Megasquirt MS3 Pro with Low Impedance Injectors
08-15-13, 11:11 AM
#4
Hey Aaron I have a puzzling question. The MS3 Pro has 3 high current (5 amp) general purpose outputs - 2 can be reconfigured as additional injector drivers. The microsquirt(I'm guessing uses the same drivers) states this:
"The fuel injector drives will max out at 5 amps each, enough to drive one low-impedance (or 4 high-impedance) injector per bank. To get everything to fit without lots of heat sinking, MicroSquirt uses the ST VND5N07 from STMicroelectronics to drive the injectors. This is not a 'peak and hold' driver, but it does clamp the current at 5 amps, so it can be used with one low-impedance injector per bank, however the close time may be a tad higher (or you can use resistors)."
On my car |I have 2 high impedance primaries, and 2 low impedance secondaries(1680cc). Could I drive these injectors as is? I really don't want to fork out more cash for a driver box. Thanks!!!
"The fuel injector drives will max out at 5 amps each, enough to drive one low-impedance (or 4 high-impedance) injector per bank. To get everything to fit without lots of heat sinking, MicroSquirt uses the ST VND5N07 from STMicroelectronics to drive the injectors. This is not a 'peak and hold' driver, but it does clamp the current at 5 amps, so it can be used with one low-impedance injector per bank, however the close time may be a tad higher (or you can use resistors)."
On my car |I have 2 high impedance primaries, and 2 low impedance secondaries(1680cc). Could I drive these injectors as is? I really don't want to fork out more cash for a driver box. Thanks!!!
08-15-13, 12:41 PM
#5
The MS3-Pro's high current outputs are essentially the same thing as the injector outputs. From the MS3-Pro documentation:
The MS3-Pro documentation seems to be pretty clear that they do not want you running low-Z injectors directly.
Why not just run your 1680's with a resistor? I know it isn't ideal, but neither is running low impedance injectors on a circuit that isn't designed for it.
EDIT: I just looked up the Bosch 1680cc injector and it looks like they have a resistance of 4.5-ohm. At 13.5V they would require 3A to drive them. This isn't as low impedance as I expected, so you might be alright running them. I still wouldn't though (personally I would ditch them for new 205lb Bosch EV14 injectors).
3.3.3 High current outputs
These are ground switched outputs with a maximum current of 5 amps, just like the injector output channels (in fact, it’s the same transistor type).
These are ground switched outputs with a maximum current of 5 amps, just like the injector output channels (in fact, it’s the same transistor type).
3.3.1 Injector outputs
The injector outputs are limited to 5 amps per channel, with thermal shutdown protection. These can drive one or two high impedance injectors on each output, but will not directly run low impedance injectors.
The injector outputs are limited to 5 amps per channel, with thermal shutdown protection. These can drive one or two high impedance injectors on each output, but will not directly run low impedance injectors.
EDIT: I just looked up the Bosch 1680cc injector and it looks like they have a resistance of 4.5-ohm. At 13.5V they would require 3A to drive them. This isn't as low impedance as I expected, so you might be alright running them. I still wouldn't though (personally I would ditch them for new 205lb Bosch EV14 injectors).
08-16-13, 09:35 AM
#6
Engine, Not Motor
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The outputs of the MS3-Pro are not designed to run low impedance injectors. Even though they have enough current on paper, they can't handle the initial spike (as the inductor charges up) nor do they have the flyback circuit to handle the turn off spike.
Run them with some 6 ohm resistors if you don't want to go for a driver.
FYI, all MS3x injector outputs are high impedance only.
Run them with some 6 ohm resistors if you don't want to go for a driver.
FYI, all MS3x injector outputs are high impedance only.
08-16-13, 11:35 AM
#7
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If they are 4.5 ohm injectors, you should be able to run them no problem. The real problem with the drivers is that if you try to run a load of 5 amps on them for sustained periods of time, they get hot enough to desolder nearby parts on the board, and the fact that we have 13 of them instead of 2 on a MicroSquirt makes the heat buildup a much bigger potential problem.
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01-04-14, 06:53 PM
#8
Gen 2 Raced Hard NA 13B
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Low Impedance Injectors PRO 3
Hi All
I ran my last season of racing using the low impedance injectors with the stock Mazda resistor pack. The results were 100%, no problems, no issues. Tuning for idle and running up to 75% duty cycle on the injectors with not a problem.
I think the MS3 Pro works great and easy to program. I am still working on small changes to the maps for each race track that I run at (6 In total). Also working on small adjustments to the throttle enrichment.
Thanks for the support.
RX7RACER
I ran my last season of racing using the low impedance injectors with the stock Mazda resistor pack. The results were 100%, no problems, no issues. Tuning for idle and running up to 75% duty cycle on the injectors with not a problem.
I think the MS3 Pro works great and easy to program. I am still working on small changes to the maps for each race track that I run at (6 In total). Also working on small adjustments to the throttle enrichment.
Thanks for the support.
RX7RACER
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