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Lithium coin battery for RTC, Class 2 Div 2, hazardous concern.

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Junior Member level 3
Oct 18, 2009
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Acle, Norwich
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Is there a guideline about lithium coin battery for real-time clock mounted on the board within a diecast IP65 sealed box (about 150x150x150mm) within Class 2 Div 2 or ATEX Zone 2 (ie dog-house). Does it require further mitigation measures (ie pressure vents)? I have put a small fuse on the PCB in series with the battery.

I believe the battery delivers a few microamps of current to the RTC circuit. What kind of fuse you have used?

If you put a vent in a sealed box, the purpose is defeated.

Are you worried that the cell can explode? In the worst case, it may bulge and leak. Total amount of energy contained in the cell is too little to worry.

"If you put a vent in a sealed box, the purpose is defeated." please explain, thx
Vent by definition means a way or passage for a gas or liquid.

The free dictionary says (meaning of vent)

1. Forceful expression or release of pent-up thoughts or feelings: give vent to one's anger.
2. An opening permitting the escape of fumes, a liquid, a gas, or steam.
3. The small hole at the breech of a gun through which the charge is ignited.
4. Zoology The excretory opening of the digestive tract in animals such as birds, reptiles, amphibians, and fish.
5. Geology
a. The opening of a volcano in the earth's crust.
b. An opening on the ocean floor that emits hot water and dissolved minerals.

I mean that a sealed box cannot have an opening. That is oxymoron (like deafening silence).

You seal a box so that nothing can escape. But then you want a vent?

But you can have a seal that leaks.

For high power batteries, one would use a Teflon seal to leak H2 from over charging. But Coin cells are like tiny precharged supercaps for use with 10% voltage range but very series high resistance (kOhm) inversely related to thickness and mAh capacity.

This means no to your answer and fuses are of no value.

You could put a 2V or 3V 5mm LED across a coin cell and have no fear of overcurrent. albeit short life <1 day then decay slowly after that.

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