mAh, is not just sheep language

mAh (sometimes Ah) is an abbreviation for Milliampere-Hours (or Milliamp-Hours; Amp-Hours) and is the measurement of a battery's capacity. The battery capacity will, in part, determine how many hours of operation one can expect from an electronic device between charges (known as the discharge time).

In (Utopian) theory, a rechargeable battery with 2000mAh capacity will take 4 hours to discharge if the device to which it's connected consumes 500mA. On two-way radios, it doesn't quite work that way since the current consumption will vary drastically, depending on what the radio is doing during that period. And one has to consider Peukerts theory and self-discharge - both of which are a little too much to talk about in a single post.

5-5-90?

To give customers a sense of what sort of discharge time to expect, many manufacturers will use the so-called 5/5/90 rule. This represents a common usage pattern of: 5% transmit; 5% receive and 90% standby time. This clearly does not represent all radio users but is an agreed means to compare batteries equally under the same rules.

What should I choose?

You should choose a battery that lasts one shift or the full working day. If you work in the field and may only return to base after many hours or days, it might be worthwhile considering a 2nd battery. Batteries with up to 300mAh capacity are available for the DP4000e series radios and can provide up to 28 hours of operational time.

NiMH) or LiIon?

There are two chemistry types currently available for portable two-way radio use: Nickel-Metal Hydride (or NiMH) and Lithium-Ion (LiIon). Nickel-Cadmium is no longer produced due to its toxicity.

Some of the advantages of choosing NiMH include:
- Higher energy density when compared to NiCd.
- Does suffer from the memory effect as much.
- Safer for air transport.
- Environmentally friendly and easily recycled.

Disadvantages of NiMH include:
- Limited service life if allowed to discharge excessively and regularly.
- Cannot be fast-charged like NiCd could.
- Slightly higher self-discharge.

Some of the advantages or LiIon include:
- High energy density.
- Lower self-discharge
- Does suffer from the memory effect as much.

Disadvantages of LiIon include:
- Hazardous if damaged.
- Cannot be stored for as long as NiMH.
- Subject to transportation regulations.
- More expensive than NiMH.

Working in the cold?

For users who work in sub-zero (ca. -30°C) temperatures, the PMNN4435 battery might be useful.

Memory Effect?

If not charged and used properly, most rechargeable batteries will start to exhibit the so-called memory effect that causes them to hold less charge. The battery almost seems to remember the smaller capacity.

What is Energy Density?

This is a measurement of a battery's size versus how much energy it can deliver. Obviously, the higher the better because that means a lighter battery that can deliver more talk-time. This is measured in Joules per cubic meter (or sometimes mAh/cm³).

What sort of service life could I expect from my battery?

This is wholly dependent on observing some simple rules when it comes to using rechargeable batteries:

1. When bring a battery into service, allow it to charge for at least 12 hours.
2. When using the battery, let it discharge fully then only charge it again.
3. Don't use the charger as a radio holder.
4. Don't put the radio back onto charge if it hasn't been used much (or at all).

Remember that each time a battery gets charged and discharged, it counts to one cycle. Most rechargeable batteries can provide more than 100% of their original capacity for up to 500 of these cycles. So observing these rules is crucial for optimal service life.

Also, remember that a rechargeable battery will need a few charge-discharge cycles before it reaches its maximum potential capacity. You should consider replacing a battery when its capacity decreases to 80% of the rated capacity.

Much of the above intricacy can be reduced by using IMPRES batteries and IMPRES Fleet Management - especially if you have many batteries deployed. This allows you to get an overview of the state-of-health of all the deployed batteries.

With right usage habits and Motorola original batteries, 2 or more years seem reasonable.

Whats the different between Minimum;  Typical and Maximum Capacity?

Since no two batteries will be the same, there needs to be an appropriate means to state the capacity of any battery. Typical Capacity refers to the statistical mean capacity for a specific battery model. Minimum and Maximum refer to the statistical standard deviation above and below the mean.

What does mean and deviation mean? Imagine a school class and assume they are all girls. You measure the height of all the girls and work out the average - that's the mean. They you work out by how much each girl is shorter or taller than the average (i.e. their height minus the average) and average that - this is the devation.

Back to batteries: When a minimum capacity is given, it means that most batteries, will not be below this when new. When a maximum capacity is given, it means that most batteries will never be above this value when new.

I only use the batteries once in a while (or I will only be using them in a while), how can I store them?

New batteries can be stored for up to one year without any ill affects. If you are going to be storing them for a long time it's useful to first charge/discharge them to about 40% then take them out of storage every few months, fully charge; fully discharge and recharge them back to 40%.

The batteries should be stored away from sunlight; in a low humidity atmosphere and somewhere around 25°C.

If you are deploying a new system, that will take a long time to roll out, try to put off ordering the batteries until the last few tasks are being completed. Or only enough order radios+batteries that will go straight into service while the majority waits until the network is ready/almost ready. This way, radios are issued with fresh-from-the-factory batteries.

ATEX intrinsically safe batteries have additional safety circuitry built into the battery. These batteries will have a higher than normal self-discharge rate and if you are planning to store these batteries for a longer period, you must charge the batteries every six months.

Further reading.

The folk at CADEX have produced an excellent and comprehensive online course about batteries. This can be found at batteryuniversity.com. The course material is also available in print and Kindle via Amazon or your local bookstore.













2 comments:

  1. Memory effect on Li-Ion Batteries..? We assume Li-Ion Batteries didn't get memory effect. Pls correct if I am wrong.

    ReplyDelete
    Replies
    1. LiIon batteries are a lot more firgiving of inadequate charging but not completely immune to the memory effect.

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