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--- astra_conv:conversion:isolation_check:isolation_check [2014/03/14 23:47]
richard
+++ astra_conv:conversion:isolation_check:isolation_check [2014/04/29 11:06] (current)
richard
@@ Line 25: / Line 25: @@
-x
+The device alternatingly establishes high-impedance connections to two different taps on the traction battery cell chain. In case a noticeable current is flowing, this will quickly (within fractions of a second) create an intermittent warning beep. If this condition persists, after some seconds an "isolation fault" alarm will be raised, which is fed to the immobilizer latch.
+The tap inputs can be seen at the bottom left of the diagram. Each of the two yellow tap wires also has an additional 22k series resistor close to the tap, for safety reasons. The two LCA110 solid state relays alternatingly connect them to chassis ground, over some more resistors and the two SFH617 optocouplers. With the 56k + 22k series resistors, the total isolation resistance sums up to a total of 100kOhms, which is safely above the required 50k. The LM2903 on the top left derives  the control signals for the solid state relays  from a sawtooth signal produced by a simple 555 oscillator.
+If either of the two optocouplers' output transistors gets conductive, the voltage at the low-pass stage below will rise. Another LM2903 will trigger and create the warning signal, if a certain threshold is exceeded. The 555 timer in the following stage will trigger if this condition persists for a few seconds.
-The "isolation check" circuit is continuously powered (i.e. not dependent on ignition). It's function can always be verified by a test button at the rear side of the rear battery box, that simulates a slight isolation fault (see chapter "rear traction battery box" below).
+The device has two outputs (active low and active high) for the "isolation check failed" alarm.
+Front and rear view of the unit.
+{{ :astra_conv:conversion:wiring:p1110470.jpg?550 |}}{{ :astra_conv:conversion:wiring:p1110471.jpg?550 |}}
+The "isolation check" circuit is continuously powered (i.e. not dependent on ignition). It's function can always be verified by a test button at the rear side of the rear battery box, that simulates a slight isolation fault (see chapter "rear traction battery box").
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