iTPC LV Power Failures

Analysis, Cause & Corrective Action

Report By Tim Camarda for the STAR collaboration

December 2024

Background

A majority of the power issues for the iTPC RDO + Front End electronics were found to be from degraded connections at the power feed at the detector side extension cables (slide #3, fig 3). The power feeds from the rack-mount power supplies were run to the detector and positioned at the outside of the detector segment at the respective clock positions. Three-foot extension cables (fig.1) are then used to carry the power to each inner RDO or in the case of the TPX sectors a wye adapter cable is used to bring power to 2x RDO’s. In total there are five Anderson disconnects to each inner RDO (disconnect at PS side is not shown in figure 1 cable diagram).

The connections are made with Anderson Power-Pole family spring type contacts and housing assemblies (PN 1330).

The contacts & housing are rated for 30A with 12AWG wiring. With a 45 amp load each contact should be averaging ~ 15ADC current with a VDROP / contact of 10mV  (~400mW / contact) as per the manufacturers specifications . Under the assumption that a negligible imbalance exist and each connection is solid (within the rated mating resistance specs), the connection should be well within the rated temperature for the contacts & housing assembly (i.e. within the current rating of the contacts). However, there is a condition that is causing increased contact resistance which is causing excessive heating. The excessive heating is melting the polycarbonate housing (figures 3 & 4). Once the housing becomes distorted, the mating force of the contacts becomes compromised thus resulting in increased contact resistance. Significant pitting is also noted on the contact plating which also causes heated connections.

 

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Full report here: