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Hi all. Just joined group today. I have an ATU-100 and am confused re the power requirement. The info says 10-15 volts dc range but the internal battery is a lithium 3.7 volt. The input on the schematic by N7DDC shows 12volts with a 5 volt regulator
downstream. This seems logical.

How does a 3.7 volt battery allow the unit to work when the supply is quoted as 12 volts?? Nick. VK4YT.

3.7 Volts will keep the microprocessor alive, but may not be enough to run the relays.?
The ATU-100 specifications say the maximum current draw (while switching relays) is 400 mA.
Current draw running the display, but not switching relays is 40 mA.?
The onboard 78L05 voltage regulator specified minimum voltage is 7 volts.
The regulator's maximum input voltage is 30 Volts, but that may provide too much current to the relays.?
I would not exceed the ATU-100 specified maximum input of 15 vols.? ?
My ATU-100 has no problem operating off of four AA cells = 6 volts.

3.7 volts will keep the microprocessor alive, but recommend 6 volts or more to operate the relays.
If you plan to use battery backup along with external 12-15 Volt external power,?
include a blocking diode to protect the battery from external power.?
?