Postive controlled PWM

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24 Apr 2021 04:11 #48379 by Mahdy
Postive controlled PWM was created by Mahdy
When Mr.Paul is introducing any circuit ID for a solenoid, he tells us to identify it's ID whether it is negative\postive controlled device.

But the question is if it a PWM postive controlled device , is it being controlled derictly by the ECU ? Does the ECU has the ability to pull up to 12V ? (OR) the ECU regulates\pulsates the control side of a relay " negative side" which as a results pulsates the relay's output 12V ending to the device ?

I hope my question is clear

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24 Apr 2021 15:30 - 24 Apr 2021 15:31 #48387 by Tyler
Replied by Tyler on topic Postive controlled PWM
If I understand you correctly, you're wondering if a given ECU can pulse width control the negative side of a relay to positive side control an output (solenoid, motor, whatever). The answer is it's possible on paper, but you're very unlikely to run into such a setup.

Relays, as electronic devices, usually don't respond well to pulse width modulation. :silly: The more their load side contacts are cycled, the more likely they are to develop high resistance, arcing, and eventually stop working correctly.

If the OEM's goal is to modulate magnetic field strength in a circuit AND make it out of the manufacturers warranty, they're much more likely to use a true positive side pulse width driver to make the magic happen.

Did that answer your question?
Last edit: 24 Apr 2021 15:31 by Tyler. Reason: Spes-a-ficity

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24 Apr 2021 17:02 #48389 by Mahdy
Replied by Mahdy on topic Postive controlled PWM
I'm speaking generally , not only relays .
So let's say can we control purge solenoid , fuel pump , fan motor by pulsing and controlling the postive side ?

Do ECUs have the ability to pull the circuit up by PWM ?

I know that most of the PWM controlled circuits are being pulsated to negative to be turned on , but can it be controlled by ordering the postive side to turn on and off ?

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24 Apr 2021 18:36 #48394 by Matt T
Replied by Matt T on topic Postive controlled PWM

If I understand you correctly, you're wondering if a given ECU can pulse width control the negative side of a relay to positive side control an output (solenoid, motor, whatever). The answer is it's possible on paper, but you're very unlikely to run into such a setup.

Relays, as electronic devices, usually don't respond well to pulse width modulation. :silly: The more their load side contacts are cycled, the more likely they are to develop high resistance, arcing, and eventually stop working correctly.


Relays are electro-mechanical devices. Any electronics inside them are there for suppression. Physically moving the contacts takes time. A few milliseconds for both on and off. That would make for a very low PWM frequency which wouldn't be much good for motor or valve control.

Another issue is relays have a rated switching cycle life in the hundreds of thousands. That would get eaten up quickly at say 10Hz. Ran the numbers on 500,000 cycles at 10Hz and it comes out at just under 14 hours. Wouldn't even make it to the first oil change :lol:

That said it is possible to implement PWM control using solid state relays but I haven't personally seen it done in an automotive application. Or at least not obviously. Something like a GM blower motor control module may just be a solid state relay in a $100 box.

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24 Apr 2021 23:13 #48402 by Ben
Replied by Ben on topic Re:Postive controlled PWM
I think your asking if it's possible to pwm control the power side or only the ground side of a device answer is yes a (we will call it a purge valve) could be pwm controlled via power or ground. but we don't call these pull up or pull down just power side or ground side switched. the term pull up and pull down term is used when referring to sensor circuit design

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