Das Beast: My E30 track / street build

[dvallis]

Well, we evidently goofed up a bit on the alternator. I had in my head it was just power and ground but obviously didn't check the ETM.



John, talk to me more about the alternator:

1) If just connected the 1.5 Blue wire to battery 12V on the starter, this would energize the field coil whenever our cutoff switch was closed, and kill it when open. Should eliminate the need for a diode, right?

2) If not, you're suggesting powering the 1.5 Blue field coil wire as a relay load, correct? And having a blocking diode on that?

Like this:

[kronus]

if you connect the alt exciter wire to +12V you'd have a short, it would fry itself, and then your alternator would stop putting out power if it managed to not burn up the voltage regulator.

toss a 10Ω 1A restistor between it and +12.

[dvallis]

So after reading the heck out of every post imaginable on alternators, here's the verdict. The ecxiter input needs about 250 mA for proper regulation. A 5W 47 ohm resistor from the big 12V post to exciter post will do fine. No need for a wire back to the cluster with a bulb since I have an AIM system monitoring Vbatt. If it drops below 12.5 - 13 volts we can blink LEDs on the data dash.

[dvallis]

Exciter wire delete for racing. 47 ohm 5 Watt resistor mounted on phenolic block with aluminum bracket.

[ForcedFirebird]

Apologies for late response. Actually the blue wire can be excited by 12+ as its a positive fed exciter. When the alternator stops charging, the light (has 12v key on) grounds backwards through the alternator to illuminate. The resistor setup will work, but still needs a diode. If you cut power inside the car, your resistor will still allow a 12v charge to keep the alternator excited during engine wind down (therefore back feeding and keeping the engine on). Unless you have an isolated coil power interrupted at the switch as mentioned earlier, there's a good chance it will fail the 2000 rpm safety test.

[ForcedFirebird]

Also both poles of the safety switch need to be isolated all the way to the battery post, or any component can back feed and keep stuff on during emgine wind down. I had a customer install a 5v usb charging port after his car was wired and ready for tech. Fortunately I did a final check before tech or he would have failed the 2000 rpm test and probably destroyed whatever component was plugged into it (or at least melt a wire and/or blow fuses). To correct it, just ran the charge port power all the way to the battery post. He wanted constant 5v to keep his tablet plugged in during a stop.

[dvallis]

Bird

Have a look at the diagram in post 886. When I cut power at the 4 post kill switch it disconnects alternator output from all systems in the car. Alternator will still generate 12V as the car winds down, but the power doesn't go anywhere. What am I missing?

What's the 2000 RPM test?

Thanks

[ForcedFirebird]

Part of race tech is you hold 2000 rpm and hit the kill switch. If the engine doesn't kill, you fail until it does. Since the engine is running at high rpm, there will be enough voltage coming from the big alternator post and will keep feeding your exciter wire keeping the alternator charging until the engine comes to a complete stop. If you don't have a diode, the regulator will need to be replaced every time the engine is cut by the kill switch (instead of ignition off severing the exciter first). Not sure how to explain it other than witnessing people changing alternators at the track because if the back feed. No issue when they have a diode in line.

[kronus]

(if you're building this care to race spec in a particular series with a particular set of rules you should probably read the tech inspection instructions)

[dvallis]

(if you're building this care to race spec in a particular series with a particular set of rules you should probably read the tech inspection instructions)

LoL. Yes. Did not make it to that paragraph yet. My last tech was a while ago.

[dvallis]

Bird

Good catch. Forgot the diode to block back EMF. Will add that in.



Thanks

[dvallis]

Diode installed. Thanks Bird.

[dvallis]

Rob's out of town so I went back to the cluster for wiring.

Looks pretty good with the flat black paint job.



Did a lot of wiring planning before touching a soldering gun. I've got most all of the parts so next time will be building it.

One pain in my a$$ is having to send back the fuel pressure gauge for a rebuild. It comes stock with a white LED backlight. At least they're open to changing it. Also ordered a set of red 158 T10 LED bulbs for the VDO gauges so backlights should all look similar in the end.

[dvallis]

My diff has this connector ....



I found the mating connector on the end of a harness in my scrap wire box



Rebuilt it with new seals and a high temperature loom ....



Installed on the diff, drilled the trunk plate, pulled the sensor lead through ...



.. and attached to the trunk harness. Job done.

[dvallis]

Finishing the cluster fabrication work. This hole for the shift lights was a real pain to cut. Working fiberglass is dirty business.



Fabbing a mounting bracket for the shift lights



And it got WAY too damn hot for working outside. I called it a day.