PWM or switch?

[RedMist]

I've a ST205 WRC water injector and although it appears to be a PWM injector it only has one lightweight feed with no return.
As such I wondered if I could test to see if it is indeed a PWM injector or just a simple 12v switch.
Also a recommendation in regards to pressure (or pump) to run to the injector would be appreciated.

[mr30%jr]

ok firstly you know what pwm is right....

pulse width modulation... its a sine wave amplified in big current forms through uses of transistors then can be tranformed due to its a/c nature

i dont know much about 205s or what your talking about but it sounds like its just a water injector you can run an injector solenoid on pulse or constant if you like. depending on its duty cycle otherwise it might burn out... prolly just confused you more than help

dont really get wat you mean about pwm

[RedMist]

ok firstly you know what pwm is right....

pulse width modulation... its a sine wave amplified in big current forms through uses of transistors then can be tranformed due to its a/c nature

i dont know much about 205s or what your talking about but it sounds like its just a water injector you can run an injector solenoid on pulse or constant if you like. depending on its duty cycle otherwise it might burn out... prolly just confused you more than help

dont really get wat you mean about pwm

Yep, know what PWM is. Water injectors can be one of two types. PWM or simple valve switch. My Link G3 can either use its second injector trigger for PWM or a general purpose switch for a simple 12 volt supply. However.... if I use a 12 v supply to an injector that I have very little hope of ever replacing, its fused and fugged. and if I use a PWM signal for a switch it probably wont open.
Can I simply measure resistance across the terminals? Open = Switch?

[Grrrrrrr!]

Measure the resistance of the injector, if its low then it is going to be PWM for sure.

Bear in mind that I=V/R and Pwr=RxI^2. The water will provide some cooling of course, but a bit of common sense would suggest that anything over 80 Ohm (= 1.8Watts) is definately switched. Anything under 20Ohm (7.2W) would be PWM for sure.

If its in between then I would suggest hookng it up to a pwm output and cranking the pulse width up till you get it flowing properly. If the pulse is too narrow it wont open, and it wont get hot fast either.
If it takes a pulse width of 80% or more to get it opening properly then you would probably be safe to assume its good to go with a switch output.

Oh, and if it measures open circuit across the injector its already fugged

HTH

[Stealer Of Souls]

Another tidbit...
Switched or PWM by design, it should still work with PWM, but might have a poor range of operation. So instead of 10-100%, it might only do 50-100%.

After impedance I would try a pwm setup with a low duty cycle and see if it works.

Electrically I can see no reason that a PWM input would do any permanent damage to a switched design injector.

[sergei]

BTW PWM is not a sine wave . sine wave looks like this:

PWM looks like this:

[mr30%jr]

sorry its an emulation. but doing lots of steping. its sawtooth then

$&#$% know it alls why didnt you answer then.

its not called switch its called constant current or pulse where the $&#$% does pwm come into it?

dont see why an injector would you PWM its either open or not... pwm is like a wave not a step

[sergei]

As far as I understood the question, it was about the injector being constantly on or controlled by duty cycle of a square wave (PWM - Pulse Width modulation). Technically you can have saw tooth PWM or even other wave form but there is no point (except peak and hold) for the injector. Peak and hold works on the principle that it is required a lot more current to open injector than to hold it open (this technique is used on a lot of solenoids, infact I can remember about 12 years ago fixing a double tape-deck of my own which had peak and hold on solenoid which was moving the head to the tape, the actual problem was that it was not peaking - due to faulty capacitor). Peak and hold is also square wave form with a spike in the beginning.

[sergei]

As said above the higher the impedance the higher likeness of the injector being constant on type (due to higher inductance = longer ""magnetise" time). Also the mechanics inside play a big role on the function.
Just measure resistance and use apropriate resistor and see how it works on PWM source (you can build one under $10 from a 555 and a CMOS transistor). I found that cold start injectors do not work really well on PWM above 50Hz. At that frequency anything below 10% or above 90% does not result in much effect. This aproximates to ~20ms of dead time. With WI water ratio vs air is not really important as long as it is arround certain level (as it does not combust).

[Mr Revhead]

dont forget this

[fivebob]

pwm is like a wave not a step

Nope it's a step, the "W" meaning the width of the step. i.e. Pulse Width Modulation, like all injectors, boost control shuttle valves, some idle speed controls and a lot of other automotive control devices. All use square wave, pulse width modulated, control signals.

[RedMist]

Measures 3.4 ohms taking into account the loss from my elcheapo DSE MM.

[fivebob]

Measures 3.4 ohms taking into account the loss from my elcheapo DSE MM.

PWM then, but I'd suspect you will have to run it thrugh a ballast resistor as that's going to give about 4 amps draw.

[sergei]

Measures 3.4 ohms taking into account the loss from my elcheapo DSE MM.

PWM then, but I'd suspect you will have to run it thrugh a ballast resistor as that's going to give about 4 amps draw.

That is the same as CS injector and they do not run PWM.

[fivebob]

Measures 3.4 ohms taking into account the loss from my elcheapo DSE MM.

PWM then, but I'd suspect you will have to run it thrugh a ballast resistor as that's going to give about 4 amps draw.

That is the same as CS injector and they do not run PWM.

true, but the CS injector only runs at start up and through a timed circuit or for around 3 secs when running through the STJ pin on the ECU. It has no need to regulate flow, unlike a water injection system.

[mr30%jr]

contriversey gets answers on toyspeed.. there are lots of clever people on here you just have to abuse them and be wrong to get the right answer

[mr30%jr]

Measures 3.4 ohms taking into account the loss from my elcheapo DSE MM.

PWM then, but I'd suspect you will have to run it thrugh a ballast resistor as that's going to give about 4 amps draw.

That is the same as CS injector and they do not run PWM.

true, but the CS injector only runs at start up and through a timed circuit or for around 3 secs when running through the STJ pin on the ECU. It has no need to regulate flow, unlike a water injection system.

further more most coldstard just ran like this

STA signal (from barrel)> THERMO SWITCH > INJECTOR so if the motor water is cold and your cranking sta it will inject

[sergei]

further more most coldstard just ran like this

STA signal (from barrel)> THERMO SWITCH > INJECTOR so if the motor water is cold and your cranking sta it will inject

You are right, today I was pulling my ST165 engine loom apart and it was exactly like that (no wires from ECU going to coldstart injector).

[mr30%jr]

this is true up untill the 20v days where its ditched alltogether