z-ya Posted October 16, 2007 Share Posted October 16, 2007 I ordered some resistors from Mouser tonight - hopefully they'll be here by the weekend so I can put them in and experiment. I've got a board under the passenger seat with the rest of the MS on it, so shouldn't be too hard to add them. What resistance/power rating did you order? Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 16, 2007 Author Share Posted October 16, 2007 I have the injectors wired into 2 groups of 3, so I'll put 2 ohms into each group. I ordered 3 x 6.2 ohms to wire in parallel for each which will result in 2 ohms. I went with 25W ceramics which are overkill, but better to err on that side than the reverse. Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 16, 2007 Share Posted October 16, 2007 I always put a single resistor in series with each +12v inejector lead. Five Ohms, 5-10W is usually OK. Run one 6.2 Ohm on each driver output. Two ohms is too low. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 16, 2007 Author Share Posted October 16, 2007 2 ohms in series with a set of three injectors is equivalent to 6 ohms for each injector if wired individually as long as I triple the power rating, which I've done. Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 17, 2007 Share Posted October 17, 2007 Is this how you plan on wiring each bank? Bank1 +12V ---- INJECTOR -----RESISTOR--------------- DRIVER1 +12V ---- INJECTOR -----RESISTOR--------------- DRIVER1 +12V ---- INJECTOR -----RESISTOR--------------- DRIVER1 Bank2 +12V ---- INJECTOR -----RESISTOR--------------- DRIVER2 +12V ---- INJECTOR -----RESISTOR--------------- DRIVER2 +12V ---- INJECTOR -----RESISTOR--------------- DRIVER2 Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 17, 2007 Author Share Posted October 17, 2007 I can't get the editor to stop removing spaces, so please see the attached file wiring.txt. Electrically it's the same as the one you drew, it's just easier to wire up as I have the injectors wired in two parallel banks of 3. Those two wires route under the passenger seat where all the rest of the MS installation resides. wiring.txt Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 17, 2007 Share Posted October 17, 2007 Stock injectors are around 2.4 Ohm So 3 in parallel = 0.8 Ohms. Your three 6 ohm resistors in parallel = 2 ohms 0.8 + 2.0 = 2.8 Ohms If you wire them like this attachment, you will have around 8.4 Ohms for each injector/resistor combination, which should be good. wiring.txt Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 17, 2007 Author Share Posted October 17, 2007 Thanks Pete, this isn't rocket science, but I always feel better when someone else comes to the same conclusion I have an old scope I picked up the other day, and when the probes (voltage only) arrive, I'll measure across the resistor to determine the opening time. In the mean time, any suggestions for where to start with the setting in MS? Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 17, 2007 Share Posted October 17, 2007 You really need a current probe to measure opening time. A voltage probe can measure the pulse width, and also confirm your PWM settings (if you use them). But to measure actual opening time, you need a current probe. Quote Link to comment Share on other sites More sharing options...
datman Posted October 17, 2007 Share Posted October 17, 2007 I only just thought about this today, I have my injectors wired in 2 banks of 3. In parallel, so they must be around .8ohms and it runs fine! how can this be? I would have thought it would have burnt out the drivers. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 17, 2007 Author Share Posted October 17, 2007 I only just thought about this today, I have my injectors wired in 2 banks of 3. In parallel, so they must be around .8ohms and it runs fine! how can this be? I would have thought it would have burnt out the drivers. The PWM settings are used to limit the average current once the injector is fully open. If PWM Current Limit % is set to 20, then that means the driver is effectively off 80% of the time and only on for 20%. This results in the average current being limited which protects the drivers from over heating. If you are saying that you aren't using the PWM settings, then perhaps you have high impedance injectors? Their resistance is higher and hence the PWM function isn't needed (can be left at 100%) without using resistors. Quote Link to comment Share on other sites More sharing options...
datman Posted October 18, 2007 Share Posted October 18, 2007 No I have low ip injectors, my settings are 1ms, 1ms and 30% i'm just surprised it hasn't caused any issues. My max duty cycle is about 50% at WOT ..the injectors are 650cc's Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 18, 2007 Share Posted October 18, 2007 The PWM settings are used to limit the average current once the injector is fully open. If PWM Current Limit % is set to 20, then that means the driver is effectively off 80% of the time and only on for 20%. This results in the average current being limited which protects the drivers from over heating. This is not entirely true. The PWM current limit % is actually the inverse of the current limit. It really should be called "PWM Current", with the limit being removed. At 100%, the current is not limited, and this is the correct setting for low Z injectors with series resistors installed. At 30%, the current is being limited 70% by the PWM circuit (or 30% of the current is being allowed, depending on how you like to look at it). None of the PWM settings have anything to do with injector duty cycle. This is entirely controlled by the required fuel variable, your VE table, and engine load/RPM. datman, your settings are fine. The PWM circuit only allows 30% of the current to flow through your injectors. The PWM circuit protects both the drivers and the injectors. Quote Link to comment Share on other sites More sharing options...
datman Posted October 18, 2007 Share Posted October 18, 2007 Thanks for the clear explanation Pete Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 21, 2007 Author Share Posted October 21, 2007 Today I installed the fuel injector resistors. I changed the PWM current limit to 100% and increased the injector opening time from 1.2 to 1.5 ms. I'm continuing to tweak the VE table as I drive and see areas that are way too rich or lean, but all in all it drives just like before. Of course, without a track I can't test for overheating of the drivers/injectors. Have to wait for next spring I suppose Having tried both approaches now I'd suggest that as long as you have some place to mount the resistors, it's no big deal to do it, and I don't think there is any appreciable performance hit (other than it appears to take a few more tenths of a millisecond for the injectors to open - something that makes no difference on my mostly street driven car.) Quote Link to comment Share on other sites More sharing options...
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