GM BCS users: Are you using a 10 ohm resistor in series with BCS?
Sep 27, 2008, 07:45 PM
#16
Thats very true, in series it will have the same voltage across the solenoid and the resistor. The only reason to use the resistor would be to limit the current draw from the output circuit. At 12v (if thats what the circuit is) and the stock BCS being 33 ohms, thats 363 milliamps (0.363 amps). If the circuit is similar to a peak n hold design it would spike up to an amp while opening the solenoid but not much more IMO.
You must be tired. Series resistances divide up the available voltage. Still, the solenoid will carry most of the voltage at the instant the circuit is engaged because of the impedance of the inductor in the solenoid.
I doubt its a peak & hold type driver. All the ECU does is ground the circuit.
Last edited by mrfred; Sep 27, 2008 at 10:56 PM.
Sep 27, 2008, 08:33 PM
#17
The GM BCS has a resistance of about 24 ohms.
You must be tired. Series resistances divide up the available voltage. Still, the solenoid will carry most of the voltage at the instance the circuit is engaged because of the impedance of the inductor in the solenoid.
I doubt its a peak & hold type driver. All the ECU does is ground the circuit.
You must be tired. Series resistances divide up the available voltage. Still, the solenoid will carry most of the voltage at the instance the circuit is engaged because of the impedance of the inductor in the solenoid.
I doubt its a peak & hold type driver. All the ECU does is ground the circuit.
So at 12 volts, with the 10 ohm resistor the GM 3port is getting 8.47 volts while drawing 0.35 amps. Compared to no resistor and getting 12v and drawing 0.5 amps.
Last edited by Jack_of_Trades; Sep 27, 2008 at 08:37 PM.
Sep 27, 2008, 08:53 PM
#19
I drop in voltage can not change frequency. How ever a drop in voltage will cause the solenoid to respond more slowly. Sorry this is off-topic, but that caught my eye. My own opinion is that you should run the correct voltage for the solenoid. A 10ohm resistor will not cause much of any voltage drop, but will reduce the current thru the solenoid, prolonging its life.
The question has always been whether or not it would damage the ECU, not the BCS. I wouldn't be surprised though if you couldn't draw enough from that portion of the ECU if it was pre-regulated inside the ECU. I could see the solenoid life being shorter, but running at too low of a current is bad for some devices also and can cause corrosion buildup etc
Sep 27, 2008, 08:53 PM
#20
Its not the current thats I think worries people but the current draw from the output circuit in the ECU that people were trying to protect. If its rated for 12 volts and its 24 ohms, its gonna draw 0.5 amps regardless and that is part of its design. I guess it would be nice to know what the output voltage is at 100% duty cycle in a GM vehicle that uses one. That would be very helpful info to have.
EDIT: I hate posting at the exact same time someone else does,lol.
EDIT: I hate posting at the exact same time someone else does,lol.
Last edited by Jack_of_Trades; Sep 27, 2008 at 08:58 PM.
Sep 28, 2008, 08:51 AM
#22
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Its not the current thats I think worries people but the current draw from the output circuit in the ECU that people were trying to protect. If its rated for 12 volts and its 24 ohms, its gonna draw 0.5 amps regardless and that is part of its design. I guess it would be nice to know what the output voltage is at 100% duty cycle in a GM vehicle that uses one. That would be very helpful info to have.
EDIT: I hate posting at the exact same time someone else does,lol.
EDIT: I hate posting at the exact same time someone else does,lol.
As Jack told it is not a great deal to build a "transistor booster" for the GM, but you need an additional 12V Power line for this circuit.
Sep 29, 2008, 02:12 PM
#24
Does anyone know what the current limit on the ECU output is? I found the literature for the Evo ECU somewhere once and posted it up here, but now I don't know what happened to it.
The most damaging thing in the circuit is the back EMF when you turn off the solenoid. Unless there's some kind of freewheeling diode setup inside the solenoid itself, you're spiking to at least 50 or 60 volts every time the solenoid switches off (possibly MUCH higher).
As far as not being able to move the solenoid, if you're running closed loop boost control it doesn't matter. If the solenoid isn't coming all the way open and you're not making enough boost, the control system will up the duty cycle until you are making enough boost.
The most damaging thing in the circuit is the back EMF when you turn off the solenoid. Unless there's some kind of freewheeling diode setup inside the solenoid itself, you're spiking to at least 50 or 60 volts every time the solenoid switches off (possibly MUCH higher).
As far as not being able to move the solenoid, if you're running closed loop boost control it doesn't matter. If the solenoid isn't coming all the way open and you're not making enough boost, the control system will up the duty cycle until you are making enough boost.
Sep 29, 2008, 02:37 PM
#25
Does anyone know what the current limit on the ECU output is? I found the literature for the Evo ECU somewhere once and posted it up here, but now I don't know what happened to it.
The most damaging thing in the circuit is the back EMF when you turn off the solenoid. Unless there's some kind of freewheeling diode setup inside the solenoid itself, you're spiking to at least 50 or 60 volts every time the solenoid switches off (possibly MUCH higher).
As far as not being able to move the solenoid, if you're running closed loop boost control it doesn't matter. If the solenoid isn't coming all the way open and you're not making enough boost, the control system will up the duty cycle until you are making enough boost.
The most damaging thing in the circuit is the back EMF when you turn off the solenoid. Unless there's some kind of freewheeling diode setup inside the solenoid itself, you're spiking to at least 50 or 60 volts every time the solenoid switches off (possibly MUCH higher).
As far as not being able to move the solenoid, if you're running closed loop boost control it doesn't matter. If the solenoid isn't coming all the way open and you're not making enough boost, the control system will up the duty cycle until you are making enough boost.
Sep 29, 2008, 03:29 PM
#26
It'd be simple enough to install the proper sized zener diode across the coil to control the spikes (same way you do for a fuel injector circuit) but if MrFred is right, it'd freak out the ECU even more and throw a CEL I'd imagine. If it does in fact read the spikes than we wouldn't be able to place our own amplified circuit inline.
Sep 29, 2008, 03:53 PM
#27
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I thought the ecu gave the ground for the coil and the 12v is switched power from the main relay. At least that is how my DSM does the BCS.
At any rate flyback voltage usually breaks down the contacts in mechanical relays. Thus we run antiflyback RC units on the coil side of them. Solid state outputs/relays (such as the active low output of the ECU) usually aren't affected by this, at least they weren't when I was dicking with them years ago.
I think even if the BCS isn't getting the full voltage it needs nobody will notice the difference anyways. Basically the tick lower current is only causing a slight drop in latency making you have to artificially run more duty cycle to open in, maybe 1-2 more %, nothing big. Even at that when at 100% DC latency is nilled out as the coil is in a static state.
At any rate flyback voltage usually breaks down the contacts in mechanical relays. Thus we run antiflyback RC units on the coil side of them. Solid state outputs/relays (such as the active low output of the ECU) usually aren't affected by this, at least they weren't when I was dicking with them years ago.
I think even if the BCS isn't getting the full voltage it needs nobody will notice the difference anyways. Basically the tick lower current is only causing a slight drop in latency making you have to artificially run more duty cycle to open in, maybe 1-2 more %, nothing big. Even at that when at 100% DC latency is nilled out as the coil is in a static state.
Sep 29, 2008, 08:41 PM
#30
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More than likely it has to do with a different port size than the latency change I'm speaking of. I don't know what Hz the ecu switches the output but even if I did, and we did the math, and accounting for the latency on the BCS, I'm going to have to say its negligible at best.