Valhalla Scientific 4300C, Operation Manual

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75
Disconnecting the Cables
When disconnecting the test leads from the load or from the 4300C, extreme care must be taken to ensure
that the inductor has been discharged to prevent an extremely high energy, high voltage "kick-back" which
can be LETHAL to the user and can certainly damage the 4300C. There are two methods of discharging the
energy in the inductor listed below.
a) Using the "Flyback Diode" in the 4300C.
The 4300C has an internal diode which can sink the excess current being discharged from the inductor.
Therefore, turning off the test current and/or reducing the 4300C's current range from the original test
current to a low value (less than 10mA) will automatically discharge the inductor into the Flyback diode.
The cables should not be disconnected until the SAFE cable disconnect status LED is illuminated.
The time required to discharge the inductor into the Flyback diode is given by the formula:
T = (L x I)/V
T = Discharge time in seconds
L = Inductance in Henries
I = Current range (in Amps)
V = Flyback Diode voltage drop (typically 6V)
For example, a 1000 Henry inductor will take approximately 30 minutes to discharge. During discharge
the 4300C display will read overload until the inductor has completely discharged. The reading will then
return close to zero.
b) Using a Shorting Switch
When using a shorting switch instead of the 4300C flyback diode, the current stored in the inductor
discharges through the cables and switch. The current discharges with a time constant calculated from
the formula below which is dependent on the test current that was used to charge the inductor:
Test Current Discharge Time
Range Used: (in Seconds):
10 Amps 7 x L ÷ R
1 Amp 5 x L ÷ R
.1 Amp 2 x L ÷ R
< .1 Amp Not required