SCR Testing
8.5 SCR Testing
8.5.1 Resistance
The SCRs in the starter can be checked with a standard ohmmeter to determine their condition.
Remove power from the starter before performing these checks.
Check from L to T on each phase. The resistance should be over 50k ohms.
Check between the gate leads for each SCR (red and white twisted pair).
The resistance should be from 8 to 50 ohms.
z NOTE: The resistance measurements may not be within these values and the SCR may still be good. The checks are to determine if
an SCR is shorted "L" to "T" of if the gate in an SCR is shorted or open. An SCR could also still be damaged even though the
measurements are within the above specifications.
8.5.2 Voltage
When the starter is running, the operation of the SCRs can be confirmed with a voltmeter.
Extreme caution must be observed while performing these checks since the starter has lethal voltages applied while operating.
While the starter is running and up to speed, use an AC voltmeter, check the voltage from "L" to "T" of each phase. The voltage should
be less than 1.5 Volts. If the starter has a bypass contactor, the voltage drop should be less than 0.3 volts.
Using a DC voltmeter, check between the gate leads for each SCR (red and white twisted pair). The voltage should between 0.5 and 2.0
volts.
8.5.3 Integral Bypass
A voltage check from "L" to "T" of each phase of the RediStart starter should be preformed every 6 months to confirm the bypass
contactors are operating correctly.
Extreme caution must be observed while performing these checks since the starter has lethal voltages applied while operating.
While the starter is running and Up to Speed, use an AC voltmeter; check the voltage from "L" to "T" of each phase. The voltage drop
across the contactor contacts should be less than 300mV. If greater that 300mV the integral bypass should be disassembled. It may be
necessary to clean the contact tips or replace the contactor.
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8 - TROUBLESHOOTING & MAINTENANCE
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