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Old 10-23-2009, 07:12 PM   #1
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Default Quick Question re: Current Limiting Circuit

Is it true that if you are running Hi-Res code you can omit the current limiting circuit during assembly? This being R37, R38, Q14 and Q15...

I remember reading this somewhere and cannot find it.
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Old 10-26-2009, 12:22 PM   #2
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It ignores the PWM current limiting - but I'd leave the overcurrent protection in unless you had a very good reason not to.
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Old 10-26-2009, 12:51 PM   #3
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You can remove the PWM stuff (Q12 & 9, R30-32 & 34-36), but you'll wanna leave the components you mentioned above.



take a look at the circuits in the dotted boxes and read the notes for each.
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Old 10-26-2009, 03:12 PM   #4
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I removed the current limit circuit with my high imp injectors. I don't plan on shortcircuiting the circuit or installing lo imp injectors. Shrug.
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Old 10-26-2009, 04:00 PM   #5
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The current-limit circuit is code-independent. It is purely a function of the voltage drop generated as the injector current sinks to ground through R37 & R38.

Those resistors are 0.05 ohm, and VBE for saturation on a 2N3904 is typically 0.7 to 0.8 volts, so the current limiter is going to operate somewhere in the 15A neighborhood. This will be the case regardless of what kind of injectors you have, what code you're running, whether or not the flyback circuit is present, etc.

There is relatively little downside to having the current-limit circuit in place. Assuming a pair of high-impedance injectors per circuit, that resistor is only causing about 100-120mV drop.
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Old 10-26-2009, 04:15 PM   #6
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I went ahead and installed it. No big deal. Just figured i'd save spots on the heat sink in case curly wanted to install EBC or something later down the road. He can just use the case if he wants that.

Thanks guys.
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Old 10-26-2009, 04:22 PM   #7
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just leave q12 and q9 off like i suggested. if you leave that whole circuit off, you have (4) 270ohm resistors left over to use for your spark pull-up.
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Old 10-26-2009, 04:24 PM   #8
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Quote:
Originally Posted by Braineack View Post
just leave q12 and q9 off like i suggested. if you leave that whole circuit off, you have (4) 270ohm resistors left over to use for your spark pull-up.
Thats the circuit I was confusing with the current limiting circuit. Since i already installed it, its staying.
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