Sparkies question-theoretical voltage from homade generator

"Eric R Snow" wrote: (clip)How does one determine the number of windings to get a desired voltage? ^^^^^^^^^^^^^ This question does not have an easy answer. It will depend on how strong the flywheel's magnets are, how fast it is turning, and how well the field is coupled to your coil. Are you planning to make an iron core, with shaped polpieces to fit closely to the flywheel? ^^^^^^^^^^^^ Also, if no load is put across the windings, how much drag will it produce? ^^^^^^^^^^^^ None, if there is no load. ^^^^^^^^^^^^^ Just looking for a way to power lighting on a small boat that doesn't require lugging a big battery around ^^^^^^^^^^^^^ This contradicts the no-load stipulation in the previous question. In order to produce light, you have to produce power. If you know how much lighting wattage you are going to need, and then divide by the expected efficiency of the coil/light setup, you will have a ballpark answer.

In my opinion, this is a very challenging (difficult) way to get some light. It's a cute idea, and if you can make it work, your fortune will be made.

Read another thread on whether to apply for a patent. :-)

Well it worked just fine for Henry Ford. All the model Ts he manufactured had exactly that scheme (magnets on the flywheel, coils around its circumference) to produce current for lighting and ignition.

Lucas used this 'dynamo' principle for many of their motorcycle electrical systems. Though, that's *hardly* a testament to its efficacy! :^)

Jim

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Actually, it's as common as dirt. Well almost - electric start lawn mowers use this to charge their batteries. Like Eric's idea, they use the ignition magnet that's built into the flywheel. In fact, it might be a good source for Eric's generator.

Bob

Well, I was thinking about using a magneto's core and winding my own coil to it. Because the core is iron, there must be some drag just from the magnetic attraction. And during the day there will be no need for lighting-hence the no load question. Putting the coil under the flywheel precludes moving the core away from the magnets to reduce drag. It looks like the voltage will be all over the place. So maybe this won't work without regulation. Just kina thinking out loud. ERS

Could always hook it up like an alternator, put some slip rings on the flywheel and replace the permanent magnet with an electromagnet; varying the DC voltage, and thus current through this magnet, will change the field intensity, allowing you to reduce voltage at high RPMs, increase at low, and account for load variation as well.

Or you can slap on an alternator from a car. ;)

Tim

-- In the immortal words of Ned Flanders: "No foot longs!" Website @

Just go to your local small engine shop and buy a standard voltage regulator. Most are rated for current capability with 10 and 15 amp being the most common. Standard small Briggs just use a diode for rectification but they don't charge real well and most mowers are used at a fairly fixed rpm. But higher amp systems use actual regulators with full wave rectification. You might also look into the coils off various small engines. If you're lucky you might find one the right diameter.

Wayne Cook Shamrock, TX

Question I have would be if the boat has a motor/ what kind, and size? You obviously have access to the flywheel (by removing a cover or whatever) . Would it be possible to run an automotive alternator via a rubber drive wheel or something similar? (you couldn't use a belt as the ignition coil for the motor is probably mounted externally to the flywheel OD and it would be in the way). How many lights would you need? Would a bicycle generator (a better quality one) work if driven from the motor? Ken.

why not use a gm alternater or a marine alternator hooked to a small engine?

Go to a lawn equipment shop and ask for a generic 3-terminal voltage regulator for some common riding mower that has electric start with a

12V battery and a magneto charger and a conventional points-and-coil ignition. Ask them to show you how it is wired up. Also get a small 12V battery, riding mower or motorcycle size. Then just duplicate that part of the circuit. Wire your lights to the battery, then you have lights whether the motor is running, idling or stopped and with luck the charging circuit will keep the battery topped off. It might work with a really small battery or even a capacitor, I don't know.

Bob

What's the source of the rotation on the shaft? I'm a bit confused. Do you have an engine, and you want to make a generator? Why not buy a generator? Or are you talking about using a flywheel driven by a motor that you spin up by running the motor onshore?

Yep - much less current. Less energy comes out as heat. LED lights are cool! They're currently quite expensive, but do bear in mind that they'll last for years... at least 15 years, from memory, before charge carrier drift might even begin to be a problem. But I wouldn't be surprised if they lasted more than 50.

Don't knock regulation - it's pretty easy to wire up a linear regulator or a switched mode PSU if the load is high enough (which I guess it might be). You can get SM PSU modules for a few tens of dollars in the US, I expect.

Note that the coil output will be AC if both north and south poles of the magnet are allowed to sweep past the coil - interleaved positive and negative pulses - so feeding it direct into LEDs would be a bad idea :-) The SMPSU ought to be able to handle that, however, and produce nice smooth DC outputs at constant voltage. LEDs like constant voltage; drop the voltage too far and they just go out, and raise it too high and they burn.

Well, the motor is about 3 HP. I don't know yet if the coil is under the flywheel or outside. It'd be better if mounted outside. Then, making another coil or two and adding them wouldn't be too much trouble. Running an auto alternator or even a motorcycle one would overwhelm the motor. Now, a bicycle generator would probably work. Didn't think of using a friction drive. The boat is twelve feet long. The light is really so other boats can see me. Not for searchlights or anything. ERS