General Alternator Question
Thread Starter
Racer
Joined: Jan 2004
Posts: 294
Likes: 0
From: cincinnati oh
General Alternator Question
I have a new (rebuilt) alternator that I bought for a 68 I owned about 2 years ago and I have a question about it you guys may know. I want to use it for a school project where it would generate 12 volts to the system, but I need to know the minimum RPM at the alt in order to design the drive system. Anyone know what RPM it needs to generate power? I spun the alt by hand as fast as possible with a meter on the BATT and GND terminals with no output at all. It is a Duralast that has been sitting in the box for two years and never been mounted. Any advice would be greatly appreciated.
Race Director
Joined: Jul 2004
Posts: 12,711
Likes: 329
From: Scottsdale Arizona
As an absolute guess, I would say that the circumferance of the alternator pully is half that of the drive shaft one. Assuming reasonable output at full idle, that would mean a minimum of 1000 RPM to get output. Probably a little more than you can do by hand. 
Pro
Joined: Sep 2002
Posts: 620
Likes: 2
From: San Antonio TX
I agree, you should be able to get your voltage at around 1000 RPM. What are you going to drive it with? Remember that it actually takes a fair amount of power to turn that thing when there is a load on it. Assuming you are not trying to power up a photon accelerator or something similar, you may need a 1/4 HP or more to run it. A new 1/4HP 110VAC motor will run you well over $100.00. You might be able to find an old used one from an appliance repair store fairly cheap. Heck, the guy might even let you borrow one for your project, sort of like a sponsor!
Thread Starter
Racer
Joined: Jan 2004
Posts: 294
Likes: 0
From: cincinnati oh
Thanks guys for the response. I also was thinkingg along the lines of what CA-Legal-Vette said about the pulleys coming into play and adding to the RPM of the alt (big turns small=more RPM). I am actually going to use human power to run it. It is for the 2007 ASME Student Design contest. The alt will provide 12 VDC to some heaters to boil water for purification. I realized that spinning it by hand was a weak attempt to get some output, but I had to try. 
If anybody has any other ideas on an alt that will give me high output at lower RPM and not cost big $$$ let me know.
If anybody has any other ideas on an alt that will give me high output at lower RPM and not cost big $$$ let me know.
