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# how to make ldr do high power work(12v motor) without becoming hot? Answered

my ldr works fine in controlling 1.5 & 5v motor but connecting in series but when i switch to 9v and 12v motor it becomes hot
maybe i can decrease its heat by adding resistor parallel to ldr so motor will get required current and ldr wont have to suffer all current

or maybe i have also changed power source in second case to a 12v and 3amp
i thought i am not ta\ing 3 amp current according to I=V/R but P=VI so if current decrese my power source's voltage .

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## 6 Replies

Josehf Murchison (author)2013-10-26

I am assuming you mean a photo resistor.

You can parallel them however your motors will get twice the current on the same candlelight. (Candlelight is a measure of light)

If you are going to use things like “LCD” you will find saying “Liquid Crystal Display” works better for getting an answer.

Joe

rickharris (author)2013-10-26

When you say LDR I assume you mean a Light Dependent Resistor and you using this to control a motor? You circuit would be helpful.

IF you want to control higher current device you need to use a transistor as a switch. The LDR turns the transistor on and off and the transistor controls the motor.

Lots of possible circuits here

Or indeed a relay - the relay may need the transistor drive it anyway.

Atul009 (author)2013-10-26

I got a problem with arranging a relay maybe i'll soon get my hands on one
but if i dont i have tried transisor method and it becomes hot at a higher rate i was thinking how can i use multiple transistors as switch so each transistor will do less work(a npn transistor)
just want to KNOW! also if it dosn't work well or not at all

mpilchfamily (author)2013-10-26

The more power you put through a device the more heat it will produce. Adding resistors in parallel will help to minimize the current flow through the LDR but may mess up your circuit. Either way the same amount of power is flowing through the circuit and the same if not more heat will be generated just spread out over multiple components.

Atul009 (author)2013-10-26

so if I am ready to mess up my circuit i can add more resistors in circuit to make LDR heat up lesser
or case 2
i can power multiple motors with same power if thats what you mean by multiple components

mpilchfamily (author)2013-10-26

Multiple components as in adding resistors. The LDR is just a resistor that varies it's resistance based on light levels. The motor will draw a good bit of current which is going to generate heat when it has to pass through a resistor. Now you can have all that current and heat going through the LDR or spread out across multiple resistors (components). Either way your still generating heat and sometimes when you add more components to the mix more heat is generated and more power is lost.

Your best bet is to take rickharris' suggestion and use the LDR to trigger a transistor to turn the motor on and off. If your trying to control the speed of the motor based on light levels you will need a more complex circuit to do ti right and not damage any components.