March 27, 2019

# NiMH Battery Packs

Chargers

## For loose cells and custom battery packs click here: For a chart of the sizes and weights of cylindrical batteries click here:

Pack Design Considerations

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:

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 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 is nested to take up less room. Calculating the size takes a little geometry.

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.

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

Over 80% greater run time versus lead acid of the same size.

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.

Also available in custom voltages, sizes, capacities, and configurations. This is PowerStream!

Low cost compared with other NiMH manufacturers.

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.

Thank you for considering PowerStream

Wednesday, 08-Dec-2021 02:05:16 EST
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