Non Distructive testing (letting the smoke out)

[Don.F.Broadus at ucm.com]

  I would not worry about the current handling of the transistor that much
since the pulsed current rating is usually 5 times the 
  continuous rating. I would worry about the increased inductive kick when
the injector turns off. The zener diode that clamps this
energy may fail due to a higher voltage spike. The zener would degrade over
time and if it didn't short it would leave the transistor
 unprotected and the transistor would fail shortly after. Sooo beef up the
zener and everything should be fine , IMHO 
 
Don 



> -----Original Message-----
> From:	Putter C [SMTP:Cputter at sed.sun.ac.za]
> Sent:	Tuesday, January 12, 1999 7:34 AM
> To:	'diy_efi at efi332.eng.ohio-state.edu'
> Subject:	RE: Non Distructive testing (letting the smoke out)
> 
> Hi
> 
> I am not a expert on this, but if the ECU uses a current controlled driver
> then it would force a constant current through a injector. This current is
> the independant of the resistance and inductance of the injector. So if
> this is the case then you can put as many injectors in series as possible
> ?! That is if the turn-on current can be achieved by the voltage accross
> each injector.
> 
> So the question is, what kind of driver are the ECU using, is it quasi
> current controlled, open loop or square voltage driven?
> 
> Cheers
> Carlo
> 
> 	-----Original Message-----
> 	From:	Roland Johansson [SMTP:scirocco at mail.bip.net]
> 	Sent:	Tuesday, January 12, 1999 12:02 PM
> 	To:	diy_efi at efi332.eng.ohio-state.edu
> 	Subject:	SV: Non Distructive testing (letting the smoke out)
> 
> 	If you place a finger on the drive transistor/or several and
> 	start it with normal number of injektors, simulate full throttle
> 	for longest on times. The transistor/s should get wam but not
> 	burn your finger in about 10-15 minutes time, try with bigger
> 	number of injektors, if you burn your finger you will be closer
> 	to the limit, probobly over if out temp are high
> 
> 	This is not scientific but could give you a good estimation if
> 	it will work. If the drivers get what you think is to hot, try
> 	add a old computer fan and test again.
> 
> 
> 	Roland Johansson
> 	Scirocco 1,6l TIC -82
> 
> 
> 
> 	> Nother thing, what would be a "safe test" for how long
> 	overloading
> 	> a driver would take.  If I wanted to see if something was
> 	going to
> 	> work on injector drivers, how long in running them would it
> 	take to
> 	> see if they fail?.
> 	>   I have two items to test, running 16 injectors off of a 8
> 	cyl TPI ecm
> 	>   Running 4 P+H injectors where 2 are normally fittted.
> 	> I would figure if the ecm gets only warm to the touch that
> 	would be one
> 	> clue.
> 	> Cheers
> 	> Bruce