Good day. This year I have completed a project that I have been thinking about for a long time. It is an electronic protection of the lithium-ion battery (3s 12 V) against excessive discharge and, consequently, against permanent damage. The whole is in the form of a printed circuit board with a multi-turn potentiometer to adjust the operating voltage. The exact diagram and principle of operation are presented in this episode.
What immediately catches the eye - the use of through-hole components instead of SMD. It is a pity, the board could be smaller and much simpler. There are also a lot of tall elements, which also make the entire device large. If it is a security circuit, in my opinion it should be as small as possible. If we add electronics to the battery, we could also try to monitor the temperature with a thermistor and cut off the battery from the energy receiver when the set threshold is exceeded.
What are the costs of building the system? Maybe some diagram? Where will the chip be used?
Of course, the circuit could be on SMD elements, but for now I'm at the design level on THT elements. The thermistor could be added by adding one more TL431 chip with a few resistors to the project. It's good that you paid attention to it.
Answering the questions: The tile was ordered at JLCPCB, the price with delivery for 5 such tiles is about PLN 30. I think you can buy the necessary elements for PLN 30. You can see the diagram in the video, in addition I will attach it here. The device has a several-second delay before it self-switches off after connecting the power supply. I am going to use the system together with the battery in the LED lamp. There is a charger for it that I made myself. A separate episode was created about it.
With all due respect, building such a system is actually pointless in my opinion. There are ready-made "hardware secondary protection" circuits, which are tiny, quite cheap, with a handful of small elements attached to them and you get a ready-made system. Compared to the system made of specialized elements - the presented system is monstrous. Somewhere there is information about a supply current of about 1 mA - this current is huge, specialized systems require a current of several uA and in the OVD sleep mode even below one uA.
It has become a bit more expensive recently. I paid $ 12.66 for 10 100x100 tiles at the end of September, which is about PLN 50 at today's rate. Shipping $ 7.66, or about PLN 30. As of today, the cheapest shipping is actually $ 10.50.
Another thing is that $ 5 for tiles and (even) $ 7 shipping (I can't remember cheaper) is a bit more than PLN 30 :-)
With all due respect, but in my opinion, building such a system is actually pointless. There are ready-made "hardware secondary protection" circuits, which are tiny, quite cheap, with a handful of small elements attached to them and you get a ready-made system.
On the other hand, you can build a protection system from a handful of small elements (6-7), where the largest is the mosfet that cuts off the power supply. Somewhere after this forum there is a protection scheme for a lead battery (in which it is enough to change the zener diode to match the activation threshold), and it only takes the gate leakage current after activation.
Compared to the system made of specialized elements - the presented system is monstrous.
It is monstrous even in comparison to the sensible "self-made", but that does not mean that it is a disadvantage - it depends on how to use it. Although in terms of size - it would be best if this plate was a little larger, so that a basket for the entire package could be placed on it.
Somewhere there is information about a supply current of about 1 mA - this current is huge, specialized systems require a current of several uA and in the OVD sleep mode even below one uA.
It depends on how this system is used, if after switching off the packet will be charged within a few hours, that's ok, maybe this 1 mA is also worse, as there is a risk that the packet will be left for a week after discharging.
Without a balancer? the cells in the package will be dispersed quickly.
Active balancer will be added, it came yesterday, no problem to apply it.
@krzysiek_krm If we give up the light that lights up when the protection is connected to the battery, this current will drop even further. The protection will be used in the 25 W LED flashlight and will be disabled for the next day with a switch that cuts off the battery from the rest of the system.
@zgierzman I ordered the board by regular shipment, which takes a month. I will see the current prices soon (maybe something has changed). I remember that the first order was for PLN 8 ($ 2 with free shipping), then about PLN 30, and if you ordered 2 or 3 projects in one shipment, each subsequent order was for + $ 4 to the basic price.
Added after 30 [minutes]:
It has become a bit more expensive recently. I paid $ 12.66 for 10 100x100 tiles at the end of September, which is about PLN 50 at today's rate. Shipping is $ 7.66, or about PLN 30. As of today, the cheapest shipping is actually $ 10.50.
Another thing is that $ 5 for tiles and (even) $ 7 shipping (I can't remember cheaper) is a bit more than PLN 30
You scared me a little that it was so expensive I have it as it was and always the price of $ 2 for the first order in a package, I don't know what it depends on.
It's nice that someone else does something on their own. I used to like to design and do these things myself. Now, in the era of Chinese bms modules with a 3s balancer for PLN 7 on ali and PLN 15 in pl, it probably makes no sense.
And do a security greater than the package itself, because there is no need to push smd? A completely pointless approach. If there were to be a bms and a charger there, maybe, but such a size is absolutely pointless and completely impractical.
Does amateur mean that it should have no utility and may not be thought out? A bit of logic in that. As an amateur, you can do something really cool that can be used normally. Reduce a bit, a little smd and it will be able to be stuffed into the battery housing in a sensible way. A large tile? This is to push the BMS there to significantly increase the usability. And now? Done, it works, dimensions senseless and practical is not. So yes, it does make a big difference.
The main purpose of the protection circuit is not to protect the battery from under-voltage (UV) conditions. Li-ion battery protection is mainly used for over-voltage (OV) protection during charge and over-current (OC) during discharge (aka short circuit). These two conditions can lead to a failure that poses a risk to human safety, i.e a fire.
TI includes undervoltage protection because it's dead simple to implement, the control circuit and FETs are needed for OV and OC protection regardless, so might as well add UV protection too.
For your application (as you mentioned) there are ways of not needing dedicate UV protection. However, without the battery protection, you are not protecting yourself from the other faults. These still need protection, so I highly recommend the use of a dedicated protection IC.