In a message dated 12/12/04 14:48:57 GMT Standard Time, [EMAIL PROTECTED] writes:
Yes, I was over-simplifying it. But a battery at 13.8 Volts will not take a charge with a 13.8 Volt source. What happens I assume is that the battery discharges a bit so it is lower than 13.8 Volts, and then the trickle charge commences. -------------------------------------------------- I still maintain that even with the supply source at 13.8V, there will be a small, but finite float current drawn by the battery and am anxious to dispel the idea that the battery will not take any current at all when on normal float service when fully charged at 13.8V. The 12V 7Ah SLA batteries I obtain surplus from security alarms are marked with their float maintenance current. It will of course depend on the actual float voltage in the alarm panel to the float current taken by the battery, but there will always be some. This factor can be used by the alarm technician in part as an indication as to the state of the battery, if it was going high impedance or had leakage across the cells. Normally the batteries are changed routinely long before this would happen. I had believed in the past that once a battery had reached it's peak charge that on the nominal float voltage for the type of battery in use the current into the battery would fall to zero. In practice was to find out over the years that it does not. Had an occasion a few years back to test this out when adding an emergency back up battery to our local low power UHF repeater. This is fed with an Advance/Gould 13.8V stabilised PSU that had been set at 13.80V. The SLA battery was nominally charged before installation and when first connected to the PSU the battery drew about 250mA for a short period then fell back slowly to a constant 25mA which was maintained from then onwards. The voltage remained at 13.80V. At this point I rest my case and beg to differ. With regard to the lowest voltage a lead acid battery should be taken to in service, in the telecom, fiber and microwave systems I was involved in maintaining, these had their LVD (low voltage disconnect) points set at 1.75V per cell. This equates to 10.5V in a 12V battery system. There are deep discharge batteries available a much higher costs, but am led to believe that a normal lead acid battery could be permanently damaged in available capacity by deep discharging. With this in mind and using normal SLA batteries, fitted 10.5V LVD devices to the two local amateur repeaters that both use 13.8V power systems. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
