Power supply replacement for the Antminer S4
Dear loyal customers,
Today we have found out that the batch of power supplies shipped out in batch 1 and the first part of batch 2 Antminer S4s contain a critical defect. The customized power supply produced by AplusPower Co. Ltd is suffering from an unacceptably high failure rate and will be replaced with immediate effect.
We take full responsibility for the problems caused and had not anticipated the unique loading conditions of a miner when selecting and testing the suitability of these power supplies. You can read more about the defect in the post below.
We are now taking steps to ensure that customers are impacted as little as possible. The rest of batch 2 S4s will come with the improved power supply as standard.
The following actions are being taken for miners already delivered:
1) If your PSU has already failed:
• Submit a RMA request with some pictures and proof [ie with your username in the photo] of your PSU’s failure to
info@bitmaintech.com.
• We will then ship a new PSU out as soon as possible.
• We will also issue compensation to the value of 10 days of mining profit calculated starting from shipping date
2) If your PSU has not failed and the miner is running normally:
• We will ship a new PSU to you.
• Please do not contact support yet, you will receive an email asking to confirm your shipping.
Analysis of power supply failures within the first batch of Antminer S4s
We are sorry for the inconvenience you may have experienced regarding power supply failures, or even sporadic events of smoke from our first batch of Antminer S4s. We immediately set out to investigate the reports of failed power supplies from customers, and have made immediate changes to improve the quality of future deliveries. What happened with these power supplies is not acceptable.
The power supplies failed by two different mechanisms:
1) Failed TR1 or TR2 MOSFETs on the power factor correction (PFC) circuitry.
After investigations, it was found that the unusual service conditions a miner puts on its power supply was the cause of the failure. The repeated abrupt, dynamic loading generated significant current through the PFC circuits, eventually leading to the failure of the TR1 or TR2 MOSFETs.
The replacement power supplies have significantly upgraded PFC circuits in order to improve performance and prevent a recurrence of the problem.
2) Failed MOSFET on the output Synchronous rectifier circuit
A MOSFET on the output Synchronous rectification circuit was also found to be failing, due to the repeated and sudden load changes during the miners’ operation.
During normal operation, the output MOSFET is expected to carry a current of approximately 30A and operate at a surface temperature of around 80C. The failing MOSFET was found to be heating up significantly further than this, causing the carbonized black PCBs and smoking thermal pad.
It is worth noting that although a failed output MOSFET at high temperatures may result in some smoke from the PCB and thermal pad, it will not start a fire. All internal components of the PSU meet the requirements of the UL94-V0 flame retardancy standard, which certifies that any ignition will self-extinguish within a maximum of 10 seconds.
In response to this problem, the sample filter in the Synchronous rectifier circuits have been altered to erase the excessive current, and so the MOSFET will not fail again. In addition, several high temperature prevention circuits have been added which will better protect the power supply from overloading and excessive temperatures.
Moving forwards
We always perform significant dynamic testing on chosen power supplies, however in this case we failed to recognize the special conditions and specific loading characteristics the miner would place on the power supply. Our testing has been altered to replicate and include these loading characteristics on any power supplies introduced in the future. Once again, we are sorry.
