boxer4 said:Err... Two questions:
1. Are you controlling supplementary fuel injectors or are these solenoids going to bleed boost? Just want to be certain, for issue 2:
2. O2 sensors on startup will read 0V as if it's running really lean. O2 sensors in closed loop/idle can possibly hit fairly low voltage when operating normally. Are you going to inject more fuel or bleed boost in these situations?
Optoisolators are really weak. You may have to use another external transistor (or darlingtons as posted earlier, which is the same thing) to amplify the signal a bit so that enough base current is drawn from the TIP42 to fully turn on the solenoids. But I'm thinking there's another, better way to hook up these power transistors for solenoids without the (expensive, and probably completely unnecessary) optoisolators here. However with the first two questions I don't know yet...
Oh, I guess since people are going off topic here, I'm a DSM'er and a WRX'er... though my faith in 4G63T has diminished due to my DSM's state...
boxer4 said:Confidence is something you get before you fully understand the situation... I see your issue now. The biggest problem is that your LEDs are adjustable brightness, and that complicates things. The Optoisolators is probably the easiest solution after all, since now you're decoupled from current and voltage (not saying there aren't other solutions.)
You will need to have multiple stages of amplification, it looks like the 4N25 can't really sink enough current to fight the pulldown. I'd probably use a secondary transistor - so 3 transistors total. Optoisolator, a GP transistor, say 2N3904, and the (crappy hFE=40) TIP42 all in common-emitter configuration (tip42 being PNP, E=VCC). The Optoisolator has a pullup of about 10K, Collector connects to base of the 2N3904. The 2N3904's collector will pull the TIP42's base down through a 390 ohm resistor, providing the current needed to saturate that transistor.
Sorry for a text description of how to connect but I think this should turn on a typical solenoid at saturation whenever the opto is "dark".
All the ones I've seen are petrol.audioguru said:We have the tiny SMART car in Canada now. It sells for the same price as a "normal small (much bigger) car". I laugh when I see one.
Hero999 said:All the ones I've seen are petrol.
They are supposed have good fuel economy I've heard aroung 60MPG but they're slow and have a top speed of only 85MPH.
I'd rather stick with my bike which will do 120MPH and is just as good on fuel.
audioguru said:Transistors have current gain. A small base current makes a high collector current.
Your injectors are 14 ohms so they need 12V/14 ohms= 857mA of current.
The 1.6k resistor causes a base current of 11.3V/1.6k= 7mA.
But the minimum gain of a TIP42 is only about 20.
The TIP42 amplifies it at least 20 times to only 140ma.
As i said before, use TIP125 PNP darlington transistors that have a minimum current gain of 1000. Then the circuit will be exactly the same as you have now but the injectors will operate at full current. A darlington transistor has two transistors inside connected to boost the current.
It is obvious that the TIP125 darlington transistor has a current gain that is at least 50 times more than the TIP42 transistor.TheEquineFencer said:When looking at specs on a data sheet for something like this what do I need to compare? Just get a TIP125 and a TIP42 sheet and see what the differance is?
From your earlier post you said:audioguru said:It is obvious that the TIP125 darlington transistor has a current gain that is at least 50 times more than the TIP42 transistor.
ericgibbs said:Hi Floyd,
>>If I have it it in a running car the Alternator output will probably be closer to 14.2VDC, that would put it around 1.1A for each injector.
This would be about what I would expect.
>> when I tested the Injector solenoids with a 12V battery with my Fluke, max 10A capability, it went to OL, then recovered to around .400A and dropped to around .014A when the coil was saturated.
These test results do not make any sense for a 14ohm resistance solenoid coil?
You say that the solenoid coil resistance is 14R, is that correct?
If you are not sure, use a ohm meter to measure the solenoid resistance, its value will determine the current it draws.
If you have a datsheet or part number for the solenoid, please post it.
>> I've not ordered any parts yet, I'll wait until I here back from you before I proceed. If you take my drawing and shoot me one with the plan you have in mind I'll give it a shot and see if I can get it to work.
Dont order any components until we can finalise the total current drawn by the 8 solenoids.
>> I was wondering if it would help if I put a resistor in series or parallel with each solenoid coil to change the load on the coils.
If the solenoids are designed to work from 12/14Vdc adding resistors will not help.
>> Yes I know I need a clamping diode for the solenoids.
I was wondering if a MOV might work better. I was thinking it might cause the solenoid to close faster by dropping the inductance spike faster.
I would recommend a clamp diode.
Eric
EDIT:
Important: is the solenoid coil isolated from the solenoid casing?, NOT connected to the solenoid metalwork.
Look at the datasheets for the VNP20N07 and STF20NM50D MOSFET's
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