Weak charging under load

[MicroMachinery]

I just recently got back from the trip to JCCS, and was made aware of an issue my 610 has with charging. I found this out at night while driving in So Cal, that when I switched my fan and A/C on, my charge light would come on. The more items I turned on, the brighter it got. I watched my Voltmeter and it dropped to around 12v. All this was using an IR 35A alternator.

Fast forward to today, I was at the wrecking yard looking for a 280zx alternator. I found one, but immediately afterwards, I found a nearly identical 720 alternator that looked like it had much less exposure to the elements. The year of the 720 was an '82, so I knew it had to either be a 50A or 60A. It was identical to the 280zx alternator(except nicer), so I went with the 720 alternator.

Got it home and installed it into my 610. Fired it up and the Voltmeter shot up to 14V. I put my DVOM onto the battery, and sure enough, it was sitting pretty at 14.3V. I decided to load test the system now, so I started turning on accessories. By the time I had my lights, A/C, blower motor, electric fan, windshield wipers, stereo(just the deck and 4 speakers, not a system)and hazards on, I was only charging at about 12.5V. I looked and the charge light was back on. With everything turned off, it charges at about 14.25V. However, with anything more than headlights on at night, the charge light starts coming on.

Could it be that 50A isn't a high enough output? I doubt it, as this is the same situation I was experiencing before with the 35A alternator.. is there something I'm overlooking? Do I need to go up to a 60A? I wouldn't think so, as none of these accessories are above and beyond what came from the factory, except for the electric fan...

[banzai510(hainz)]

Far as ai know the 610 used a exeternal volt reg. with the stock alternator

The 720 uses a Internal volt reg alternator

 

so One has to assume you did the conversion if you havent done this already(since your a long time member). And you know it been on here almost a million times since Im sure you read all the threads already.

 

So you could be double regulating the voltage. But untill we know more that What I think it is

[MicroMachinery]

I have indeed done the conversion. I've been reading on this forum and others trying to find answers, and had I had daylight at the time of the original post, I would have been in the driveway, under the hood double checking connections etc. I was just wondering if by the off chance someone had seen this before or knew about how much electrical "responsibility" a 50A alternator was capable of handling.

[banzai510(hainz)]

my 50 amper is enough but loading it down with lights and heater@ idle can put it on the edge but alot better than my 35amper.

[ggzilla]

35A is enough to run all those things. You won't get full voltage at idle, the FSM says to test it at 1200 RPM, if I recall correctly.

 

You might want to use an Ammeter in this case, to track down which if any component is pulling too many amps.

[DanielC]

A 50 amp alternator should put out... 50 amps. That should keep up with about 600 watts of electrical load.

I did not notice, but is the alternator you are having problems with internal regulated, or external regulated?

 

On a stock 521, with a 35 amp alternator, I have seen a situation where at low engine speeds, the charge (IGN) light is on, but it goes out at higher RPM. This was caused by worn brushes in the alternator.

 

Another possibility is a poor connection, in either the positive side, or the ground side of the alternator, and possibly voltage regulator.

Lets say you have a poor connection somewhere in the charging system. It is still connected, but not good enough. When the alternator puts out a lot of current, the voltage drop across the poor connection fools the alternator, (or regulator) into thinking the voltage is high enough, but in reality, it is not.

[datsunaholic]

Worn brushes, bad connections, or you have one heck of a parasitic load that's already pulling a bunch (or part of the headlights). Time for an ammeter to see what's pulling so much.

[MicroMachinery]

So today I did some looking, and apparently, the alternator is putting out a steady 14.32V at idle. .. where I am reading 13.8V at the Battery.. I didn't really need to, but I tested the voltage drop between the alternator and battery, and just like good math, it read 1.54222..V. I'm losing a volt and a half between the alternator and battery, somehow. I found that when I unplug the "T" connector, the voltage at the battery jumps up to 14.9V. I also found that when all accessories are "ON", the positive wire on the alternator gets HOT. This wire runs from the engine bay into the passenger compartment, and from there off to various places. Ugh.. I really don't want to have to tear my entire dash out to check for a short. I'm sure I won't have to, but my brain is kinda fried from the day right now, and it's not working optimally; I'm sure there is a simple cause, and it's just evading me at this point...

[ggzilla]

The voltage drop has to be from the ALT to the BAT -- it doesn't go through the dash.

 

Start with cleaning the BAT terminals and cable ends. Both ends.

[datzenmike]

Yup. And it might not be all on the positive side. A circuit requires a completed loop through the ground. Check the ground cable where it bolts to the head and the positive where it bolts to the starter.

[MicroMachinery]

The first thing I did this morning was clean the cables. I'm not sure if it's an anomaly, but on the 610 wagon, the wire from the alternator goes through a connector which in turn goes through the firewall and under the dash. According to the wiring diagram, from there is splits off to various places before returning to the battery. I'll go get the diagram again and see if I've overlooked something, somehow.

[ggzilla]

It should run directly from the back of the ALT to the Fusible Link which is part of the POS battery cable.

 

yes, it goes into the engine compartment wiring harness, and a branch goes to the dash harness. But the main thick wire goes directly to the Fusible Link.

 

Wiring Diagram is a schematic, it does not detail the actual physical placement of the wiring.

[MicroMachinery]

You are right. It SHOULD run right to the Pos(+) battery cable. However, the engineers who designed the 610's wiring harness had other plans.

 

It runs from the alternator up to the relay box. From there, through a green, 6 prong connector into another harness. This harness travels along the side of the fender, then through the firewall. From there, it goes through a blue connector behind the glove box. At this point, it splits off to:

-Air Conditioner(via Blue wire)

-Fuse Block(via White wire)

-Rear Window Defroster(via Black wire)

-Dimmer switch(via Red wire)

-Light switch(via Red wire)

-and finally, the Fusible link(via White wire, back through ANOTHER Black connector into the engine compartment, which then switches to a Black/Yellow wire to the Fusible Link, then on toward the Battery Pos(+).

 

I know that in most cases, the fusible link comes right off the alternator, then to the Battery Pos(+). I don't know why they did it this way with the 610's, but that's how they did it. One big "U-turn" :blink:

[MicroMachinery]

Cleaned out the connections, put it together, and the wire is still getting hot. I think it's just too much amperage for that single wire, especially with how long it is and how many connections it has to go through. I'm going add a shorter wire that goes directly from the Alternator to the Battery POS(+), like is normally seen. I'm gonna use 16ga wire and I'll add a .8mm Fusible link(comparable to the .85mm Red fusible link used for the other, original circuit), as well.

[MicroMachinery]

.

[DanielC]

To handle the 50 amp output of the alternator, I would use a 8 Ga or a 6 Ga wire, but that is me. 50 amps through a 14 Ga wire is pretty close to what is used for a fuse able link.

[MicroMachinery]

It's 2 circuits sharing the load, so I think it'll be ok. I ran around today with everything on, and neither one gets hot now.

 

Thanks for the input everyone :)

[Gearshredder]

sigh... thats my current project lol PO melted the wiring a little but everything still works lol.. Time to redesign! thx for the posts on the progress and sucess lol