i'm running my project by using car battery,future will change to deep cycle battery, i'm using below battery indicator circuit to indicate the voltage level of battery, when the voltage drop until red LED, red LED light will turn on and my system will switch off.i'm using below power relay (SRU-12Vdc-SL-C,10A) to test by connecting with transistor (do not know what is the suitable value, just test on 2n3904) and resistor(1K).unfortunately when i switch on all the system, LED will automatically on without any control, probably power relay is not suitable use for this application.

the output of LED is around 11.6V, 12V will be using to power my system

Or i just using 12 V transistor as a switch?
any opinion?

 

A power relay is good and also the fact you have already got it.

The relay in the following circuit will operate to cut off the system when the LED at LM3914 pin#1 lights. The LED current from Pin#1 turns ON the transistor to drive the relay. You'll need to use a PNP type transistor. Any diode from 1N4001 to 1N4007 can be used instead. You can even omit the 220 resistor at the base of PNP and connects the base pin directly to the LED.

 

Eblc1388 is right because the outputs pf the LM3914 which drive the LEDs are high and go low when the LEDs turn on. This is the reason the circuit turns on.

 

A power relay is good and also the fact you have already got it.

The relay in the following circuit will operate to cut off the system when the LED at LM3914 pin#1 lights. The LED current from Pin#1 turns ON the transistor to drive the relay. You'll need to use a PNP type transistor. Any diode from 1N4001 to 1N4007 can be used instead. You can even omit the 220 resistor at the base of PNP and connects the base pin directly to the LED.

thanks for your information
i will try on that

 

anyone can answer me
i tried on above connection, it does not have any effect on the switch relay
eg, when i switch it to normally on, my system will on, when i switch it to normally close, my system will off

The on/off of LED does not effect my system,
anyone know what is the problem?
the relay switch i use is SRU-12VDC-SL-C,10A
should i change it to smaller amp?

 

it can working well already........thanks for u all...just the transistor putting wrong