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Welder Restoration and the Importance of OCV

The phrase OCV is an acronym for Open Circuit Voltage. It is the unloaded DC voltage that is current at the Weld output terminals of a Welder. This voltage typically averages between 60-90 VDC in Stick (SMAW) mode of operation. The a single exception to this (in which an AC voltage is current) happens when dealing with a Transformer based Stick Welder (frequently called a Buzz box) which has no DC rectification of the transformers secondary voltage. In other modes of operation (Weld processes) such as MIG (GMAW), or TIG (GTAW), the OCV will be various to that specified in Remain mode. The Weld procedure that is selected is centered on the performance of the Welder. Not all Welders are capable of several processes. For instance, simpler Welders have Stay mode of operation only.

When Problems Shooting an SCR (Silicon Controlled Rectifier) primarily based Welder, an OCV measurement offers a beneficial device towards an efficient repair. The initial step in this procedure is to talk to the Welders Support Manual. The Specifications web page will show the Highest OCV for the selected Weld procedure. Report this voltage!

Next, consult the Schematic to reveal the quantity of SCR's in the layout, and the efficient amount of switched existing paths. Report the quantity of present paths! In this situation, a present path is a branch from the Transformers secondary winding, via an SCR (Anode to Cathode), and culminating into a current node prior to filtering by the output Inductor (Reactor). The present node normally has multiple branches feeding into it with one dedicated output.

Utilizing a DVM (Digital Volt Meter) measure the OCV of the Welder. If it is close to the Highest OCV then this signifies that all SCR's are firing (triggered from an applied gating voltage), and would be an ideal circumstance. If not, divide the Maximum OCV by the quantity of switched existing paths. This amount represents the Voltage that each SCR or existing path provides as component of the layout. Subtract this worth from the Highest OCV. If the value (Voltage) equals the Welders measured voltage then one SCR or existing route is faulty. If not, carry on this method for the variety of present paths that are staying utilized.

An illustration of this is a Welder with a Highest OCV of 60V created by synchronously firing three SCR's. The measured OCV from this Welder is only 40V.

60-(60/three) = 40. This would indicate a difficulty with a single of the SCR's or a triggering matter. As you can see, this method is capable of pointing the Fix Technician in the direction of a speedy fault resolution.

Up right up until this point, the measurements that have been used (namely, OCV) occurred with no opening the Welders situation. The following paragraphs refer to part place Useful Analyze procedures. To move forward with this, the elements (SCR's, IGBT's or MOSFET's) must be eliminated from the suspect Welder earlier to carrying out these steps. For security causes, below no circumstances ought to the elements staying tried be electrically connected to any other devices or Power Supplies apart from the Analyze Products becoming applied to determine component defects. If you are not experienced in Electronic Restore, and don't have a solid electric background do not attempt any kind of electric restore on this kind of products. Within a Welder, there are Substantial voltages current that can Kill. This warning is not to be taken lightly! In other words, if you are not a qualified Electronics Technician, Electric/Electronics Engineer, or Electrician then treat this info as reference material only. Refer your restore to competent personnel.

The SCR's must then be individually tried out of circuit utilizing an SCR Tester or Ingredient Analyzer. This sort of Analyze Gear is able of triggering the Gadget-Below-Analyze. A DVM will not. Another essential concern is ESD safety of the SCR throughout this screening phase. Select Check Gear that grounds (or connects) all SCR terminals to the exact same probable whilst completing Useful Test. If there is no possible distinction (voltage as a function of charge) among the SCR's terminals, there is no probable for ESD destruction!

When Problems Shooting an Inverter primarily based Welder, a reduced OCV normally shows a Switching concern with the Welders IGBT's (Insulated Gate Bipolar Transistor), or MOSFET's (Metal Oxide Semiconductor Field Effect Transistor). This is typically induced by a faulty Gate Driver or Handle Board. The two of these issues are solved by means of board replacement, or element level restore.

When the measured OCV is at VDC (and the Welder isn't blowing fuses or Circuit Breakers) the Switching Parts should be tried for features (Out-Of Circuit).

An IGBT & MOSFET Tester or Component Analyzer ought to be employed to execute these tests. As with the SCR Useful Check Method, a DVM can not Gate these products. There are nevertheless some exceptions with MOSFET screening due to the substantial Gate input capacitance in some units. Also, as previously stated: a DVM does not supply any amount of ESD protection for the part even though undergoing Useful Test. If a long lasting, high quality restoration is attempted, ESD safety via good Check Products variety ought to be a main problem.
Get more information here: Electronic Equipment Testing

About the Author

Ian Pooley is writing technical articles