ESAB LAW 400, Service Manual

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10 CRATER FILLING
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The crater filling function can be used only with an MEK 4, 4S or 4SP wire feed
unit. When the wire feed unit sends a crater fill signal to the power unit, input L4
switches high and low four times. Each time that the voltage changes, the welding
voltage is reduced. The table below shows the percentage of the set voltage at each
step, together with the corresponding L4 signal levels.
Normal crater filling Crater filling during pulse welding
(only with MEK 4SP)
Phase
1
2
3
4
L4
low
high
low
high
%
90
72
65
58
Phase
1
2
3
4
L4
low
high
low
high
%Utop
80
62
55
40
Phase
1
2
3
4
L4
low
high
low
high
%Ub
87
70
63
55
In the table above Utop is the pulse voltage and Ub is the background voltage.
Each step lasts for a maximum of 1.27 seconds.
See the MEK 4 and MEK 4S/SP service manual for further information.
11
START / STOP
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The closing contact in the MEK wire feeders that activates the power unit start input
is a triac. In order to ensure that it has sufficient holding current, resistor R149
provides a load of 1 k τ 5 W at input L5.