Tejas Gell Cell charger

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From: Tom Bowman (tbowman@nbn.net)
Date: Sun Dec 31 1995 - 13:33:54 EST


-- [ From: Tom Bowman * EMC.Ver #2.5.02 ] --

        Thanks to all who responded to my question about the low float voltage I've
been measuring out of my Tejas charger. i finally got a chance to take the
charger apart and found trimpot R7 measured 400 ohms, not the specified 500
ohms. Sure wish I would have measured that pot when I was assembling the
charger....
              With all 400 ohms cranked into the circuit, I was only seeing
about 13.2 VDC across a fully-charged battery.
        The cure was simple: I broke the PC board path and added a 150 ohm, 1/2
watt resistor between R7 and the base of the 7805 regulator. Now I've got an
easy 13.5 volts output for the float voltage.
        That 13.5 VDC float voltage is critical, one list reader said, to maintain
the health of gell cells.
        One other note about the 7805: When building the Tejas charger, I mounted
my 7805 UNDER the PC board and heat sinked (sank??) it to the case using a
mica insulator to keep the 7805 above cabinet ground. Made more sense to me
then using a heatsink attached to the 7805 tab.
        Best wishes to all on qrp-l for a fine New Year.....
        

--
Tom Bowman, WA3REY, tbowman@nbn.net


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