Quick Question re: Current Limiting Circuit
#1
Elite Member
Thread Starter
iTrader: (8)
Join Date: Aug 2007
Location: Bellingham, Wa
Posts: 2,712
Total Cats: 4
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.
I remember reading this somewhere and cannot find it.
#3
Boost Czar
iTrader: (62)
Join Date: May 2005
Location: Chantilly, VA
Posts: 79,493
Total Cats: 4,080
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.
take a look at the circuits in the dotted boxes and read the notes for each.
#5
Boost Pope
iTrader: (8)
Join Date: Sep 2005
Location: Chicago. (The less-murder part.)
Posts: 33,022
Total Cats: 6,590
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.
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.
#6
Elite Member
Thread Starter
iTrader: (8)
Join Date: Aug 2007
Location: Bellingham, Wa
Posts: 2,712
Total Cats: 4
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.
Thanks guys.
Thread
Thread Starter
Forum
Replies
Last Post