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Trimmer Engine Generator Answered

   Hello Instructables community.
   I was thinking of making a 12 volt battery charger with a trimmer engine (pictured) connected to a scraped car alternator (I found several on eBay). But I have a few questions: 1. Would such a combination work as shown in the illustration?  2. Would it be best if I directly connected the engine to the alternator with no drive belts or chains, or would the high gear of the large engine gear and small generator gear be worth the extra trouble.  3. What is the best way to connect the two? And 4. Where should I remove the engine from the "trimming part". Any answers will be appreciated.
                                                                                                                 Confused DIYer


Sorry for bringing this back to life, but I need some help. Let's say that I hook on a trimmer engine a motor that is described as a 12v dc 18500rpm. If the engine spins for example at 3000rpm the motor, will it produce 12v, so a power inverter connected to it can work? Or the motor has to be spun at 18500 rpm for it to be able to produce 12v? I appreciate any help!

Hello Instructables Community

Me and my dad have made a succesful generator. it may be crude but it does produce over 12 volts.

Snapshot 1 (28-07-2016 3-03 PM).png

I was planning to do that, but the process may be different for someone else due to different engine and parts, and I have neglected to take photos of building it.

im going to be a negative nancy, but those trimmer heads dont have a whole lot of torque to spin a alternator/generator, especially if you put an electrical load on the system.

I didn't consider that, If it doesn't work by connecting the two parts together, I will use a gearing system to produce more torque.

I have done some of these "generators" back in the day for camping use.
Long before real generators became quite and cheap enough.
The key is the right speed for what you need for the alternator.
For example:
In a car the alternator is able to produce quite good amps already at around 2000rpm - for the engine.
But just to charge a battery anything above 1000rpm should do fine.
Your motor will be slower, so a bigger pulley on the motor and a smaller pulley on the alternator would be a good start.
I doubt you will have problems with the engine torque so unless the alternator is not giing out enough you won't need extreme speeds.

How fast is the engine? I looked online and didn't get good results. Some say around 5000 rpm and others 8000 rpm. I don't believe it's that fast. You guys know? It's a Ryobi 725r trimmer.

I've ridden a bike powered by one of those little engines. It was fast(for a bicycle). So u oughta hav enuf power one way or another, methinkst.

I found a new problem: do I have to buy an external regulator and if so, how do I wire it to the alternator and battery?

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Get a cheap car alternator with regulator build in ;)
Most actually are designed this way as the generator provides AC, so the regulator is usually included with the rectifier.
As for the coupling I think the best option is to use pulleys and belt.
Far easier than mechanical coupling directly on the axle and easier to work with if you need to repair things.

I considered using a self regulating alternator (one wire I believe), but I found them to be prohibitively expensive. I found one with a 3 pin regulator port and an external regulator for only $47 total. Would that allow me to connect it directly to a battery and how would I wire it? Thanks for your response.

Without a regulator it is useless for charging.
You would need an external regulator or charge controller, so a little alternator from the wreckers would be still cheaper.

I'm a bit confused by what you mean by "A little alternator from the wreckers." How much would this cost me?

As said: A little alternator from the wrecker - what is confusing about this?
You need something that spins and provides charge to a 12V battery, so an alternator springs to my mind.
Will cost you anything between nothing and a few hundred bucks depending where in the world you are and how much you look/ask around.

I do know what an alternator is, but what I'm confused about is that could I find a one wire (with built in regulator / rectifier) one from the wreckers (I assume a scrapyard) for an affordable price ($30-40) just as I could with one without a regulator. I hope this clears things up. Sorry about the bad wording of my previous reply.

And as said, you will need the regulator to charge the battery.
So go for the one with regulator built in.
Those without any regulator or rectifier (in the higher mp region) are often modified to be used as simple stick welder on farms.

Well, I guess the higher price is worth it, thank you. I'll give you all an update when I finish the project.

Even better: Take some pics on the way, add some instructions and parts lists to make an Instructable out of it.
You might even want to enter it in some of the running contests ;)

what rpm does the engine. Run at?

What rpm does the alternator "like"?

either research those numbers, or put somethin together as quick n dirty as you can. No sense buildin a polished prototype if the concept is wrong.

There are shaft to shaft direct linkages which allow a bit of flex. This way, your mounting doesn't havta be perfectly straight.

Okay, but where would I find such a shaft?

not the shaft, per se, but a way to connect 2 shafts.

The smaller hardware stores tend to carry this stuff. Not the big box stores. It's likely to be in the section with fan belts, pulleys, etc. In my area, that's Meyer hardware, ace hardware, maybe that place with small engine stuff... just need to know what shaft diameter.

or Google "flexible shaft couplers" and buy online.

1. Would such a combination work

In theory: Yes, why not? In real life: Yes, maybe.

2. Would it be best if I directly connected
the engine to the alternator with no drive belts or chains

Yes. Any kind of gear system / belts will waste some energy. Unless they are needed to match the optimal speeds of engine and generator.

3. What is the best way to connect the two?

As direct and as short as possible. Or, if you need gears / belt discs - as few as possible.

Where should I remove the engine from the "trimming part".

As close to the engine as possible - or as close as you can manage with the knowledge and tools you have access to - you didn't tell us about that.

Thank you Verence. I was wondering however: if I did a gear system, wouldn't the higher rpm on the generator produce more electricity? Or is there no difference?

A gear system will not change the energy. You can only get higher RPM - with lower torque, or a higher torque - with lower RPM. The power is always the same (minus the losses in the gears). But your generator may have a sweet spot (frequency), where it converts more of that mechanical energy to electrical energy. Same, your engine may have a sweet spot where it runs most efficiently. If those RPMs are too far apart, a gear system is a good idea. You can never get more energy out than you put into the system (in form of fuel), but you can minimize the losses in each step.

Oh, I didn't think of that, thank you!