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Discussion Starter #1
I just rebuilt my CS 130 alternator, after I found it at the junkyard. The inside was clean, but needed new bearings. I tested the rotor and stator and found no shorts or grounds. I bought new bearings and brushes, and sprayed new varnish/insulation on the rotor and stator windings.

After I get the think back together, I take it to the parts store to have it tested. They report the charging voltage is 10.5 volts. AC ripple is zero (good). "Lamp on" voltage is 3.64 (good), but "lamp off" volts is 0 (bad). So, it failed the "Lamp off" volts and charging voltage. I took it to another parts store and they said that when it was energized, it seemed to produce full current and stalled their machine. I don't know what the lamp on/off means though...

To me this sounds like a bad voltage regulator. What do you guys think?
 

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Regulator is bad, "Lamp Off" means it applying full field, 12-14 volts, current it is trying to generate is more than its rated, 105 vs a whole lot!
 

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Thanks Everett, that makes sense. Is it correct to assume that if there was some AC ripple over 0.5 volt, a diode went bad? Just trying to understand things here.
 

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Not necessarily was the diode broken by AC ripple, alt is electronic, could of happened any time, who knows?
 

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If the diode was shorted you would see AC ripple. If it was open, you probably would also see ripple to a lesser degree. It would depend on the load in the case of an open diode.
 

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Discussion Starter #6
Thanks for the information.

What does the "lamp on" voltage mean?
 

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Field cut-in relay voltage, typically, 2.3-3.7 volts on an external reg system.

This is applied to one side of the bulb, the other side gets battery voltage. Bulb 'sees' a difference in potential, and filament glows. When this happens, alternator is outputing max current if carbon pile resistor is hooked up.
 

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Discussion Starter #8
Ok, still having problems after I replaced the regulator. Nothing has changed.

Shuck's machine again said "Lamp Off" voltage is zero, and apparently that's not good. Nobody can tell me what that means though (not even the local rebuilder house). I tested it again at Napa, and their machine said "Energized C.B. open". Don't know what that means also.

So, the regulator is not the problem. I tested the diodes, and they were OK. And the rotor and stator have no shorts or grounds. Brushes are new. Please help!
 

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Diodes front-to-back ratio are checked with one end of the diode desoldered from the circuit.

You may be missing an insulator for the teriminal post the regulator attached. This action could be grounding this particular output.

Maybe, both places hooked up their machine wrong. Have one of them try one of their alts from the shelf.
 

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Discussion Starter #10
Everett-
I believe I have the insulator on the BAT post. The little black plastic deal that goes in between the housing the the post. The nut on the inside contacts directly on the regulator. I'll take another look.

I'll also have them check one of their own also.
 

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Discussion Starter #11
The insulator looks good, and it's not grounded.

I noticed in my alternator repair book, it says to full field the alternator you need to ground out the "ground" brush (general statement, not just for the CS130). In this alternator, I noticed the brush contact was already grounded. For giggles, I insulated it, re-tested it, and got no change. Lamp off voltage is still zero is battery voltage is still about 10.5. I'm not sure if this sheds any light on anything.
 

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Came home from work and read my dually Helms manual as it has a CS130 alt. The four prong plug has P'L'I'S' labeled for pins.
P = Stator reading, for TACH reading of a diesel.
L = goes t ALT light through a 30-ohm resistor, or voltmeter as in my case.
I = Tied to a switch for turn on, usually through another resistor. May be unhooked if L terminal is connected.
S = Sense wire to monitor voltage at any point chosen.

Mine has a wire attached to L terminal for volt meter and of course, BAT. Manual as long as it doesn't gp below 13 volts or over 16 and is within 15 amps of rated output, alt is good.

If unplug 4-prong connector and gen or alt light goes out with engine running, alt is bad. If plugged in, light on with engine running, alt is bad.

So, if eng CB is off, it may mean the test machine may not be setup correctly. Meaning not enough resistors tied to L & I terminals.

Check library for a schematic. It will explain all.
 

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Discussion Starter #13
Turned out to be a bad rectifier AND stator. Never had a stator go bad before...
 
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