Alternator control in the modern era
#1
Alternator control in the modern era
Alternator control as we have traditionally been doing it is sort of an application-specific hack. I believe that the goal is to use one of the many spare PWM outputs of the ECU, and configure it such that BattV is used as the X-axis variable in the map. As Ben said, this is in the early test stages, but will obviously be a reality quite soon. The Miata isn't the only vehicle with an ECU-controlled alternator these days, so it's high on the list.
#3
Alternator control in the modern era
It will read the crank / cam sensors of a '99 Miata without changing anything internally, as well as the crank / cam sensors or pretty much any other vehicle in existence.
Ditto for aircon. This has been a native function of the MS3 for a while now.
Alternator control as we have traditionally been doing it is sort of an application-specific hack. I believe that the goal is to use one of the many spare PWM outputs of the ECU, and configure it such that BattV is used as the X-axis variable in the map. As Ben said, this is in the early test stages, but will obviously be a reality quite soon. The Miata isn't the only vehicle with an ECU-controlled alternator these days, so it's high on the list.
EDIT: I just did some browsing of the dev board, and apparently this is already implemented in the latest Alpha code. So there you go.
Ditto for aircon. This has been a native function of the MS3 for a while now.
Alternator control as we have traditionally been doing it is sort of an application-specific hack. I believe that the goal is to use one of the many spare PWM outputs of the ECU, and configure it such that BattV is used as the X-axis variable in the map. As Ben said, this is in the early test stages, but will obviously be a reality quite soon. The Miata isn't the only vehicle with an ECU-controlled alternator these days, so it's high on the list.
EDIT: I just did some browsing of the dev board, and apparently this is already implemented in the latest Alpha code. So there you go.
#4
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Shutting off the alternator at WOT could be achieved using existing functionality by switching the field drive with a relay that is activated by the MS under certain conditions. I honestly have no idea how to calculate what the potential benefits of this would be.
Actually, that's not true. I know exactly how to calculate this.
Under a typical load, we'll say that the alternator is putting out 30 amps. (running the engine, a few lights, etc.) At 13.8 volts, that's 414 watts. A typical alternator is about 55% efficient, so it's taking in 753 watts of mechanical energy. 1 hp = 745 watts, so the alternator is consuming 1.01 horsepower.
Hmm.
A typical alternator is around 50-60% efficient
#5
At present, the software control for the alternator is in its infancy, piggy-backing on an existing application. Anything is possible, it's just a question of code development.
Shutting off the alternator at WOT could be achieved using existing functionality by switching the field drive with a relay that is activated by the MS under certain conditions. I honestly have no idea how to calculate what the potential benefits of this would be.
Actually, that's not true. I know exactly how to calculate this.
Under a typical load, we'll say that the alternator is putting out 30 amps. (running the engine, a few lights, etc.) At 13.8 volts, that's 414 watts. A typical alternator is about 55% efficient, so it's taking in 753 watts of mechanical energy. 1 hp = 745 watts, so the alternator is consuming 1.01 horsepower.
Hmm.
A typical alternator is around 50-60% efficient
Shutting off the alternator at WOT could be achieved using existing functionality by switching the field drive with a relay that is activated by the MS under certain conditions. I honestly have no idea how to calculate what the potential benefits of this would be.
Actually, that's not true. I know exactly how to calculate this.
Under a typical load, we'll say that the alternator is putting out 30 amps. (running the engine, a few lights, etc.) At 13.8 volts, that's 414 watts. A typical alternator is about 55% efficient, so it's taking in 753 watts of mechanical energy. 1 hp = 745 watts, so the alternator is consuming 1.01 horsepower.
Hmm.
A typical alternator is around 50-60% efficient
#6
It's a hysteretic controller that simply makes a new decision every 1.5 ms or so.
That is, every 1.5 ms it will decide whether or not to turn the field on or off. The decision is simply: is the voltage is higher or lower than the setpoint or not? The voltage needs to be filtered with about a 100-300 us time constant.
Trust me it works well. If you doubt me, realize that the field voltage to output current characteristic of an alternator is an integrator. A hysteretic controller will innately produce the "PWM" signal you need, and is inherently stable if the sampling period is fast enough.
I can tell you it works better than the alternator control in my 540i. I blip the gas at idle in the 540, the lights flare briefly. Not in the miata.
Edit
P.S. My circuit has about 50 mV of hysteresis, IIRC.
P.P.S. The resulting "PWM" on the field signal, is closer to "pulse density modulation", if you wanna get fancy.
Last edited by JasonC SBB; 12-05-2012 at 11:10 AM.
#7
At present, the software control for the alternator is in its infancy, piggy-backing on an existing application. Anything is possible, it's just a question of code development.
Shutting off the alternator at WOT could be achieved using existing functionality by switching the field drive with a relay that is activated by the MS under certain conditions. I honestly have no idea how to calculate what the potential benefits of this would be.
Shutting off the alternator at WOT could be achieved using existing functionality by switching the field drive with a relay that is activated by the MS under certain conditions. I honestly have no idea how to calculate what the potential benefits of this would be.
If you want to see useful things to do with alternators and MPG, check out what Honda did with the early-mid 90s Civic HX. It was discussed at length at one of the popular MPG geek sites.
Other fancy things you should do:
- use a separate pin for sensing batt volts - in my NB the pin that is connected to the injector power line is not accurate. There's a different pin that is (I forgot which one, I think it's called "room fuse")
- keep alternator off below 500 rpm or so
- pinch off the setpoint below 800 RPM (e.g. 14.2V at 800 RPM, sliding to 12.6V at 600 RPM), to help with anti-stall.
Last edited by JasonC SBB; 12-04-2012 at 09:08 PM.
#8
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Whats this about the HX alternator?
I havent seen or heard anything about that, and it would have to be OBD-I to be early mid 90s, and I dont know of anything in the ECU I tried googling but found nothing.
I havent seen or heard anything about that, and it would have to be OBD-I to be early mid 90s, and I dont know of anything in the ECU I tried googling but found nothing.
#10
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I do know alternator control is on the docate for the MS3 code, just unsure when Ken will get to it and hoe he'll implemint it.
#13
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At present, the software control for the alternator is in its infancy, piggy-backing on an existing application. Anything is possible, it's just a question of code development.
Shutting off the alternator at WOT could be achieved using existing functionality by switching the field drive with a relay that is activated by the MS under certain conditions. I honestly have no idea how to calculate what the potential benefits of this would be.
Actually, that's not true. I know exactly how to calculate this.
Under a typical load, we'll say that the alternator is putting out 30 amps. (running the engine, a few lights, etc.) At 13.8 volts, that's 414 watts. A typical alternator is about 55% efficient, so it's taking in 753 watts of mechanical energy. 1 hp = 745 watts, so the alternator is consuming 1.01 horsepower.
Hmm.
A typical alternator is around 50-60% efficient
Shutting off the alternator at WOT could be achieved using existing functionality by switching the field drive with a relay that is activated by the MS under certain conditions. I honestly have no idea how to calculate what the potential benefits of this would be.
Actually, that's not true. I know exactly how to calculate this.
Under a typical load, we'll say that the alternator is putting out 30 amps. (running the engine, a few lights, etc.) At 13.8 volts, that's 414 watts. A typical alternator is about 55% efficient, so it's taking in 753 watts of mechanical energy. 1 hp = 745 watts, so the alternator is consuming 1.01 horsepower.
Hmm.
A typical alternator is around 50-60% efficient
#14
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Random real world experience with alternator control:
The MS3 compensates for voltage, but not for load. With the constant-voltage control of the alternator, there is not really any more need for voltage compensation except for (maybe) at startup where the alternator is only working against the battery.
Sadly, the current MS3 software gets all crazy when you have a steady voltage and varying load alternator: you turn on the headlights, the idle dips and gets sad. turn them off and it swells.
The MS3 compensates for voltage, but not for load. With the constant-voltage control of the alternator, there is not really any more need for voltage compensation except for (maybe) at startup where the alternator is only working against the battery.
Sadly, the current MS3 software gets all crazy when you have a steady voltage and varying load alternator: you turn on the headlights, the idle dips and gets sad. turn them off and it swells.
#15
KERS via alternator
The Braille boys were talking about the ALMS cars (Corvettes, etceteras) shutting down the alternator during WOT for the additional horsepower, and then turning it back on during off-throttle or braking to recharge the battery. It's just another way to free up some horsepower.
I wonder when they're engaging the alternator if they're simply turning it back "on", or if it's being ramped up over a short period to avoid damage to the alternator or the belt system. Jeez, I wonder if this was one of the issues with the F1 alternators.
I wonder when they're engaging the alternator if they're simply turning it back "on", or if it's being ramped up over a short period to avoid damage to the alternator or the belt system. Jeez, I wonder if this was one of the issues with the F1 alternators.
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