Operating instructions

FC Operation & Maintenance Guide (20 & 25 Amp)

Test #2: With one or both leads disconnected from the inductor, measure the resistance across the

inductor terminals. If the resistance is less than 0.25 ohms, the inductor is OK.

Test #3: Disconnect wire connected to the diode. Using an ohmmeter on the RX1 scale, a good

diode will cause the ohmmeter to read approximately 1/2 scale when the leads are

connected one way, and infinity when the leads are connected in reverse. A similar

reading in both directions indicates a defective diode.

Test #4: Disconnect all the leads to the SCR and its heat sink. Connect a voltmeter across the

1K? resistor to measure the voltage drop. With the battery connected as shown, V

drop

should read approximately 2.3 volts (V

source

- 0.7 volts). Remove the voltage source

to the gate, but keep it connected to the 1K? resistor and cathode. V

drop

should equal

zero. Reconnect the gate and reverse the battery polarity. V

drop

should equal zero.

Readings other than these indicate a defective SCR. See Figure 6.3

Test #5: Due to the modest cost of the control circuit, we recommend that the entire unit be

replaced rather than attempting to repair it. If the troubleshooting guide has not revealed

any defective components (tests #1-4), the control circuit should be replaced as a unit.

Test #6: Remove all wires from the current shunt. Place a milliohmmeter across the two terminals.

The following formula should be used to determine the correct resistance:

Resistance = 0.5/Output current rating of the charger

If the resistance is more than 20% too low, the current shunt should be replaced.

FIGURE 6.3

SCR test setup

25 ž

approx.

3 volt source(2 "D"

batteries in series)

Cathode

Gate

SCR

Anode

drop

1 Kž