my protection circuit - 18650 high drain battery

Many of you know that this lazy old geek likes azhanos.
Many of my projects are portable and require a battery Source: So, I 've been using the $5 Adafruit 6 AA battery stand.
6 AA rechargeable batteries in section 00. (See Picture)
Another option is $3 for the Adafruit 9 v battery stand.
95 my complaint: this is what I don't like about monthly alkaline batteriesExpensive ~ $ 3Low capacity ~ 600 Usain Ma Hongshi comparison, I bought the action that will be taken for $5 3000 mA MH rechargeable battery. 38 on ebay.
AA costs $3.
50, but the capacity is 5 times, and it is rechargeable.
My complaint with AAs is: OK, so I am a geek and I am not very happy with the setup of 6 AA batteries.
So, I 've been looking for another option. Hark!
I know about 18650. These are Li-
Nominal ion battery7V. Li-
Ion batteries are like the ones used in most laptops.
Now, I did some research on Li-
Ion battery and they as: to 10 dollars of price of purchasing the 6 a 18650 3200 mAh battery. 85 on ebay.
I don't think this is still available, but you can find that the price is very similar.
The 18650 battery is good, but it also has its own problem.
Problem: It's a bit bigger than the AA battery, so it needs its own stand.
Solution: You can buy two battery cases for $1. 08 on ebay. (See Picture)
Ht_4068wt_902 the reason I chose two batteries in series is to provide enough voltage to Arduino.
Problem: It is not a standard battery type, so need your own charger.
Solution: I bought a charger for $3. 46 on ebay. (See Picture)
Ht_2522wt_952 problem: the bigger problem is that the battery I bought is "unprotected ".
This is slightly different from the NiMH rechargeable battery, which can be discharged to about 1 v. If Li-
The ion battery is discharged too much to charge.
18650 is nominally 3.
7 volts, will charge to about 4.
25 V, but not less than 2 v. 7 volts.
I believe there are some other requirements regarding incorrect charging, but I (assuming)
My charger is working on this issue.
Don't discharge too fast, but hopefully my circuit will prevent this from happening.
Warning: if proper charging and discharging methods are not used, the 18650 battery is clearly in danger of an explosion.
Solution: see next Solution 1: You can purchase a "protected" 18650 battery with a built-in circuit.
However, they seem to be about twice the cost.
Solution 2: You can purchase a separate battery protection circuit and add it to the battery.
I just found a protection circuit for $1.
27 @ from the trading extreme.
Since I am designing batteries for Arduino, I need to use two 18650 batteries in series.
This will provide a nominal 7.
4 Vdc and 8.
5 Vdc when fully charged.
Solution 3: You can purchase a battery protection circuit designed for two batteries.
Buy one for $4.
49: now I am a geek, so I decided to build my own geek.
Design: My main concern is not to allow 18650 batteries to discharge less than 6 V or 3 V per section.
So I tried this circuit with an experimental audio amplifier and as expected I forgot and let it stay connected.
My amplifier chip is burnt out and short-circuited.
The good news is that when the total number of batteries drops to about 6Vdc, my circuit disconnects the battery.
The bad news is that the battery discharge is uneven.
One battery is about three.
7Vdc, about 2 others. 2Vdc.
This is below the proposed emission limit.
It seems that both batteries are charging correctly, which is not a bad news.
Now my point is that this uneven discharge is due to the fact that the short-circuited amplifier generates too much current (unevenly).
But this is a warning that this design may not protect your battery properly.
I redesigned the circuit and am waiting for some people.
Test and complete the design of the 8 v Zener diode.
I will add it to this structure once I start working.
Simple solution: I can keep an eye on them at any time and charge them regularly. Li-
Ions are usually not hurt by charging too often.
But I'm old and may forget to keep them in touch.
My solution: So I decided to design a comparator that turns off the voltage when the Arduino drops to about 6 Vdc.
So I used a comparator to disconnect the power from the Arduino.
For purists: Yes, I realize that most Arduinos have 5 v regulators, and many use 7805, indicating that the input voltage is at least 7 v.
Well, I'm very familiar with ardunos and most of them work up to about 4 Vdc.
One issue you may be concerned about is that if you are measuring the analog voltage and using 5 Vdc as a reference then your measurement will be turned off.
Well, I 've been using 3 for all my analog circuits.
3Vdc as Aref.
One of the reasons is that most computer USB ports are not 5 Vdc when using USB as a power supply, but can be around 4 volts. 7 Vdc anyway.
Another option: my circuit can be changed so that it can be turned off at 7 Vdc and "guaranteed 5Vdc ".
Operating principle: originally wanted to design the circuit, so that the comparator was also disconnected when the voltage was too low.
Well, I can't get it to work.
So I have been connecting my computer together. See schematic. Z1 is a 5.
1 Vdc Zener diode.
R1 provides enough current to bias the diode.
So the analog comparison pin 2, LM393 will have 5. 1 Vdc on it.
The voltage divider is composed of R2 and R3.
Pin 3 will be higher than 5 when the battery voltage is higher than 6 Vdc.
1 Vdc, high output.
This will turn on the FET, Q1 a b170, which will provide ground to the output that goes into the Arduino.
Positive voltage is delivered directly from the battery.
The R5 and D1 are active when the power supply is available, so the LED will indicate that the power will flow to the Arduino.
By the way, the high and low voltage on pins 6 and 5 makes these inputs not float.
I don't like to keep unused inputs floating.
In theory, the floating input can cause oscillation, which consumes a lot of power and runs out of the battery faster.
Alternative: The LED does not need to be in the circuit in order to reduce battery consumption (~20mA)
For different trip points, R2 and R3 can be changed.
For different battery sources, Z1, R2 and R3 can be replaced.
For my circuit, I actually made some pcb using toner transfer, but will save the details for another Instructable.
Pcblm393 $0 is not included.
138-pin IC socket $0. 021N4733 $0.
03 resistance 1/4 W metal film 1. 2K2. 7K1M2. 4K13Kabout $0. 02@LED 3mm$0. 02FET b170 $0. 26 2.
1mm power plug $0.
The total cost of 20 is less than $0. 70.
I know shipping is not included.
If you order together, you may need another $3. 99.
I ordered a lot of parts on ebay from Lazdag.
, Usually like $50 resistor 0.
Including 99 shipments.
For large mixed orders, it may be cheaper to buy directly from voddaelectronics. com.
So I almost explained why I didn't use the 9 v battery source.
Here's a comparison between this 18650 system and the AA NiMH battery I have.
18650 $18650. 621 holder $0.
$541 guard. 00Total $5.
16AA nim6 AA NiMH $3. $5 871 Adafruit. 00Total $8.
Battery 26 voltage 8. 5-68. 4-
6 capacity 3200 mAh 3000 mAh discharge time varies depending on the load cost of $5. 16$8. 87Weight ~2.
5 ounces ~ I don't have a scale for 6 ounces, but use my postal scale to see which one is heavier (See Picture)1. 7”x3. 5” 2. 5”x4.
Cost, weight and size win 5 "18650.
Advantages and disadvantages: battery technology aa NiMH: memory problem, high self-discharge rate
Ion: no memory problem, low self-discharge rate, aging problem. My other complaint about AA NiMH batteries is that they automatically discharge if you don't use them for the time being.
The self-discharge rate for 18650 seconds should be 10 times lower.
I didn't do much testing, but it seems to work well.
Kabbabble: one of the tests I did was to measure the current with a protective circuit that was connected but did not have a load. It was only 6.
25 mA even if the LED lights up.
This means that when the protection circuit drops below about 6 Vdc and disconnects the power supply with the Arduino, it still draws the current, but it will take a long time to drop the current to 2.
7 volts, dangerous voltage.
Attention: one of the problems that my circuit has not solved for other geeks is whether the battery is discharged at different speeds.
Ideally, the battery protection circuit should be for each battery, not for two batteries at the same time.
I'm pretty sure the batteries will discharge fairly evenly because they have the same capacity and age.
But I will try to monitor this in use.