Cut off voltage lithium battery?

The LED current is not the biggest problem. If the LED is a 1.8V red one and the supply to its 470 ohm resistor is 5V then its current is only (5V - 1.8V)/470= 6.8mA. But the 5V relay's 70 ohms coil draws a whopping current of 5V/70= 71.4mA.

I made specs circuit this evening. Probably looks terrible. Will test run it tomorrow.
If you see anything I made wrong or in a bad way please tell me. (Battery in to the left and load to the right)

Just realized maybe wires in circuit are to thin?

I just tested circuit with 14v in and with 10K resistor as load. Multimeter shows zero
If I measure over mosfet fron G to S or D I get 14v. Am I doing something wrong or is it just failure in my circuit?

Rorut said:

I just tested circuit with 14v in and with 10K resistor as load. Multimeter shows zero
If I measure over mosfet fron G to S or D I get 14v. Am I doing something wrong or is it just failure in my circuit?

Click to expand...

What are the voltages measured from 0V to MOSFET source, gate and drain?

spec

I first tried to adjust with pot but nothing happened. I had to turn very many turns and now it seems to work!!! Amazing Its a bit hard to adjust with pot.

spec said:

What are the voltages measured from 0V to MOSFET source, gate and drain?

spec

Click to expand...

with 14.2v from source I get 2.495v between 0 and pin G. Between 0 and pin S i get 14.26v

Adjusted down to 12.4v and i cuts perfectly below that. Didn't test with battery yet beacuse they are fully loaded. But with adjustable power supply. Very happy I managed to get it together. Only thing left now is to understand how the circuit works

Rorut said:

with 14.2v from source I get 2.495v between 0 and pin G. Between 0 and pin S i get 14.26v

Click to expand...

Can you answer these questions:

With the common lead of the multimeter connected to the 0V supply line. What are the following indicated voltages when you connect the input lead of the multimeter as follows:
(1) on source pin on MOSFET
(2) on gate pin of MOSFET
(3) on drain pin of MOSFET

Could you please answer in the same form as the questions ie (1) (2), (3).

spec

Rorut said:

I first tried to adjust with pot but nothing happened. I had to turn very many turns and now it seems to work!!! Amazing Its a bit hard to adjust with pot.

Click to expand...

Our posts got crossed. Yes those potentiometers are multiturn and take ages to adjust. There is a special but cheap tool for the job which makes adjustment much easier.

I am pleased and relived that the circuit appears to work.

spec

Rorut said:

with 14.2v from source I get 2.495v between 0 and pin G. Between 0 and pin S i get 14.26v

Adjusted down to 12.4v and i cuts perfectly below that. Didn't test with battery yet beacuse they are fully loaded. But with adjustable power supply. Very happy I managed to get it together. Only thing left now is to understand how the circuit works

Click to expand...

The functioning of the circuit is fairly simple so it should be easy to understand. The first thing is to understand the fundamental function of the Zener, PMOSFET, and comparitor. If you want, I will post a full description if you get stuck.

spec

spec said:

Can you answer these questions:

With the common lead of the multimeter connected to the 0V supply line. What are the following indicated voltages when you connect the input lead of the multimeter as follows:
(1) on source pin on MOSFET
(2) on gate pin of MOSFET
(3) on drain pin of MOSFET

Could you please answer in the same form as the questions ie (1) (2), (3).

spec

Click to expand...

with 12.43v from power supply

(1) on source pin on MOSFET
12.43v
(2) on gate pin of MOSFET
2.496v
(3) on drain pin of MOSFET
12.43v

Another question about my circuit. Is it ok with thickness of wires? Thinking if 3-5A is going through, can cables handle that or am I thinking wrong?

I will try to find and learn some more about "Zener, PMOSFET, and comparitor". You don´t have to write anything yet. Have done more than enough already I will ask here if I get stuck on something Can´t thank you enough!

Rorut said:

with 12.43v from power supply

(1) on source pin on MOSFET
12.43v
(2) on gate pin of MOSFET
2.496v
(3) on drain pin of MOSFET
12.43v

Another question about my circuit. Is it ok with thickness of wires? Thinking if 3-5A is going through, can cables handle that or am I thinking wrong?

I will try to find and learn some more about "Zener, PMOSFET, and comparitor". You don´t have to write anything yet. Have done more than enough already I will ask here if I get stuck on something Can´t thank you enough!

Click to expand...

No sweat Rorut,

Those voltage are all to design.

When I described the route for learning about electronics in an earlier post, the number of things you need to know about MOSFETs and comparators ar mentioned. I did not cover Zener diodes, but they are quite simple.

Glad it all seems to be working OK

spec

spec said:

No sweat Rorut,

Those voltage are all to design.

When I described the route for learning about electronics in an earlier post, the number of things you need to know about MOSFETs and comparators ar mentioned. I did not cover Zener diodes, but they are quite simple.

Glad it all seems to be working OK

spec

Click to expand...

Thanks, I will spend some time learn about what you described in the earlier posts.

But is cable thickness ok? Or is it going to melt/burn on higher amps

Are you talking about the wire on your circuit board, of some other cable. The wire on the circuit board will be OK.

spec

spec said:

Are you talking about the wire on your circuit board, of some other bable.

spec

Click to expand...

Yes thoose red and black ones. They are not very thick. 0.28mm2

Our posts crossed. The circuit board wiring will be OK.

Use 5A or higher cable elsewhere.

spec

I'm so happy with the circuit just wondering how to configure the circuit the best way for different battery packs (1s,2s,3s,6s)?
Thank you!

Rorut said:

I'm so happy with the circuit just wondering how to configure the circuit the best way for different battery packs (1s,2s,3s,6s)?
Thank you!

Click to expand...

That's great. It is difficult to design a circuit without testing it in real life.

Funnily enough I was going to design the circuit to cope with a range of battery stacks and did a few trial designs. I will give it further thought.

spec

spec said:

That's great. It is difficult to design a circuit without testing it in real life.

Funnily enough I was going to design the circuit to cope with a range of battery stacks and did a few trial designs. I will give it further thought.

spec

Click to expand...

Sounds great! looking forward for an update like that .

But if I make the same one again but for a different cut off voltage like lets say 9.3v. What components should be changed and can I calculate for it somehow?

I guess its maybe best to wait for your update

Issue 3 of 2016_05_28

Hy Rorut,

Here is a universal voltage cutoff circuit:

ERRATA
(1) IC3 should read N2
(2) N2 should read N1
(3) The resistor across the LED should read R8, 100K
(4) A blue LED has too higher forward voltage to illuminate with a cut off voltage 0f 2.7V but LED 1 can be:
(4.1) Red: VLMS30K2L2-xxxx (where xxxx is either GS08 or GS18)
(4.2) Orange: VLMO3L1M2-xxxx
(4.3) Yellow: VLMY30K2M1-xxxx
or any LED shown on the data sheet referenced below

NOTES
(1) The maximum input voltage is, 30V (limited by Q1 VDS). This will allow up to seven LiIon cells to be used in series (7 * 4.2V = 29.4V)
(2) The minimum cutoff voltage, is 2.7V (limited by the collector saturation voltage of Q2-1). This will allow one LiIon cell to be used. In practice, the minimum cutoff voltage will be close to 2.5V.
(3) The cutoff voltage (Vco) is set according to the formula: Vco = R2 + RV2 resistance setting, where R2 and RV2 are in M Ohms. For example if R2 were 2.5M Ohms and RV2 were set to the mid point of its travel (500K Ohms) the total resistance would be 3M Ohms, so the cutoff voltage would be 3V. The cut-on voltage would then be 3.1V, allowing 100mV battery rebound.
(4) RV2 allows the cutoff voltage to be adjusted by 1V
(5) The hysteresis is 100mV and can be easily adjusted by adjusting R3
(6) Neglecting the LED current, the circuit takes a constant 9uA, turned on or off and regardless of battery pack voltage
(7) The LED will illuminate when the circuit is turned on regardless if a load is connected or not
(8) R7 should be adjusted to give the required LED current and hence LED brightness. The higher the value of R7 the better. Additional circuitry can be added to give a constant LED current, regardless of battery pack voltage.
(9) This circuit may work with the original PMOSFET, but it will depend on a sufficiently low gate threshold voltage of the individual PMOSFET sample.
(10) Q2-1 and Q2-2 are matched transistors in one case. They are configured as a current mirror.
(11) N2 is a constant current generator set to 4.5 uA.

DATA SHEETS & SOURCES
(1) SiA453EDJ Extremely Low Gate Drive PMOSFET
https://www.vishay.com/docs/62864/sia453edj.pdf
(2) TLV3701 Nano Power Comparator
https://www.ti.com/lit/ds/symlink/tlv3701.pdf
(3) LM334 Constant Current Generator
https://www.ti.com/lit/ds/symlink/lm134.pdf
(4) BCM846BS NPN Matched Transistor Pair
**broken link removed**
(5) MAX6008 Precision Low Current Zener Diode
https://datasheets.maximintegrated.com/en/ds/MAX6006A-MAX6009B.pdf
(6) Low Current Red, Orange, or Yellow LED
https://www.vishay.com/docs/81322/vlmosy30.pdf

This is awesome! I will definitely make and use this one for all projects including lithium batteries. Can't thank you enough for all help and fast feedback spec! And I can admit I'm a bit jealous of all your knowledge
I will try to update my moser list with components above and post it here.