What does a power supply do and how does it work?
12v power refers to the amount of regulated power that an adapter can provide or a device needs to operate.
A power supply is an electrical device that supplies electric power to an electric load. It draws power from a source with the correct voltage and current to power a corresponding electrical device.
You’ve probably noticed that 12V power supplies are the most frequently used power supplies. From the medical industry to computer peripherals, 12V is used to power everything from mobile equipment, lighting modules, iPads, laptops, and more.
In this article, we discuss 12v power and what it means. I also explain how voltages are important for a device to operate smoothly while powering electronic products in boats and RVs.
What is 12v power?
As discussed,12v power can refer to the amount of regulated power that an adapter can provide or a device needs to operate. V represents volt or voltage. Voltage is the number of volts that can be supplied to an electronic device or circuit. So, a 12v device needs to be given 12v power and a 12v power supply can provide it.
In the case of an adapter, one end with the pins goes into the power source and the other end with an output plug goes into the device.
- In general, a 12V DC output is obtained from the mains AC (power grid) and converted to low-voltage DC power for routers, computers, or other devices.
12v power and Car Batteries:
Cars or other automobiles such as trucks and RVs are generally fitted with a 12v battery.
A “12V battery” means it provides a standard 12v output under nominal load. The battery provides power to the radio, lights, and other electrical components of the vehicle.
A 12v car battery has six cells batteries and is considered fully charged at 12.6v or more.
What is a 12-volt power outlet?
A 12V outlet outputs 12v.
You have these in your computer in the form of Molex connectors for optical drives or hard drives. More famously, modern cars have a de facto cigar lighter or receptacle, which is a 12V socket.
Cars may also feature 12v Auxiliary power outlet(s) for portable electronics. The outlet is used to power USB chargers, car vacuums, dash cams, and other accessories.
Power Supply: Voltage, Polarity, and Rated Current
We need to understand three basic concepts if we truly want to understand how an adapter or power supply works.
Polarity:
Polarity indicates the electric potential at the ends of a circuit.
You may be familiar with this concept if you have used a AAA battery that has these markings. The marking will indicate positive (+) or negative (–) polarity of the tip on both sides.
For the most part, you can ascertain the polarity from a diagram or symbol on the backplate (or rating plate) of the adapter.
The drawing has three circles with a positive, negative, and black dot. The marking on the right of the black dot determines the polarity of the power supply.
The polarity of the output plug of your power supply should always match the polarity of the device it powers. Simply put, positive mates with positive and negative mates with negative.
If the marking is absent or erased, you can use a multimeter to determine the polarity. This video shows how to use a multimeter to identify the polarity of any DC power supply.
Voltage:
Voltage refers to how much power can be drawn from the source.
Power supplies range from small batteries to SMPS and can supply 3V to 24V. The backplate or product manual of a device will specify the particulate voltage a device needs.
Always use a power supply with identical voltage to avoid damage or burnout.
Current Rating or Rated Output Current:
Rated Output Current refers to the max current that can flow continuously through a circuit. In other words, it is the max load current your power supply can provide without overstressing or overheating an electrical device.
The amount of current is denoted in amperage.
A = Ampere and mA = milliampere or milliamp.
Every circuit breaker has a predetermined amperage mentioned on the label. Generally, household devices are rated 15 to 20 amps. Circuit breakers can only deal with 80% of amperage.
By now, you should have a broad idea about power supplies and electronic devices based on the above information.
- A 12v 1.5A power supply has 12v voltage and a 1.5 amp rating. In other words, the power supply can draw 12v power up to 1.5 amps and supply it to your device.
Similarly, a 12v 1A adapter can draw 12v power up to 1 amp.
Again, always check the output plug to ensure that the polarity is correct. Now, let’s look at common questions related to 12v power in the context of recreational vehicles.
Is 12v AC or DC?
The answer depends on whether you are using a 12v AC or 12v DC adapter. 12v power supplies are generally DC as most consumer electronics such as laptops, televisions, and radios need DC power.
Mobile phones need low-voltage DC current (5v) to charge. A 12v adapter draws power from a wall socket (110v to 220v AC), converts it, and outputs 12v DC power to the device.
AC stands for alternating current while DC is direct current.
DC flows in only one direction consistently. AC, as the name suggests, cycles back and forth (alternates) periodically. DC is used in devices that have a battery for a power source.
All batteries ranging from lithium-ion to car batteries run on (one-way) direct current.
Direct current requires complex circuitry and AC is easier to transport with a transformer.
- You cannot use AC and DC power supplies interchangeably. It can damage your device.
Is 12v the same as 120v?
12v is not the same as 120v.
120v is called high voltage or standard voltage – the voltage that comes directly into our homes.
12v is known as low voltage. 120v is the full line power that requires an electrician for all connections. 12v is the safer, lower voltage obtained from 120v using a step-down transformer.
- 12v is used for low voltage fixtures such as doorbells, smoke detectors, thermostats, and LED lights. 120v is used for bulky and demanding high voltage devices such as commercial lighting.
Most household outlets (receptacles) are 120v outlets. Exposure to 120v can be fatal, which is why an experienced electrician makes 120v connections.
12v is more efficient, easy to relocate, and only gives a slight shock if you come into contact with it. Thereby, 12v makes it relatively safe to operate electronic systems.
How long can a TV run on a 12v battery (when used in RV)?
A standard 12v battery can power a small or portable TV for anything between 2 to 10 hours. The answer depends on what kind of TV you are powering and the strength/capacity of your battery.
Plasma TVs may range between 1 to 4 hours. LED TVs may run for 8 to 15 hours. That said, you need a power inverter to convert DC from a 12v battery to run a TV.
A little math can yield the exact number. Find out the amp draw of your TV – how many watts your TV will use. Secondly, check the amp-hour (Ah) capacity of the 12v battery. A standard 12-volt car battery has a 50 to 60Ah capacity. A 32” LED TV would use 3 amps at 12volts.
Divide the amp-hours (Ah) with the amp draw. This gives you a formula: Ah/amps used by the TV. As per the values above, it is 60 / 3 = 20 hours. Batteries are not 100% efficient.
Factor in a 15% energy loss to account for the power lost while converting 12v DC to 120v AC. So, you can expect a 32” LED TV to run for 16 to 17 hours on a 12v battery.
These are approximate values as other variables may affect the outcome.
Should you run a TV on a 12v car battery?
Car batteries are not designed for deep-cycle applications used in large or flat-screen TVs. i.e. when the engine is not running. A 12v starting battery is designed to start up the car systems and allow the alternator to keep them topped off.
A TV (or other electronic devices) needs continuous power for a long duration.
Trying to use a starter battery for deep discharges can damage it. Additionally, a car battery is damaged if it is discharged more than 50%. You need a deep-cycle 12v battery for recreational vehicles.
Additionally, you can find 12v TVs made for recreational vehicles and off-road entertainment here.
They are TVs that operate on low voltage 12v DC electricity. 12v TVs are specially designed to run off an RV, boat, or car battery and can be coupled with cable or Apple TV.
Can you run a TV using a power inverter?
A TV can run off an inverter if it doesn’t exceed the inverter’s wattage limits.
You can calculate the wattage your TV requires in the product manual and the capacity of your inverter printed on the plate.
The right setup can easily allow a TV to run off the inverter because TVs don’t demand a ton of amperage.
You can read more about it in my post on the best size inverters to power a TV, Fridge, and Air Conditioner. You can find this post here.
In Conclusion
An electronic device without a power supply is nothing more than a box of plastic and metal.
Hopefully, you are now acquainted with some vital concepts about powering devices. I’ll leave you with a link to my post on whether you can use a 12v power supply on a 9v device and other frequently asked questions.
