Idea for adding an external alternator to your engine.

I was watching a video ( @doc sprocket I think) where he showed adding a flat idler pulley to the engine crankshaft to make an emergency rope start add-on.






I thought that was a great idea and considered that if one were to use a V idler pulley, it could drive an alternator also.

Then, this morning this video (from one of my favorite youtubers, Mustie1 ) showed up on my youtube home page, showing exactly that. Now I like it even more.

Note, the pic shows a hydraulic pump actually, but either (or both?) could be used. Easy power take-off.

It is a good idea especially if you're going to be running alot of accessories (incandescent lights, linear actuators ect.) or plan on doing alot of winching but it will need to be planned out really well and you'd want to underdrive it or most of your engines power could be wasted on the alternator itself, most car alternators will suck up 3-8hp in their natural habitat of being in a car, for arguments sake let's say it's on a mid 80's Chevy smallblock which is something that has less demand than newer vehicles so you can probably reduce that figure by 30% or so. You could in fact counter that by adding a toggle switch to the "field coil" so it only charges when you want it to but everything but the "field coil" toggle is only my theory (I know the toggle works - used it on race cars) so let's ask @mr.modified for his personal experience shall we!? He used a Buick alternator on his Baja Sears build so he'll know better than us the real world outcome!

https://www.atltf.com/t3157p69-baja-sears-build

And, you could just flip the belt off or get fancy and have a clutch to turn it off.

Nevadablue wrote:

And, you could just flip the belt off or get fancy and have a clutch to turn it off.

It would be even better if it was an AC generator, you could also have a compressor pump as well, I was thinking about running a compressor/generator on the UTV with a toolbox in the back as well but I decided against it until my wallet isn't feeling so underfed

Nevadablue wrote:

And, you could just flip the belt off or get fancy and have a clutch to turn it off.

True and true! Lol

@TechnoChicken, automotive alternators are actually AC 3 phase in fact, the diode rectifier is what converts it to useable DC power. They can be rewired to do the task but it would be easier to run a decent alternator and a store bought converter instead, then you keep your DC charging and can plug in AC accessories. As for a air compressor pump... you can actually use a 12v DC air compressor for a air ride system and modify it to work, they can put out up to 100psi I'm pretty sure. I've seen it on a offroad recovery tow truck on YouTube, I'll do my best to find and post a link to it later, it's been a long time since I saw it but think I can track it down.

Exactly. A good alternator and battery and an inverter.
12 volt DC compressor is fine for tires.

Otherwise, I will just get out my service truck.



(I was doing some tire work on it when that pic was taken)

Got the beast in 2015 for 3 grand! 1992 F700 with huge winch and 28’ knuckle boom. Will lift a ton at full extension. Works great for picking up stuck tractors. LOL

Oh wow @Nevadablue that's awesome!

Here's a link to the YouTube videos for on board air
https://www.atltf.com/t6883-on-board-air-on-the-cheap

I made an auxiliary power unit with an alternator driven off a 6 hp engine. The pulley ratio is 1 to 1 roughly. Used a 10si internally regulated alternator (the GM alternator mentioned above). Added a circuit to full field the alternator for when I jump start cars. It's about a 100 amp. alternator. It has a regular regulator in it, so when it fully charges the battery, it senses it and just idles. The equation for building something like this that I used is- 1hp to make 27amps for picking a motor or seeing if an existing motor on a rig will work. Around 3000 rpms on the rotor shaft (pulley) of the alternator is needed for full output of an alternator generally speaking.  

If you use a different ratio for the pulleys then you will change the power requirements and rpms needed to run the alternator without stalling motor. For example- a 5 inch pulley on the motor and a 2 1/2 inch pulley on the alternator will need 2hp to make 27 amps at 1500 rpms. To make the same 27 amps with a 2 1/2 inch engine pulley and a 2 1/2 inch alternator pulley at 3000 rpms is needed.

I still have this APU and works great for working on cars. I prefer using the 1 to 1 ratio and have the engine revved up, then having the engine just off idle to run the alternator because when the demand was needed the engine rpms would fluctuate more with a 1.5 ratio then the 1 to 1 ratio.

Hope it helps.

That's extremely helpful and makes @Nevadablue very thankful! Lol