APO3 Menu▼

APO3 Menu


The APO3 is a black box designed to prevent a vehicle battery from being discharged and damaged by a DC load. Typically it is used to switch a radio transceiver off 10 minutes after the vehicle is shut off.

The APO3 is designed for 12 volt vehicle electrical systems with negative ground. It can switch up to 20 amps and carry up to 30 amps. The shutdown voltage can be set to one of four pre-programmed voltages (11.8, 12.1, 12.7, 13.05 volts) using two DIP switches; the shutdown delay can be set to one of four pre-programmed times (0, 5, 10, 20 minutes). The device is housed in a sturdy ABS plastic case.


Dimensions: 84mm x 121mm x 34mm (3.3in x 4.75in x 1.35in)
Weight: 5.5 ounces (158 grams) with Anderson connectors
Input Voltage: 7-20 volts DC
Input Current: 1.734 mA @ 12.0 VDC with LED off and relay off
60 mA @ 13.8 VDC with LED off and relay on
61.25mA @ 12.7 VDC with LED on and relay on
Load Current: 30 amps holding, 20 amps switching
Internal Protection: Thermal, Over Current
Case Material: Flame retardant ABS plastic. UL's best flame rating of 94-5VA (case only).
Voltage Set Points: 11.8, 12.1, 12.7, 13.05 volts DC. Selectable by DIP switch.
Time Delays: 0, 5, 10, 20 minutes. Selectable by DIP switch.

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Pricing and Purchasing

Now you can purchase these products directly through our sister website: Off Grid Options

APO3's are also available from our fine stocking distributors:

APO3: Automatic Power Off 3 (bare wire leads)

$59.95 USD

Part: APRS5000
Weight: 1.00 lbs

APO3C with bare wire leads. Packaged in a cardboard box with printed instruction sheet.

APO3: Automatic Power Off 3 (powerpole connectors)

$59.95 USD

Part: APRS5001
Weight: 1.00 lbs

APO3C with Anderson Powerpole 30 amp connectors. 30 amp Anderson Powerpoles will mate with 15, 30 and 45 amp connectors. Packaged in a cardboard box with printed instruction sheet.

APO3: Automatic Power Off 3 (OEM radio connector)

$59.95 USD

Part: APRS5002
Weight: 1.00 lbs

APO3C with OEM T connector. This is the connector that is typically found on the back of mobile amateur radio transceivers. Packaged in a cardboard box with printed instruction sheet.

Automatic Power Off, Solid State (APO3SS), bare wire leads

$89.95 USD

Part: APRS5010
Weight: 1.00 lbs

APO3SS with bare wire leads. Packaged in a cardboard box with printed instruction sheet.

Automatic Power Off, Solid State (APO3SS), circuit board with bare wire leads

$79.95 USD

Part: APRS5013
Weight: 1.00 lbs

APO3SS board only with bare wire leads. Packaged in anti-static bubble bag.

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What It Does and How It Works

The APO3 is basically a voltage controlled switch. When the vehicle voltage is higher than the APO3 set point, the relay is turned on and power is provided to the load side. When the voltage drops below the APO3 voltage set point and stays there for longer than the time set point, the APO3 relay turns off and power is removed from the load side.

The APO3 has a bright-yellow LED to indicate its status and it has a slide switch that can be used to turn the load on regardless of the input voltage.

Using the factory default settings, the APO3 will turn on the load when the vehicle voltage rises above 13.05 volts. This typically occurs within a few seconds of starting the vehicle. The load remains powered as long as the engine is running. When the engine is shut off, the vehicle voltage sinks below 13.05. The APO3 waits until the voltage has been less than 13.05 volts for 10 minutes and then turns the load off.

The APO3 is ideal for use with mobile APRS / AVL stations. It allows the radio to transmit a few position reports after the vehicle is shut off before turning off the radio and GPS. This reduces clutter on the APRS / AVL channel and prevents the vehicle battery from discharging.

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The APO3 is installed between the vehicle battery and the DC load. Typically, the load is a mobile radio transceiver along with accessories. Standard installation involves cutting the DC feed to the radio and using butt splice connectors to install the APO3. This usually takes 10 minutes or less. If you use Anderson Power Pole connectors, we offer an APO3 with Power Poles already installed; this makes installation a literal snap. If you want to change the factory set points, you will need to remove the cover and flip a couple of small switches. Important: The APO3 is not suitable for installation within the engine compartment.

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Steve Hicks, AB5ZW writes:

I've had my TM-D700 in my car for about 6 months, and I was always forgetting to turn the rig on when I got in, or I'd forget to turn it off when I got to wherever I was going. I'm an electrical engineer, and I've built a variety of custom circuits, so I was thinking of designing a circuit to control the power to the radio. But then I saw the APRS World booth at the Dayton Hamvention, and realized that the APO3 did everything I needed, and more. It has more features and is cheaper than anything I could have designed and built myself. I like the fact that it leaves the radio on for 10 minutes (or 3 other settings) after I shut the car off, which allows my final position to get transmitted at least once. And the override switch is handy for those times when I want to use the rig when the engine is off. I was able to use the default voltage setting, but I like that there are 3 other voltage settings just in case. It installed in my car in about 5 minutes, and has been working flawlessly for almost 2 months now. I just bought another D700 for my truck, and I'm getting another APO3 for it. In my opinion, the APO3 is a very useful, high-quality product that any ham with a mobile radio would find extremely helpful.

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