Non-Cali - One for the Electricity wizards

[kurienp]

I know some basics - if I connected batteries like in serial - 2 x 1.5 v serially I get 3 volts.



I connect batteries in parallel - 2 x 1.5 volts gives me 1.5 volts … but for longer.



What will this circuit below give me as an output (EDITED) as voltage?


For context - disassembled a 5 year old ~26000 mAh battery pack that had gone bust. It has 8 LG 11865 batteries, that I plan to replace with new LG 18650 batteries. Just wanted to understand the circuit before I go ahead and replace them.

This is what came out



Thanks

 

[andyinluton]

Ignore that I miss read the battery spec

 

[flying banana]

3v?

 

[kurienp]

Twice the voltage for 4x the capacity of a single LG 18650 battery. Should be about 41000mAh?

Thank you. Just updated my question - what would be the output as voltage?

 

[kurienp]

3v?

Thank you. I suspect yes, but just wanted to be sure.

 

[andyinluton]

Thank you. Just updated my question - what would be the output as voltage?

No I got it wrong the original batteries are 3000mAh at 3.7v each, your new ones are 2500mAh each at 3.7v so you have reduced your capacity by a 6th

 

[kurienp]

No I got it wrong the original batteries are 3000mAh at 3.7v each, your new ones are 2500mAh each at 3.7v so you have reduced your capacity by a 6th

planning for the 3500 mAh ones ... so should have a slight increase in capacity.

... though - a new anker battery pack is available at ~50 GBP

8 new 18650 3500mAh will be ~55 GBP + ~50 for a spot welder to assemble. More expensive to repair/rebuild than buy a new one. But I shall rebuild as the spot welder can be reused.

On the question though - what would be the output voltage. with 1.5 volt cells the output in my last diagram will be 3 v?

So on the 18650 cells the info I have is - 18650s may have a voltage range between 2.5 volts and 4.2 volts, or a charging voltage of 4.2 volts, but the nominal voltage of a standard 18650 is 3.7 volts.

So approx 3.7 x 2 = 7.4 v - if all the cells in my last diagram are 18650?

 

[Mansfieldman750]

planning for the 3500 mAh ones ... so should have a slight increase in capacity.

... though - a new anker battery pack is available at ~50 GBP

8 new 18650 3500mA….

I think yes, you have 4 parallel pairs connected in series so 3.7 x 2 = 7.4v.
Isn’t that how the batteries in an electric car are connected so that if you floor the pedal there is enough current ?

 

[Steve1]

I know some basics - if I connected batteries like in serial - 2 x 1.5 v serially I get 3 volts.

View attachment 103490

I connect batteries in parallel - 2 x 1.5 volts gives me 1.5 volts … but for longer.

View attachment 103491

What will this circuit below give me as an output (EDITED) as voltage?

View attachment 103492
For context - disassembled a 5 year old ~26000 mAh battery pack that had gone bust. It has 8 LG 11865 batteries, that I plan to replace with new LG 18650 batteries. Just wanted to understand the circuit before I go ahead and replace them.

This is what came out

View attachment 103493

Thanks

All the others are right if they are 1.5V per cell, then the output of your last diagram will be 3.0V.

 

[Steve1]

I know some basics - if I connected batteries like in serial - 2 x 1.5 v serially I get 3 volts.

View attachment 103490

I connect batteries in parallel - 2 x 1.5 volts gives me 1.5 volts … but for longer.

View attachment 103491

What will this circuit below give me as an output (EDITED) as voltage?

View attachment 103492
For context - disassembled a 5 year old ~26000 mAh battery pack that had gone bust. It has 8 LG 11865 batteries, that I plan to replace with new LG 18650 batteries. Just wanted to understand the circuit before I go ahead and replace them.

This is what came out

View attachment 103493

Thanks

All the others are right if they are 1.5V per cell, then the output of your last diagram will be 3.0V.

 

[yossarian]

The jargon description of that pack is 2S 4P (or 4P 2S). Don't neglect to manually balance the cells before spot welding.

 

[Hawthorn37]

Agree with others, the output voltage will be equal to the number of batt cells in series x voltage of a single cell. In my experience it’s tricky soldering connections onto the ends of cells without damaging them (or getting a dry joint due to insufficient heat). But don’t let that put you off - but I’d fully test before enclosing the power pack in anything.

 

[yossarian]

Here's a typical discharge curve https://cdn-learn.adafruit.com/asse...al/components_tenergydischarge.gif?1447976645

And it's worth reading these notes:

Li-Ion & LiPoly Batteries

If you want to take your project portable you'll need a battery pack! For beginners, we suggest alkaline batteries, such as the venerable AA or 9V cell, great for making into larger multi-battery packs, easy to find and carry plenty of charge. If you want to go rechargeable to save money and...

learn.adafruit.com

Lipo is always (reasonably) safe to use at the more conservative voltage limits. LiFePo4 is generally a better and safer chemistry to use in a vehicle and has higher cycle limits.