Damaged power resistors

Published:  15 February, 2007

The answer to this month's Trouble Shooting teaser is provided by Peter Duncan, a director of Cressall Resistors.


Q:

As a plant manager one problem I often encounter is replacing damaged power resistors. Often, the original supplier no longer exists in the UK market, or has a presence but doesn't supply resistors any longer. I've had this problem on crane controls, as well as pumps, fans and compressors - what's the solution? Should I replace the control system or is there an alternative supplier that can supply identical replacements for the old parts. 


A:

Firstly, you"re right about the lack of suppliers in the UK. The power resistors market has consolidated over the years, as the global electrical players have stripped away non-core products. However, if you type the right phrase, such as 'slip ring starter’ or ‘crane controls’; into Google you should find a trustworthy partner.

For reasons of speed, simplicity and cost it is usually more economical to replace old resistors rather than to take out a whole drive system and replace it with squirrel cage motors and modern drives. In addition, if your application is safety-critical or infrequently started, such as a motor on a drainage pump, the proven reliability of a resistor-started wound-rotor motor is worth retaining. Of course, the replacement resistor cost is normally lower than fitting a new system so it does no harm to your capital expenditure.

If you do opt for a replacement resistor system you should always send the original to the partner company you have entrusted with the job. Although it may not be possible to produce a carbon copy it is normally feasible to produce resistors that are functionally identical in terms of electrical and thermal performance and physical size. The resistor itself may be different but trust me; the laws of thermodynamics remain the same.

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