Maker Pro
Maker Pro

Solenoid drive current limiting.

Tonymura

Jul 25, 2021
30
Joined
Jul 25, 2021
Messages
30
Hi all
Ive been experimenting around using this 555 circuit to drive a pressure control solenoid for my car in a bid to see if i can control the opening and closing of the pressure ports.
From what i have measured with my meter under my car i found that the following values to be at 9khz frequency and that the duty cycle was showing me to be at 90% i assume this would be the solenoid valve when fully in the open position
I am trying to limit the current flow to a value to that no more than 120ma to be on the safe side so that it will not burn out.
Using the 555 timer schematic circuit to drive the Mosfet
I have worked out in practical terms but not fully understanding if this will be correct values of the resistors? or if there should be other components in this circuit to better the control of current flow.
The solenoid resistance when measured with my meter shows a value of 5 ohms but i have not worked out the value of the inductance of the coil.
Just wanting to know is this the best way to control the limit of the current flow through the circuit to the solenoid?
Any suggestions would greatly appreciate your help.
Thank you in advance.
 

Attachments

  • 555 timer S5 solinoid.jpg
    555 timer S5 solinoid.jpg
    30 KB · Views: 6

Bluejets

Oct 5, 2014
5,995
Joined
Oct 5, 2014
Messages
5,995
Solenoid characteristics would need to have 9Khz as it's design frequency for correct impedance values and hense current draw.
 

crutschow

May 7, 2021
520
Joined
May 7, 2021
Messages
520
Is this a new solenoid or one already in the car?

What "pressure ports" are you trying to control?
 

Tonymura

Jul 25, 2021
30
Joined
Jul 25, 2021
Messages
30
This is a spare solenoid in which i am testing.
I took my reading while my car was running as i backed probed the wiring harness to get these values of 9Khz with a the duty cycle of 90%
I am told by a transmission specialist in the USA that i should be hearing a buzzing sound as i adjust the duty cycle up and down while applying a pressure of 45psi immersed in transmission fluid and has warned me to be vary cautious as to not apply to much current or else this unit will burn out.
There is an adjusting screw at the back that needs to be set at this pressure or else there will be hard shifting while driving.
( please note i did not measure while the car was running what the voltage across these two wires were, that ran into the coil )
 

Attachments

  • Ford pressure control solenoid S5.jpg
    Ford pressure control solenoid S5.jpg
    2.9 KB · Views: 0

Tonymura

Jul 25, 2021
30
Joined
Jul 25, 2021
Messages
30
I’ve connected up a dummy load resistor 10 ohms @ 10 watt from top rail 12 volts across the flyback diode to see what current reading i am getting and it reads .5 amp @ 4.77 volt.
Still way to high
Just wondering can i place in series some sort of limiting circuit to limit the current OR should i be using some sort of power transistor instead of the Mosfet?
 

crutschow

May 7, 2021
520
Joined
May 7, 2021
Messages
520
’ve connected up a dummy load resistor 10 ohms @ 10 watt from top rail 12 volts across the flyback diode to see what current reading i am getting and it reads .5 amp @ 4.77 volt.
Not clear what you did.:confused:
Please post a diagram of all the components and there exact connection.
should i be using some sort of power transistor instead of the Mosfet?
A MOSFET (Metal Oxide Field Effect Transistor) is a transistor and so is a BJT.
Each can work fine as a switch if they are properly rated and driven.
 

Tonymura

Jul 25, 2021
30
Joined
Jul 25, 2021
Messages
30
Hi
Sorry for the confusion but all i did was add a 10 ohm resistor at 10 Watt to see how much current flow was going through the circuit.As see in the image.
Is it possible to reduce the current flow by adding a limiter in series with the Source lead?
Im so out of touch with electronics now that i need help, this is why Im posting my topic.
 

Attachments

  • S5 circuit.jpg
    S5 circuit.jpg
    9.5 KB · Views: 5

Harald Kapp

Moderator
Moderator
Nov 17, 2011
12,774
Joined
Nov 17, 2011
Messages
12,774
Is it possible to reduce the current flow by adding a limiter in series with the Source lead?
No. A MOSFET is driven by the gate-source voltage. The current into the gate is negligible, almost 0 mA.
I am trying to limit the current flow to a value to that no more than 120ma
That is why pwm is used, reduce the duty cycle to a smaller value. With the resistor as a load the current is directly proportional to the duty cycle:
I = DC × 12 V / Rload[\SUB] with DC being the duty cycle from 0 % to 100 %.
A resistor is, however, not an adequate substitue for a solenoid. The current through the resistor is proportional to the voltage:
I[sub]resistor[\sub\ = V/R
whereas the current through an inductor is proportional to the integral of teh voltage across the solenoid or in other, more common terms, voltage is proportional to the schange in current:
V = L × di/dt
This results in a triangular current through the solenoid when driven by a rectangular waveform. The effective current is therefore different from that through a resistor.
 

Tonymura

Jul 25, 2021
30
Joined
Jul 25, 2021
Messages
30
You are correct by varying the potentiometer this does adjust the duty cycle increasing the voltage and the current at the same time through the dummy load resistor.
So....What i will do is, connect my solenoid and carefully monitor the current flow as to not make it exceed way to high over 200 ma that is if it will work due to the voltage being way to low. ( not to sure about this voltage threshold )
I hope i can make the solenoid work by hearing a buzzing sound first before i immerse it in hydraulic oil for further testing.
 

Tonymura

Jul 25, 2021
30
Joined
Jul 25, 2021
Messages
30
ok im back...! Summary, if interested.
I just set up and tested the solenoid in question and these are my results.
Apologies for the messy breadboard setup but it did the job for me.
My findings were

Pressure solenoid coil values were
23 millihenries of the coil
Frequency was set @ PWM to 9 khz
Voltage across the coil measured 5 volts when energized .
Current through the coil when energized was at 1.1 amperes
XL reading inductance reactance was found to be @ 1.3K ohms
Resistance value when measured through the multimeter was found to be 5 ohms
duty cycle when coil is energized was @ 70%

I have yet to have this in a container of transmission fluid and pressurize it to 45 psi
But i did have it hooked up to my bike pump up to 20 psi but i found there were to many air leaks so i will need to print me another better manifold to eliminate this issue.

But this will be for another day.
 

Attachments

  • S5 solenoid testing.jpg
    S5 solenoid testing.jpg
    37.9 KB · Views: 2
Top