Battery pack building

[ColorMaker]

I have been building battery packs for 5 months now with alot of input from this forum. Thank you everyone for your replies.

To build a pack AA, C and D we first test each cell for capacity then assemble packs with equal capacities.

The tested Cells capacity ranges: ( ranges assembled)
AA 2400 - 2590
(2400-2450) (2451-2500) (2551-above)
C cell 4600 - 5100
(4600-4750) (4751-4900) (4901-above)
D cell 9800 - 10400
(9800-9950) (9951-10100) (10101-above)

With this spread is the capacity matching going to make a diffrence ?

AA cells testing goes relatively fast. We use 30 Maha C9000 and can test 60 cells a day. Its the C and D that is time consuming with only 8 cells a day.

Any input from anyone that builds NimH batteries would be greatly apreciated.

Packs are as follows

AA 10 in series for 12 volts
C (5 in series for 6 volts) then these are assembled 4 packs for each device for 24 volts
D Same as C


JM

 

[mdocod]

the closer they are matched, the longer the pack will last and the fewer maintenance cycles will need to be performed. Another consideration from what I have heard besides capacity is cell RESISTANCE. Matching based on both capacity and resistance would be best.

 

[SilverFox]

Hello JM,

The whole reason for matching is to make sure that all your cells empty in the same amount of time. This will give you the best performance from your battery pack.

The degree of matching is related to the cut off voltage of the device. From there, you can then look at probability of a cell dying.

For example, if you have 10 cells in the pack and use a cut of voltage of 10 volts, you can have 10 volts with 9 cells at 1.11 volts and one cell a 0 volts. If you have 2 cells at 0 volts, the remaining 8 would have to be at 1.25 volts. That is a little above the working voltage of the pack, so when two cells go bad, the pack should just register as bad.

If you raise the cut off voltage to 1.1 volts, then if one cell goes to 0 volts, the other 9 would have to be above 1.22 volts for the device to work.

As you can see, if you increase the number of cells in the battery pack to 20, things get more interesting.

I think that cell matching is important and actually pays dividends, but I am not the one trying to meet a production schedule.

If you added a hobby charger and 2 of the CBA units, you could triple your C and D cell testing. With 3 CBA units, and what you already have, you could get up to 32 cells a day. If you add another CBA unit, you would most likely have to add another hobby charger as well, depending on what the capability of the charger is. My Schulze is capable of charging a maximum of 36 NiMh cells at a time, but I was only figuring on doing a maximum of 24.

Good luck.

Tom

 

[ColorMaker]

Hello JM,

The whole reason for matching is to make sure that all your cells empty in the same amount of time. This will give you the best performance from your battery pack.

The degree of matching is related to the cut off voltage of the device. From there, you can then look at probability of a cell dying.

For example, if you have 10 cells in the pack and use a cut of voltage of 10 volts, you can have 10 volts with 9 cells at 1.11 volts and one cell a 0 volts. If you have 2 cells at 0 volts, the remaining 8 would have to be at 1.25 volts. That is a little above the working voltage of the pack, so when two cells go bad, the pack should just register as bad.

If you raise the cut off voltage to 1.1 volts, then if one cell goes to 0 volts, the other 9 would have to be above 1.22 volts for the device to work.

As you can see, if you increase the number of cells in the battery pack to 20, things get more interesting.

I think that cell matching is important and actually pays dividends, but I am not the one trying to meet a production schedule.

If you added a hobby charger and 2 of the CBA units, you could triple your C and D cell testing. With 3 CBA units, and what you already have, you could get up to 32 cells a day. If you add another CBA unit, you would most likely have to add another hobby charger as well, depending on what the capability of the charger is. My Schulze is capable of charging a maximum of 36 NiMh cells at a time, but I was only figuring on doing a maximum of 24.

Good luck.

Tom

CBA ? Do you have a link

Thanks for your input I was hoping you would respond. We are going to continue testing each cell we will just have to increase our testing equipment.

JM

 

[LuxLuthor]

http://www.westmountainradio.com/CBA.htm

To answer your question. Matching does matter. It matters more with certain brands of cells, and much more important with low resistance high current output cells (i.e. Elite brand).

Pre-screening of cells is essential, which includes arrival voltage assessment (if low, I reject immediately), charge/discharge/condition charge--check voltages at each phase, and several hours after condition, & 12-24hrs later, and again a couple days later. I sort particular voltage performances together, and have no hesitation to reject "lemon" cells. "Marginal" cells are put through another set of cycles before I make a final status determination. I use the guide of "how would I feel if this was my own pack" when going through these steps.

I am aware that plain voltage measurement is not an adequate performance test with NiMH, but it has a use when combined with other methodoligies, and experience with individual cell brand model performance.

Once I started doing the test cycling/voltage testing, I have not had feedback that packs have failed that I made. It's still possible for cells/packs to fail, but I think it is very important to screen and match cells initially. If this delays your pack delivery time, so be it.

 

[ColorMaker]

http://www.westmountainradio.com/CBA.htm

To answer your question. Matching does matter. It matters more with certain brands of cells, and much more important with low resistance high current output cells (i.e. Elite brand).

Pre-screening of cells is essential, which includes arrival voltage assessment (if low, I reject immediately), charge/discharge/condition charge--check voltages at each phase, and several hours after condition, & 12-24hrs later, and again a couple days later. I sort particular voltage performances together, and have no hesitation to reject "lemon" cells. "Marginal" cells are put through another set of cycles before I make a final status determination. I use the guide of "how would I feel if this was my own pack" when going through these steps.

I am aware that plain voltage measurement is not an adequate performance test with NiMH, but it has a use when combined with other methodoligies, and experience with individual cell brand model performance.

Once I started doing the test cycling/voltage testing, I have not had feedback that packs have failed that I made. It's still possible for cells/packs to fail, but I think it is very important to screen and match cells initially. If this delays your pack delivery time, so be it.

What cells do you use ? What cells would you not recomend for 12 and 24 volt pack building ? I could use some input from someone with more experience that build packs on a production level. Please feel free to contact me on any off topic messages.
[email protected]
(407) 862-3363

 

[LuxLuthor]

Jerry, off the top of my head, I have used Titanium, Powerex, Eneloop, Elite, Intellect, Sanyo, GB, Duracel, and probably a few others. You have to first decide on current needed, then size of cells--with AA being the most plentiful variety, then quality/price of selected cell. There are many pro's and con's with various brands/sizes/price.

 

[ColorMaker]

Jerry, off the top of my head, I have used Titanium, Powerex, Eneloop, Elite, Intellect, Sanyo, GB, Duracel, and probably a few others. You have to first decide on current needed, then size of cells--with AA being the most plentiful variety, then quality/price of selected cell. There are many pro's and con's with various brands/sizes/price.

Thank you

 

[ColorMaker]

Jerry, off the top of my head, I have used Titanium, Powerex, Eneloop, Elite, Intellect, Sanyo, GB, Duracel, and probably a few others. You have to first decide on current needed, then size of cells--with AA being the most plentiful variety, then quality/price of selected cell. There are many pro's and con's with various brands/sizes/price.

What battery tester / Anylizer do you use to check capacities ?

JM

 

[LuxLuthor]

Hyperion 1210i discharge/cycle modes, eStation BC-6, ZTS-MBT-1, CBA-II, Maha C-9000, Fluke 179 voltmeter for Lithium Ion cells.