Separating the power and signal grounds on a V3 board

[calkai]

Need to discuss one point about Battery Voltage Sensing.

In the above photo, the Battery Vol Sensing circuit is attached on the input of U5, but at this point the voltage had been regulated by before circuit, right?

May the Battery Voltage not be correctly reflected?

Would the injector and ignition be affected?

[gearhead]

Group,

I have just finished a similar modification. When I build a V3 board, I do not install the current limiting nor the PWM circuitry, so this modification to take to power ground off the board is simplified substantially. I use a PWM valve and needed to take this to the power ground as well. I will document and photo my board in my next post. Another thing to consider is that all outputs should have a ground separate from the inputs. This goes for the spark outputs as well. To do this requires pulling the top leg of the LED drive transistors and routing it to the power ground as well. Ideally, this sould be a separate ground from the injection power gnd, but it should be kept off the signal ground (inputs).

Gearhead

[johu]

I modified my 3.0 board to separate TIP125's, TIP42's and current sense resistors as shown on Dave's post. I also added resistor and capacitor to VBatt. Board seems to work when testing with JimStim, but I'm bit worried if Q14 and Q15 (2N3904) are really supposed to get too hot to touch? Thermometer I had shows only up to 45C and these are more than that. Heat is depending on simulated RPM as if I drop it down to 1000 or so they get merely warm. Since I assembled board with these changes from beginning can't say if there's something else that's wrong or if incorrect settings on software side might cause it.

[gearhead]

Why do you want to limit current to 14A anyway? I have never used those. Short the power resistors (R37 and R38) and remove Q14 and Q15.

Gearhead

[Fred]

Mosfets are pretty rugged, I ran mine without protection for a few weeks with no hassles, though i do have the stuff setup to use that feature.

[gearhead]

Thinking about this a bit more. Are you saying that it was getting warm on the bench or in the car? If on the bench, I have no idea how that could happen. If in the car, I agree with Fred in that the FETs are rugged. I have never installed the current limiting (it was not there on the V2.2) and have had no FET failures in 4 years of running. Keep in mind that I was using one FET to drive 4 injectors for 3 and a half years. It was only recently that I rewired to run 2 then 4 injection outputs.

Gearhead

[johu]

Q14 and Q15 get hot in bench with just JimStim v1.4 connected. Haven't tried in car yet so only JimStim as load, no injectors.

Injectors I have are stock on 6.1L Chryslers. Based on information from web they should be Siemens DEKA IV, 30 lb with 43.5 psi at 100% duty, 35 lb with 58 psi at 100% duty. Both Corvette filter+regulator I'm using and stock Chrysler unit put out 58 psi. Injectors are high impedance, 12.8 ohm.

[jbelanger]

The only way I can see Q14 and Q15 get warm is if R37 and R38 are not there and there isn't a jumper replacing them. But that would also warm up R15 and R20. You also would need a power supply that can supply a good size current to heat them up.

Jean

[johu]

It seems R15 and R20 get hot as Jean suspected. Replacing R37 and R38 with jumpers has no effect on Q14 and Q15, they're still hot. After I removed Q14 and Q15 I noticed that now R31 and R35 get hot. Next I took off Q10 and Q13. Since now R31 and R35 go nowhere they're no longer generating heat.

[johu]

Ok, it seems to work now. Thanks guys!

I put Q10, Q13, Q14 and Q15 back as well as R37 and R38. No more hot components, not even warm.

Reason for my troubles? I took +12V and GND for power side of MS from JimStim connector X4 as it had easy to use screw terminals. I incorrectly assumed this would be connected parallel to X5.

As for power consumption my PSU gives out 11.7V (2A max) and load with wrong setup was 0,8A. Now when I have it wired properly it's 0,33A (was 0,25A with R37+R38 jumpered and Q10, Q13, Q14, Q15 removed).