DC Supply! Industrial Electrical Ezine

CBC Design (tm) - Issue 18, 2002/2004. ISSN 1475-3464
Email: cbc_design@btconnect.com

"...Maintaining a reliable DC supply."



- Introduction
Battery Problems (Article)
- Readers Questions
- Subscriber Ads


Welcome to issue 18.
Well it has been many many months since our last issue and I hope the articles we
have published in the past have proved useful to you. Based upon the total absence
of questions or comments since our last release, your existing installations are
obviously working well enough.
None of us should ever be complacent where batteries are concerned and in this issue,
I will be discussing a problem which many of you will hopefully never experience,
exploding laptop batteries!
Enjoy the article and hope you will continue to subscribe to our publication.
Happy Reading!  

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                           Editor: Alan Fidler.

Alan is the owner and manager of CBC Design, a leading battery management company                            based in the UK. He has worked in the industry for over Eighteen years and has designed                         charging equipment and battery monitors for some of the world largest companies.

ARTICLE: Battery Problems. Author: Alan Fidler.
Over the last 12 months or so, we have read reports of people who have suffered a
catastrophic failure of their laptop caused by exploding batteries. This raises concerns
about the safety of the latest cell packs and it would be sensible to understand
why it happens so we can try to avoid problems ourselves.
All of the reports I have read focus on one type of battery, specifically Lithium Ion
which are rapidly replacing the older NiCad and NiMh cells which were so popular just
a few years ago.
There were good reasons behind the changes in laptop power batteries, more power,
less weight and no memory effect were all positive reasons to switch to lithium ion.
Unfortunately, many contain Cobalt Oxide which can in certain circumstances go
into a condition known as thermal runaway. This condition can be described as a
substance or device which gets hot which results in increased conduction or burning 
which results in more heat and so on and so forth until failure occurs.
Explosive conditions are quite rare thankfully but they do happen and when they go,
the results is lots of smoke and possibly fire too. So why does it happen and what can
we do to avoid it?
Firstly, it is imperative to avoid short circuiting the battery. This will result in a large
uncontrolled current flow through the battery which will generate a lot of heat. Never
short out the battery terminals either directly or indirectly.
Secondly, do not over charge the cells. Again, heat will be the result and you could
push the battery into thermal runaway quite easily.
Thirdly, and this may sound obvious, do not expose the laptop and battery to direct or
indirect sunlight or heat from any artificial source. Keeping the battery cool at all times
is the key to avoiding problems.
Whilst we are on the subject of heat, please remember that vehicles can get quite warm,
particularly when left in full sunshine for most of the day. You really cannot afford to
leave your laptop anywhere in your car, including the boot.
Fourth, replace the battery at the end of its serviceable life.
If you follow these simple guidelines, you should be able to avoid any problems with
your lithium ion cells. They are certainly very good batteries and as long as they are
treated with respect, will give many years of reliable service.
Remember: Look after your batteries and your batteries will look after you!


Our latest NiCad charger automatically conditions NiCad batteries by discharging the
cells to a specified potential before applying a 3 stage charging cycle to recharge
the cells safely and completely.
Automatic discharge as required before charging cycle commences!
3 stage charging, Constant Current (Boost) Float Charge and Trickle charge!
Led indications for Battery Connected, Discharging, Charging and Battery Charged!
Available with 110/120 or 220/230 Mains input!
RFI Suppression!
Designed for fixed recharge applications!
Ideal for Switch Tripping applications!
Can be used to recharge Lithium Ion Cells!

Go to
http://www.cbcdesign.co.uk/ and click the "New Products!" link for more information.



12 & 24V DC DIMMER SWITCHES in 60W, 150W & 300W
*Adjust 12 or 24V lamps from a dim glow to bright light with a CBC Dimmer Assembly*
*Extends bulb life and reduces battery power consumption*
*Works just like the dimmers in your house*
*Easy to install with integral connections*
*20 year industrial design life*
Visit our website http://www.cbcdesign.co.uk for details

Questions from in-house 
1. What is the optimum charging voltage for Nicad or NiMH Cells?
1.41 Volts Per Cell.
2. What is the preferred charging regime for the same cells?
Constant current terminated by time, voltage drop sensing or voltage peak.

                                                                                                                                                SUBSCRIBER ADS.
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your own risk!

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