I just baught an LCD for my car. it needs 12v DC 500mA can i just wire directly to cig. lighter? what kind of fuse do i need to protect it ? do i need an inverter / converter ? ? ?

yelp!

 

I would use a 12 volt transformer from Radio Shack, this is because the car electrical system is not pure 12 volts, and the differences in voltage may damage the LCD.

You can get a 12 volt 500 mA transformer for around $10.

 

You do not use a transformer for DC current.

 

500mA = 0.5A I would suggest a 3/4A or 1A fuse to protect the LCD.

Ericdwong is right, you will not get exactly 12vdc in your auto electrical system. You will most likely see 12.75-13.5V. Check the specs on the LCD, they will usually indicate the operating voltage range.

Maximus97SE is also right, a transformer is for alternating current circuits. You may need a voltage regulator.

 

you do not need a fuse. The cig lighter is already fuse protected. You also do not need an inverter/converter because the cig lighter is already wired for 12 V DC. If you have to maintain a constant 12 VDC, a voltage regulator will do the job, but it'll cost you $$$$$$, and is not necessary after all. The car's electrical system already takes care of it. Your LCD will not be damaged @ 12 to 15 VDC.

 

The lighter probably has a 15 or 20A fuse on it, that will not protect the LCD. If the LCD has internal fusing, then I agree with you; but don't think that a fuse rated at 30 to 40 times the full load current of the LCD will blow before the LCD gets fried.

 

Usually fuse is for the car wiring protection, not for the device connected to it? Unless for some reason there is a voltage spark, or a surge current on the wire going to LCD...

 

i appreciate the input from you guys... has anyone actually done this though ?

the input is great.. but more valuable to me is input from people who have actually done/experienced.


I am sure i can put a seperate fuse for the device to protect it from cig lighter. 1A or less..

so.. voltage regulator will keep it DC and guarantee that that no more than 12 volts make it through ?

the only spec i have on the LCD is 12VCD 500mA.. but i managed to find a 12vDC 400mA adapter (from houshold current, think it belonged to a handheld game at one point) and it seems to be working fine..

will lower Amps from power supply affect the device ? higher amp damages it, right ? too low amp, just won't work ?

please continue your input if you can... but if you actually have done this.. yelp!

 

Typically, lower amp than required from power supply will cause the actual voltage to drop. the heavier the load the more it drops. High amp won't damage your LCD. It just means it has the capability to provide high amp, ie. it won't force that rated amp into your LCD. Well unless it is a special power supply with a constant amp no matter what the load is. You better take a look at its spec.

 

This is not necessary. However, if if makes you feel better, you can use the 7812 regulator chip. Radio shack should have it.
No. 400mA is not sufficient. If it requires 500mA, it may not work with that adaptor. If you try to use that 400mA adaptor, it (the adaptor) will probably overheat and eventually fail and the LCD should be ok. The LCD is a active device and will draw what current it needs provided that the power supply is able to supply it. The power supply will not dictate the current draw for the LCD.