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Topic: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit  (Read 5353 times) previous topic - next topic

valerio_sperati

You can wire three "protected" cells in series by yourself!
Yep! But this is exactly the information i'm trying to retrieve!   :)
I do not know how to do it!
How can I connect the 3 cells pack Turnigy with the circuit pointed here?

http://www.all-battery.com/PCBfor11.1VLIPO_Li-Ion_Li-MnNiBatteryPack-32071.aspx

Turnigy has 4 wires (red, blue , yellow, black), used when I recharge the battery.
Are the coloured wires the 1's , 2's and 3'd  positive terminals, as requested by the connection instruction?
Is the black wire the 3's cell negative terminal?  


B+: Connect to cell 1's positive terminal.
B-: Connect to cell 3's negative terminal.
B1-: Connect to cell 2's positive terminal.
B2-: Connect to cell 3's positive terminal.
P+: Connect to the battery's output or the charger's positive terminal.
P-: Connect to the battery's output or the charger's negative terminal.  

I need a schema!
Thanks :)


jremington

What we are suggesting is to buy three individual, protected 3.7V cells and wire them in series, one after the other, negative of one cell to positive of another. This will create a (nominal) 11.1 V battery pack. Like this:



You do not need to add another protection circuit.

valerio_sperati

What we are saying is to buy three individual, protected 3.7V cells and wire them in series, one after the other, negative of one cell to positive of another. This will create a (nominal) 11.1 V battery pack. Like this:



You do not need to add another protection circuit.
Ok. But how can I recharge these new battery pack?

jremington

Use the same charger you are now using for your 11.1V (3 S) pack.

raschemmel

Quote
A theoretical discussion only. The battery protection circuits usually cut out at 2.8 V or less. The one pointed to by the OP has this cutout:
Obviously you don't use the batteries and believe whatever you read. It's not theoretical when you have to pay for the replacement battery.
I wouldn't use a cutout lower than 3.2V /per cell no matter what.

According to the people who use the batteries
RC GROUPS

Quote
urnigy has 4 wires (red, blue , yellow, black), used when I recharge the battery.
Are the coloured wires the 1's , 2's and 3'd  positive terminals, as requested by the connection instruction?
Is the black wire the 3's cell negative terminal?   
Use a voltmeter to answer that question.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

valerio_sperati

Use the same charger you are now using for your 11.1V (3 S) pack.
Please, be patient :)
This is the charger I'm using:

http://www.himotoracing.com/product/electronic/electronic_027/images/electronic_027_01.jpg


so a JST connector with 4 wires. If I connect three cells in series , I guess I would end with 2 terminals only(GND and +11.1v), is it right?

jremington

Quote
Obviously you don't use the batteries and believe whatever you read.
I do use LiPo battery packs, and I find, experimentally, that what the manufacturer states about the protection circuitry is correct.

raschemmel

Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

jremington

Quote
This is the charger I'm using:
http://www.himotoracing.com/product/electronic/electronic_027/images/electronic_027_01.jpg
That is a balancing charger, and usually, three of the four wires are connected to the three positive terminals of the three cells in an 11.1V battery pack. The other lead is connected to the battery pack negative terminal, as shown here (the wire colors MAY NOT be correct).



You have to know which wire in the charger connects to which cell in your original pack in order to use it with a different 3 cell battery pack.

It is possible to determine those connections from your original battery pack using a voltmeter. The voltages on the individual wires coming from either battery pack will have voltages of roughly 4, 8 and 12 volts, measuring from the negative terminal.

Connect those leads from the charger, in the same order, to your new battery pack.

valerio_sperati

Thanks a lot Jremington! This is exactly the schema and data about voltages I was looking for.  I'll try to build my own 11.1v 3sp1 battery pack, 1200Mah, using the  protected Lipo from Adafruit

https://www.adafruit.com/products/258

I guess that the last thing I need to check, is that the charger current rate does not overhelm 500mAh for the battery I selected (my current charger reports "Max Charge current: 3x900mA", I guess this is too much).

thanks again!

raschemmel

Quote
Thanks a lot Jremington! This is exactly the schema and data about voltages I was looking for.
How is this different from what you would have arrived at if you measured the voltages ?
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

valerio_sperati

Mmmm... not sure I understood your question (my English is bad). What I meant is that I did not know that 3 cells were assembled in such way, and I did not know that measuring voltages on individual wires from battery pack should gives about 4,8,12 volts.
Valerio   

raschemmel

Did you try taking the voltage measurements just to see for yourself how it corresponds to the illustration jremington posted ? (just for curiosity) After doing so, does it make sense that the schematic is really unnecessary if you can read the voltages ? Which would you think would be more reliable, the schematic or the actual voltages ?
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

jremington

Quote
my current charger reports "Max Charge current: 3x900mA", I guess this is too much
I'm not quite sure what that means, but I suspect it means that each of 3 cells is charged at a rate of 900 mA. That would be fine for a battery pack of 1200 mAh cells, as most people consider charging at a rate of "C" (1200 mA for a 1200 mAh cell) to be safe. Your decision. Charging should take no more than about 1.5 hours.

Note that Adafruit is being very cautious when they tell you
Quote
However, even with this protection it is very important that you only use a LiIon/LiPoly constant-voltage/constant-current charger to recharge them and at a rate of 500mA or less. Like most lipos, the batteries we sell do not have thermistors built in. This is why we suggest charging at 1/2C or even less - 500mA max in this case which is how much you can get from a USB port.
You can measure the charge current with your multimeter, but you have to open a battery lead to do so.

valerio_sperati

Did you try taking the voltage measurements just to see for yourself how it corresponds to the illustration jremington posted ? (just for curiosity) After doing so, does it make sense that the schematic is really unnecessary if you can read the voltages ? Which would you think would be more reliable, the schematic or the actual voltages ?
I checked right now, and the voltage is about 4 ,8, 12 volts on individual wires. The schematic is necessary for me because I ignored how the individual cells were assembled inside the pack!

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