MegaMeet 2008 - bgsoflex.combgsoflex.com/megameet2008/megameet2008_gnding.pdf · 7 Understanding...
Transcript of MegaMeet 2008 - bgsoflex.combgsoflex.com/megameet2008/megameet2008_gnding.pdf · 7 Understanding...
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MegaSquirt and MegaSquirt Logo are trademarks of BG Soflex, LLC.
MegaMeet 2008
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MegaSquirt and MegaSquirt Logo are trademarks of BG Soflex, LLC.
MegaSquirtNoise – it’s your fault…
Bowling & Grippo
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MegaSquirt and MegaSquirt Logo are trademarks of BG Soflex, LLC.
Understanding Noise
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Understanding Noise
If you strike a child witha stick, the child will cry…
Who should we blame?
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Understanding NoiseUnderstanding Noise? The Automotive Environment is perhaps the most
hostile environment: – Temperature Extremes (-50 C to 150 C)– Vibration– Electrical Noise – Spikes/Undervoltage/Overvoltage
? By far the most challenging is Electrical Noise.? All Automotive Electronics are Affected by Noise:
– Electronics have protective circuits for noise and out-of-range voltages.
– Reaction of a particular device depends on many factors– No two installations are alike, even for same vehicle types– Use should protect their electronics (baby) from noise (stick)
the best way possible.– Simple solutions go a long way… ..
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Understanding NoiseUnderstanding Noise? Sources of Vehicle Electrical Noise – Radiated Noise
– Ignition – primary currents and secondary voltages– Injectors– Electric motors (starter, wiper, heater)
? Sources of Electrical Supply Noise– Charging (alternator)– Electric motors (starter, etc)– Resistance/Inductance in wiring
? Noise Can Occur When:– Starting (radiated and voltage-drop, a.k.a. “IR Drop”)– Running (injector/ignition/solenoids)– Activating Accessories (heater, headlights, wiper)
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Radiated Noise Source
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Radiated Noise Source
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Radiated Noise Source
Ignition WiresCan Radiate Noise!
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Detecting Radiated Noise
Simple Transistor AM RadioMakes an Excellent Noise Sniffer!
Listen for the buzz…
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High-Current Noise Sources
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High-Current Noise Sources
Resistance in wiring can cause Voltage Drops
Voltage Drops are bad…
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Finding Noise Sources
Remember this rule!
Voltage Drop = Current x Resistance
? The voltage drop across a wire is equal to the resistance of the wire multiplied by the current flowing thru the wire – a.k.a. “IR Drop”
? High current sources include:– Starter– Charging System– Headlights– Horn– Heater/Wipers
? Use a voltmeter to determine the voltage drop…
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Finding Noise Sources
Remember this rule!
Total Voltage = Sum of Voltage Drops
? The sum of all of the voltage drops equals the battery (potential) voltage.
? Very useful relationship in determining where a voltage offset is occurring.
? The use of these two rules together is POWERFUL!
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Finding Noise Sources
Step 1 - Determine battery voltage during cranking
Call this Vtotal
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Finding Noise Sources
Step 2 – Measure wirevoltage drop
while cranking
Call this Vwire
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Finding Noise Sources
Step 3 – Measure startervoltage drop
while cranking
Call this Vstarter
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Finding Noise Sources
Step 4 – Measure groundvoltage drop
while cranking
Call this Vgnd
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Finding Noise Sources
Example Analysis: Vtotal = 10.0 volts
Vwire = 1.5 voltsVstarter = 8.0 voltsVgnd = 0.5 volts
Vwire + Vstarter + Vgnd ~= Vtotal
Vwire and Vgnd should be as low as possible!
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MegaSquirt Hardware Wiring? In some cases the source of the noise cannot be
eliminated - or even located…? The V3 MegaSquirt has built-in noise-protection
circuitry – however there are some instances where more noise resistance is required
? Simple changes in wiring strategy can go a long way:– Sensor ground returns separate from high-power grounds– Multiple ground wires from MS to engine block– Tach input leads physically separated from high-current wires
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MegaSquirt Hardware Wiring
Run Sensors on Separate Ground Return Path to MS:
Sensor Ground Bus
Main MS Ground Bus
High currents on sensor returns will cause voltage drops,resulting in noise and inaccuracies… … .
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MegaSquirt Hardware Wiring
Run Multiple Engine Grounds Back to MegaSquirt:
Sensor Ground Bus
Main MS Ground Bus
Each wire acts as a series resistor/inductor.Multiple wires act like resistors/inductors in parallel… .
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MegaSquirt Hardware Wiring
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MegaSquirt Hardware Wiring
High-CurrentGround Plane
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MegaSquirt Hardware Wiring
5-V Ground Plane
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MegaSquirt Low-Z Injector PWM? When multiple low-impedance injector are used on
MegaSquirt, the PWM switchmode current limiting can introduce noise on the +12V battery rail.
? Voltage transients from PWM caused by “IR” voltage drops in vehicle +12 volt supply wiring
? Solutions include:– Improving vehicle wiring for +12V source to injectors and MS
board to reduce resistance– Board modification to provide separate return for flyback
currents– External shunt and storage capacitance on +12V vehicle
supply.
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MegaSquirt Low-Z Injector PWM
Injector Activated (ON)
+12V
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MegaSquirt Low-Z Injector PWM
Injector PWM Flyback
+12V
Vehicle +12V Wiring
Resistance in vehicle wiringwill cause voltage drop… ...
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MegaSquirt Low-Z Injector PWM
Cut this trace (+12V) andbring it out separate,return directly back
to injector +12V
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MegaSquirt Low-Z Injector PWM
+12V
Connect capacitor and resistor in series with injector bank (snubber)Starting values are 0.1uf and 100 ohm, adjust…
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MegaSquirt Low-Z Injector PWM
+12V
Stereo Capacitor connected to MegaSquirt +12V supply (thru ECU relay)Works Wonders!
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MegaSquirt Fast Idle PWM? The fast idle driver transistor was originally designed
for on-off operation. However, the use of the output for PWM idle valve operation is quite popular!
? The driver transistor grounds are not optimal on the V3 board for PWM use, but there are a few user-changes that can improve this.
? The transistor overcurrent circuit can cause issues with PWM idle valve use due to activation during flyback.
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MegaSquirt Fast Idle PWM
These grounds should go to the High-Power Groundplane… .
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MegaSquirt Fast Idle PWM
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MegaSquirt VR Circuit? There are hundreds of different VR sensor
configurations, each generating outputs of wildly different voltages/currents.
? The V3 VR circuit was designed with some adjustability for different sensor signals.
? However, there are some situations where the signal needs to be “pruned” a bit:
– Voltage amplitude– Current– Irregular signals
? Here is a background on the VR circuit operation:
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MegaSquirt VR Circuit
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MegaSquirt VR Circuit
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MegaSquirt VR Circuit
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MegaSquirt VR Circuit
Hysteresis
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MegaSquirt VR Circuit
Hysteresis
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MegaSquirt VR Circuit? Here are some proven VR circuit tweaks:
– Increase series resistance R45 from 1K to up to 10K– Increase capacitance C31 up to 0.1 (Note - this will cause a
phase shift for high toothcount wheels at high RPM)– Resets from VR can be cured by supplying separate VR return
ground back directly back to C31 (next slide… )– Provide hysteresis capacitor (later slide)
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MegaSquirt VR Circuit
VR-
Bring VR return signal back to C1 or Q22 ground to localizeground circulation currents for VR circuit.
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MegaSquirt VR Circuit
Hysteresis Capacitor