Cut off voltage lithium battery?

[spec]

Is that the same as 6.8A?
2*3.4

Yes, that is correct. 'C' in battery nomenclature stands for capacity. In the case of the NCR1865B, 3.4 A/Hr (3400 mA/Hr).

The less the discharge current, the more capacity can be used and the longer the battery life.

spec

 

[MrAl]

Hi,

Just to note, you should be very careful when charging Li-ion batteries. Make sure you have a good design or else very bad things can happen.

 

[spec]

Thank you very very much for all the research!
Did not expect this project to grow so much but it is very fun and Im learning a lot from it

No probs. I always learn a lot from ETO questions and posts too.

I'm afraid posts tend to grow a bit when I am involved.

The reason to cut off at 3.5v is because I have been told that it is not good for the batteries going lower than that. But if it is ok to go lower like 3.1 to 3.3v or something I'm more than happy. A second protection if the PCB fails seems to be good as well.

While a cut off of 3.5V would certainly be good for battery life, you would be losing an awful lot of battery capacity. The nominal voltage of the NCR18650B is 3.6V rather than the other common 3.7V, so for a good compromise I would recommend discharging down to 3.1V and charging up to 4.1V. It is all a matter of balance; remember you are hitting the battery quite hard with the discharge current of 2 to 3A with a max of 5A. This is around 1C which is not good for battery life, compared to C/10 for discharge and charge which would give optimum practical life.

Temperature is not a problem. (Well it depends how you see it only having summer a day or two every year ). Im only going to use it during summer days or inside.

A high temperature increases battery capacity and a low temperature increases life.

I don't know if cut off circuit current consumption is imortant? Just thought it would be a good idea to cut everything at a certain voltage.

The cut off circuit (COC) always consumes current, but then so does the battery itself (you could say). A very good COC would consume 10% of the battery equivalent self discharge current so that, in practical terms, the COC would not affect the battery shelf life. Even when the COC turns off it will normally consume some current.

The self discharge of a LiIon battery is around 1.7% per month at 25 deg C (around 20% per year) (LiIon are the best common rechargeable battery in this respect). For the NCR18650C, this equates to an equivalent discharge current of 82uA, so a good COC would consume no more than 8.2uA. While COC chips are available that only consume a few micro amps, they lack flexibility and you would need a chip for each battery and a different chip for different cut off voltages.

Approximately At the same time I joined here I found this circuit that should be doing the same thing like mikes. I dont know if they are equal or which one is better? https://3.bp.blogspot.com/-Y1MicUfYujY/UlTqUj6jwlI/AAAAAAAAFYw/ryuPSF4z1Mg/s1600/low+voltage+cutoff+circuit.png

Mike's circuit is in a different league in all respects.

Incidentally, if you need any more genuine batteries at a good price this is a good source: https://www.fasttech.com/products/0/10001980/1141100-panasonic-ncr18650b-rechargeable-3400mah-3-7v (delivery about 4 weeks).

 

[audioguru]

it is a 40w class d amp

A Lithium battery cell averages 3.7V during a discharge so four make 14.8V. How does an amplifier produce 40W from such a low power supply voltage? Oh, 40 Whats?

Do your amplifiers use the Tripath TA2024 class-D amplifier IC? Tripath went bankrupt a number of years ago and a Chinese company copies their IC lately. Its maximum supply voltage is recommended to be 13.2V which is exceeded by your 16.8V fully charged battery. It produces only 5.6W into 8 ohms or 9.6W into 4 ohms at clipping per channel with a 12V supply. The datasheet does not show any other supply voltage.

 

[Rorut]

No probs. I always learn a lot from ETO questions and posts too.

I'm afraid posts tend to grow a bit when I am involved.

For me it is only interesting so that is absolutely not problem

While a cut off of 3.5V would certainly be good for battery life, you would be losing an awful lot of battery capacity. The nominal voltage of the NCR18650B is 3.6V rather than the other common 3.7V, so for a good compromise I would recommend discharging down to 3.1V and charging up to 4.1V. It is all a matter of balance; remember you are hitting the battery quite hard with the discharge current of 2 to 3A with a max of 5A. This is around 1C which is not good for battery life, compared to C/10 for discharge and charge which would give optimum practical life.

Sound very good, I will go for what you recommend. Can I go for 3.1*4=12.4v
With same setup that mike gave me?
I feel bad about asking him change the resistors to different values if I want to go for something between 3.1-3.4. Would be great if I could just trim it with the pot with same setup.

The cut off circuit (COC) always consumes current, but then so does the battery itself (you could say). A very good COC would consume 10% of the battery equivalent self discharge current so that, in practical terms, the COC would not affect the battery shelf life. Even when the COC turns off it will normally consume some current.

The self discharge of a LiIon battery is around 1.7% per month at 25 deg C (around 20% per year) (LiIon are the best common rechargeable battery in this respect). For the NCR18650C, this equates to an equivalent discharge current of 82uA, so a good COC would consume no more than 8.2uA.

Is it possible to say how much current mikes circuit consume?

A Lithium battery cell averages 3.7V during a discharge so four make 14.8V. How does an amplifier produce 40W from such a low power supply voltage? Oh, 40 Whats?

Do your amplifiers use the Tripath TA2024 class-D amplifier IC? Tripath went bankrupt a number of years ago and a Chinese company copies their IC lately. Its maximum supply voltage is recommended to be 13.2V which is exceeded by your 16.8V fully charged battery. It produces only 5.6W into 8 ohms or 9.6W into 4 ohms at clipping per channel with a 12V supply. The datasheet does not show any other supply voltage.

I''m using s mono class d amp TPA3110 from 9-
24v.
This one:
**broken link removed**

 

[spec]

For me it is only interesting so that is absolutely not problem

That's good to hear.

Sound very good, I will go for what you recommend. Can I go for 3.1*4=12.4v
With same setup that mike gave me?

Yes, no problem. We can even give you a simple formula so you can work out the resistor values for yourself.

I feel bad about asking him change the resistors to different values if I want to go for something between 3.1-3.4.

I can't answer for Mike, but going by his many posts on ETO, he is always pleased to help.

Would be great if I could just trim it with the pot with same setup.

That would be possible

Is it possible to say how much current Mike's circuit consumes?

Yes, that can easily be calculated.

As a general point, don't hesitate to ask any question, however trivial or complex you might think. Most ETO members are into electronics and like designing and discussing the subject.

spec

 

[Rorut]

Sounds great!
Then I only need to know a few things before buying components.
1. Formula how to calculate for that resistor (other things) depending on cut off. Would like to try between 3.1-3.5. Or for different packs in future.
2. Im not sure about "M1 that has a low Ron". A specific link would be helpful to one I can buy.
Would be great if it works on different setups?
3. Circuit consume is interesting

Thank you very much!

 

[spec]

Sounds great!
Then I only need to know a few things before buying components.
1. Formula how to calculate for that resistor (other things) depending on cut off. Would like to try between 3.1-3.5. Or for different packs in future.
2. Im not sure about "M1 that has a low Ron". A specific link would be helpful to one I can buy.
Would be great if it works on different setups?
3. Circuit consume is interesting

Thank you very much!

OK. I am still working on the circuit that I mentioned previously. If it turns out OK I will post that for your consideration, in addition to Mike's circuit, quite soon. If the circuit does not work out I will also tell you. I would not be surprised if other members didn't post circuits too.

I will let you know what bits to order for my circuit and perhaps Mike will advise you on the questions about his circuit.

spec

 

[MikeMl]

... Can I go for 3.1*4=12.4v
With same setup that mike gave me?
I feel bad about asking him change the resistors to different values if I want to go for something between 3.1-3.4. Would be great if I could just trim it with the pot with same setup.


Is it possible to say how much current mikes circuit consume?
...

Make R8=42.2K (nearest 1% value). The trim pot makes it adjustable from ~12V to ~13V.

After it disconnects the load, the circuit draws ~170uA from the batteries. While the load is still connected, the battery current is the load current +~170uA.

Put the ON-OFF switch between the batteries and my circuit.

 

[audioguru]

The datasheet from Texas Instruments for the TPA3110 amplifier IC shows that the output is 40 Whats at very high distortion into 4 ohms when it is overheating, has both of its bridged channels in parallel and uses an 18VDC power supply. With your 14.8V average supply it produces about 22 Watts with fairly low distortion. It will be hot but not overheating. Will you use two of these amplifiers for stereo?

 

[Rorut]

OK. I am still working on the circuit that I mentioned previously. If it turns out OK I will post that for your consideration, in addition to Mike's circuit, quite soon. If the circuit does not work out I will also tell you. I would not be surprised if other members didn't post circuits too.

I will let you know what bits to order for my circuit and perhaps Mike will advise you on the questions about his circuit.
spec

Looking forward to see what you are working on. I will build both of them

Make R8=42.2K (nearest 1% value). The trim pot makes it adjustable from ~12V to ~13V.

After it disconnects the load, the circuit draws ~170uA from the batteries. While the load is still connected, the battery current is the load current +~170uA.

Put the ON-OFF switch between the batteries and my circuit.

Thank you Mike! Don't think I understand how it was calculated but appreciate helping me.

That M1 is still making me confused and I'm worried if I buy a wrong one or one not good enough. Sorry for asking same and many qustions. Knowledge about this is a bit far from me...

The datasheet from Texas Instruments for the TPA3110 amplifier IC shows that the output is 40 Whats at very high distortion into 4 ohms when it is overheating, has both of its bridged channels in parallel and uses an 18VDC power supply. With your 14.8V average supply it produces about 22 Watts with fairly low distortion. It will be hot but not overheating. Will you use two of these amplifiers for stereo?

Thanks for looking at the datasheet!

I'm also having a 19.5v 4.5A AC/DC Power supply that will switch off battery circuits completely with a relay when connected.

The box is very small and I don't think I could here any difference between stereo and mono from it outside. This is not for hifi, more for easy to bring to the beach or the smaller barbeque.

But I thought about stereo vs mono for this little box a lot and I do not hope I made a bad choice. If I change my mind I can always go with the stereo version later on. Same voltage input.
**broken link removed**

 

[bountyhunter]

I have just been having a look at the NCR18650B datasheet. I don't like to be a kill-joy, but it appears that you would be lucky to get 500 mA/H from your batteries with a cutoff of 3.5V and that would be at a temperature of 25 deg C.

Also, I suspect that having a cut off voltage just 100mV below the battery nominal of 3.6V is going to cause all sorts of problems. For example when you consider the drop in terminal voltage due to the load current and the battery internal resistance, especially when switching on in a cold environment.

Not only that, but the terminal voltage drops with a decrease in temperature, so on a cold day the circuit may never turn on. I believe it gets a bit cold in Sweden from time to time. Battery rebound also makes the situation more critical. To further compound the problems, the datasheet applies to brand new batteries: with use, battery characteristics deteriorate.

spec

NCR1865B datasheet
**broken link removed**

I was going to add: you really need some kind of latching comparator circuit or it will just keep chattering on and off since the battery voltage will jump up when the load is removed.

Here is what I suggest:

If you know the load that the batteries will be subject to and the battery capacity (get that from the data sheet) set it up to kick off when you discharge down to about 30% of total charge remaining. Measure the batt voltage as it discharges using a resistor equivalent load to get accurate voltage data at that load. Use that data to set up the comparator's trip point. Build in enough hysteresis so it doesn't restart until recharge up to maybe 60% or similar level.

 

[bountyhunter]

Thank you very very much for all the research!
The reason to cut off at 3.5v is because I have been told that it is not good for the batteries going lower than that. But if it is ok to go lower like 3.1-3.3v or something Im more than happy. A second protection if the PCB fails seems to be good as well.

The battery maker should know this data but it depends on load current.

 

[MikeMl]

I was going to add: you really need some kind of latching comparator circuit or it will just keep chattering on and off since the battery voltage will jump up when the load is removed....

That is why I put hysteresis into the Load disconnect circuit I posted. A single resistor controls the cutOut-cutIn differential.

 

[Rorut]

Does this look correct connecting batteries, pcb, charger, lvc and load? And a 5A fuse close to battery.
This is my PCB:
**broken link removed**
Thanks

 

[spec]

Hy all,

Fully agree with your comments about battery rebound.

After many interruptions: UK bank holiday, socializing etc, mowing the lawn, but the mower wouldn't start, then the central heating packed up and so on, I have finally done a LiIon battery cut off voltage circuit. The outline characteristics are:
(1) Cut off voltage adjustable by a trimmer resistor: 3.1V nominal +- 400mV
(2) Hysteresis: +100mV but can be changed by resistor change.
(3) Current consumption: 5uA
(4) Reasonably size components: comparator 8 pin thru hole for example
(5) Components freely available (Mouser)
(6) Total cost: around £12 UK

I have just got to put the circuit in EAGLE and then I will post.

spec

 

[kinarfi]

Here's one I used on my camper so I wouldn't run the battery too low to start the truck, it worked real good, except for the fact that I put the reset button in a very awkward place.
Because some batteries regenerate their voltage once the load is removed, I made this so it locks itself out until reset or bypassed, either one will reset it if the voltage is above cut off, bypass has to carry the full current of the load, reset button has minimal current.
I show several switches, but that is get different switching times for simulation, only one is needed for resetting the circuit once the battery is recharged.
Jeff

 

[spec]

2016_05_08 Issue 03.00 Also see post #69

Here is the LiIon battery voltage cut off circuit that I mentioned previously:

​

ERRATA
(1) Delete C4
(2) Change C3 to 22uF 25V ceramic type (no leakage current)
(3) Change R4 from 750K to 82K
(4) Change R3 from 1M5 to 2M
(5) On parts list PMOSFET DMP4051 should read DMP4015 (the Mouser link is for the correct part though)

NOTES
(1) N1 is a low current (1uA) comparator with a CMOS push pull output
(2) ZD1 is a 2.5V low current (1uA) precision (+-0.2%) Zener diode
(3) R5/R4 provide 100mV hysteresis per battery (3.1V and 3.2V) to take care of battery rebound.
(4) RV1 sets the cut off voltage to 3.1V per cell and can be adjusted to give +-400mV variation in cut off voltage
(5) The circuit layout and routing of lines is important and should be as shown on the schematic to maintain accuracy and reduce the likelihood of frequency instability.
(6) The capacitors are for decoupling to assist frequency stability and have no function in regard to the basic circuit operation. They should be physically as shown on the schematic.
(7) R1 is a gate stopper to prevent the PMOSFET from oscillating at a high frequency (not peculiar to this circuit) and should be mounted on the PMOSFET gate pin. R1 plays no part in the basic circuit function.
(8) The total current drain of the circuit is, 3uA while cut on and 4uA while cut off

PARTS LIST

 

[audioguru]

Does this look correct connecting batteries, pcb, charger, lvc and load?

A problem with the Chinese board are that they cannot explain in English if it is a charger or if it is a protection circuit because they say both.
Other problems are that its overvoltage limit is too high, its undervoltage limit is too low and its current is way too high. Therefore it will provide NO protection for your little battery.

 

[Rorut]

Here's one I used on my camper so I wouldn't run the battery too low to start the truck, it worked real good, except for the fact that I put the reset button in a very awkward place.
Because some batteries regenerate their voltage once the load is removed, I made this so it locks itself out until reset or bypassed, either one will reset it if the voltage is above cut off, bypass has to carry the full current of the load, reset button has minimal current.
I show several switches, but that is get different switching times for simulation, only one is needed for resetting the circuit once the battery is recharged.
Jeff
View attachment 99295

Thank you! I will spend some time try understanding this as well.

Here is another LiIon voltage cut off circuit (I haven't optimized the resistor values yet):

View attachment 99300
​

NOTES
(1) N1 is a low current (1uA) comparator with a CMOS push pull output
(2) ZD1 is a 2.5V low current (1uA) precision (+-0.2%) Zener diode
(3) R5/R4 provides hysteresis to take care of battery rebound.
(4) RV1 sets the cut off voltage to 3.1V per cell and can be adjusted to give +-400mV variation in cut off voltage
(5) The circuit layout and routing of lines is important and should be as shown on the schematic to maintain accuracy and reduce the likelihood of frequency instability.
(6) The capacitors are for decoupling to assist frequency stability and have no function in regard to the basic circuit operation. They should be physically as shown on the schematic.
(7) R1 is a gate stopper to prevent the PMOSFET from oscillating at a high frequency (not peculiar to this circuit) and should be mounted on the PMOSFET gate pin. It plays no part in the basic circuit function.

PARTS LIST

To Be Defined

Wow, Impressive and easy to read. I´m overwhelmed by all help I´m having here. I really hope this thread will be an asset for other rookies like me.
I will definitely make this one together with mikes (when I know which "M1" to buy ) Is it easy to tweak if I want to try and cut between 3.1-3.4?
Or if I´m going with a 3s pack. Would be great to know what parts I'll put the focus on? Above kinarfi wrote in his cirduit "opamp works much better than comparator" curious why?

A problem with the Chinese board are that they cannot explain in English if it is a charger or if it is a protection circuit because they say both.
Other problems are that its overvoltage limit is too high, its undervoltage limit is too low and its current is way too high. Therefore it will provide NO protection for your little battery.

The way I see it and what I read on other sellers descriptions it´s not a charger, just a PCB that checks each cells voltage. My balance charger will not charge more than 4.2v and will stop after that.
Whats the difference between "lift voltage" and "detection voltage"? I agree 4.25v overcharge and 2.5v over discharge is bad but is better than nothing. If it´s stops at 4.15v and 3v it´s more ok.
I don´t agree it will provide NO protection compared to no protection at all.
I thought current specification was that it can handle more current without cut off? For example if batteries can provide 5A and PCB only can handle 2A, it blocks for what I need

If you know a PCB with better specification for my purpose I would be very happy to buy it?

I'm confused about what they write:
what is "lift" and what is "detection"?
overcharge detection voltage :4.25±0.025V
overcharge Lift the voltage:4.15±0.05V
over discharge detection voltage :2.50±0.08V
over discharge Lift the voltage:3.00±0.1V
overcurrent current:20-30A
working current:15A(Natural cooling 10.A, add heat sink 15A, the maximum instantaneous current 30A)

Thank you all for your enrichment!