DC Supply! Monthly Electrical Ezine

CBC Design (tm) - August 2002 Issue. ISSN 1475-3464
Email: cbc_design@btconnect.com
http://www.cbcdesign.co.uk

"...Maintaining a reliable DC supply."

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IN THIS MONTHS ISSUE

- Editorial
Temperature Compensation. (Article)
Automatic Boost. (Article)
- Competition - Win FREE battery pack!.
- Readers Questions
- Subscriber Ads

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EDITORIAL. 

We
lcome to our August issue of DC Supply.
This is the first issue of the second year of our publication, DC Supply.
Many of you have been subscribing since our first issue was released
and we hope that you have found the articles we have produced up to
now, useful.
 
Please note that we will no longer be posting a copy of each months
publication to our website. It is becoming increasingly difficult to update
the site on a regular basis and this is leading to issue delays. You will
continue to receive your copy on a subscription basis for as long as you
wish of course.
 
This month we look at temperature compensation and automatic boost.
Batteries, lead acid in particular, must be maintained at a specific voltage
to get the best performance from them. Our article on temperature 
compensation will show you how to make sure your batteries perform 
regardless of temperature fluctuations.
 
Boost is a feature often required on charging systems. Often the facility
is manually operated but there are applications in which an automatic
boost facility is required. Take a look at our second article where we
explain where, how and why auto boost is required. 
 
We hope you enjoy this months issue.
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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 nineteen years and has designed charging equipment and battery monitors for some of the world largest companies.
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ARTICLE: Temperature Compensation: Alan Fidler.
 
In some environments where ambient temperatures vary over a wide range, batteries
cannot perform to the best of their ability unless the charging voltage is raised or
lowered in accordance with a fall or rise in temperature.
 
Typically, a lead acid battery has a compensation value of about 2.5mV per cell per oC
depending upon the battery type. This would mean a 12V battery charged at 2.26 volts
per cell at 25oC would require a charging voltage of approx 13.75VDC at 15oC and
13.9VDC at 5oC. In all cases, the charging voltage increases as the temperature falls
and visa versa.
 
Sadly, temperature compensation is rarely used and the result is premature failure
of hundreds of thousands of batteries worldwide. This may be good news for battery
suppliers but is certainly bad news for us and the environment too. The facility is often
inexpensive, consisting of nothing more that an RT (resistor/temperature) matched probe
connected to the charger control circuit.
 
Certainly long life batteries designed to operate for 7 years or more must be properly
charged at the most appropriate level. They will never perform to specification if the
float voltage is too high or too low for a given ambient and the result will be premature
failure. If you use 7 or 10 year life batteries in your installation and they fail before they
should, look at the charging method and take ambient temperature readings. It may be
that your charging equipment needs to be temperature compensated.
 
Contact your charger supplier and ask them if temperature compensation can be
retro fitted to your installation. If not, you may need to adjust your charging voltage
manually, depending upon the temperature. Reputable battery manufacturers will
be able to provide you with the actual charging potentials required for a given
temperature.
 
One thing is certain, a lack of compensation on a battery installation subjected
to wide temperature variations will be detrimental to the health of your cells. They
will fail well before they should and you'll be throwing money away.
 
Remember: Look after your batteries and your batteries will look after you!
 
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ARTICLE: Auto boost. Author: Alan Fidler. 
 
Most of us are familiar with the word boost but for those of you who are not, it is a
term used to describe a condition under which the charging voltage is raised to
increase current into the battery, i.e. boost.
 
Most boost facilities are included for equalisation purposes. It is unfortunate that
batteries connected in series have a tendency, over time, to become slightly
unbalanced. Boost corrects this by taking the battery to a specific potential
that forces each cell to display the same on charge voltage, i.e, equalisation.
The boost function is often manually controlled using a simple switch.
 
As well as the manual boost system, an automatic boost system is also used
in applications where some degree of automation is required. The two most
widely used boost systems include semi or fully automatic boost.
 
Semi automatic boost is used in an equalising role. The boost function is
manually initiated and a timer switches the charging system back to float
mode after a pre-set period. This sort of system is used one a month as part
of an established maintenance regime.
 
Fully automatic boost systems tend to be used on batteries which require
a high initial charging voltage that switches down to float when the battery
reaches a pre-set potential or a timer operates, whichever comes first. This
type of boost facility is particularly suited to applications where the batteries
are subjected to deep discharge.
 
More complicated automatic boost systems include voltage monitors which
determine if and when the boost facility is required. An battery installation
that is subjected to both deep or partial discharge will not necessarily require
boost on every charging cycle. The depth of discharge determines if and when
to activate the boost function to prevent excessive gassing following a light discharge
cycle.
 
In all cases, consult the battery manufacturers documentation to determine
if and when a boost facility may be required. Using boost unnecessarily will
damage your batteries and invalidate the warranty. It is worth noting that
temperature compensated chargers are rarely fitted with boost.  
 
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COMPETITION:

Subscribe to our ezine and you will be automatically entered into our competition where you can win a FREE Nicad "AA" battery pack.

Simply send your email address (No free email) to cbc_design@btconnect.com with the words
"SUBSCRIBE" in the subject line.

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READERS QUESTIONS.

Questions from Damon Wood
 
Question 1.
What is an accumulator?
 
An accumulator is a battery. The term accumulator was widely used
in the past and has been replaced by the term battery.

Question 2.
What is a Controlled Rectifier?.
 
A controlled rectifier is a half or full wave bridge rectifier which converts
AC into DC. Unlike un-controlled rectifiers, a controlled type can be
used to regulate output current and/or voltage. They are widely used
in industrial charging applications.
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