Alternator Control box for standalone MS install for NB
 

The following information is courtest of AbeFM. I credit all of the following information to him and his website.


Ok, picked one up - had a little trouble with it for a bit, eventually proved to myselve stuff was working by putting at 20 turn pot between power and the signal in line to the altenator, and finding out that ~0.980 volts got it charging to around 14.3V.

Anyway, armed with said knowledge, I found out the correct wiring for this. Thought I'd note it here for posperity:
To wire up NAPA part number:
New Voltage Reg Napa online MPEVR38SB $15.29 "VR38SB"
Connector for VR above Napa online ECHVRC38 $12.64 (8.99?) "VRC38"
on a '00 miata:

Ground the case, I found it convenient to mount it near the radiator overflow bottle.
Hook the BLUE wire to switched(?) " 12v" battery voltage
Hook the GREEN wire to the Grey/Red wire on the alternator, pin 1-O on the factory ECU.

I let line 1-T hang, I'm not really sure what it is, it seems to be measuring the voltage of one coil of the generator, before rectification. Not sure what that's good for, maybe you could get engine RPM out of it, or total altenator capacity.

Anyway, hooked it all up and everything works well enough. It seems to only charge to like 13.5-13.7, I think this is due to the Mopar part only putting out 580 mV, where I got better charing feeding ~980 mV. Much more than that and you're rapidly feeding 15, as much as 18V into the system.

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Text and images courtest of AbeFM forum member. For image captions follow the following link.

Original Website for mod: http://abefm.smugmug.com/gallery/409...38576775_nSs5m

Heh! Thanks, that's awesome! I'm way too lazy to take the time for that.

I need to add something to that, basically don't get the wrong part. A friend did, and instead of putting out half a volt it was putting out 3 or 4, and his battery was showing over 17V.

It was a similar number, I think it was something like VR38615s. I might be able to find out. It also had a different color plug. When I find out, I'll edit this post.

Nice....looks like i wont be buying an na alternator after all.

sweet. at one point, jason c made me a similar device that was wired in between the alternator field coil and battery voltage. this was pre hydra's ability to reliably control the alternator.

Hmmm, what was in that box, I wonder? Sounds like the same thing. This uses case ground (I think) and those same two wires....

Ok, so hook up the blue wire coming from the regulator pigtail to switched 12V+
Green wire from regulator pigtail to grey/red wire on alternator
And ground case and it charges? That's it? Nothing more or less?

Sober, I would be all over that. But I do remember it being two wires, one to +12V, one to the altenator, and the case I did screw to the body (don't know if it needs ground or not, but even my faith would be stressed to imagine it wouldn't.

My car has been running months on that set up.

Details on my smug mug.

There isn't a 1:1 correspondence between the alternator control input voltage and the output voltage. There is just a minimum reuired *current* into the alternator input pin that is needed for the alternator to give out maximum output (all appliances on, battery not fully charged). The voltage at the input pin for a given input current will vary with temperature.

Interesting! I didn't know that - certainly it was black-box operation to me, I just read somewhere it could be done and worked out how to make it work. Not my favorite way to operate, but certainly it was expedient.

Er, how happy were you with your box, Jason? What goes in it, does it dump a lot of power?

As I'm considering this interposer board, I was just going to leave wires hanging off for the mopar box, but if you think yours would work better, be smaller, or cheaper, I'd like to incorporate it. Tell me a bit more about it?

Just a comment. Since this is for NB installs... maybe make a point of it in the original post or the title. That way the people who don't require it... don't come in here thinking "oh great... something else I have to do".

Jason,
I never asked - you built a circuit to do this? I'd like to see it, for personal reasons just to see it, and to borrow if you don't mind.

Just saw your post. Hmm, I'll have to dig up the schematic and PCB layout, and I'm too sleepy right now to do it. :p

Knock knock - hey Jason, ever find this?? :-)

I just found out, btw, why mine works on my car, and not on anyone else's. I put in my little write up to use pin 1O when it's really 1T, now I got to go fix this on all my drawings. Thanks to pschimt on here for catching this!

Schematic

Give me a quick talk through, since you know, I didn't major in engineering or anything. It sinks current (sources) based on the ratios of the resistors, such that it turns on if the voltage is too low, and off if it's too high?

Does the diode just protect stuff, or is it there as a voltage reference?

I think it'll make sense when I look through it. Have you used it? Does it get hot (are those big transistors?)? What voltage does it "like" in a miata?

It might be a cool thing to make a simple board for.

Those are small transistors.
The TL431 is a voltage reference / error amplifier.
It's configured as a "hysteretic" controller. The setpoint is set by R4 and it's at 14.2V.
I've used it and so have 3 other people.

would you say this circuit is more accurate than the hydra 2D map and PID control?

Faster responding, yes.
More accurate, probably.

dont know why I ever pulled it out and expected to tune the hydra.

Tuning controls is a pain, best avoided. I see now why my buddy was so into analog controls when he was in college. :-)

That's awesome, Jason. Do you care if I use it in a "for sale" if not for profit device? PM if you could.

BTW - which plug on the harness do you use? My car is a salvage title, but I assume the alternator is stock. I have my Mopar controller hooked to the Gray/Red wire (ECU Pin 1-O), but according to the schematic, I assumed it would be the Gray wire (Pin 1-T). The gray wire has a pink dot on it, on both ends, but it's certainly gray.

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It's hard to tell but I carefully verified last night, it has a stripe, the other does not.


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It sure looks like that control transistor is there to turn the field coil on and off, and the wire I'm using watches the AC generated by the alternator. Or, am I just totally wrong here?

Either way, I've been driving 9 months or something like that on this, and my battery hasn't died, so I keep thinking it's working. The connector is strongly keyed, there's no way it's in backwards...