MedWeld 4000 Overview
MedWeld 4000 Operator’s Guide
Modified: 12/16/08
1 - 9
M-032116 Programs #T03300, #T02300 and #T02400
As supplied from the circuit breaker’s manufacturer, the magnetic trip
coil is set to its minimum setting. The customer must adjust this setting
as the application requires. It is CRITICAL to set this threshold
correctly, for these reasons:
•
Setting the magnetic trip to a too-high value can cause the upstream
bus fuse to blow before the circuit breaker trips in response to an
overload. This means that the fuse needs to be replaced (a time-
consuming job) rather than simply resetting the circuit breaker. This
is a convenience issue, not a safety issue.
•
Setting the magnetic trip setting too low may cause the circuit
breaker to trip under normal welding currents (even if there is no
overcurrent fault). This is a nuisance issue, not a safety issue.
Isolation Contactor
The isolation contactor acts to isolate voltage from the weld transformer.
It removes power from this transformer’s primary circuit. This allows
safely servicing the weld electrode tips or weld machine while the
control is idle (or when a fault occurs).The timer monitors the state of
the isolation contactor via the auxiliary contacts.
The isolation contactor is driven by a single solid-state relay, based on
the status of the CONTROL STOP and WELD/NO WELD inputs, and a
TURN ON function. Refer to page 4-8 and TURN ON/OFF
CONTACTOR SELECT #n (page 4-23) for more information about
these functions. Also, refer to the drawing packet of schematics
provided with your MedWeld 4000.
Control Transformer
Supply voltage (380, 480 or 600 VAC) from below the circuit breaker
goes to a control transformer. It reduces the supply voltage to 120 VAC,
and 24 VAC. The 120 VAC is used to pull in the isolation contactor, and
to activate the circuit breaker shunt trip. This transformer supplies 24
VAC to power the timer assembly. The timer assembly, in turn, provides
optional 24 VDC that can power discrete inputs and outputs.
Current Coils
The standard MedWeld 4000 has a coil to measure primary current. An
optional coil measures secondary current.
The primary current coil is the doughnut-shaped device located near the
SCR assembly in the control enclosure. It has an iron core.The control
uses this device to measure the welder’s primary current. Welding
current flows through the center of the coil, inducing a current in the
coil at the ratio of 200:1. (For example, for every 1,000 A. of primary
current, 5 A. flows in the secondary.)
The optional secondary current coil has an air core. It produces current
which is proportional to the secondary current’s instantaneous rate of
change. A Secondary Current Interface Board (Page 1-21) takes this
information and determines true current values.