chaztuna(at)adelphia.net
Guest
|
 Posted: Fri Jul 07, 2006 6:20 am Post subject: Fwd: Re: Alternator failure thoughts |
 |
|
| Quote: | To: aeroelectric-list(at)matronics.com
Sender: owner-aeroelectric-list-server(at)matronics.com
Reply-To: aeroelectric-list(at)matronics.com
At 06:57 AM 7/5/2006, you wrote:
| Quote: | In a message dated 7/4/2006 9:25:44 PM Eastern Standard Time, chaztuna(at)adelphia.net writes: For the purposes of the alternators we use, the rectifier is comprised of 6 diodes. These diodes can fail in two modes, open or short. Failing open (diode blows apart) is the more common failure mode. In this mode, each diode that fails will reduce the alternator's output by 1/6th. Charlie,
Charlie:
Why 6 diodes? Half wave rectification only requires 2 diodes. And Full wave reverification only requires 4 diodes. So why 6 and how are they hooked up?
Barry
"Chop'd Liver" |
Barry,
The ND alternators actually DO have 8 diodes. 6 of these rectify the AC current from the 3 windings of the stator into DC current. The main function of the other two diodes is to prevent the battery from discharging back into the alternator when the engine is not running. You have to remember that a DC motor and a generator are very similar. You apply current into a motor to create mechanical motion. With a generator (or alternator in this case) you apply mechanical motion and a magnetic field to create electrical current.
If either of these two isolation diodes were to fail short, the battery would discharge into the alternator. The alternator would act like a seized motor. The input current from the battery can not turn over the engine, via the alternator's pulley and drive belt.
Have you ever had a vehicle which operated OK when driven daily. Yet, if allowed to sit unused for a number of days, the vehicle would have a dead battery? Shorted isolation diodes in the alternator are one possible cause of this situation.
Charlie Kuss |
Barry & Listers,
(Voice of Auggie Doggie) Oh, the shame of it all! I really stepped in deep doo doo on the post above. Please ignore it, as it's all incorrect. Brian's earlier post (which I hadn't read) correctly described the function of the 2 extra diodes.
My apologizes
Charlie Kuss
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
