Should a voltage regulator especially for a stand-by backup battery be=20 constructed that senses battery condition that charges when necessary a= nd=20 provides 13.8 VDC float voltage during stand-by times if no charge= is=20 needed?

The BB diode drops the charging voltage .2 currently (to 13.9 - 14.1 VD= C),=20 this is good because it is almost the float voltage but in the summer the=20 voltage will be much higher than the float voltage. Am I damaging= the=20 stand-by backup battery?

>>>>>>>>>>>>>>>

Finally, I was able to answer my own questions.

No special regulator or system to maintain a float voltage need be=20 constructed or utilized.

There are at least three things that shorten the life of SLA=20 batteries - multiple deep discharges, long term overcharging, multiple long=20 periods of disuse (measured in several months). By shortened life I me= an=20 lack of ability to deliver rated Amp Hours service including, for starting=20 batteries, Cold Crank Amps and otherwise the delivery of voltage/current ove= r=20 usage time.

There is one thing that extends the life of SLA batteries and that is=20 maintaining a continuous constant float voltage at a small current=20 level. Thus a standby battery maintenance scheme was=20 considered.

Normal life (several years) can be achieved by normal usage. =20 Discharging to a single digit percent of its rating, recharging at the prope= r=20 voltage level and limiting the current as the battery becomes charged accomp= lish=20 this end. In an airplane, such management of the main battery is=20 accomplished by the voltage regulator as long as it is matched to the=20 battery.

So, if I did construct a float voltage device for my standby battery, t= he=20 fact that it is cycled at each Master Switch cycle and then operates only fo= r=20 the duration of each flight means that it would not necessarily=20 extend its life. The slight over voltage charge rate during each=20 flight will probably not shorten the life to any less than the mai= n=20 battery.

Conclusion: Replace the standby battery on the same=20 schedule that the main battery is replaced. I.E. Every two t= o=20 three years or when the preflight voltage tests indicate a drop of more than= .2=20 volts from the previous trend (See Battery Tender FAQs re: How to tell if a=20 battery is bad).

BTW, I considered modifying a Battery Tender Jr (120 VAC in) to=20 provide the float voltage. It was interesting to note that most of the= =20 weight and space inside the unit was taken up by a transformer that dropped=20= the=20 120 VAC to 13.7 VAC.=20

Scott Krueger=20 AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)

Mer= ry=20 Christmas to all!

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