm, so there is plenty of speed to drive a magneto. A lawnmower engine doesn't go over 2000rpm if I recall, and the flywheel radius is much smaller also. Much lower available juice for a given magnet and coil.

    Pulling much power off the existing magneto risks degrading the spark for the mower engine.
     
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  20. Reloadron

    Active Member

    Jan 15, 2015
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    More from for what it's worth. My old Briggs and Stratton gasoline powered generator is a 4,000 watt continuous rated using an 8 HP engine so in that case we get about 2 HP per KW and that is at 3,600 RPM for the 60 Hz output. The 50 Hz versions would run at 3,000 RPM. That is a 4KW continuous, 5 KW peak for short periods. That unit could run the entire house for lighting, home computers and just about anything as long as you don't try and run the electric clothes drier. :)

    Several years ago we did some major home renovations and I installed a whole house automatic transfer emergency generator that runs on LPG or NG and for use runs on Natural Gas. At 18KW I can support half the street I live on.

    House5.png

    Power goes out and within 10 seconds power is restored. No muss and no fuss.

    Ron
     
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