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November 12, 2017

NiMH Battery Packs

NiMH and NiCad battery chargersChargers


NiMH and NiCad Charger Index

For loose cells and custom battery packs click here: NiMH & NiCad Batteries from PowerStream For a chart of the sizes and weights of cylindrical batteries click here:Battery size chart

For more battery engineering resources click here: Battery Engineering Resources

Pack Design Considerations

"Ladder", linear, F type, or radial

Note that the electrodes will both come off the top when there are an even number of cells, and one off the top, the other off the bottom when there is an odd number of cells. With a connector and heat shrink wrap they look like this:
 6 cell pack of 2/3 AA NiCad Cells

The size of a linear pack is roughly calculated by the formulaD x nD x H where D is the diameter of the cell, n is the number of cells, and H is the height of the cells.

Multi-row cells
There are two ways to start packing them. One could be called the cubic, and the other face centered cubic, or nested.
Cubic Packing

Cubic packing is in neat rows. The size of such a pack is nD x mD x H, where n is the number of cells in a row, m is the number of rows, D is the cell diameter, and H is the cell height.

Face centered cubic packing

Face centered cubic packing is nested to take up less room. Calculating the size takes a little geometry.
Close Packed 10 cell pack
The size is L x W x H where

L = (n +½)D
W = [0.866(p-1)+1] D
H=H
p is the number of rows wide.

If there are alternating long and short rows, such as the 3,4,3 ten cell pack, the formulas are

L = mD
W = [0.866(p-1)+1] D
H = H

Where m is the number of cells in the longest layer, and p is the number of layers. With heat shrink it looks like this:


For a 3 cell pack, you can put the cells in a tube



The diameter of the outer circle is 2.16 D.

For a four cell pack in a circular tube



The diameter of the circumscribed circle is 2.41 D.

Advantages:

OEM Battery ChargersNiMH batteries are smaller and lighter than lead acid batteries, making them a good choice for high performance bicycles and scooters.

OEM Battery ChargersOver 80% greater run time versus lead acid of the same size.

OEM Power Supplies Sustained operating voltage makes the scooter seem to have a fresh charge over most of the operating time. Lead acid voltage sags continuously over the discharge curve making the scooter slower through most of the run time.

OEM Power SuppliesAlso available in custom voltages, sizes, capacities, and configurations. This is PowerStream!

Universal Power Input OEM Power Supplies and OEM Battery Chargers Low cost compared with other NiMH manufacturers.

Universal Power Input OEM Power Supplies and OEM Battery Chargers We set out to design a drop-in replacement for lead acid in personal electric vehicles. This is a smaller, lighter, better performing replacement, but with a premium cost.

Data:

The following comparison tests were done with a 24 volt "Amplifier" electric scooter:

  Lead Acid NiMH Improvement
Battery Format 2 x 12V SLA Batteries 20 x 1.2 V D cells
Rated Capacity 8 AH 8.5 AH
Battery Mass 5.5 kg (12 lb) 3.4 kg (7.5 lb) 40 % lighter
Battery Size 12 x 2.6 x 3.7 in. 10.2 x 2.4 x 3.6 in. 24% less volume
Maximum operating current (note 1) 29.8 Amps 30.1 Amps
Average Operating Current (note 1) 11.1 Amps 10.6 Amps
Total run time
(note 4)
27 minutes 46 minutes 70% longer
Reduced Performance
(note 2)
21 minutes 35 minutes 66% longer
Loss Performance (note 3) 24 minutes 45 minutes 88% longer
Test differences Multiple rest cycles One rest cycle
Test differences Total run time includes three loss of power events with rests in between Test terminated upon the first loss of power
Notes:
1)156 lb test engineer on residential/business area test course, almost constant slopes up and down .
2) Indicated time is the first instance of a noticeable loss in performance .
3) Indicated time is the first instance of a complete loss of performance
4) Total run time is greater than the loss of performance time because the scooter was run again after a rest without recharging.



Note: these chargers are OEM only, minimum purchase quantities apply.


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