Lincoln Electric NA-5NF, NA-5SF service manual Automatic Shutdown, Start Circuitry

B-10 OPERATING INSTRUCTIONS B-10

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AUTOMATIC SHUTDOWN

If the NA-5 voltage control is unable to supply the “Set” value of the arc voltage while welding, the automatic shutdown circuit will activate. This protection circuit immediately returns the NA-5 control to idle state within a few seconds after the arc voltage discrepancy occurs.

Typical causes that activate this protective shutdown circuit are as follows:

1.“Set” value of arc voltage is outside the power source range.

2.Power source voltage control not set for “Remote”.

3.Misconnection of NA-5 control cable leads to the power source.

4.Incorrect weld polarity connections, or settings, at NA-5 or power source.

5.Lost connection of NA-5 voltage sensing leads (#67 and #21) between arc and voltage control or a blown 1/8 amp fuse on voltage PC boards built since 1983.

With NA-5 units above Code 8300, the conditions of causes 4 and 5 above would result in the wrong wire feed direction when the weld is started. See the section on Cold

Start Circuitry.

In the case of full-range control power sources, such as the DC-600, this protective shutdown circuit could prevent welding under the conditions of causes 3, 4 and 5 above by holding the power output at minimum, possibly providing too low of a power source output to even establish an arc, or causing the field fuse to blow because of rapid field reversals with NA-5 controls above Code 8300. See the section on Cold Start Circuitry.

Although out of range shutdown can occur with all power sources when working with very low or very high arc voltages, it is most

likely to occur when using the R3S models with the somewhat limited voltage ranges of the various taps. For instance, if the R3S- 400 triangle tap setting is for 31 volts, the range of control from the remote circuit is approximately 7 volts, i.e. 27.5 to 34.5 volts at nominal input voltage. If the NA-5 controls are set for 29 volts, and the input voltage to the R3S goes up, it may not be possible for the NA-5 control circuit to hold the 29 volts, so the welding will shut down. By changing to the 27 volt triangle setting, the range will be approximately 23.5 to 30.5 volts, and at high input voltage, there will be sufficient control to hold the “Set” arc voltage. On these machines, if the NA-5 stops welding, follow this procedure:

1.Move the NA-5 voltage set point 2 volts lower than the desired procedure and make a test weld.

a.If the NA-5 still shuts down, go to step 2 below.

b.If the NA-5 keeps welding, change the R3S triangle setting

to the next higher voltage and reset the NA-5 set point to the desired procedure. The R3S is now set properly unless there is a significant change in input voltage. Skip the following step.

2.Move the NA-5 voltage setting set point 2 volts higher than the desired procedure and make a test weld.

a.If the NA-5 keeps welding, change the R3S triangle setting to the next lower voltage and reset the NA-5 set point to the desired procedure. The R3S is now set properly unless there is a significant change in input voltage. Skip the following step.

b.If the NA-5 still shuts down, refer to the following paragraph and other causes previously listed.

NA-5