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Using Arduino => General Electronics => Topic started by: valerio_sperati on Sep 19, 2016, 04:30 pm

Title: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 19, 2016, 04:30 pm
Hi all,
I'm working on a project on autism therapy, the +ME experimental device,
http://www.plusme.it/last-prototype-to-experiment-with-children/ (http://www.plusme.it/last-prototype-to-experiment-with-children/)
which is powered by a commercial 11.1V Lipo battery, 500mAh.

I realised right now that our commercial battery lacks of the protection circuitry preventing the cell to discharge below the safety voltage (3.0v). As  far as I know, this could be very very dangerous. I tought it was a standard safety component, but it is not!

https://learn.adafruit.com/li-ion-and-lipoly-batteries/protection-circuitry (https://learn.adafruit.com/li-ion-and-lipoly-batteries/protection-circuitry)

Adafruit suggested me to  add this protection circuit to the pack battery

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

but obviously this means I need to disassemble the original pack battery, de-sold and put together again in the right way: it sounds to me not a trivial work, even because I've not experience about it.
In your opinion:

1) is it feasible for an hobbyst like me to perform such operation in safety? If yes, can you suggest some tutorial about assembling 3 lipo cells + this protection circuit?

2) I looked on google for 11.1v lipo battery 500 mAh already endowed with this protection circuit, but   at the moment I found only Adafruit selling this protected battery, unfortunately only 3.7 battery. Do you know some site selling these products? It would solve my problem!

Thanks a lot. Please help me because the project is really important!

PS: some (hopefully) useful info:
-the power consumption of the device is about 110 mAh (device on, lights and sounds off), and reaches 200 mAh when all lights and sounds are on (the worst situation!). In average, it request about 150 mAh (device on and some light or sound on). We need the device to work for 1 hour, no more.   


Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: raschemmel on Sep 19, 2016, 04:33 pm
I don't have time to read your post in detail right now but I can tell you for a FACT that a 3S Lipo battery is 12.54V , fully charged. (11.1V would be almost discharged. 9.6V is fully discharged)
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: allanhurst on Sep 19, 2016, 04:34 pm
Quote
I realised right now that our commercial battery lacks of the protection circuitry preventing the cell to discharge below the safety voltage (3.0v). As  far as I know, this could be very very dangerous.
Well it won't do the battery much good, but apart from that no great problem

regards

Allan
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 19, 2016, 04:41 pm
Well it won't do the battery much good, but apart from that no great problem

regards

Allan
Mmmm... not sure I understood. Are you telling this is not dangerous? As far as I know, when a pack is below 3.0 V it becomes "fat", and can break itself! Is it true? Or not?
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: jremington on Sep 19, 2016, 05:20 pm
It is a good idea, and relatively simple to add the protection circuit. If you are not comfortable with soldering, find someone who is, to help.

The battery won't explode or catch fire if it is discharged below about 2.8 V/cell, but it can be damaged to the extent that it won't take a charge (and attempting to charge such a battery could be dangerous).
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 20, 2016, 11:47 am
The battery won't explode or catch fire if it is discharged below about 2.8 V/cell, but it can be damaged to the extent that it won't take a charge (and attempting to charge such a battery could be dangerous).
Ok, this reassure me. So, in your opinion, it is not dangerous to reach the threshold of 2.8v/cell, but rather the attempt to charge again the (damaged) battery. Is it right?   


It is a good idea, and relatively simple to add the protection circuit. If you are not comfortable with soldering, find someone who is, to help.
Good! But I need some tutorial :) I'm very comfortable with soldering , but I need some schema to follow explaining to me how to assemble 3 cells in 1 pack, so that: 1) it is protected by the circuit 2) it is well assembled so that i can recharge the pack in safety with a commercial recharger. Can you suggest one? Thanks a lot!
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: ad2049q on Sep 20, 2016, 12:27 pm
Don't do that !
Taking apart a three cell Lithium battery is unlikely to improve its reliability.

Lithiums really don't like being heavily run down or left empty and once full they don't pass through "overflow" if the next cell is not full yet.

To get a more predictable lifetime, will it work with a six cell "12V" Pb H2SO4 motorcycle battery or smaller ?
Expected maintenance cycle is for complete replacement in 1000 cycles or 3 years whichever is soonest.
Lead batteries might seem to need less cell to cell balancing than Lithiums, at the expense of being heavy .
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 20, 2016, 12:42 pm
To get a more predictable lifetime, will it work with a six cell "12V" Pb H2SO4 motorcycle battery or smaller ?
Expected maintenance cycle is for complete replacement in 1000 cycles or 3 years whichever is soonest.
Lead batteries might seem to need less cell to cell balancing than Lithiums, at the expense of being heavy .
Unfortunately, this is unfeasible for my project! The battery I'm using right now is 49gr weight, 56x30x19 mm in dimensions. A motorcycle battery is huge!

Don't do that !
Taking apart a three cell Lithium battery is unlikely to improve its reliability
It seems to me very strange that adding a protection circuit like this
http://www.all-battery.com/PCBfor11.1VLIPO_Li-Ion_Li-MnNiBatteryPack-32071.aspx (http://www.all-battery.com/PCBfor11.1VLIPO_Li-Ion_Li-MnNiBatteryPack-32071.aspx)
to the Lipo Pack is so difficult! I assume that in order to add such circuit I need to disassemble the pack. Am I wrong?  

               
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: raschemmel on Sep 20, 2016, 02:15 pm
Disassembling a Lipo pack is dangerous and likely to end in it bursting into flames.
In ten years of RC aircraft flying , most of the Lipos that"puffed up" , did so after discharging them to less than 3.2 V/per cell, not 2.8 V/per cell. Only a few of them "puffed up" during charging.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: Chagrin on Sep 20, 2016, 02:30 pm
all-battery.com sells round cells with built-in protection (http://www.all-battery.com/Li-Ion186503.7VRechargeableBatterymodulewithPCBandBareLeads-30027.aspx) and you can get them with or without the wires. Very simple to work with. Just connect three in series and you're good to go.

If you already have a battery pack you could use a BPC that doesn't have connections to the individual cells (http://www.all-battery.com/PCB11-1V32048.aspx) in the pack and eliminate the need to disassemble your pack. For the most part, assuming your project doesn't involve high current drain or require fast charging, the cells in the pack will stay balanced in voltage and the individual cell connections aren't required. If the cells aren't staying balanced then you need a new battery pack or cell anyway.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 20, 2016, 03:15 pm
In ten years of RC aircraft flying , most of the Lipos that"puffed up" , did so after discharging them to less than 3.2 V/per cell, not 2.8 V/per cell.
Ok, so the safe threshold is 3.2v. Anyway, how can you know that your battery is approaching this threshold? Does your drone warn you in some way (with light or sound)? Another question: do you agree with the other user Allanhurts (see previous replies) that a "puffed" battery is not dangerous by itself, but only if I try to charge it again? Thanks for your opinion   
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: raschemmel on Sep 20, 2016, 03:24 pm
Quote
Ok, so the safe threshold is 3.2v. Anyway, how can you know that your battery is approaching this threshold? Does your drone warn you in some way (with light or sound)? Another question: do you agree with the other user Allanhurts (see previous replies) that a "puffed" battery is not dangerous by itself, but only if I try to charge it again? Thanks for your opinion     
To my knowledge, ALL RC ESCs (Electronic Speed Controls) have a configuration menu that is typically entered by setting some specific transmitter control sequence , like poweing on ESC with throttle at full , then moving to midpoint , then back to full, in conjunction with tones emitted by the ESC. The "trigger" sequence required to enter programming mode is different for each brand of ESC. The ESC instructions have all the details. One of the programming settings is "Soft-cut/Hard-cut voltage threshold". where you can choose the default 3.2 V or something else.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 20, 2016, 03:27 pm
all-battery.com sells round cells with built-in protection (http://www.all-battery.com/Li-Ion186503.7VRechargeableBatterymodulewithPCBandBareLeads-30027.aspx) and you can get them with or without the wires. Very simple to work with. Just connect three in series and you're good to go.
yep! I find this site some minute ago  :) I found a lipo 11.1v 800mAh  with protection circuit (more than 30 dollars!). About the round battery you suggest, this is not feasible for my project, because an individual round cell is about 50gr, and I need three of them! Too much weight!

If you already have a battery pack you could use a BPC that doesn't have connections to the individual cells (http://www.all-battery.com/PCB11-1V32048.aspx) in the pack and eliminate the need to disassemble your pack.
mmm.. interesting but I still miss how to connect this circuit to the battery pack. Just to know, the battery I'm using now is a turnigy 11.1v 500mAh

http://www.hobbyking.com/hobbyking/store/__9275__Turnigy_500mAh_3S_20C_Lipo_Pack.html (http://www.hobbyking.com/hobbyking/store/__9275__Turnigy_500mAh_3S_20C_Lipo_Pack.html)

As you can see, there are four wires coming from the battery pack:red, yellow, blue. black. Should I connect the red blue yellow cables to cell1 cell2 cell3 pad  and black wire to cell- pad?
Thanks!
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: raschemmel on Sep 20, 2016, 04:31 pm
Never do anything with a lipo without measuring the voltages on the connector to be sure.
The voltages will make it obvious where the wires are coming from.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: jremington on Sep 20, 2016, 04:39 pm
Quote
In ten years of RC aircraft flying , most of the Lipos that"puffed up" , did so after discharging them to less than 3.2 V/per cell, not 2.8 V/per cell.

Ok, so the safe threshold is 3.2v. Anyway, how can you know that your battery is approaching this threshold?
A theoretical discussion only. The battery protection circuits usually cut out at 2.8 V or less. The one pointed to by the OP (http://www.all-battery.com/PCBfor11.1VLIPO_Li-Ion_Li-MnNiBatteryPack-32071.aspx) has this cutout:

Quote
Over discharge protection Over discharge detection voltage (Cell) 2.5±0.080V
Quote
mmm.. interesting but I still miss how to connect this circuit to the battery pack. Just to know, the battery I'm using now is a turnigy 11.1v 500mAh
The turnigy battery you are using is three cells in series.

You can wire three "protected" cells in series by yourself!
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 20, 2016, 05:37 pm
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 (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 :)

Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: jremington on Sep 20, 2016, 05:44 pm
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:

(http://forum.arduino.cc/index.php?action=dlattach;topic=424824.0;attach=181004)

You do not need to add another protection circuit.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 20, 2016, 05:53 pm
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:

(http://forum.arduino.cc/index.php?action=dlattach;topic=424824.0;attach=181004)

You do not need to add another protection circuit.
Ok. But how can I recharge these new battery pack?
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: jremington on Sep 20, 2016, 05:59 pm
Use the same charger you are now using for your 11.1V (3 S) pack.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: raschemmel on Sep 20, 2016, 06:08 pm
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 (http://www.rcgroups.com/forums/showthread.php?t=2015863)

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.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 20, 2016, 06:17 pm
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 (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?
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: jremington on Sep 20, 2016, 06:26 pm
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.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: raschemmel on Sep 20, 2016, 07:08 pm
Maybe they have improved over the years.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: jremington on Sep 20, 2016, 09:45 pm
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).
(http://3.bp.blogspot.com/-wewLx9uRss0/U_ndbP4XMCI/AAAAAAAAIDk/FJRJtvbDiFs/s1600/index.jpg)


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.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 21, 2016, 11:42 am
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 (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!
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: raschemmel on Sep 21, 2016, 03:00 pm
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 ?
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 21, 2016, 03:16 pm
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   
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: raschemmel on Sep 21, 2016, 04:26 pm
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 ?
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: jremington on Sep 21, 2016, 04:44 pm
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.
Title: Re: assembling a 11.1v battery using 3 Lipo 3.7v with a protection circuit
Post by: valerio_sperati on Sep 21, 2016, 05:10 pm
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!