Any electrical engineers in?
Discussion
I was wondering if any kind electrical engineers might be able to offer me some guidance? I’m a mechanical engineer by trade so go easy on me, my electrical knowledge isn’t brilliant!
What I’m trying to do is make a small device to actuate the solenoid valves used in the E36 M3 Evo. BMW have a small black box that they use to do this
– one end connects to the battery the other to the solenoids, but they won’t sell you one and if you can find a dealer who will they’re alledgedly £200. Call me tight but it doesn’t look like £200 worth of electronics!
So far I know the solenoids are controlled via PWM and they have a resistance of 4k Ohms. What I want to know is what other information will I need in order to make a device to control these? So far I’m thinking I need to know the voltage and current of the signal and the frequency (I’m guessing an oscilloscope will tell me these), then it’s just a case of flipping between 0% and 100% duty cycle to actuate the solenoids on and off. Does this sound about right?
Any advice would be much appreciated.
What I’m trying to do is make a small device to actuate the solenoid valves used in the E36 M3 Evo. BMW have a small black box that they use to do this
– one end connects to the battery the other to the solenoids, but they won’t sell you one and if you can find a dealer who will they’re alledgedly £200. Call me tight but it doesn’t look like £200 worth of electronics!
So far I know the solenoids are controlled via PWM and they have a resistance of 4k Ohms. What I want to know is what other information will I need in order to make a device to control these? So far I’m thinking I need to know the voltage and current of the signal and the frequency (I’m guessing an oscilloscope will tell me these), then it’s just a case of flipping between 0% and 100% duty cycle to actuate the solenoids on and off. Does this sound about right?
Any advice would be much appreciated.
Do you mean acutate for test purposes, or actuate on a running engine ??
(And i assume you mean the cam position activation solenoids??)
You need to get a multimeter (prefferably a scopemeter) onto a running engine, and record the PWM frequency and Duty cycle, and DC resistance for the valves.
They will almost certainly be driven by BattV (12v) and the activation electronics will be a "low side drive" (i.e. the ground side of the sols is "pulled down to ground" to switch them on.
There are 2 possible drive waveforms, Pulse width Modulation (PWM) at a fixed frequency, or Frequency modulation at a fixed pulse width (usually 50%)
If you want to make a stand alone device to drive these sols you will need either a frequency generation chip (555 timer etc) or a microcontroller (ardinuio etc) via a suitable power driver (transistor/ MOSFET)
If you want to just test they move, then simply switching 12v DC across them for a short period of time will show this (if they have a DC resistance of less than say 6ohms i would suggest testing them at a reduced voltage to avoid buring them out, say 6v dc)
PS the 4Kohm figure sounds a bit suspect, that's a high resistance for any 12v power source (only 3mA current, and 0.036watts power, useless for anything) I suspect they are actually 4ohms (=3Amps / 36watts)
(And i assume you mean the cam position activation solenoids??)
You need to get a multimeter (prefferably a scopemeter) onto a running engine, and record the PWM frequency and Duty cycle, and DC resistance for the valves.
They will almost certainly be driven by BattV (12v) and the activation electronics will be a "low side drive" (i.e. the ground side of the sols is "pulled down to ground" to switch them on.
There are 2 possible drive waveforms, Pulse width Modulation (PWM) at a fixed frequency, or Frequency modulation at a fixed pulse width (usually 50%)
If you want to make a stand alone device to drive these sols you will need either a frequency generation chip (555 timer etc) or a microcontroller (ardinuio etc) via a suitable power driver (transistor/ MOSFET)
If you want to just test they move, then simply switching 12v DC across them for a short period of time will show this (if they have a DC resistance of less than say 6ohms i would suggest testing them at a reduced voltage to avoid buring them out, say 6v dc)
PS the 4Kohm figure sounds a bit suspect, that's a high resistance for any 12v power source (only 3mA current, and 0.036watts power, useless for anything) I suspect they are actually 4ohms (=3Amps / 36watts)
Edited by anonymous-user on Thursday 20th October 13:15
Sorry for the cross post, I wasn't sure where electrical bits went for the best.
Thanks for the detailed reply MaxTorque
I'm just meaning actuate for test purposes away from the engine. The solenoids control oil flow to the vanos pistons which then in turn retard/advance the cams.
Is it possible then to get all those parameters with just a multimeter? I was expecting to need a scope. From what I gather from my research the frequency is in the 100Hz range
I read that it's likely the solenoids will be in series with a FET switch (with a microprocessor controlled PWM input) and the battery source, sound likely?
Yeah you're probably very right about that, I couldn't remember off hand but 4 Ohms it probably is.
All I want to do really is move them full in and full out, if I get a power supply what sort of amperage should I aim for and I'm guessing that by reducing the voltage I'll not need to worry about damaging them (it's been reported that putting battery voltage to them to test them results in their demise)?
Although if I could make a simple enough device as to how they're controlled as standard that would be nice!
Thanks for the detailed reply MaxTorque
Max_Torque said:
Do you mean acutate for test purposes, or actuate on a running engine ??
(And i assume you mean the cam position activation solenoids??)
(And i assume you mean the cam position activation solenoids??)
I'm just meaning actuate for test purposes away from the engine. The solenoids control oil flow to the vanos pistons which then in turn retard/advance the cams.
Max_Torque said:
You need to get a multimeter (prefferably a scopemeter) onto a running engine, and record the PWM frequency and Duty cycle, and DC resistance for the valves.
Is it possible then to get all those parameters with just a multimeter? I was expecting to need a scope. From what I gather from my research the frequency is in the 100Hz range
Max_Torque said:
They will almost certainly be driven by BattV (12v) and the activation electronics will be a "low side drive" (i.e. the ground side of the sols is "pulled down to ground" to switch them on.
Apparently they are 12V switched rather than ground which is I believe as you say not the 'norm'I read that it's likely the solenoids will be in series with a FET switch (with a microprocessor controlled PWM input) and the battery source, sound likely?
Max_Torque said:
There are 2 possible drive waveforms, Pulse width Modulation (PWM) at a fixed frequency, or Frequency modulation at a fixed pulse width (usually 50%)
If you want to make a stand alone device to drive these sols you will need either a frequency generation chip (555 timer etc) or a microcontroller (ardinuio etc) via a suitable power driver (transistor/ MOSFET)
If you want to just test they move, then simply switching 12v DC across them for a short period of time will show this (if they have a DC resistance of less than say 6ohms i would suggest testing them at a reduced voltage to avoid buring them out, say 6v dc)
PS the 4Kohm figure sounds a bit suspect, that's a high resistance for any 12v power source (only 3mA current, and 0.036watts power, useless for anything) I suspect they are actually 4ohms (=3Amps / 36watts)
If you want to make a stand alone device to drive these sols you will need either a frequency generation chip (555 timer etc) or a microcontroller (ardinuio etc) via a suitable power driver (transistor/ MOSFET)
If you want to just test they move, then simply switching 12v DC across them for a short period of time will show this (if they have a DC resistance of less than say 6ohms i would suggest testing them at a reduced voltage to avoid buring them out, say 6v dc)
PS the 4Kohm figure sounds a bit suspect, that's a high resistance for any 12v power source (only 3mA current, and 0.036watts power, useless for anything) I suspect they are actually 4ohms (=3Amps / 36watts)
Yeah you're probably very right about that, I couldn't remember off hand but 4 Ohms it probably is.
All I want to do really is move them full in and full out, if I get a power supply what sort of amperage should I aim for and I'm guessing that by reducing the voltage I'll not need to worry about damaging them (it's been reported that putting battery voltage to them to test them results in their demise)?
Although if I could make a simple enough device as to how they're controlled as standard that would be nice!
Measure the solenoids DC resistance with a multimeter. Then apply the same amount of voltage as the ohms resistance, which because V=IR, will mean 1 ampere will flow through the solenoid (this is a "safe" amount of current that is extremely unlikely to overheat anything).
If you cannot see the solenoid plunger moving, then increase the voltage carefully untill it does (if you get to 12v without any movement, it's probably broken!)
If you cannot see the solenoid plunger moving, then increase the voltage carefully untill it does (if you get to 12v without any movement, it's probably broken!)
That sounds like the best way to go. So I'm looking at 4V if the resistance is 4 Ohms.
Now here's where I show my lack of electrical knowledge........ does the output current of the power supply matter? For instance if I used a 4V 3A output would this be OK?
Is there an easy way of reducing the car battery voltage down to 4V, 8 Ohm resister inline with the solenoid maybe?
Thanks for your help so far MaxTorque, I should've paid more attention in those electrical modules at uni!
Now here's where I show my lack of electrical knowledge........ does the output current of the power supply matter? For instance if I used a 4V 3A output would this be OK?
Is there an easy way of reducing the car battery voltage down to 4V, 8 Ohm resister inline with the solenoid maybe?
Thanks for your help so far MaxTorque, I should've paid more attention in those electrical modules at uni!
just remember V=IR, or Voltage[Volts] = Current[Amperes] x Resistance[Ohms]
The resistance is what sets the current for any given voltage.
So apply 4v into 4ohms and 1 Amp will flow
Your power supply must be capable of supply enough amps for your load. But the actualy current that flows is set by the loads resistance and the voltage applied.
So you 4V 3A PSU will be fine, as your 4Ohm solenoid resistance will limit the current flowing to just 1Amp (with 4V applied across it)
The resistance is what sets the current for any given voltage.
So apply 4v into 4ohms and 1 Amp will flow
Your power supply must be capable of supply enough amps for your load. But the actualy current that flows is set by the loads resistance and the voltage applied.
So you 4V 3A PSU will be fine, as your 4Ohm solenoid resistance will limit the current flowing to just 1Amp (with 4V applied across it)
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