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Engineering Guidelines for Designing with Batteries |
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Custom design and manufacture of state-of-the-art battery chargers, DC/DC Converters, and power
supplies
 Battery Chemistry
Tutorial and FAQ
Battery Technology Comparison Chart
How to Calculate Battery Run Time
How to Store
Batteries (Lead Acid, SLA, LiIon, NiMH, NiCad)
Chart of Standard
Cylindrical Battery Sizes
Chart of Standard
Sealed Lead Acid Battery Size
How to Charge Sealed Lead Acid
Batteries
How
To Charge NiCad Batteries
How to Charge
NiMH Batteries
Low Power Connector FAQ
Battery Pack Design
Special Design
Rules for Large Battery Packs
Mechanical Considerations
1. Batteries are not made to precision
tolerances. Allow ±0.5 mm tolerance for both diameter and length for cylindrical batteries, and as much as ±5 mm
tolerance for lead acid and sealed lead acid parallelepipeds.
2. Batteries also expand and contract during charge and
discharge. Potting a battery is not a good idea, unless there is some provision made for this dimension change.
3. Over
the course of life most batteries release hydrogen, and sometimes oxygen. Take this into account if you are designing a closed
system, such as waterproof lights, weatherproof installations, etc. Some method of releasing or absorbing the hydrogen,
flooding with air or inert gas should be used. In closed cabinets some provision for ventilation is necessary to prevent
hydrogen gas from accumulating.
5. When using battery packs be careful not to inadvertently short the cells. A pack of
cells wired in series will become shorted if the cases of adjacent batteries touch, since the outer case is a terminal. This
can happen if the cells are shrink wrapped, film wrapped or painted and the batteries rub against each other. Brittle shrink
wrap is known to shred under stress, leaving the bare cell walls to touch.
6. When using or designing battery holders
make sure there is adequate provision for short cells, long cells, or wide cells. Keep sharp clip edges from touching the cell
where they could cut the film or paint, causing a short between cells held by the same clip.
7. Position the cells away
from heat sources if possible. Heat will cause an increase in self-discharge, and will also decrease the life of the battery.
The old rule-of-thumb of twice the self discharge every 10°C increase in temperature still holds.
8. Don't measure
the length of a live cell with metal calipers! Be careful--batteries are different than other components. They can short from
keys, from metal tools, or coins, so be careful of putting them in your purse, tool box, or pocket.
9. When making
fixtures to hold removable cylindrical batteries use contact forces of 1-2 pounds, depending on the weight of the battery and
the roughness of handling expected.
10. There is a helpful ANSI standard C18 which gives a lot of guidance for battery
power devices.
Electronic
Considerations
1. If there are alternate ways to power your device, make sure to isolate the battery
from the alternate sources of power to prevent inadvertent charging. In the case of high voltage batteries isolate the battery
from terminals of alternate power sources.
2. Some cells, such as CMOS maintenance lithium batteries are designed for a
very low rate of discharge. Some meters will load them down with too much current, and so will give incorrect readings. Make
sure you are using a high impedance meter.
3. Open Cell Voltage (voltage measured with a high impedance meter) is a
function of the cell chemistry and internal leakage. Even dead cells can register the same OCV as good cells. The test of a
battery is its voltage under load.
4. Be careful to match the cells in a battery pack. When a battery pack is near zero
volts under load the weaker cells will go into reversal, and suffer damage and perhaps venting.
5. When using
rechargeable cells, don't overdischarge below the rated discharge voltage. For NiCad and NiMH this is about 1 volt per cell.
For lead acid, it is about 1.75 volts per cell (10.5 volts for a 12 volt battery).
6. Take care when designing a battery
holder to use batteries in parallel. A backwards battery will short out the pack, and customers typically expect the batteries
to alternate orientation.
7. How much capacity do I need? Click here for a tutorial.
8. There should be some provision for removing the battery from the circuit when the voltage gets too low. This
will prevent leakage and corrosion from non-rechargeable primary batteries, and extend the service life of rechargeable
batteries greatly.
Designing with Alkaline and Carbon-Zinc Batteries
Whereas rechargeable batteries tend to be rated at a nominal voltage, primary batteries are most often rated at their
peak voltage. In the case of the manganese dioxide-zinc chemistries (alkaline, carbon-zinc, leclanche) the rated voltage is 1.5
V, but this is only the peak voltage. Since there is no pronounced hook at the end of charge, these cells are serviceable down
to 0.6 volts. so (1.5 + 0.6)/2 = 1.05 volts might be used as the nominal voltage.
Many engineers have made the mistake
of designing their equipment for an alklaine battery voltage range of 1.5-1.2 volts, meaning the cell becomes unusable when 70%
of the chemical energy is left in the cell. Don't be among them!
It is almost impossible to get the manufacturers of
alkaline cells to give a capacity in amp hours, but here are some approximate numbers. The first column is a generic list,
rated for 60+ hour discharge rates. For 2-4 hour discharge rates multiply the capacity by 0.4, for 5-10 hour discharge rates
multiply by 0.6, for 15-20 hour discharge rates multiply by 0.8, and for 50 hour discharge rates multiply by 0.92. The the
other columns are famous brand with the manufacturer's trademark slightly obscured. Charts measuring the different brands are
linked to below.
| Capacities in milliamp hours for a slow
discharge (60+ hours) |
| Size |
Standard
Alkaline Primary Cells |
Premium Alkaline Cells
12 mA discharge rate |
Long Life Alkalines |
"Professional" Alkaline |
"Top" Alkaline |
Extra Heavy Duty Carbon Zinc at 5 mA discharge rate |
Extra Heavy Duty
Carbon Zinc at 12 mA discharge rate |
Extra Heavy Duty Carbon Zinc at 240 mA discharge rate |
Super Heavy Duty Carbon Zinc |
| AAAA |
350 mAH |
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| N |
500 mAH |
580 mAH |
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360 mAH |
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| 1/3 A |
600 mAH |
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| AAA |
800 mAH |
780 mAH |
1150 |
1100 |
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480 mAH |
460 mAH |
240 mAH |
540 mAH |
| AA** |
1700 mAH |
2,000 mAH |
2850 |
2450 |
2050 |
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1320 mAH |
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950 mAH |
| C |
5000 mAH |
4,560 mAH |
7800 |
7100 |
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3000 mAH |
| D |
10,000 mAH |
14,400 mAH |
15000 |
14000 |
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5900 mAH |
| F |
20,000 mAH |
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| G |
20,000 mAH |
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| 9 Volt transistor radio style* |
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580 |
565 |
550 |
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30 mAH |
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400 mAH |
| 6 volt '908' Lantern |
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20,000 |
13,000 |
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12,000 mAH |
| 6 volt '918' Lantern |
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40,000 |
27,000 |
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*
For Discharge Curves for
9 volt batteries click here
**For Discharge curves for AA alkaline and NiMH cells click
here
Designing with Zinc/Air batteries
The zinc air battery is a wonderful thing if
you have the right application. Since you don't have to carry the oxygen source with you, it has very high energy density. For
more information about these cells see the battery chemistry FAQ listed at the top of the page.
The voltage versus
discharge of these cells is amazingly flat, at about 1.2 volts. At low relative humidities (such in Utah, where we live) the
voltage will start to sag with 40% of the capacity
remaining, but at 75% relative humidity it stays up above 1.2 volts for
95% of the capacity. The cell can said to be exhausted at 1 volt, since at this point the voltage is dropping like a slam
dunk.
Product Considerations
1. It is better to over-design the
battery run time than to under-design. Under-design might save some costs, but the customer will perceive that you have a poor
product if the battery life is lower than he expects. This is a lesson to be learned from PDAs. They use a lot of power, but
they must be small, so they use disposable alkalines, which give twice the run time of rechargeable batteries.
2.
Remember that most people will remove the batteries from a device before noting their orientation. Clear instructions on the
position, orientation, and order of new battery installation are expected.
3. You have a choice between using
off-the-shelf or custom, common or hard-to-get batteries and packs. Using common, locally available batteries saves money in
development cost, development time, and logistics. But sometimes a common battery size won't work.
Another
consideration in some industries is theft. An equipment manufacturer that decides to use a commonly available camcorder battery
for his equipment might find that his industrial customer is spending a lot of money to replace stolen batteries. |
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PowerStream Technology: 140 South Mountainway Drive, Orem
Utah 84058
Phone: 801-764-9060, 9062, 9063, or 9064
Fax: 801-764-9061 |
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PowerStream Technology
140 South Mountainway
Dr.
Orem, UT 84058
Phone: 801-764-9060, 9062, 9063, or 9064
Fax: 801-764-9061
Map &
Directions |
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© Copyright 2000-2004, 2006, 2007 Lund Instrument Engineering, Inc. All
rights reserved This material is copyrighted original work. It is forbidden to use this information, text, or
graphics in full or in part on another web site without written permission. This prohibition forbids making derivative text
using automatic thesaurus substitution software. |
Industrial battery engineering. Battery design. Custom batteries. Building battery packs. Battery
information. Battery info. |
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