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From: "Rumburg, William" <william.rumburg@cdicorp.com>
To: Lancair List <lancair.list@olsusa.com>
Subject: RE: Charging Diodes
Date: Tue, 18 Jul 2000 09:19:42 -0400
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> If the charge of a Lead Acid battery is determined by the cell voltage at
> the end of charge then how can two batteries, one being charged directly
> and
> one being charged through a diode, both reach the same level of charge?
> The
> diode has a 0.6V nominal forward conduction loss so either one battery
> will
> be under charged or one will be overcharged (or both).
> 
> Brent Regan
> 
	Brent -
	Your observation is correct. My VMS 1000 indicates a steady-state
charging voltage of 14.0 V DC to the Concorde RG-25 system battery. The
charging voltage through the diode to the backup battery is then [14.0 -
0.6] = 13.4 V DC. 
	I called Concorde (800) 767-7593 and spoke with Don Grunke (an
electrical applications engineer). He told me that the recommended charging
voltage for their RG series battery is 13.8 to 14.2 V DC and that this would
also be the charging voltage for my Sears Die-Hard lead-acid backup battery.
However, he stated that Concorde has found during testing that a voltage as
low as 13.5 VDC will maintain full charge on a sealed lead-acid battery. 
	The use of a diode is my Keep It Simple solution for charging and
isolating the backup battery. Don stated that he felt it likely that 13.4 V
DC would maintain the backup battery at or near full charge, but if there
was any concern about that, the backup battery could be connected directly
to the charging bus by means of a relay, which would automatically
disconnect (isolate) it upon switching. 
	Another problem I've noted is that the electric gyros will drop off
line at a higher voltage than I would have expected, about 12.0 to 12.2 V
DC, depending on manufacturer. I'm going to operate the backup system to
determine at what voltage each electric gyro "flags" off and how long before
the backup battery's voltage decays to those levels under actual operation.
If it's longer than 2 to 3 hours, I'd consider that sufficient. Jeff Rose
states that his electronic ignition requires only 3/4 amp and will function
down to 6 V DC. I'll report the results of this to the LML in the near
future.
	Bill Rumburg
	N403WR  (Sonic bOOm)
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