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Category: Electrical
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Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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# I'm trying to use a 12 volt system in a car and restrict

### Customer Question

Hi. I'm trying to use a 12 volt system in a car and restrict power to an LED light to .03 amps or 3 milliamps. What kind of resister do I need?
Submitted: 1 year ago.
Category: Electrical
Expert:  Kevin replied 1 year ago.
Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question. 1) What is the forward diode voltage of the LED? All LED's will contain a forward diode voltage rating. 2) 3mA = .003 amps and NOT .03 amps. Need confirmation on the circuit current value?
Customer: replied 1 year ago.
It is 3mA so .003.I'm not sure how to answer your 1) question.This is the light I need to power up: http://www.ebay.com/itm/Waterproof-RGB-10W-Underwater-IP68-LED-Spot-Light-Lamp-Flood-Pool-Garden-Remote-/361147504220?hash=item541611965c:g:yeUAAOSwQJhUiAcP
Expert:  Kevin replied 1 year ago.
Thanks for the replies. 1) I suspect this type of LED light already has a built-in current limiting resistor since it is a multi-color version. However, to play it safe, I would obtain confirmation on this from the LED manufacturer. Usually, it is the smaller (individual color) LED's that require a current limiting resistor. Smaller LED's may or may not have built-in current limiting resistors. Larger LED's such as this type typically will have a built-in resistor. 2) The spec's show this LED is 10 watts. By applying Watts Law where P = I x E and solving for I, the current (I) is equal to P/E = 10/12 = .833 amps or 833 mA. This current value is based on the assumption that the full 10 watts is required for maximum LED brightness and using a nominal battery voltage of 12 VDC. 3) How did you determine the 3 mA value? I don't see anything on the spec's showing the forward current value?
Expert:  Kevin replied 1 year ago.
If you have any additional questions, just let me know and I’ll be glad to answer them for you. Otherwise, don’t forget to rate me before you log Off. Thanks...............Kevin:)
Expert:  Kevin replied 1 year ago.
If you have any additional questions, just let me know and I’ll be glad to answer them for you. Otherwise, don’t forget to rate me before you log Off. Thanks..............Kevin:)
Customer: replied 1 year ago.
I'm sorry I was wrong. The light is .3 amps. I got this information from a couple of sellers. Today I asked a few more sellers and will see what they say just so I can be 110% sure.From what I'm hearing it is a .3 amp light. My vehicle's power supply will send a huge amount of amps so I need to resist it.There is a small motherboard / chip looking thing that the lights are connected to so I'm sure it has a resister of its own. However when I hard wire it to my vehicle it gets incredibly hot very quickly and its only a matter of time before the lights burn up because there is no way for me to cool it off.Here is some info I received from one of the sellers. Not sure if its helpful:◆Voltage: AC200-240V
◆Power: 10W±0.5W
◆Size: Φ73MM*H103MM
◆LED quantity: 1pcs
◆Beam angle: 230°
◆Base:
◆Color :RGB
◆Lumen: --So what do you think?
Expert:  Kevin replied 1 year ago.
Thanks for the replies. 1) I assume that your vehicle voltage is a 12 VDC battery. Are you using an inverter to change it from 12 VDC to 200VAC or 240VAC or are you direct connecting the LED to the 12V battery? The spec's that you just posted show the voltage as AC200-240V? Thus, there is a big difference between 12 VDC and 240 VAC voltages. I've never heard of an LED that is capable of 200 to 240 volts before unless it has a built-in driver/electronics and an inverter is used to change the voltage output to an AC sinewave? 2) Yes, a traditional LED requires some form of a current limiting resistor. Otherwise as you state, the LED will quickly burn up. 3) I suspect that the LED you purchased is not made for the intended application?
Expert:  Kevin replied 1 year ago.
If you have any additional questions, just let me know and I’ll be glad to answer them for you. Otherwise, don’t forget to rate me before you log Off. Thanks...............Kevin:)