NiCd batteries for data collection and communication in an outdoor application

The Dutch Motorway Traffic Management System (MTMS) installed to ease congestion on the Netherlands' 2600 km motorway network, has been continuously expanded and upgraded, and traffic on the motorway network now relies on the system to smooth the flow and reduce the number of accidents. There are now 2100 systems that accurately monitor the traffic flow and 'convert' that data into speed restrictions and lane control signs on the gantries. In carrying out these installations each gantry is supported by a DC no-break system with a NiCd battery. These systems serve as a standby power backup in case of mains outage or complete interruption of the mains voltage. The DC no-break systems are designed to take over the control of the signalling system and the lane control sign on the gantries. After more than 10 years of operation a large number of NiCd cells have been tested on their performance. The results of the tests proves the high quality and reliability of the NiCd batteries in an outdoor application. Also a test on two systems has been started in 1991 to obtain data on operating conditions and status by constant monitoring of one VRLA and one NiCd battery system along the side of the motorway over a period of more than 6 years. In this side-by-side test the VRLA battery failed in less than 6 years while the NiCd battery is still in good health. Both batteries operated under normal conditions. No deep discharges occurred, the number of cycles was limited to 15 and the ambient temperature was is a range of -15/spl deg/C to +40/spl deg/C. The results and the obtained data of both tests are described in this paper.