arduino battery - 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: All prices were set in early 2012.
So, I 've been using the Adafruit 6 AA battery stand for $5.
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.
The recharge fee is $3.
50, but the capacity is 5 times, and it is rechargeable.
My complaint: 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-
I bought 6 18650 3200 batteries for $10. 85 on ebay.
I don't think this is still available, but you might find the price 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 stands for $1. 08 on ebay. (See Picture)
Ht_4068wt_902 problem: it is not a standard voltage, 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 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 1: You can purchase the "protected" 18650 battery with the 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.
From trading extreme 27.
Arduino: 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.
This will work well for Arduinos with a voltage regulator.
Solution 3: You can purchase a battery protection circuit designed for two batteries.
Buy one for $4.
49: Design: My main concern is that 18650 batteries are not allowed to discharge below about 6 Vdc.
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.
Better solution: So I decided to design a comparator that will turn off the Arduino voltage if a battery drops to about 3vdc, or both of them drop below 6 v.
If any of these happens, it will disconnect the Arduino's power supply.
For purists: Yes, I realize that most Arduinos have a 5 volt regulator, usually 7805, indicating that the input voltage is at least 7 volts.
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.
Alternative: my circuit can be changed to turn off at 7 Vdc.
Operational Theory: this is Revision 2, by the way.
Two 18650 batteries are connected in series.
My battery circuit is connected to the ground side, the midpoint between the two batteries and the output.
If the midpoint (
The first battery is higher than 3 v and the high end is higher than 6 v, and the battery voltage will be output to the output connector connected to the Arduino.
If either of these two conditions is not met, the voltage will not go to Arduino.
Geek stuff: you might notice that I'm switching the ground side instead of the high side.
It's okay for battery operation. 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.
Z2 should be 1. 8V zener.
It makes a similar comparison of the midpoint with R6, R7, and R8.
This is the wire connected between the two batteries in the bracket.
Geek stuff: Geek may have noticed that I 've connected two comparators with one pull-up resistor.
This is actually valid when the output is called an open collector.
I believe this device is called the opening "and" door. It works.
Alternative: The LED does not need to be in the circuit in order to reduce battery consumption (~20mA)
Resistance and zeners can be replaced for different trip points or battery sources.
For my circuit, I actually made some pcb using toner transfer, but will save the details for another Instructable.
Price: pcblm393 $0 is not included.
138-pin IC socket $0. 021N4733 $0.
03 resistance 1/4 W metal film 1. 2K2. 7K3. 6K4. 3K4. 53K1M2. 4K13Kabout $0. 02LED 3mm$0. 02FET b170 $0. 26 2.
1mm power plug $0. 201.
8 v Zina is about $0. 04 (
No longer available? ? See below)
The total cost is less than $0. 80.
I know shipping is not included.
If you order together, it's about $3. 99.
I ordered a lot of parts on ebay from Lazdag.
, Usually like $50 resistor 0.
Including 99 shipments.
Direct ordering may be cheaper for large orders.
Question: I bought 25 Zener diodes that claim to be 1. 8V zeners.
When I try them out, they don't have Zina at 1. 8V.
In fact, they do not have Zener at any particular voltage and change with the bias resistance.
Solution: Well, I built a test circuit and got enough Zener action so that if the voltage drops below 3 volts it will trigger the comparator so that these diodes
QUESTION: Well, now I see no 1.
8 v zeners on Ebay, except for the $5 surface bracket.
I think it might work.
Solution: 1 if someone else wants to build this circuit.
Digikey offers 8 v zeners.
However, the value of the resistor must be adjusted.
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 see which one is heavier with my postal scale (See Picture)Size1. 7”x3. 5” 2. 5”x4.
Capacity, cost, weight and size are 5 "18650 wins.
Advantages and disadvantages of 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.