Ques about delay switch or transistor

[hcchuar]

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?

 

[ericgibbs]

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?

hi,
IIRC the LM outputs are not individually isolated from 0V.
The previous designs using a LM in this way have a opto coupler in the LM ouput, the output of the opto drives a transistor/relay.

OK.?

 

[hcchuar]

hi,
IIRC the LM outputs are not individually isolated from 0V.
The previous designs using a LM in this way have a opto coupler in the LM ouput, the output of the opto drives a transistor/relay.

OK.?

what u means is put a optocoupler at the output of LM3914 and the opto drives the transistor,as show as below is correct?

what types of opto is suitable for me?and also transistor

my system need about 7A-10A,12V

 

[ericgibbs]

what u means is put a optocoupler at the output of LM3914 and the opto drives the transistor,as show as below is correct?

what types of opto is suitable for me?and also transistor

my system need about 7A-10A,12V

hi,
I'll look thru some opto's.

What are you doing with the 7 to 10A.?

EDIT: look here.
AVAGO TECHNOLOGIES|4N35-000E|OPTOCOUPLER, TRANSISTOR O/P | Farnell United Kingdom

 

[hcchuar]

hi,
I'll look thru some opto's.

What are you doing with the 7 to 10A.?

EDIT: look here.
AVAGO TECHNOLOGIES|4N35-000E|OPTOCOUPLER, TRANSISTOR O/P | Farnell United Kingdom

thanks for helping me
that means
1,2 = LED
4 =ground
5 =12V
6 =connect to pin 2

is correct?

 

[ericgibbs]

thanks for helping me
that means
1,2 = LED
4 =ground
5 =12V
6 =connect to pin 2

is correct?

Do you know how to connect the opto to the LM and transistor.??

 

[hcchuar]

Do you know how to connect the opto to the LM and transistor.??

erm.......i'm haven't touch opto before,
can u explain to me how to make a connection?

 

[audioguru]

The outputs of the LM3914 go low when they are active, they do not go high. So they cannot be used to turn on an NPN transistor.

You don't need an opto-isolator, you just need PNP transistors. The relay coil should have a reverse-connected diode across it to prevent its high voltage spike from destroying the transistor.

 

[hcchuar]

The outputs of the LM3914 go low when they are active, they do not go high. So they cannot be used to turn on an NPN transistor.

You don't need an opto-isolator, you just need PNP transistors. The relay coil should have a reverse-connected diode across it to prevent its high voltage spike from destroying the transistor.

Thanks for audioguru idea,
i will try on ur idea

 

[hcchuar]

The outputs of the LM3914 go low when they are active, they do not go high. So they cannot be used to turn on an NPN transistor.

You don't need an opto-isolator, you just need PNP transistors. The relay coil should have a reverse-connected diode across it to prevent its high voltage spike from destroying the transistor.

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?

 

[hcchuar]

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

 

[audioguru]

You should always look at the datasheet of a transistor to see which pin is what.
When the pins on a transistor are connected backwards then it works very poorly.