alternator connector re-wiring

[NoDOHC]

Vex:

Fred is right, only he is not using the Quote feature, so it is very confusing.

If you look at the circuit configuration that I posted above, you can see that there are diodes to prevent current from the B+ post on the alternator or the voltage feedback (B/W wire) from supplying the fields while the alternator is not generating voltage.

That circuit that I posted is a schematic of how the voltage is regulated. The alternator output is controlled by controlling the current to the field.
No field current = very little output.
More field current = more output.

What Fred is saying (and he is correct) is that the alternator must receive some current (a very small amount) from the W/B wire in order to excite the fields at low engine speeds. Once there is field current flowing, the fields will self excite. The instrument lights light because the alternator is drawing current through the coil in the warning light cluster.

Your alternator will still work (after the internal voltage caused by residual magnetism reaches a sufficient level to start current flowing in the field) but you may have to rev the engine significantly to make the alternator start charging and you will lose the feature of all your warning lights lighting up when the key is on and the alternator is not spinning (convenient for thrown-belt notification).

Fred: That functionality is lost, I have already tested it.

On my S4 alternator, I had to rev to about 6,000 rpm to get it to self excite on the residual magnetism.

Vex is right, your sentence structure is a little bit confusing. You obviously know a lot about the RX7, and I am really glad that you are helping Vex, but I think that you should proof-read your posts before posting.

[vex]

Cool. Thanks. So just the sanity check: Since I'm bypassing the warning functionality I'll need to put some voltage on the W/B line--and I'll need 12V+ switched on the B/W line. Does it matter if they're the same source, or should I throw on a resistor to drop the voltage down to 3 Ohm for the W/B line.

[FRED]

******* The instrument lights light because the alternator is drawing current through the coil in the warning light cluster.******

Not to complain, but this is a series four car and the Warning Light unit does not have any wiring going directly to the alternator at all. Series five are different concerning the wiring from alt to warning light cluster. No alt relay in the CPU for series five.

See the series four Turbo and non turbo diagrams I posted in one of my other posts. The warning lights all alight if the alt relay in the CPU pulls in and puts a ground on the warning light clusters light bulbs (all of 'em). Once the alternator starts putting out the Alt relay relaxes and the gnd to the Warning Light assy is there no 'mo and the lights go off in the warning light cluster.

Frankly I still don't see why you don't just run a single wire from the CPU's white/black to the L terminal of the alternator for excitation. Your CPU is still there from what I gather. IF not then you need to look into how to get the turn signals to work without it. One wire from the drivers side of the engine compartment to the alternator. Nobody will notice it. String tie it to the harness going to the CAS etc.

[FRED]

By the way, the coil of the alt relay is 50 ohms and there is a blocking diode b/t it and the alternators L terminal. That would work. You could just install them just prior to the L terminals connector and use the already existing black/white wire for the feed for it. Like splice into the black/white for power for the L.........but like I say, those items already exist in the CPU and you just need to run one wire from the black/white of the CPU plug to the alternators L terminal. I assume you already have the black/white wire at the alternator for the switched voltage for the S terminal.

[FRED]

Tell you what. I went out to lunch and went by RS and picked up two 100 ohm resistors and a couple of diodes. Resistor part number 271-1108 (100 ohms, 1/2 watt) and the diodes were 1N4001.

They didn't have any 50 ohm resistors so I put two 100 ohm in parallel (50 equiv) and one diode of the end of the outfit that attaches to the alternator. Soldered a spade on the end of the diode. Picked off the power from the series four elect plug where the the black/white exists and spliced one wire off there going to the top spade on the alt jack and spliced another wire from the black/white to the end of the resistors.

Key on engine off...............L wire reads 2.65 vdc. Engine on and running , the alt is putting out 14.02 vdc and the L wire reads in the area of 11.5 vdc give or take. Normal as can be. "B" wire reads the 14.02

I'll attach a picture of the *outfit*. This is not professional and was done on the fly just to get results. YOU can make the thing cleaner/smaller and wrap in heat shrink. Like I said, this was done on the fly just to prove something.

I had to remove the series five alt and install one of my old series four to do this. Say "thank you".

I'm not sure you positively need the diodes. I think that is a safety feature just in case the alt goes bad internally and the diode would prevent battery power from backfeeding into the interior fuse boxes circuit. Like drain the batt down overnight if there was a failure of some sort.

Hmmm, come to think of it I don't like the S wire reading 11.5 vdc when the alt is putting out the 14.02. I think what I'd do if I were you , is to find another source of power for the L wire (white/black) and the 50 ohm resistor/diode. That way the S wire should read a normal reading of ??? 14 vdc or so and not the 11.5 as I just mentioned. S wire power comes from the ENGINE fuse and that normally matches whatever the alt is putting out give or take a tash.

[vex]

Originally Posted by FRED

Tell you what. I went out to lunch and went by RS and picked up two 100 ohm resistors and a couple of diodes. Resistor part number 271-1108 (100 ohms, 1/2 watt) and the diodes were 1N4001.

They didn't have any 50 ohm resistors so I put two 100 ohm in parallel (50 equiv) and one diode of the end of the outfit that attaches to the alternator. Soldered a spade on the end of the diode. Picked off the power from the series four elect plug where the the black/white exists and spliced one wire off there going to the top spade on the alt jack and spliced another wire from the black/white to the end of the resistors.

Key on engine off...............L wire reads 2.65 vdc. Engine on and running , the alt is putting out 14.02 vdc and the L wire reads in the area of 11.5 vdc give or take. Normal as can be. "B" wire reads the 14.02

I'll attach a picture of the *outfit*. This is not professional and was done on the fly just to get results. YOU can make the thing cleaner/smaller and wrap in heat shrink. Like I said, this was done on the fly just to prove something.

I had to remove the series five alt and install one of my old series four to do this. Say "thank you".

Hey, I appreciate it. Gratis.

I'm not sure you positively need the diodes. I think that is a safety feature just in case the alt goes bad internally and the diode would prevent battery power from backfeeding into the interior fuse boxes circuit. Like drain the batt down overnight if there was a failure of some sort.

That was my thought as well. I'll probably put in one anyways.

Hmmm, come to think of it I don't like the S wire reading 11.5 vdc when the alt is putting out the 14.02. I think what I'd do if I were you , is to find another source of power for the L wire (white/black) and the 50 ohm resistor/diode. That way the S wire should read a normal reading of ??? 14 vdc or so and not the 11.5 as I just mentioned. S wire power comes from the ENGINE fuse and that normally matches whatever the alt is putting out give or take a tash.

Any particular reason to be concerned with the S terminal reading lower?

[FRED]

S terminal voltage? Bothers me but I have no known reason for being bothered other than on a stk car it would be seeing what the interior fuse box would be seeing......which would be the output of the alternator voltage around 13-14vdc. I just like to see what is the norm.

I probably shouldn't be concerned about that. I put my series five alt back in the car and put the series four back in the shed.

Pretty expensive rig I made. Cost $ 2.40 total.

EDIT: I see where in the beginning I said the L and S wire reading 11.5vdc was *normal* and later had doubts about that voltage. Conflicting thoughts at best. At this miniute in time I would not worry about it not being in the 13-14vdc range.

[NoDOHC]

Fred, you are awesome! Going to that much work to test a theory.

The reason that the blocking diode is in the circuit is that if the 8 gauge alternator output wire were to fall off, the alternator would attempt to charge the battery and operate all the electrical components in the car through the W/B wire and the warning light coil. The diode prevents this.

The 11.5 Volts is not normal at all. The L and S terminals should both be reading somewhere near the alternator output voltage.

[FRED]

Yeah the 11 whatever puzzles me a bit but the alt is outputting the 14.1 read at the positive post of the battery.

Then again the busses that feed the Meter and Engine fuse are powered off the ignition switch power wire that is...............directly tied to the alternator output cable.

I must have been reading the 11.5 the other side of the 50 ohm resistor (two 100 in parallel) or??. No way I'm going to reinstall the S4 alt and resistor(s) to double check that. I KNOW the alt was putting out 14 plus volts at its output terminal plus the volt gauge in the car was on the 14 hash mark.