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Posted by David Sherman on Monday, December 29, 2008 at 16:43:38 :
In Reply to: Electrical Questions posted by Sam on Monday, December 29, 2008 at 16:18:09 :
I have messed with 2 one-wire alternators (can't say I was impressed) and they both had diodes in them. Basically, they bring out the internally rectified 3-phase output to a terminal just like a regular alternator, and then they added another plate with two diodes in it on the back which connected to a different terminal. They were both motorola units, so I don't know how Delco does it. I would be surprised if the original design really needed you to add an external diode. If you did, it would have to be able to carry the full output current rating of the alternator. Since a diode drops roughly a volt at high currents, it would need to be able to dissipate as many watts as the alternator can generate in amps. That means it would have to be mounted on a heat sink.
What did not impress me about my one-wire motorola alternator was that it wouldn't kick in and start generating unless the RPMs were extremely high -- higher than my 230 turned except at full speed even with an extra-small alternator pulley that I made myself. The problem was that the output diodes block the internal regulator from getting any battery voltage to start it up. I cobbled together a workaround by running a small diode (pointed towards the generator) and a resistor from the ignition circuit to the internal (upstream of the output diodes) terminal on the alternator. I hope that makes sense. What it does is provides just enough juice whenever the ignition is on to get the alternator started. This is obviously not the way it was supposed to be, and I wouldn't recommend it, but it's been working okay.
Are you asking the question because your alternator isn't putting out any current, or because it's running the battery down? My impression is that one-wire alternators are SUPPOSED to be totally simple to hook up and shouldn't need any external anything. Personally, I like DC generators and electromechanical regulators because I want to know my truck will keep running even if there's a nearby nuclear weapon detonation whose electromagnetic pulse, fast neutrons, and gamma ray flux destroys all solid-state electronics. But that's just me.
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