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oldcorollas Forums Junkie Location: Kita-Ku, Sapporo, Japan Registered: January 2003	Re: RX7 Injectors Fri, 23 April 2004 11:49 3T-GTE wrote on Fri, 23 April 2004 19:37 Hi Stewart... This may be a little off-topic, but very relevant to my current project....seeing you know a "little" about the MegaSquirt ... Can you tell me if there is any disadvantage to running in line resistors vs using the Flyback board that can handle the low impedance?? Cheers, 3T-GTE http://www.megasquirt.info/index.html then click on "Injectors and Fuel Supply" on LHS menu. looks like you can use up to 4 2.4ohm injectors using only PWM in the MS. more than 4 injectors requires resistors or flyback board (to be safe) apparently injuector opening and closing is a little faster with the flyback board installed, but running resistors does not make it any worse than if you were using high impedance injectors anyway! the only disadvantage to running resistors with big injectors (relative to the motor size, ie 550's on a 2L) is that the minimum opening time may not be small enough to give you good resolution at idle speeds. flyback board is only $35, and 4 resistors is about $25-30... i'd be happy to run either, but i think i'd prefer to run the flyback board... Cya, Stewart Quote: Pulse Width Modulation Injectors are either high impedance or low impedance. High impedance injectors (usually about 12-16 ohms) can take a 12 supply directly, without a form of current control. Low impedance injectors (generally below 3 ohms) require some form of current limiting. With MegaSquirt, you can use resistors to limit current, or you can use Pulse Width Modulation (PWM), which is a software solution built in to MegaSquirt. PWM works by switching the 12 volt ground to the injector on and off very rapidly (in about 0.000059 seconds!). The ratio of the "on" time to the "off" time determines the current through the injectors. However, the easiest way to think of the PWM% is as a percentage of the supply voltage, so 50% PWM on a 14 volt supply becomes effectively 7 volts on average, 28% would be 4 volts, etc. Remember that pulse width and PWM% are two different things. Pulse width is the total duration of the signal whereas PWM% is the ratio of 'on-time' to 'off-time' within the pulse. So in the above illustration, the pulse width for both is the same, but the PWM% for the first is 50%, while for the second it is 25%. The PWM% you will be able to use depends on the flyback circuit you have. Version 2.2 hardware generally requires about 55% to 75% PWM. Often the engine will run with lower values, but will not have enough voltage to re-start. Note that using embedded code version 2.986 or higher will disable PWM during cranking, allowing somewhat lower PWM% values. The FlyBack Board allows you to lower the PWM% dramatically, generally to 30% or less. It also helps close the injectors faster. With better flyback control, you can reduce injector opening times (recall that the injector opening time is really the sum of the opening and closing times), and increase the duration of the 'controllable' part of the pulse width (i.e. after the opening time), To exceed the recommended number of injectors (see below) either requires resistors in series with each injector or a modified flyback setup. [Report message to a moderator]

	Subject	Poster	Date
	RX7 Injectors	3T-GTE	Thu, 22 April 2004 04:30
	Re: RX7 Injectors	SRacin	Thu, 22 April 2004 06:53
	Re: RX7 Injectors	TurboRA28	Thu, 22 April 2004 07:27
	Re: RX7 Injectors	Chris Davey	Thu, 22 April 2004 11:06
	Re: RX7 Injectors	Norbie	Fri, 23 April 2004 01:26
	Re: RX7 Injectors	oldcorollas	Fri, 23 April 2004 08:05
	Re: RX7 Injectors	3T-GTE	Fri, 23 April 2004 09:37
	Re: RX7 Injectors	oldcorollas	Fri, 23 April 2004 11:49
	Re: RX7 Injectors	oldcorollas	Fri, 23 April 2004 16:06
	Re: RX7 Injectors	3T-GTE	Sun, 25 April 2004 23:19
	Re: RX7 Injectors	chris philpott	Thu, 22 April 2004 13:03
	Re: RX7 Injectors	3T-GTE	Fri, 23 April 2004 00:01

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