The high-power switching power supplies connected in series and parallel successfully. However, the payment makes us frustrated!

This is an Australian inquiry but used in India case. The power supply is used for field geological exploration applications. The general principle is to test the conductivity of underground materials through the output of a DC power supply to determine whether there are valuable metal materials underground.

At the beginning of 2017, the customer bought a 600V20A power supply and it was in good use. The customer wanted to purchase a power supply with the same output specifications but can obtain higher voltage and current output by series & parallel connection of multi-unit power supplies. 

However, because the first unit power supply did not consider the expansion port of series and parallel, there is no control board for average output control of multi-units, it is impossible to directly make another power supply with the same output to customers for direct series and parallel connection.

The customer put forward the following requirements after consideration

two power supplies option, 750V50A DC output, the power supply supports parallel and series output, the output after parallel connection is 750V100A, and the power supply output after series connection is 1500V50A

This was a difficult customization task. We actually regretted accepting this case later, because in the end it took us 7 months to complete the power supply. The research and development cost and labor cost completely exceeded the selling price of the two power supplies. However, the biggest problem was that the power supply was sent without receiving the customer's balance payment based on our trust on the customer. Unfortunately, the customer's balance payment was late for 13 months after several times follow up mails and calls. Only after we contacted the customer through a third party, the customer completed the payment, which made us quite frustrated so we were very cautious about the credit-based settlement method since then, and even disgusted!

However, through this case, we have a basic understanding of the design of series and parallel of multi-units DC power supplies.