Internally Regulated Alternator Trivia - Bootstrap Current?

[Chickenman]

1976 280Z Federal Model ( Arizona car )

[Captain Obvious]

According to the wiring diagrams, both 76 and 77 used the same "always powered" relay coil, but the internals of the 76 brake warning relay was different than the internals of the 77. Implication being, they used a different relay between the two years and maybe the relays they used in 76 are more robust than the ones used in 77?  I don't know for sure, but you might not suffer the same hot coil crispy fate with your 76 relay style.

 

Does remind me about another point about the relay and the alternator upgrade though... The brake warning relays used in 76 and 77 are designed to actuate (pull in) at a coil voltage less than the full alternator output. If you've done the internally regulated alternator and rewired your brake warning relay as a result of that upgrade, you're probably applying more voltage to the relay than it was designed to handle and might have inadvertently accelerated the hot crispy coil burnout.

 

The relays are originally driven by the "N" output of the alternator which is actually the "Neutral" output from a three phase generator system. The voltage at this neutral connection is full output divided by the square root of three. Because of this, the brake relays are designed to pull in at about 60% of the alternator output voltage, or about 7 Volts. If you've reconnected that relay coil to full alternator output voltage as part of the alternator upgrade, you're overdriving the relay.

 

Zed Head, How did you reconfigure your relay when you did the upgrade to make the light go out?

[Zed Head]

I ran a new fused wire to the fuel pump power supply, at the harness junction next to the passenger seat.  So the relay gets powered with the fuel pump.  The relay seemed to be the typical Nissan relay, I think I measured 0.3 amps draw while I was trying to figure out what was draining my battery.  

 

More worrisome for me is the fact that high water mark under the passenger seat was about halfway up the relay body.  Pretty sure it's been wet.  

 

That should really be one of my winter projects.  The relay, the parallel L circuit, and cleaning up the wire ends that are still poking out of the harness from where I cut off the regulator plug.  They're insulated but hanging in space.  Mementos of my first modification.

[Chickenman]

My brake warning relay seems to be OK still. I'm still using an externally regulated Alternator, although that may change down the road. I'm looking at installing an 80 or 90 AMP 1985 Maxima alternator ( Mitsubishi small frame ) down the road

Edited August 2, 2015 by Chickenman

[Captain Obvious]

Zed Head, Water mark on the outside of the relay body? Nice! That's an interesting story if it could tell it, huh?

 

So if you measured 0.3A to the relay, then you're dissipating between 3 and 4 Watts inside that tiny little box. It's gonna get hot in there.

 

For both you guys, next chance I get, I'll take some pics of my 77 relay with the cover off. Mine went intermittent after being on and baking for however many hours it took to accumulate just under 100K miles on my car. IIRC, it's crispy...

[Chickenman]

My AC relay was absolutely fried. Replaced it with a Bosch 40 Amp universal relay.

 

Next up is a HD relay kit for Headlamps.

[Zed Head]

Zed Head, Water mark on the outside of the relay body? Nice! That's an interesting story if it could tell it, huh?

 

So if you measured 0.3A to the relay, then you're dissipating between 3 and 4 Watts inside that tiny little box. It's gonna get hot in there.

 

For both you guys, next chance I get, I'll take some pics of my 77 relay with the cover off. Mine went intermittent after being on and baking for however many hours it took to accumulate just under 100K miles on my car. IIRC, it's crispy...

I think that's normal relay pull isn't it.  The EFI and fuel pump relay pull the same?

 

Here's a picture.  At the time, I was in "just make it work" mode so didn't even look inside the relay.  I'd forgotten how bad it looked.  Definitely on the fix list now.  I think that the electrical tape is there to hold my fuel pump power circuit tap line in place.

 

After I had the car a little while and started parking it outside I found that it had a pretty serious leak through the windshield seal.  It probably sat outside and filled with water before I got it.  Had a hole under the driver's seat also.

[Captain Obvious]

Nope. Everything on the entire car is driven from the "Line to Line" output on the alternator except  for the charge relay inside the mechanical voltage regulator and the brake warning relay. Those two things (charge relay and brake relay) are the only two things driven from the "Line to Neutral" output from the alternator. And because of the three phase nature of the alternator, the line to line is SQRT(3) times the line to neutral.

 

In other words, everything on the entire car runs on normal alternator output of 12 to 14 Volts EXCEPT those two relays which run on alternator output divided by SQRT(3) or about 8 Volts.

 

Now, of course, all relays have a range over which their coils will pull in and they are constructed and spec'ed such that they are guaranteed to have pulled in above a certain voltage, but Datsun designed the voltage regulator relay to be guaranteed to pull in at a voltage well below full output, and it's my belief (assumption?) they did the same with the brake relay.

 

There is a bunch of discussion about the charge relay portion of the voltage regulator on pages EE-23 and EE-24 (76 FSM). And in that area it talks about the voltage expected to be seen on the "N" terminal. Also the chart on EE-24 indicates the relay is designed to pull in between 4.2 and 5.2 volts (Guaranteed to be pulled in by 5.2 volts).

 

I haven't found that level of detail about the brake warning relay, but I would expect it to be the same?

[Captain Obvious]

Oh, and by the way... I keep referring to the "N" terminal out of the alternator as the "Neutral". I kinda made that up as I've never seen it referenced that way in any of the literature. I can tell you, however, that the "N" connection IS  a neutral connection out of a three phase generating system, but for all I know the "N" stands for some Japanese word that has nothing to do with "Neutral".

 

Myself? I'm going to continue to refer to it as the neutral connection until someone shows me literature to the contrary. 

[Zed Head]

I've spent all of these years avoiding the assemblage of odd things that were used to generate electricity and now you've dumped me right back in to it.  Rust, corrosion, over-voltage...  My bliss is gone.  Thanks a lot!  

 

I wonder how my fuel pump relay is doing since it's been supplying a pump and an over-voltaged check relay.  Might as well rewire the whole car.

[Zed Head]

If I read this diagram right, two of the pins on the BWLCR aren't even used and a simple normally closed relay could replace it.  Looks it might even be a two way relay, maybe the same one is used in 78, just wired NO instead of NC.  I'd take it out and look but seat removal is required, and we'll be up in the 80's today.  

 

A common Bosch relay.  I can get my current draw back down and cool things off.  Might keep the old rusty one there though, just for the history.

 

 

 

[Captain Obvious]

Yup. You're reading it right. There are both NO and NC contacts in the 76 relay, but only the NC contacts are used. With the way you have your relay connected, you could replace it using the NC contacts inside pretty much any SPDT relay that is designed to run on 12V.

 

In 77 they used the exact same normally closed scheme, but they changed the relay. The way I know that is the number of contacts in the connector going to the relay. Your 76 has six positions. Five of which are populated on the relay side and three that are populated on the harness side. The 77 has four positions in the connector with three populated on both sides.

 

And I wouldn't worry to much about your fuel pump relay, even if you are overdriving the brake check relay some, I bet the fuel pump still draws way more than the relay. In other words, I bet the fuel pump draws the lion's share of the current and the brake check relay is a drop in the bucket compared to the total.

 

I also wouldn't worry too much about the brake check relay either. If it eventually decides it doesn't like the current any more, it will just go open circuit on the coil side. You'll know it has happened because your brake warning lamp will stay lit and won't go out like it's supposed to. At that point, reach under the seat and pull the connector off the brake relay and the lamp should go out.