Alternator Help Please

Old 02-20-2011, 07:57 AM
  #1  
streetrod2934
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Default Alternator Help Please

I hope this question is in the right place, My question is the alternator that I have on my 1937 Chevy has the 1 post for a battery cable, the it has a plug in that has 2 wires, 1 wire is also connected to the alternator the other runs into the wiring harness. I have looked up GM alternators and have found articles that have confused me. all the alternator numbers etc. My question is can I just replace it with a 1 wire only alternator, or do I have to replace it with whats there. I am having some charging issues according to my gauge. It will read 14 + volts at times, but at night with the lights and ac/heat on it will read around 12.5 volts and at idle sometimes will drop to 11 volts and then again it may read 13 volts. It is up and down the scale, I hope all this makes sense, I think this is just a 100 amp unit. Thanks for your time
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Old 02-20-2011, 08:05 AM
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fast75vega
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doesnt sound unusual..... average charging for a chevy while running at idle is around 13.8 volts and it should drop down when lights and electrical stuff is turned on ..... :wink:
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Old 02-20-2011, 09:10 AM
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bcw49
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I would keep the three wire ALT. set up you have. A one wire ALT. you have to rev the engine to get it to self excite. JMO.
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Old 03-14-2011, 06:15 PM
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burgessdg
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Default alternator help

Not sure what you have. GM first generation Alt had a 2 wire plug as did the second generation (1972 thru 80"s?). I would not waste time with first gen it had an external regulator. Second gen had an internal regulator. I have put the second gen in dozens of pre-72 cars. I am not sure how a 1-wire works, but I would guess it is the similar to my method only internal to the alternator. My method comes from a 1976 Chiltons manual (testing section), here's what I do... Battery connection on alternator goes to Pos battery or thru ammeter if you have one and then to battery. Flat plug terminal 2 goes directly to pos battery (not thru ammeter). Flat plug terminal 1 goes to a 10 ohm (6 watt) resistor and the to pos battery. I abandon the wires from the plug unless they go where they need to. I don't care about idiot lights.

As far as charging voltage, specs are like 12.8 to 14.5 volts. If you are putting out 13.8 at idle with no accessories, when you turn accessories on, voltage might dip slightly, but should recover to 13.8. That's the regulator adjusting for load. If voltage does not recover, you have a bad regulator or alternator. Or, your alternator is too small for your loads. They made 35 amp thru 100 amp alternators. I have a 35 on my '59 'cause it's what I had and all I have is lights and wipers. I have a 60 amp on my '69 'cause it has power windows.

Good luck,
Dan
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Old 03-14-2011, 06:17 PM
  #5  
burgessdg
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Default alternator help

Not sure what you have. GM first generation Alt had a 2 wire plug as did the second generation (1972 thru 80"s?). I would not waste time with first gen it had an external regulator. Second gen had an internal regulator. I have put the second gen in dozens of pre-72 cars. I am not sure how a 1-wire works, but I would guess it is the similar to my method only internal to the alternator. My method comes from a 1976 Chiltons manual (testing section), here's what I do... Battery connection on alternator goes to Pos battery or thru ammeter if you have one and then to battery. Flat plug terminal 2 goes directly to pos battery (not thru ammeter). Flat plug terminal 1 goes to a 10 ohm (6 watt) resistor and the to pos battery. I abandon the wires from the plug unless they go where they need to. I don't care about idiot lights.

As far as charging voltage, specs are like 12.8 to 14.5 volts. If you are putting out 13.8 at idle with no accessories, when you turn accessories on, voltage might dip slightly, but should recover to 13.8. That's the regulator adjusting for load. If voltage does not recover, you have a bad regulator or alternator. Or, your alternator is too small for your loads. They made 35 amp thru 100 amp alternators. I have a 35 on my '59 'cause it's what I had and all I have is lights and wipers. I have a 60 amp on my '69 'cause it has power windows.

Good luck,
Dan
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Old 03-14-2011, 06:17 PM
  #6  
burgessdg
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Default alternator help

Not sure what you have. GM first generation Alt had a 2 wire plug as did the second generation (1972 thru 80"s?). I would not waste time with first gen it had an external regulator. Second gen had an internal regulator. I have put the second gen in dozens of pre-72 cars. I am not sure how a 1-wire works, but I would guess it is the similar to my method only internal to the alternator. My method comes from a 1976 Chiltons manual (testing section), here's what I do... Battery connection on alternator goes to Pos battery or thru ammeter if you have one and then to battery. Flat plug terminal 2 goes directly to pos battery (not thru ammeter). Flat plug terminal 1 goes to a 10 ohm (6 watt) resistor and the to pos battery. I abandon the wires from the plug unless they go where they need to. I don't care about idiot lights.

As far as charging voltage, specs are like 12.8 to 14.5 volts. If you are putting out 13.8 at idle with no accessories, when you turn accessories on, voltage might dip slightly, but should recover to 13.8. That's the regulator adjusting for load. If voltage does not recover, you have a bad regulator or alternator. Or, your alternator is too small for your loads. They made 35 amp thru 100 amp alternators. I have a 35 on my '59 'cause it's what I had and all I have is lights and wipers. I have a 60 amp on my '69 'cause it has power windows.

Good luck,
Dan
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Old 03-14-2011, 07:11 PM
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TheYellaBrick
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Unless you've completely replaced all the wiring in your hotrod, you could be getting a voltage drop in a higher demand situation from resistance in the old wiring.
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Old 03-14-2011, 09:02 PM
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dragonmaster093
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tried to get pn line article but cant find but in sept '10 issue of street rodder there was an article on getting the right size alt
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Old 03-28-2011, 03:18 PM
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I put a 1 wire on my 40 Buick coupe (1973 455 power) and it works just fine , will charge at idle, Halogen headlights , sterio,elec. fuel pump,and easy to install, I sell chrome ones for $98.50 on my site www.rodsncustoms.com
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