Hi
Have this setup .
Use of a TL431
When voltage is over fixed value, ex 24,24V then LED is on, and off again at 23,81 V
when changed from JUMPER 1-5 i can select different voltages to on/off
Use of 5 different resistors from 1050 - 1070 -1100 - 1130 -1150 Ohm
Gives me a on/off voltage from
On 24,24v off 23,81v
On 24,62v off 24,19v
On 25,23v off 24,78v
On 25,86v off 25,41v
On 26,31v off 25,84v

These values is ok for me,
I just want to know if this will work IRL,

 

Below is the LTspice simulation of your circuit.
Note that the TL431 has a relatively broad turn-on and turn-off due to it's gain being only about 600.
What is the purpose of the 500kΩ resistor? It's the wrong polarity to generate hysteresis.



If you want a sharper switching function you could add a transistor to the circuit (below).
Hysteresis polarity is now correct.

 

Run a little behind in this, and have now got an extra feature to it.

The circuit should sit and measure on battery 24-28V and when voltages comes below ex 23,5-24V then circuit should activate a relay and keep the relay activated until a switch is pressed-
How should I construct that ?
The relay is 12 v DC Coil. and contacts is operating 220VAC.

 

The circuit should sit and measure on battery 24-28V and when voltages comes below ex 23,5-24V then circuit should activate a relay and keep the relay activated until a switch is pressed-
How should I construct that ?
The relay is 12 v DC Coil. and contacts is operating 220VAC.

Do you have 12V to power the relay?
It might be better if you used a 24V relay and powered it from the battery.

 

Your easiest solution would be to use a 24V coil, and use a Thyristor fed from the bottom circuit in post#2, the Gate can get it's trigger from the Cathode of the Tl431 .

 

Here's my circuit with an added 24V relay and a reset switch (S1).
Positive feedback through D2 and R6 latches the circuit when tripped, until S1 resets it (at 1.6s in the simulation).

 

Look good . But Will this trigger the relay when battery is loosing voltage and reach ex 23.5v. Or is it trigger when voltage is more than 23.5v ?

 

I've had some fairly good luck with relays that came out of an old dishwasher control board. They were 24 volt rated and I ran them in the car at 13.8 to 14.4 volts. The seemed to work well enough. Not sure if 12 volts will do the trick but 13.8 seemed to. I suppose I could go down into my laboratory and set up my 12V supply and see if one of these used relays will click in. But I just don't feel like going down there right now.

 

Here's my circuit with an added 24V relay and a reset switch (S1).
Positive feedback through D2 and R6 latches the circuit when tripped, until S1 resets it (at 1.6s in the simulation).

View attachment 147194

Hi

Why not just use an LM339 and transistor driver?

eT

 

Look good . But Will this trigger the relay when battery is loosing voltage and reach ex 23.5v. Or is it trigger when voltage is more than 23.5v ?

Opps. I misread your post #3.
It triggers when the voltage is above the set point.
Back to the drawing board.

 

Why not just use an LM339 and transistor driver?

Why add an IC if you don't have to?
I'm a KISS sort of guy when it comes to circuits.

 

Okay, take three.
Here's the circuit modified so that it turns on the 24V relay (and the LED) when the voltage drops below the set point and latches until its reset by S1.

 

Why add an IC if you don't have to?
I'm a KISS sort of guy when it comes to circuits.

Gotcha

Just seems like there’s a lot of parts already.
eT

 

Just seems like there’s a lot of parts already.
eT

There may be.
But most are diodes, resistors and capacitors.
And what does that that to do with adding an extra uneeded IC to the mix?

If have a lower parts count design to do the job, that would be good.

 

There may be.
But most are diodes, resistors and capacitors.
And what does that that to do with adding an extra uneeded IC to the mix?
If have a lower parts count design to do the job, that would be good.

Using a comparator chip just would have been a different approach.
I'm not disagreeing with your circuit.....just asked why you didn't use a comparator chip...hoping for a little knowledge sharing here.

eT

 

just asked why you didn't use a comparator chip

For the TS's requirement, you need some form of accurate voltage reference to provide a stable trip point for the comparator.
So, to simplify the circuit, I used a voltage reference (TL431) that can be configured as a comparator with an accurate trip point.
Thus I only need the voltage reference.
An added comparator becomes redundant.

 

For the TS's requirement, you need some form of accurate voltage reference to provide a stable trip point for the comparator.
So, to simplify the circuit, I used a voltage reference (TL431) that can be configured as a comparator with an accurate trip point.
Thus I only need the voltage reference.
An added comparator becomes redundant.

Thank you sir...

eT

 

Thanx, will try it out.

Some questions.

D2 = ?? some kind om zener diode or ?

I know B and B should be connected, End just "floating" when not pussed,
and to ground when reset ?

What is "k" ?

 

Personally I think i'd have gone down the comparator route, I've done something similar with a comparator (may have been a 339), a zener, a handful of resistors and a 2N2222 to drive an NC relay........ The primary reason for this was low quiescent drain (down to several uA, as it's for a vehicle), it needs to turn something off when the engine is running, but I wanted it running direct from the battery and not the ignition circuit.

I'm a big advocate for KISS, but it's whether or not the simplest approach will cause me any other issues (like a flat car battery in my case)

 

D2 = ?? some kind om zener diode or ?

Yes, it's a 3.3V zener.

I know B and B should be connected, End just "floating" when not pussed,
and to ground when reset ?

Yes.

What is "k" ?

Just a node name for the cathode of the voltage reference.