Hey all!

I've been meddling with power banks and li-po batteries for a while now. The way I normally set them up is one or two batteries in parallel, giving me about 3000mAh, and then I connect them to a PCB that has a voltage overcharge protection and allows them to be recharge through microUSB. Here's a link to one of the PCB's I've bought:
http://www.ebay.com/itm/3-7V-Li-ion...pply-Module-5V-1A-Charge-Module-/291644400220

I've wanted to make a 'flexible' powerbank strip for a while and I realized that normal li-po batteries are definitely not recommended for bending or stresses of any kind. I've talked to some suppliers of what they call 'flexible and thin' li-po (about 3mm thinckness), but they've assured me that this is not a good idea with this type of product.

That's when I thought of using small rechargeable button cells (the LIR2032 3.6V rechargeable model fits my needs well) and wiring about 30 of them in parallel to get to a modest 1.350mAh, just for initial testing purposes. I'll keep a small 5mm gap between them, which will make the powerbank strip somewhat flexible.

If I simply connect them all in parallel and wire this assembly to the PCB I linked above, will this be enough? I'm quite an amateur really and I'm quite concerned with exploding batteries or safety issues. Also, how is the charge rate determined?

Thank you and sorry for the ignorance on the matter!

 

Hey all!

I've been meddling with power banks and li-po batteries for a while now. The way I normally set them up is one or two batteries in parallel, giving me about 3000mAh, and then I connect them to a PCB that has a voltage overcharge protection and allows them to be recharge through microUSB. Here's a link to one of the PCB's I've bought:
http://www.ebay.com/itm/3-7V-Li-ion...pply-Module-5V-1A-Charge-Module-/291644400220

I've wanted to make a 'flexible' powerbank strip for a while and I realized that normal li-po batteries are definitely not recommended for bending or stresses of any kind. I've talked to some suppliers of what they call 'flexible and thin' li-po (about 3mm thinckness), but they've assured me that this is not a good idea with this type of product.

That's when I thought of using small rechargeable button cells (the LIR2032 3.6V rechargeable model fits my needs well) and wiring about 30 of them in parallel to get to a modest 1.350mAh, just for initial testing purposes. I'll keep a small 5mm gap between them, which will make the powerbank strip somewhat flexible.

If I simply connect them all in parallel and wire this assembly to the PCB I linked above, will this be enough? I'm quite an amateur really and I'm quite concerned with exploding batteries or safety issues. Also, how is the charge rate determined?

Thank you and sorry for the ignorance on the matter!

Life expectancy would be a concern. With 30 batteries the probability of a failure increases by, maybe, 30 times.

 

Life expectancy would be a concern. With 30 batteries the probability of a failure increases by, maybe, 30 times.

Is there a way to minimize this? And also, could I just simply connect them, or is there a risk of overcharge?

Thank you for your answer

 

It sounds like you have overlooked a couple of points. The most important of which is that you do not want to charge and discharge those batteries at anything like the rate on the label. For example if you have a 3500 mAh battery you do not want to pull 3.5 Amperes over 1 hour out of that battery. It should be more like 350 mA for 10 hours. The same for charging. All of this information and more is at Battery University.

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

Also, it is OK to operate batteries in parallel, but you need to take precautions charging them in series or parallel.

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

 

@Papabravo thank you for your detailed response, really appreciate it!

As for the charging rate, I completely understand what you mean. However, the link I've provided as an example is a PCB that regulates at 1A the discharge/charge rate. That is well below the stated 3500mAh. However, the problem I'm facing is what happens if I have 30 batteries in parallel with, say, 2000mAh. Will there be any risks if I use this PCB? I know that my voltage overcharge is protected, but what happens to the life cycle efficiency and safety of the batteries? (Looked at the second link and didn't see a relation to this, thanks for the link, though)

 

@Papabravo thank you for your detailed response, really appreciate it!

As for the charging rate, I completely understand what you mean. However, the link I've provided as an example is a PCB that regulates at 1A the discharge/charge rate. That is well below the stated 3500mAh. However, the problem I'm facing is what happens if I have 30 batteries in parallel with, say, 2000mAh. Will there be any risks if I use this PCB? I know that my voltage overcharge is protected, but what happens to the life cycle efficiency and safety of the batteries? (Looked at the second link and didn't see a relation to this, thanks for the link, though)

One of the ways to prolong the life is limiting the charge/discharge rate. At least that is what I remember after going through a similar exercise to the one you are going through now.