u/Sexual_Congressman

Take a mosfet like FDP55N06 whose spec sheet I just happened to have opened. Its max avalanche pulse rating is 480mJ. The only thing I can think of is that's the amount of energy the device is guaranteed to survive if turnt off while conducting an inductive load at the specified reference temp, usually 25°C.

So e.g. if a FDP55N06 is acting as a ground switch for a stalled motor and it's shut off while conducting 10A, the source to drain voltage will increase to say 60V, which means its instantaneous dissipation is 60*10 = 600W or 600k mJ per second. Thus, a 480mJ avalanche pulse rating would imply as long as the inductance is low enough that it takes no more than 0.0008s (800μs, if I'm doing the math in my head right) to stop conducting, the device can survive the kickback without the need for external freewheel diodes or snubber circuits (as long as it can cool back down to the reference temp before doing it again).

Of course in reality, the instantaneous dissipation would immediately begin to decrease, but there's probably a simple function to get solve for a max current given the inductance (or like in my example's case, the min inductance given the starting current).

When a +1V DC source is connected to one end of an uncharged 1Ω 1mH electromagnetic coil and 0V/ground to the other, after 1ms the voltage drop from resistance heating will be about ~680mV while the voltage drop from its inductance will be ~320mV, and about 680mA of current will be flowing, so if my simplification is right, the cemf at t=1ms would be -320mV, which is "up" from the -1000mV it was at t=0.

I've been puzzled for years trying to identify this DIP-20 IC used in my car's wiper control module because it was coated in some kind of red translucent enamel that made it impossible to make out anything more than "NEC Japan". Yesterday I had the idea to just dunk the PCB in a jar of acetone and sure enough, the red washed off and if you Google "nec swf918616", you can see exactly what it looks like in the first and only relevant English result (on eBay).

Unlike most 20+ year old esoteric automotive ICs, this one seems to have tons of Google hits, but it's all Japanese, Russian, and Indonesian links, and after spending probably 30 minutes loading 30 different pages, I still have no idea what it's supposed to do.

By the way, the wiper logic is extremely simple: the switch has OFF, INT1, INT2, INT3, LO, HI, WASH, and ONCE (which is identical to LO/WASH but does a single wipe) settings, and each one corresponds to a particular resistance value from ~91Ω for WASH to ~3k for INT1. The HI setting also grounds a relay that causes the wiper motor to spin about 25% faster than the other settings while also bypassing the timing functions that swf918616 IC and the other still unidentified DIP-8 IC ("M88AT", definitely not a 555) accomplish.

Most of power used by the PCM itself is in the power transistor gate/base drivers, which doesn't require much, almost certainly less than 1A in total with everything on. E.g. O2S2 heater can require several amps when cold, but the PCM itself will only drawing a few milliamps itself to PWM the driver. The heater coil power supply actually comes from the EGR/EMISS fuse.

The only two components with unknown to me power supplies are the fuel pump relay coil (circuit 465, accessible via the "fuel probe" hole in the fuse side of the IPJB) and the EVO solenoid, and it would be incredibly stupid to power those components using the single #22 PCM-I wire when PCM-B has two #18 wires. My guess is "vehicle shutdown" is determined by a combination of criteria, including the loss of crankshaft sensor and cylinder 4 ICM pulses, so after that happens, the PCM watches the PCM-I circuit voltage and initiates a new ignition cycle (turning FPUMP relay on, firing plugs, etc) only when it comes to within a few millivolts of the PCM-B reading. I'm also guessing there is more info on its purpose buried somewhere in the FSM error code docs.

Anyway the reason I'm curious is I've been seeing another highly modified gen 2 running around town lately and it's got me concerned how easy these cars are to steal. Even a 99 with RKE, the immobilizer can be bypassed in literally seconds without any extra equipment, so I'm thinking about creating my own security system. If I'm right about the PCM-I fuse just being a redundant way for the PCM to determine ignition switch position, it should be possible to put a switch on the PCM-I wire to interrupt the circuit unless a Bluetooth device is in range (i.e. how modern cars do it), which would not only be as effective as modern systems, I think it'd actually be safer, since it's trivial to design a latching electronic switch, especially if that circuit doesn't carry significant current. I'd much rather the car continue to run at 100% even if the key is tossed out the window, rather than going into limp mode. Yeah, someone as big of a nerd as me would know how to beat my little system but in my experience real life nerds have better things to do than try to steal 30 year old hoopties.

I'm betting within seconds of hitting submit I'll find the errror code describing PCM-I's entire function and that'll still be longer than it takes to defeat the joke of the OEM gen 2 Saturn immobilizer.

As you know, the rear window regulators of the sedans used this shitty nylon rectangular guide to keep the arm aligned in the track. Inevitably, the nylon will degrade and the stress fracture that was created when the guide was pressed on will fail. The arm will pop out of the guide and the window will have to be manually jiggled until the arm happens to pop back in, assuming it always breaks in such a way. Of the 20 or so S-series rear windows, 19 of them failed in this way and the one that didn't still had a broken guide, it just wasn't broken in a way that disabled the ability to reliably open and close the window. Ironically, the motor is fried and I'm going to spend a day dissecting it but that's for another time!

So what exactly is the fix? A M12 zinc washer (lowes part number 755850), a id=5/15 od=5/8 rubber grommet (lowes part number 139355), and a 1/16 x 13/32 x 1 nylon washer (lowes part number 881539). The way it works is simple. Put a grommet in a zinc washer and push that on the regulator ball stud thing until it just pokes through. You'll probably need some of the grease from the regulator to get it to go on.

The tracks are about 22mm tall, and you'll have to use a file or something to get rid of the burs at the end opposite of the hinge. With a file or 100 grit sandpaper, file down a single edge of the nylon washer until it can fit. It's extremely important that the nylon washer doesn't spin. Next, I cut the ends of some nylon zip ties off in the shape of a ~2mmx2mm quare and superglued them to the outer edges of the nylon washer, parallel to the filed down edge. So imagine the middle of the filed edge is at 12 oclock, the first "nylon bump" is at 3 oclock, and the second nylon bump is at 9 oclock. 6 oclock is rounded. Lastly, superglue a circular pad of nylon webbing like from a backpack strap or old seat belt to the end of the regulator, such that it covers the the flat part perfectly. Not sure if all the regulator designs use a ball stud with a flat end, but the ones from 1996-2002 definitely do.

So it should take some finagling but eventually you should be able to get the arm in the track. The rubber grommet should not be contacting the track and the only metal on metal contact should be at either the top or bottom of the zinc washer. I had intended to coat my zinc washer with ptfe thread sealant but when I tested it I found it completely unnecessary.

I probably spent 2 hours today just sliding that thing trying to get it to fail and I just couldn't. Even if the ball stud eventually pops out of the nylon washer, the worst that can happen is it'll screech and have slightly more resistance. There's just no way it's going to be able to pop out of the rubber grommet on its own. Also, the only force on the super glued bumps are them getting compressed, so I doubt those will fail, but even if they do, I think the only effect it would have is slightly increased resistance/noise and a slightly higher chance for the ball stud to pop out of the nylon washer.

Guess I should have given it a few more days to make sure it handles multiple thermal cycles and storms... but I wanted to write it down before I inevitably lose the receipts and packages for those washers.