Safety product manufacturer MSA reports that it is currently investigating a solution to the charging cycles of new-generation cap lamp batteries.

The charging cycles of the cap lamps are affected by ripple voltage, which the company says, can put miners in a precarious position.

MSA Africa product manager for fixed gas detection instrumentation and mine lighting Emmanuel Manaka says: “Mines depend entirely on charging racks to charge their cap lamps and ensure that personnel have enough light for all the workers. The older type of charging racks was designed using step-down transformers and chokes. Not much filtering was performed on the output voltage, and the key was to achieve the 5,1-V charging voltage.”

Manaka notes that, in the past, there was a significant amount of ac ripple voltage found on the output charging voltage. However, it was never a concern because it did not affect the lead acid battery in the cap lamps. Such ac ripple voltage affects the efficiency of the charging racks.

“However, new developments in cap lamp charging rack power supplies have seen most charging rack manufacturers switching the mode of power supplies, mainly owing to the fact that they produce a clean output voltage to the charger without any ripple, as well as being lightweight when compared with the older power supplies.”

MSA says that as technology develops and mines switch to new-generation cap lamps, it is becoming critical to monitor the quality of the charging voltage. “The reason for this is that the new-generation cap lamps use electronic circuits to regulate the under- and over- voltage entering the cap lamp from the charger,” Manaka explains.

“The electronics are located inside the headpiece or in the battery pack of the cap lamp,” he says. When ripple voltage is present in the charger, a number of challenges can occur. There may be a premature cutoff of the cap lamp charging circuit and the cap lamp battery may not be fully charged. In addition, flickering can occur in the cap lamp which distorts vision and the battery life is reduced, which also results in reduced charging cycles.

In the case of new-generation cap lamps, the battery technology primarily used is the lithium ion or lithium polymer and is extremely sensitive to the ac ripple voltage on its input terminals.

Manaka says that the voltage controlling circuit, which forms part of the electronics of the cap lamp and monitors the charging voltage and the low battery voltage, does not operate accurately under these circumstances.

This could result in cap lamps being charged to different levels, even though they are all charged at the same time and for the same length of time. “This means that one or two miners could have loss of power in their cap lamps after a short time, while others may last a whole shift. The danger here is the unpredictability,” he adds.

Despite manufacturers of charging racks changing to switch-mode power supplies on their charging racks, which is primarily bene- ficial for new mines, older mines are challenged by the use of new-generation cap lamps with old power infrastructure.

MSA is currently working on implementing an electronic filter circuit that will eliminate the ac ripple voltage effect from affecting the charging of cap lamps. Tests are being conducted at various mines that use the MSA cap lamps to determine the extent of the magnitude of the ripple voltage.

“MSA is looking at how to improve existing filters. This is a safety issue and we aim to offer a solution sooner rather than later,” he concludes.

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