1986 Honda Prelude Charging Voltage Drop

1986 HONDA PRELUDE
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JOSMIALO
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I have a 1986 honda prelude with the 1.8L engine in it. when you increase the rpm's above idle or turn on a perifial device such as the head lights the voltage drops to 11.5v. At no point will the voltage go above 12.5v I have put in a new alternator, a new belt, a new external voltage regulator. I also have new battery cables, a new battery and a new starter. What else can I check?
May 4, 2006 at 6:50 AM
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LOSONE
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Replace the alternator, it will fix the problem. It has an internal voltage regulator that sometimes fails
May 4, 2006 at 8:03 AM
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JOSMIALO
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I did replace the alternator 3 times. still the same problem.
May 6, 2006 at 4:07 AM
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LOSONE
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Where did you purchase the alternators? Discount stores are a poor choice because sometimes a core is cleaned and reboxed and sold as rebuilt. I have experienced 85% returns on alternators and starters. The only thing I buy from adiscount store I can pour out of a bottle. It's always the mechanics saying "pay me now or pay me later." I am a pro with a pros experience.

Also you need to check the grounds on the battery side. REMOVE all grounds that are attached to the engine, frame and engine to fire wall. Clean them GOOD so the metal is shiny on both surfaces. Sometimes a bad ground will cause an alternator overload in excess of it's rated output.
May 6, 2006 at 6:03 AM
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JOSMIALO
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Ok, so i took the alternator back to auto zone, where i got it. they tested it and said it was good. i then took it to 2 other places where it tested bad. my new one will be here in 3 days. I just replaced the external voltage regulator a few days ago. could it have been the reason i burned out 4 alternators?
i also cleaned all my ground connections when i replaced the regulator.
May 6, 2006 at 6:44 AM
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LOSONE
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As a good rule of thumb, it is always necessary to replace the voltage regulator with the alternator.
May 6, 2006 at 8:14 AM
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Suggested Repair

Replace the alternator and external voltage regulator together, using a quality unit rather than a questionable discount-store rebuild. Have the alternator tested at more than one shop, and clean all battery, engine, frame, and firewall grounds until both mating surfaces are shiny metal.

Conversation Summary

A 1986 Honda Prelude 1.8L charging system stays at or below 12.5 volts and drops to about 11.5 volts when engine speed rises or accessories such as the headlights are turned on. The owner had already replaced the alternator, belt, external voltage regulator, battery, cables, and starter. The expert advised replacing the alternator because its internal regulator can fail, warned that discount-store rebuilds are often defective, and recommended thoroughly cleaning all engine, frame, and firewall grounds. After conflicting tests, the owner ordered another alternator; the expert said the voltage regulator should always be replaced with the alternator.

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