Injector Driver Module

[mrvette]

Say what?  at 6000 rpm.....ign. pulses are 100 hz....and so are injector pulses
in sequential......if batch it's dviided by 4     not the pulse width, but the
rate.....GENE

Don.F.Broadus at ucm.com wrote:
> 
> I'm working on an  injector driving module also. If you are going to fire
> the injectors sequentially, then one injector would be on at a time in the
> firing order sequence (1-8-4-3-6-5-7-2 GM V-8)  If you are going to batch
> fire the injectors
> Then only 4 would be on at a time.  The factory heat sinks on the driver
> transistors are not that big so I doubt that the power dissipated is very
> high.  The duty cycle is a combination of on time and off time, so even at
> 85% the injector would
> Only be on for less than half of the time. The frequency of the injector
> pulse needs to be known, at 6000 rpm the ignition
>  pulses are 400 HZ. I would guess that the injector pulses would be the same
> frequency for sequential firing and half of that for batch firing.  So far
> my bench setup is a batch fire with  2msec on time at idle  and 10 msec at
> wot. Any advice would be appreciated.
> 
> 
> Thanks Don
> 
>         -----Original Message-----
>         From:   Jose  Rodriguez [SMTP:JRodriguez at impcotechnologies.com]
>         Sent:   Thursday, August 06, 1998 11:12 AM
>         To:     DIY_EFI at efi332.eng.ohio-state.edu
>         Subject:        Injector Driver Module
> 
>           I am designing an injector driver module. I would like your input,
> to see if my calculations are correct, particularly in my assumption that
> all eight injectors could be on at the same time, for up to 85% duty cycle.
> Thanks in advance for your answers!
> 
>           The current specs I have are:
> 
>           Eight injectors.
>           Injector coil resistance: 1.5 ohms (it could also be 2.3 ohms)
>           Injector current: 4A peak, 1A hold.
>           Duty cycle: up to 80..85%
>           Operating ambient temp: -40C..125C
>           Operating voltage: 4.5V to 16V.
> 
>           I did some calculations, to estimate how much power would I need
> to dissipate, worst case, ASSUMING ALL EIGHT INJECTORS COULD BE ON, FOR 85%
> OF THE TIME (is this assumption correct?)
> 
>           First, I set Vbatt=14V. In order to have 4A circulating, the
> driver's output voltage would be (14-4*1.5)=8V. Injector's coil voltage =
> (14-8) = 6V.
>           Instantaneous power at the driver: (8V)*(4A) = 32W. Instantaneous
> power through injector's coil: (6V)*(4A) = 24W.
>           The 4A will only circulate for a brief period of time, so average
> power over one cycle will be much less.
> 
>           One amp, sustaining, automatically means (14*1)=14W have to be
> dissipated between the injector driver and the injector coil (100% duty
> cycle).
>           In order to have the 1A sustaining, the driver's output voltage
> would be (14-1*1.5)=12.5V. Injector's voltage =(14-12.5) = 1.5V.
>           Inst. power at driver: (12.5V)*(1A) = 12.5W. Inst. power at
> injector: (1.5V)*(1A) = 1.5W. (total=14W, as predicted).
> 
>           Thus, since the Duty Cycle can be up to 85%, and disregarding the
> initial 4A power peak, and the switching power losses, then the average
> power for each injector driver is (12.5W)*(0.85) = 10.625W. The average
> power for each injector coil is (1.5W)*(0.85)=1.275W.
> 
>           If all 8 injectors could be on 85% of the time, then the maximum
> average power at Vbatt=14V (again, disregarding some power losses) would be
> (8)*(10.625W) = 85W at the injector driver side. Obviously, at 16V the power
> dissipation would be higher (98.6W!).
> 
>           As you can imagine, dissipating 98.6W+ into an under-the-hood
> ambient of 125C, with no expected air flow, is a formidable task. The heat
> sink's surface temperature should not be allowed to go above 150C; that
> would mean the thermal resistance from the heat sink to ambient would be
> (150-125)/98.6 = 0.25C/W. I can not see any feasible heat sink doing that,
> without the need for forced cooling.
> 
> 

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