Access Point requires AC power adapter with 12V and 1A output. Can I use cigarette lighter adapter (usually intended to be used to charge laptops in a car) for this device? Cigarette lighter adapter has input 12V and output 15V with 3500mA output current. Is it safe?
The output voltage of the laptop power adapter is too far from the router's input voltage. If the router is designed to take 12 V, a safe input voltage range would likely be 11.4–12.6 V (12 V ± 5%). 15 V is too high and will likely damage the router or greatly shorten its operating life.
Furthermore, the automotive electrical system does not provide regulated power and not all power adapters can cope with the wild input voltage fluctuations which can occur during normal operation. While a high-quality adapter should safely handle such fluctuations, there is no guarantee harmful transients will not reach the device.
Your safest bet, as others have noted, is to use a 12 VDC to 120 VAC inverter and power the router from the inverter using its factory-supplied AC adapter. In addition to ensuring that your router will get the correct voltage, this will provide much stronger power isolation from the unreliable and electrically noisy automotive electrical system.
Personally, I'd use a 12V:120VAC inverter and the power supply the AP came with.
Your chances of getting decent and trouble-free life will increase exponentially with the distance from the horribly transient-prone automotive electrical system.
I know how to make it reliable, and it is not worth it for a one-off.
Most devices operate internally on a 5V or 3.3V power supply. Often either a linear or switching regulator steps down the voltage to these levels. Both have a certain maximum input voltage.
When a device requires a certain AC voltage, it's rectified internally no matter what type of regulator is used. As long as this rectified voltage is below the maximum input voltage of the regulator, it'll probably all be fine. However, you never know what kind of delicate electronics are inside of the device.
If the device accepts 15VDC and your new adapter is capable of outputting 3500mA, it doesn't mean that it's going to supply 3500mA all the time.
As a general rule, if the label says "x volts, y amps", adhere to these instructions. Probably the safest thing to do is to buy a small inverter which steps up the 12-15VDC of your car to 230 or 110VAC and plug the original adapter that came with your device into this inverter.
The main issue in using car or boat power is transients voltage that are producing by the ignition pulses, the battery disconnections, the switch-off of high power devices (i.e lights)...Modern cars are equiped with central transient suppressor device in order to protect sensitive equipment like controllers etc.
Cigaret lighter it is a simple resistor and thouse does not need souch a protection. So it is possible to found very short transient pulses of around 80V (depends of alternator size, the regulator system, the loads....).
So first is to use a well designed supressor (DVS) to cut this lethal peaks. But usually this supressor has a maximum clamping voltage higher than your equipment need (i.e 20 volts). So afte DVS it is recomended to use an apropriate DC-DC converter with a souch wide input (i.e 8 to 21 volt) and a stabilized output to meet your equipment needs in voltage and current.
By the way since I'm not a driver, is new cars equiped with cigaret lighters? If not, your car is quite old and may be there is no central supressor device on it.