Become a subscriber (Free)

Join 29,000 other subscribers to receive subscriber sale discounts and other free resources.
:
:
Don't worry -- your e-mail address is totally secure. I promise to use it only to send you MicroZine.

Intrinsically Safe Battery Circuit


This project, an intrinsically safe battery circuit from 1986,? shows how to ensure the safe operation of a battery in an unsafe environment i.e. where there could be a risk of explosion.



The idea is that intrinsically safe equipment must be safe whatever happens i.e. no sparks, no bad action if dropped etc.

Equipment and associated wiring approved as intrinsically safe may be installed in any hazardous location for which it is approved and the provisions pertaining to conventional explosion proof procedures need not apply to such installation.

Intrinsically safe equipment and wiring is incapable of releasing sufficient electrical energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture.

Abnormal conditions will include accidental damage to any part of the equipment or wiring, installation or other failure of electrical components, application of over-voltage; adjustment and maintenance operations and other similar conditions.



Executive Summary of the Intrinsically Safe Battery Circuit

An intrinsically safe battery circuit for connection between a battery and a load, such as a hand held transceiver, referred to as "HT's". The circuit includes a minor current path through a switching transistor and a major current path through a SCR.

The circuit is a hybrid circuit which includes an integrated circuit timer which provides a delay in establishing the major current path subsequent to the minor current path being established, and mounts on a small printed circuit board which results in a battery that is intrinsically safe.

Background of the Intrinsically Safe Battery Circuit

1. Field of the Design

The present design pertains to an intrinsically safe battery circuit, and more particularly, to an intrinsically safe battery hybrid circuit which prevents arcing and allows full current from the battery during operation.

2. Description of the Prior Art

An intrinsically safe battery is defined as a cell pack whose energy is limited to a point so as not to cause ignition as properly used in various atmospheres. The atmospheres considered dangerous are divided into several groups, and the groups are determined by the amount of energy required to cause ignition.

A regulatory agency most recognized in the United States is Factory Mutual ("FM"). FM in an insurance company specializing in hazardous applications. All testing is dictated and conducted on site at FM. Any damage or injury occurred in an accident involving a battery or other equipment not "FM Approved" voids Factory Mutual's liability. For this reason, customers insist on "FM Approved" batteries which are intrinsically safe.

Testing involves a variety of dielectric and physical construction checks. These checks are intended to insure the stability of the components used or limit the energy from the cells. Electrical testing is conducted on a spark generator.

A chamber is constructed which is air tight and includes a viewing window. Inside, a random spaced circular set of contact pins, resembling nails, are attached to one terminal of the battery. The other terminal attaches to a rotating arm whose tip contacts the contact pins. This essentially makes and breaks the circuit to the battery under test. Arcs are created inside the chamber, and these arcs are representative of the energy available from the battery. The different atmospheres are then pumped into the chamber and checked for ignition.

In the prior art, the most common method of making an intrinsically safe circuit for a battery has been to simply add enough series resistance to limit the energy to a safe level. This has worked well except for higher voltage cell packs such as 12 volts and over. These batteries of a larger voltage require a large value resistance at a high wattage that is physically difficult, and not acceptable to locate internally in the battery.

The present design overcomes the disadvantages of the prior art by providing a hybrid circuit to prevent arcing, which passes all electrical tests and allows full current from the battery.

Summary of the Intrinsically Safe Battery Circuit

The general purpose of the present design is to provide an intrinsically safe battery circuit which can be a hybrid circuit, and placed inside nickel-cadmium ("nicad") batteries, also referred to as nicad packs or nicad batteries. The circuit includes a minor current path and a major current path.

According to one embodiment of the present design, there is provided an intrinsically safe battery circuit for connection between a battery and a load, a circuit including a minor current path through a transistor and a major current path through a SCR. A timing circuit provides that when a load in place, the timing circuit provides an output signal after a predetermined time which switches a gate of a SCR to apply full power through the major current path. If a connection is broken such as removal of the battery, then another timing delay is again occurred. This avoids arcing which causes ignition.

Significant aspects and features of the present design is an intrinsically safe battery circuit which is a hybrid circuit and can be easily located in a nickel-cadmium battery cell housing.

Another significant aspect and feature of the present design is a hybrid circuit where the delay, when full power is applied, can be predetermined by selecting the value of the "RC" circuit across a timing integrated circuit.

A further significant aspect and feature of the present design is a hybrid circuit which is cost effective and provides 100% reliability while also allowing full power from the battery.

Having thus described principal embodiments of the present design, it is the principal object hereof to provide an intrinsically safe battery circuit.

One object of the present design is to provide an intrinsically safe battery circuit which allows full current from the battery and can be physically located within the battery housing.

Another object of the present design is to provide an intrinsically safe hybrid battery circuit.


Figure 1 : Illustrates a plan view for the intrinsically safe battery circuit



Description of the Intrinsically Safe Battery Circuit

FIG. 1 illustrates a plan view of an intrinsically safe battery circuit 10. A printed circuit board 12 supports conductors 14, 16 and 18, and components 20-34. A battery 36 with a plurality of cells in series such as nickel-cadmium cells, and a thermal activated switch 40 such as a low resistance device which breaks the circuit at high current connects between conductors 14 and 16. A load such as a hand held transceiver or a charger connects between conductors 16 and 18.


Figure 2 : Illustrates an electrical circuit schematic for the intrinsically safe battery circuit



FIG. 2 illustrates an electrical circuit schematic where all numerals correspond to those elements previously described.

A switching transistor 20 and a biasing resistor 22 connect in series with a load providing a minor current path between the battery 36 to the load 38. Resistor 24 provides biasing to turn on transistor 20 when power is applied. Diode 26 provides a reverse current path for charging the battery from the terminals 18. During the minor limited flow of current, the IC 28, such as an integrated circuit 555 timing circuit is powered and develops a high logic signal on pin 3 after a period of time based on the value of the RC circuit of a resistor 30 and a capacitor 32. The high signal at pin 3 switches the gate of the SCR 34 energizing the major current path to the load 38. The diode 36 provides for more rapid decay of the RC timing circuit when power is removed applied to the IC 28. A low resistance thermal switch device 40 such as a poly-switch, manufactured by RayChem, is inserted in series with the plurality of nickel-cadmium battery cells 36.

MODE OF OPERATION


Figure 3 : Illustrates a plan view of a nickel-cadmium battery pack for the intrinsically safe battery circuit



FIG. 3 illustrates a plan view of a nickel-cadmium battery pack showing the circuit 10 as a hybrid circuit physically placed and to be electrically connected in the battery pack 50 not illustrates for sake of brevity.

In operation, when the circuit 10 senses that a load is in place, the circuit waits one half second, by way of example and for purposes of illustration only before applying full power. If the load connection is broken, the one half second delay is again applicable. In this manner, arcing is avoided which would cause ignition.

Current first flows through the minor current path including the transistor 20, bias resistor 24 and the resistor 22. This turns on transistor 20 and supplies power to the integrated circuit 28. The integrated circuit 28 develops a high logic level on pin 3 one half second later. This high level triggers the gate of the SCR 34 providing a main current path to the load 38. If a continuous short is applied, the polyswitch 40 protects the battery 36 by opening up until the short is removed.


Click here for more project ideas.

New! Comments

Have your say about what you just read! Leave me a comment in the box below.



Claim Your: Useful

"Arduino Software Guide"

   Right Now...





Jump from the intrinsically safe battery circuit page to
Best Microcontroller Projects Home Page.


Privacy Policy | Contact | About Me

Site Map | Terms of Use



474-9934


Visit our Facebook Page:

   Click Here



Sign up for MicroZine
''The'' Microcontroller Newsletter

Enter your first Name and primary email address in the form below:


And receive absolutely FREE a full project for:

"Measuring Analogue Voltages
Without An ADC"

(Using only one pin).

Instant Download:
You Can
Get It Right Now

Warning: This project could be  Removed 
at any time.  

It will  NOT be 
available indefinitely SO
To avoid 
disappointment  get it:

Now



:
:
Don't worry -- your e-mail address is totally secure. I promise to use it only to send you MicroZine
Remember this is a project with full description and fully debugged C Source code - and it's not available from the main website.

You can only get it through this newsletter.

To get exclusive access Enter your first name Name and primary email address Now in the form above.:



But wait !

There's more...

You'll receive more
free and exclusive reports as well as site information and site product updates


Scroll up to the form above and sign up NOW. Don't forget it's FREE and if you don't like it, you can unsubscribe at any time.

Click Here Now to use the form above to get your Valuable information absolutely free.



Readers Comments

"I wanted to thank
you so so so much
for all the information
you have provided in
your site it's

SUPERB and FANTASTIC."

- Ranish Pottath

"This site really is
the best and my favorite.
I find here many useful
projects and tips."

- Milan

bursach<at>gmail.com<

"Awesome site,
very, very easy and nice
to navigate!"


- Matt
matt_tr<at>
wolf359.cjb.net


Learn Microcontrollers

"Interested in
Microcontrollers?"

Sign up for The
Free 7 day guide:

FREE GUIDE : CLICK HERE


"I am a newbie to PIC
and I wanted to say
 how great your
site has been for me."


- Dave

de_scott<at>bellsouth.net

"Your site is a great
and perfect work.
congratulations."


- Suresh

integratredinfosys<at>
yahoo.com

"I couldn't find the correct
words to define
yourweb site.

Very useful, uncovered,
honest and clear.

Thanks so much for
your time and works.
Regards."


- Anon

Recent Articles

  1. How to use the DHT22 (or DHT11) with an Arduino; full code and description. Also including a comparison of the DHT11 vs DHT22.

    The Essential Guide to the DHT22/11 humidity sensor including a library code guide for the Arduino. Learn how to determine Humidity, Dew point and Heat Index.

    Read more

  2. How to Use the MAX7219 to drive an 8x8 LED display Matrix on the Arduino.

    The Essential Guide to the MAX7219; What it is and how you can easily use one in any of your projects.

    Read more

  3. How to use a DS18B20 (single or multiple on one wire) for temperature measurement using the Arduino Uno.

    How to Easily Use the DS18B20 Maxim One-Wire thermometer with Arduino example code showing external or parasitic power modes.

    Read more