Battery Bckup

[George, W5YR]

Several folks have asked for more details on the battery backup system I
use. Rather than try to use ASCII graphics, here is a word description as
best I can do it.

The + output terminal of the VS-35M Astron supply goes to the anode of a
high-current diode - the end with the arrow symbol pointing away from the
connection. I don't know but I suspect the diode I used will handle about 50
amps. It is required to carry only the normal load current of the station
plus the charging current for the battery. Once charged, the battery
requires only a very small keep-alive current. When first turned on, the
supply meter reads a maximum of about 20 amps to the battery; the current
quickly decays to an amp or less as the battery takes the charge.

The cathode connection to the diode - the end with the bar symbol - is
connected through a 30 amp fuse to the + terminal of the battery.

The - terminal of the battery is connected through a 60 amp fuse to the
common ground connection from the - terminal of the Astron which is the
ground or negative connection for the station equipment.

One final connection is a 60 amp fuse from the + terminal of the battery to
the station equipment as the + terminal or connection for the station
equipment.

To summarize, the Astron feeds the station equipment through a 30 amp fuse
in series with a 60 amp fuse. It also feeds the battery through the same 30
amp fuse. The battery feeds the station equipment through a 60 amp fuse in
each line.

Note that the choice of fuse size and specific connection was dictated by
the configuration of a large fuse block I removed from a defunct air
handler.

The output voltage of the VS-35M is set to provide 13.8 volts float voltage
to the battery with the station equipment turned on. In my case that is one
or two transceivers at a total load of about 5 amps for both.That same 13.8
volts is applied to the station equipment.
The voltage drop across the diode is about 0.7 volts.

I use a wet-cell deep cycle RV battery for two reasons:

1. I had a brand new one obtained in a battery trade-in adjustment

2. a deep cycle battery is much better suited to backup duty than a
conventional starting battery for a car.

Because it generates hydrogen fumes during charging, I mount the battery
outside the shack in a battery case obtainable at any RV shop. Connection is
made with #10 wire which is rated at 30 amps continuous load current. Larger
wire could be used, but my station equipment is highly unlikely to ever use
more than 30 amps. The wire connection is relatively short so line voltage
drop is negligible.

The question of mounting a gel-cell inside is another issue. True, they are
supposed to be sealed and gas-proof, but I would feel more comfortable with
such a large battery outside the shack "just in case."

I hope that these details make it a little clearer as to how I use a backup
battery. Let me stress that you MUST use the isolation diode between the
Astron and the rest of the system.

73, George W5YR
Fairview, TX
[hidden email]
http://www.w5yr.com













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