Beginners guide to batteries

[paintboy]

Hello all.
I ve understood a fair bit on battery building over the last few months and when fully confident will build a decent battery. For now I have some cheap cells and experimenting with my imax b6 ( probably a clone) charger.
It seems to work okay, it charges cells to 4.1 v individually fine, and multimeter confirms that. The cells are Samsung 15Q, so I believe they are 1500mah. When I discharge a random cell and charge the highest figure is 1207 but still 4.1v
So I d like to understand that I put 5 together, (all 4.1v) in parallel and discharged them and charged, I got 1439 may and 3.73v.

 

[vfr400]

Cells charge to 4.2v and discharge to 3.1v, which is what you should use for any capacity test.

If you get 1500mAh from 1, you should get 7500mAh from 5 in parallel.

1500mAh is really too low for an ebike battery. It'll be double the weight and size of one made with modern cells.

Where do you live?

 

[paintboy]

Hi there, Essex. I get the cells are naff, just trying to understand why I'm not getting 4.1v when charged as 5 p pack. It's a learning curve for me, for when I get some decent cells to work with. I think I ll take a cell off and see if that charges to 4.1v. If it does what does that prove? Charger is crap?

 

[Nealh]

If any cell has less capacity then another then the others will charge to the lowest denomination/capacity, that particular cell will reach 4.1v quicker then the others and then will not accept any more charge. The others in parallel will also stop accepting more charge, the average between all 5 in P will be the voltage you see. For all cells to be very even and the final voltage be very close to the final voltage you are expecting to see the cells have to be identical in IR and capacity retention.
One cell may just be very poor pulling the whole parallel group down.

 

[vfr400]

If there are any duff cells in the group, anything can happen. When building a pack and not using new cells, you must test every single cell for capacity and self-draining before doing anything else with them.

Building a battery yourself is a rewarding experience. It's useful if you need a custom battery of some sort. Don't think you can make a useful battery out of recycled cells, and don't think that you can make one cheaper than you can buy one.

 

[soundwave]

If there are any duff cells in the group, anything can happen. When building a pack and not using new cells, you must test every single cell for capacity and self-draining before doing anything else with them.

Building a battery yourself is a rewarding experience. It's useful if you need a custom battery of some sort. Don't think you can make a useful battery out of recycled cells, and don't think that you can make one cheaper than you can buy one.

or you just burn the house down

 

[Nealh]

Building a battery teaches you how the parallel and serial connections work, also how voltage flows with each serial connection to the next P group. Wiring up the BMS and the pack charge and discharge wiring also leads to more knowledge gained. Once confident one should be able to sort out any future issues with any battery, done correctly no issues should arise unless one rushes or cuts corners.

 

[paintboy]

Building a battery teaches you how the parallel and serial connections work, also how voltage flows with each serial connection to the next P group. Wiring up the BMS and the pack charge and discharge wiring also leads to more knowledge gained. Once confident one should be able to sort out any future issues with any battery, done correctly no issues should arise unless one rushes or cuts corners.

Sure, thanks I've learnt alot over past few months.
So if the cells I m referring to charged to 1439 for 5p 1s, what is 1439 referring to? Yes I'm experimenting, and the 5 cells in theory should be 7500.

 

[soundwave]

id check the connections because that is 1 cell if rated for 1500mah.

fake cells can be only 2-300mah and are very light and charge fast.

 

[vfr400]

Sure, thanks I've learnt alot over past few months.
So if the cells I m referring to charged to 1439 for 5p 1s, what is 1439 referring to? Yes I'm experimenting, and the 5 cells in theory should be 7500.

Milliamp-hours (mAh)

 

[soundwave]

 

[paintboy]

id check the connections because that is 1 cell if rated for 1500mah.

fake cells can be only 2-300mah and are very light and charge fast.
[/QUO I knew they were cheap packs and not enough grunt, they are 9s2p. Advertised as 32v 3amp. I can check voltage ok with multi meter but can I check the amps somehow?

 

[soundwave]

some pics would help but you need something like the imax charger to do discharge tests for capacity of each cell.

 

[paintboy]

I hUOTE="soundwave, post: 606097, member: 13916"]
some pics would help but you need something like the imax charger to do discharge tests for capacity of each cell.
[/QUOTE]
I have one, seems to work okay and be accurate

 

[soundwave]

thats how i charge 4 cells with that charger

 

[paintboy]

View attachment 41171


thats how i charge 4 cells with that charger

Ok, so what will your mah be when charged. I noticed that it's at 4.18 with only 8 minutes gone?

 

[soundwave]

i cant remember what i was doing with that but if a cell says it is 1500mah then a discharge test should be pretty close to that value when new.

thus why you should do this test if the cells are used and use the ones all closest together mah wise.

you dont want 1 cell being 2000mah if all others are 2500mah in the same pack because that cell will be charged first and then stop charging the pack.

 

[soundwave]

 

[paintboy]

i cant remember what i was doing with that but if a cell says it is 1500mah then a discharge test should be pretty close to that value when new.

thus why you should do this test if the cells are used and use the ones all closest together mah wise.

you dont want 1 cell being 2000mah if all others are 2500mah in the same pack because that cell will be charged first and then stop charging the pack.

Right, makes sense. Thanks
I ll have more questions when I get stuck if you don't mind helping

 

[soundwave]

if you have a 3s batt like above to charge all the cells you need to connect that white connector to th imax charger so it will charge and balance the cells.

bike battery's have a bms battery management system that basically does the same thing so only 1 connector is needed to charge the pack.

you can use lipo packs above for bikes but you have to be carful using them like this as with no bms you can drain the flat/dead if the voltage falls to low.