Adding an alternator

[chrishallett83]

Is there a place near you that does rewinding?

You might be able to get your bike alternator rewound for more amps, and fit an aftermarket diode pack to handle the increased current.

[fabr]

lol turbine speeds.   well all i was saying is that 90% of my driving is in 6th gear going fast..   atleast this whole last year was..    but ok lets say.  1980 chevy truck alternator..the alt pulley is 2.5" diameter, and the crank pulley is 7.75".....

considering alot of people are running axle driven alternators.. i find it hard to believe i would need a 30+ inch pulley.. lol

You don't seem to understand that the axle rpms are the only rpm that matters except for the alt rpm needed for whatever output minimum you need. . I don't care if the engine is running at 1000000000 rpm ,if the axle is only turning 375 axle rpm or so you will HAVE to gear that up to somewhere around 2000 alt rpm to get full output. First thing you need to do is choose an alternator you want to use and check it's output at various RPM's OF THE ALTERNATOR ITSELF. Until you do that this is just useless talk. 

[fabr]

lol turbine speeds.   well all i was saying is that 90% of my driving is in 6th gear going fast..   atleast this whole last year was..    but ok lets say.  1980 chevy truck alternator..the alt pulley is 2.5" diameter, and the crank pulley is 7.75".....

considering alot of people are running axle driven alternators.. i find it hard to believe i would need a 30+ inch pulley.. lol

true but the thing idles at approx 800 rpm. Your axle at 60 is in that range. I don't know about you but I can't average 60 mph offroad unless it's all dirt roads. You'll be LUCKY AS HELL if you average 20 mph truly offroad. You only run the roads?

[Voodoochikin04]

the only reason i was talking about engine rpms...  is so i could calculate my axle rpms while im driving..  thats all...


most of my driving is gravel and dirt roads..   

[fabr]

I just see it as easier to go from the wheel. Fewer calculations

[Boostinjdm]

the only reason i was talking about engine rpms...  is so i could calculate my axle rpms while im driving.. 

One tiny mistake in the ratios and your final figure won't be right.

 If you are driving it off the axle, then you start where the rubber meets the road.  It's that simple.

[fabr]

That's what I've been telling him but it's not sinking in I guess.  I'm that way tho at times myself. Can't see the forest for the trees thing ya know. LOL!

[Boostinjdm]

That's what I've been telling him but it's not sinking in I guess. 

I know..... I couldn't take it anymore.  That's the nicest post I could muster.

[Voodoochikin04]

you can do it either fxxking way boost..  the fxxking engine is driving the god damn rear axle... so if i take my normal crusing rpms and go through my primary, and my 6th gear through my rear end.. wha fxxking lah.. theres my damn rear axle rpms.. which i can use to figure what size pulley i need for my alternator...   to me that is way easier than figuring how many times my wheel revolves in one mile and such and such mph when i dont have a damn speedo.. so yea its sinking in.. it doesnt seem like how i was doing it was sinking in for you guys..  either way will get you the same damn thing... rear axle rpms.. which is what i needed!!!


so no.. you dont HAVE  to start where the rubber meets the road.. 


just delete this whole thread...i got what i needed from it.

[Wyattboche]

I'm confused. So how do you determine what size pulley you need?

[Voodoochikin04]

take my axle rpms..... and compare to the rpm range for the alternator, and figure what ratio of pulleys i need to run to get the alternator in that range....


but for some reason everyone seems to think its impossible to calulate rear axle rpms from your engine rpms in any given gear... the damn engine drives the rear axle... you can calculate the rear axle rpms using the engien rpms in any gear!!!


and one more time... when im flying down the road in my buggy, at 10,000rpms in 6th gear.....ill know my rear axle is turning 1036 revolutions per minute.... i didnt need to know my mph or tire size to figure that..   thats all ive been saying all this whole thread..  so my alternator with a 2.5" diameter pulley, running on a 10" diemeter axle pulley.... will be turning 4144rpms.....  again.. i didnt need tire size or mph...     so then ill know... "hey my alternator is putting out (such and such) right now, while im driving" 

how in the world is that not correct?? thats all i wanted..  i dont need the alt to put out full power while im in 2nd gear putting around the yard.


60mph with a 22" wheel is gonna give me 842rpms at the rear axle...   that does me absolutely no good, unless i figure what rpms my engine is running when im at 60mph so i can make sure im running my alternator within my driving habits...  which is exactly why i need to know what my engine rpms are......for everyone that says my engine rpms dont matter... they do matter in this situation.

[Boostinjdm]

You can figure it however you want, but if you are driving anything off the axle then figuring axle RPMs from tire dia and mph is the best way.  If you were running the alternator off the crank, then engine RPMs would be the best way.

As Fabr said, "it requires less calculations" and will give you the full picture from dead stop to top speed.  Axle RPM and MPH directly correspond to each other. Axle RPM and engine RPMs do not. (that should be reason enough right there)

I personally would figure out how fast you can safely spin the alternator and then so do the calcs so that you achieve that RPM at the buggies top speed.  I would do that to prevent damage to the alternator.  Maybe even give yourself a little head room. I haven't looked it up, but I have a feeling that would give you a decent charging rate from moderate to slow speeds and up.  Plus matching the upper limit of components just make good sense, but don't let good sense interfere with doing things the way you want.

Why is it that you started this thread again?

[Carlriddle]

  I need a beer.

[fabr]

Voodoo ,it seems like you are just interested in charging at your max speed. That is not the way to look at it. You MUST be able to make some decent alt output at much lower speeds. Whether or not you think so you WILL be spending more time near idle and at lower rpms than you will at redline. In ANY gear. Yes ,of course ,you CAN calc axle rpms from engine rpms.  Of course,as always,it's YOUR buggy. Do it however you wish. YOU asked a question and got answers.SORRY ,they don't coincide with your thinking. If you wish to get pissed at our answers ,don't ask .

[fabr]

You can figure it however you want, but if you are driving anything off the axle then figuring axle RPMs from tire dia and mph is the best way.  If you were running the alternator off the crank, then engine RPMs would be the best way.

As Fabr said, "it requires less calculations" and will give you the full picture from dead stop to top speed.  Axle RPM and MPH directly correspond to each other. Axle RPM and engine RPMs do not. (that should be reason enough right there)

I personally would figure out how fast you can safely spin the alternator and then so do the calcs so that you achieve that RPM at the buggies top speed.  I would do that to prevent damage to the alternator.  Maybe even give yourself a little head room. I haven't looked it up, but I have a feeling that would give you a decent charging rate from moderate to slow speeds and up.  Plus matching the upper limit of components just make good sense, but don't let good sense interfere with doing things the way you want.

Why is it that you started this thread again?

An alternator will take all the axle rpms it will ever see and then some. Most alts are in the range of 2-3:1 overdriven. Assume 8K redline and the alt will see 16000-24000 rpms at REDLINE. THat axle driven alt will not see that.