Matt, any idea what pin you're using? Or Jason? Those four guys, would they know?

I wired it into the hydra harness... but it's the one in the 99 manual called "generator field coil"

This mod is fine and all, but wouldn't it be easier to just pick up an NA alternator and swap pulleys?

Just a thought.

Tony

I can build this circuit in less than 30 minutes and it will cost me maybe $7 in parts. I can't do an alternator swap in less than 30 minutes and it will certainly not cost me $7.

Jim

I have a spare GM alternator control box if anyone wants to do testing.

The circuit doesn't need (more) testing, it's been used in four places.

I'm wondering what wire to put it on. But everything I can see, it looks like you want to put it on the wire I'm not using. I remember being confused at the time, since I had it on the other wire and it didn't work. When I put it on the gray/red wire, BAM, things were working. Maybe the wire colors are wrong in my book. Or... I dunno. I should check which ECU pin corresponds to the wire I'm using. Everyone PM teamplur and make him make me do it.

Abe, do you have a 2000 and a 2000 FSM?
In my FSM the alternator field and neutral wire colors were swapped IIRC.

Can a mod please change the subject to "Alternator..." instead of "Altenator..."?

Jim

Oh good lord, that's what I was thinking... At least I can pretend to have SOME understanding of how the thing works. :-)

Yes, I'm pretty sure that would be the issue - I was going to check it on my car, but it's nice to have someone else verify it. I'll hopefully do that tonight. Sucks, though, since there's more vias now on my board. :-) But I'll take a board with more vias that works over one that doesn't work at all.

o lookit wut i foundz!

sorry about the pictures. but maybe you can reverse engineer it to see if it's the same as jason's schema.

since that sucked, here's something more fun.

http://y8spec.com/miata_tech/nb_alternator_ctrl.gif

I guess since you labeled everything it means it checks out? :-)

It seems I have a strange issue (apart from being a spelling Nazi apparently). The NAPA alternator control box works as long as the stock ECU is in place: I feed B+ to the blue wire, and I get PWM on the green wire (note that the green wire in not connected to anything). I remove the stock ECU, start the car with the MS2 (standalone) and I get nothing on the green wire (voltage is at ~11.5V on the blue wire). What gives?

Jim

you got me. maybe re-verify your power source or tap right into the ig switch "on while running" circuit instead of the ECU pin?

Jason, thx for an other great circuit.
I reordered the components a bit so they fit in the proto area, pretty neat if I say so myself. On the bottom right side of the layout, you'll notice 2 unused spaces. This corresponds with the 2 missing holes in the proto area.
As the circuit only uses 50% of the proto area, there's room enough for other stuff like EBC, Vics and Fan mods.
There's probably not enough room to fit Abe's input circuits, but I built those in the VR area of the board.

re-installed the circuit today and it holds system voltage nicely just under 15V. if I switch on everything (heads, fogs, defrost, heater fan full, hold brake, and hold both window switches) it maintains about 14V. probably less if the fans come on. all at idle. I guess my alt is ok?

LOL that sure looks like my handiwork.

I have another circuit for lighting the warning light when voltage drops < 12.9V (as opposed to the typical light that means the alternator is putting out current, even if it's not enough to keep the battery charged).

Interested to see the schematic Jason.
BTW, is it necessary to use the 2% version of the TL431? Datasheet says 'guaranteed thermal stability over applicable temperature ranges'. Local shop dude looked at me like a cow to an airplane when I asked for a 2% version.
Also, I assume the 48K7 regulates current? I have little electrical stuff in my Westfield so I might need to lower current on my setup.

You can use a 1%.

If you use one looser than 2%, you can trim ithe 48.7k resistor to get the exact voltage if it's off a bit.

The circuit regulates voltage, not current.

I think the schematic is above?

Wow, that's a nice lay out, I like it - and all without resorting to unusual stacking methods. You know, with a couple of those posted, it might be possible to come up with a "standard" NB install.