Lincoln Electric IM359-G manual 9OPERATION, Automatic Protection Shutdown, Overvoltage Shutdown

B-9OPERATION

CAUTION

Do not use LN-25 models below Code 9200 with any TIG or Square Wave welding power sources. Do not use LN-25 models equipped with internal contactors with non-Lincoln TIG or Square Wave welding power sources. Damage to the LN-25 circuit can occur as a result of the high output inductance typically associated with these power sources. TIG high frequency power should never be applied to the LN-25.

While welding with a continuously fed electrode, weld current variations are continuously taking place. There are many causes for these variations, but predominantly they occur due to changes in electrical stickout (operator hand movements, nozzle tip contact variations, etc.) and the dynamic metal transfer characteristics of the process or procedure being used (short arc, globular transfer, etc.).

When using a CV power source, these current variations have essentially no effect on the welding arc stability since CV power sources can provide a wide range of weld current levels with virtually no change in average arc voltage. These “flat slope” CV power sources, therefore, provide the arc power required to produce the best welding characteristics and ease of operation for most open arc, constant wire feed speed, welding processes.

CC(formerly VV) power sources, on the other hand, permit the arc voltage to decrease with increases in welding current. The output characteristics of these power sources can range from a “drooping slope,” which provide minor arc voltage changes with weld current variations, to “steep slope” which provide broad voltage changes with only minor current variations. The steeper the slope the more difficult it becomes to maintain arc voltage stability with a constant wire speed open arc process.

To aid in stabilizing the arc voltage when welding on

CCpower sources the LN-25 is provided with a VV (CC) wire feed mode. This arc voltage sensing feed mode decreases (or increases) the wire speed when the arc voltage decreases (or increases). However, if the electrode shorts to the work, the arc voltage will essentially drop to zero and the short circuit current supplied by the CC power source may not provide enough power to re-establish the arc (especially with steeper slope machines). Under this condition the LN-25 feeder will stop, as if the trigger was released, and not restart until the short has been opened.

Arc shorting is more difficult to avoid when using a CC power source, and requires a more refined operator technique than when using a CV power source. Improved performance can be obtained on CC power source applications within the following guidelines:

1.Flatter slope power sources with higher arc force (short circuit current) will improve performance over steep slope machines. The steeper the slope, the more critical it is to hold proper electrode stickout to maintain arc stability. Welding techniques, such as weaving, will be more difficult to control. Use the highest output current tap or setting capable of providing the voltage adjustment required for the procedure.

2.Use spray or non-shorting small ball type transfer processes at higher procedure voltage levels. Generally, open arc processes with procedure voltage levels over 22 volts perform satisfactorily. Arc stability at procedure voltage levels below 22 volts may be more difficult to control, with the general exception of fine (.023—

.035) solid steel electrodes with Argon-rich shielding gas or NR-152 and NR-211 Innershield.

AUTOMATIC PROTECTION SHUTDOWN

The LN-25 control provides automatic electronic protection circuits which shut down the LN-25 for excessively high power source open circuit voltage or excessive motor overload.

OVERVOLTAGE SHUTDOWN

If the power source open circuit voltage exceeds about 110-120 volts, the LN-25 will not operate until the power source voltage drops below about 102- 110 volts.

MOTOR OVERLOAD SHUTDOWN

If excessive motor overload occurs (due to prolonged excessive feeding force, jammed drive rolls or shorted motor leads), the LN-25 will shut down within a few seconds after the overload occurs.

The shutdown will reset automatically when the gun trigger is released, but will reoccur if the overload situation is not remedied.

LN-25