Charging System Woes....working But Not Working?

[metalmonkey47]

Running back to my electrical gremlins in my '70 240Z as the temperature begins dropping outside, some of the issues become more annoying or severe. 

The PO of my car had someone 'work' on the car, which for some reason included cutting the pigtail out of the fusebox and main harness, and splicing it together with house wiring connectors (didn't even crimp it. Fail) 

I have no ammeter deflection, except when running lights, brakes, heater, etc. And the deflection is always negative. Charging voltage at idle (900) is about 13.8V, No more then 14.1 at any given time. I have NOT checked this number with accessories on, so I'll get back with you guys tomorrow about that. 

At idle with accessories/lights at night, I notice the headlights are slightly dimmer and the blower runs slower until the revs are up. Again, no positive ammeter deflection.

My primary concern is that my batter voltage is about 12.3V with the engine off. This is on a Yellow Top Optima, mind you. A full charge at 10 amps off of my charger in the house overnight leave it about 12.6 and load tests fine at about 700CCA. I have no drain on the battery overnight whatsoever. My main concern is that the alternator doesn't seem to be maintaining the battery very well, which seems to affect cold starts ever so slightly. I'd hate to see how slow it turns over when it's 20 degrees outside. 

Is it possible that the alternator might have a somewhat sufficient voltage output, but mediocre amperage output? I'm very curious, because the ammeter on the dash shows virtually nothing. How can i verify JUST the amperage output of the alternator? 

[SteveJ]

What is the battery voltage at 2500 RPM? Internally or externally regulated alternator?

 

You really need to come over. I have a clamp on ammeter that can give you a better idea of the draw.

 

I have extra time off around the holidays.

[metalmonkey47]

I think I made this more complicated then it had to be. I recall fixing an issue with the regulator wiring when I started driving it, and I think I tested the new regulator before fixing that. Dunno that I ever looked into it after that. Anyways, I think it may (and probably will) be the regulator.

 

 

             load        no load
Idle       12.6V      13.8

 

2200     load        no load

             14.2V      14.3V


Sadly, I have no time off around the holidays. I need to get with you soon though. 

[SteveJ]

That looks to be a little below the acceptable range, voltage wise. It would be good to see the current flow, as well. That's where clamp on meters are nice.

[Zed Head]

I think it may (and probably will) be the regulator.

 

 

             load        no load

Idle       12.6V      13.8

 

2200     load        no load

             14.2V      14.3V

 

Your numbers look normal and don't show any functional problems with the system.  Your alternator is just on the weak side.  They don't put out their rated current at low RPM, only at high (see attached).  Pretty common.  A different alternator, same style, might solve the problem.  It's kind of a crap shoot unfortunately.

[71Nissan240Z]

When I upgraded to a 60 amp maxima I never dropped below 13.6 even with a load. My car even idles better. I bought the alt. From a local junkyard. Took it apart. All looked good and installed the diode where the regulator used to be. Best 55 bucks I ever spent. Amp meter is much more stable and doesn't shake.

[Zed Head]

I've found also that the numerous corroded/old/dirty connections each draw a little bit more current than they were designed to.  Cleaning them up will help a little bit.  Also, as you can see from the chart I attached above, another 50-100 RPM in idle speed can get quite a bit more juice flowing.  You might get to a happy spot with just a few tweaks.