Development and pre-qualification testing of a low-dissipation battery cell open circuit protection device

A device has been developed and pre-qualified which automatically shorts a battery cell which has failed in open circuit. This approach has an important advantage over the standard 4-diode cell bypass solution which is implemented in the majority of geosynchronous spacecraft nickel-hydrogen batteries in that a failed cell does not result in long-term high thermal dissipation in the associated bypass diodes. This simplifies the thermal design of such batteries allowing mass savings in the battery structure. This advantage becomes more significant as telecommunication spacecraft batteries become larger, which is the current trend. It is even more important in the case of nickel hydrogen batteries used in low earth orbit missions because of the higher charge current which is used. This paper describes how the device was selected from a number of candidates, how it was developed to best meet the requirements and the validation testing that was carried out.