My 87 toyota supra hardware build

[Fred]

A filter cap will help your wiring not sag during peaks current, though 45uF isn't much, I guess it's quite a lot for the time frame we're talking about. Keep experimenting until you nail it.

What is the primary resistance of the coils? Normal is 0.5 to 1.5 ohms. You can determine the current/voltage drop from knowing that if you know the resistor. 0.1ohm or lower should cause relatively little influence.

I'm suspicious of your claims of dwell time mismatch. Unless there is a serious bug, but I doubt it. You can flatten the table to rule out BRV influence. You also need to know that you didn't configure fixed dwell or RPM dwell.

Let us know what you figure out with respect to your inconsistent results.

[via]

I am completely unable to reproduce the dwell time being way off. Lets just say I was doing something stupid or something. Going with higher and higher capacitance helped make everything even out, and it more or less matches between straight battery and crappy power supply. My current curve puts a point at 12.3 V and 4.1 ms.

Does this suggest I should use higher capacitance on my main power supplies too?

Resistance across the primary coil is about 0.4 ohms, and this time around I was using a .25 ohm resistor. I don't have any .1 ohm resistors, I was using a small stretch of 30 ga wire that was close to about .1 ohms last night. I guess I should go back to a small stretch of the 30 ga, even smaller perhaps, and recheck the things.

[Fred]

0.4 indicates pretty gutsy coils. Yeah, I'd use a small length of light wire, or the whole length of normal thickish (16 or 18 or 20ga?) wire (around 3 feet or so?). Ideally rig it up as you will have it in the car and measure it like that. 0.25 is going to have a huge influence on a 0.4 coil, you'll end up with over 1/3 of the voltage being lost to the resistor. Or conversely less than 2/3 to the coil.

12v - 1v of ignitor
11v * 0.6 = 6.6V @ the coil = crap.

Plus the inductance of the resistor will play into things too.

Capacitance at the coil on the supply line is typically used by OEMs, they're automotively rated and usually about 0.5uF in value. Mostly for noise suppression I would think. The main thing you need on your actual setup is decent thickish wire for the round trip from battery to coil to ignitor and back to ground. Then you get the majority of the energy spent where you need it: the coil.

Also just FYI, the peak current on those coils is going to be very high, up around 30A at the end of dwell if you allow it to dwell that long. You might find you can/should get away with much shorter dwell than optimal with these. There is no harm in going lower than optimal except reducing voltage at the plug, and reducing energy in the spark. You'd be surprised how bad of an ignition you can get away with, my old MS setup wouldn't even fire a timing light, but lit off 18psi of boost just fine. It was poorly setup per bad/wrong recommendations from that crew.

If possible, verify the scale of your current measurements to see where it plateaus? Maybe the flat bit is the current limit in the ignitor? Hard to say.

Fred.

[via]

Ok. I was talking to someone about it, is there any real reason to need a resistor? Could I not just measure the voltage across the coil, seeing as I know its resistance, to determine the charging shape?

Anyway, I'll try with the length of 18 ga.

None of this is remotely in the car. I started building the enclosure for the whole thing today, and maybe I'll get to installing it tomorrow. I don't see me finishing that this weekend, although I guess I might be able to.

Edit: repeated with a length of wire, 12.3 V is back to about 3.8 ms like last night, so I'll stick with 3.5 to err on the side of less dwell.

[Fred]

No, the voltage across the coil is quite likely always 12.2V or whatever. The current changes because the state of the inductive field in the coil changes over time once connected. At first the coil tries to block current flow, then as it charges, it works its way back to its DC state of 0.4ohm. At all times you have battery minus ignitor applied to it.

Erring on the side of caution is OK if you're actually saturating the coil. If that's a current limit, then you're probably going weaker than you need to. However, as discussed, it'll probably work quite well regardless.

Fred.

[via]

I got the injector drivers/fuel pump driver working, and I've spent most of the day building an enclosure and making things neater. Part of doing that involved setting up a nice big heat sink for the injector drivers which was using a right angle bracket and bolted to the perfboard. I have discovered, however, that apparently the drain on the driver is connected to the heat sink fin. I can't understand why it would be designed this way, it makes it impossible to use a heat sink, or even let fins touch.

The driver is a bts149. Is there an easy way around this I'm not seeing? Do you think I even need a heat sink? They're rated to 18 A, and I imagine they'll have to work with around 1-2 A.

[Fred]

Very normal, dude! You need to use proper mounting hardware. Get yourself a bag of grey (usually) silicone insulator pads, and an equal number of correct insulating washers. Then put it back together properly and be happy. Without the silicone pad you'd have had shitty conductivity anyway. And now for the really bad news: they run cold. 18 milli ohms means a lot of current produces almost no heat. It's nice to sink them anyway, though, I guess.

[via]

Yeah, I should have researched this a bit more. I didn't realize that was typical of mosfets. I'll order some mounting hardware and just not use a heatsink until it arrives.

[Fred]

Check the regulators, too, they're also connected. Almost every package like that is. That's why the thermal conductivity to the tab is good ;-)

[via]

I remounted the fets, got everything working, and completed my enclosure. At this point I'd like to think the ecu itself is more or less ready for the car.

http://imgur.com/a/U6pop

Tomorrow I'll start wiring up the sensors in the car. If I finish tomorrow (unlikely) I might be able to get to the point where I can do the pre-start testing.