Douglas Krantz - Technical Writer - Describing How It Works
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How Long Does an 8 Amp Hour Battery Last?

I have a question about something


Doug,

I'm a Sr. Maintenance tech at a large distribution center for a health company. At the moment our fire panel isn't being powered by direct electrical current due to a circuit breaker fail. We are running on two 12 V 8AH batts as a backup system. I realize the cells are 8 amp hours but do those amp hours start when the alarms go off or does the 8AH start as soon as I connect them to the panel? I'm wondering if I have to replace them every 8 hours or will they last longer without a load (sounders / strobes) on them.

Thanks, A W

Backup Batteries

The batteries are 8 amp hour batteries. However, the 8 amp hours means how much electricity they have to give, not how long they will last.

Like an 8 ounce glass of water, 8 ounces is how much water is in the glass. If the water is just sipped, the water in the glass might last for many hours. However, if the person drinking is really thirsty, the water might last only minutes, or less.

Your fire alarm system probably sips the electricity so the batteries should last about 24 hours, but don't count on it.

Fire Detection

Keep in mind if it doesn't work, the panel doesn't cause a fire. It's just that if the primary AC power and the backup batteries quit, the panel is essentially dead and won't detect a fire. In other words, if there is a fire, no one will know about it until the fire is quite large.

Horns and Strobes

The horns and strobes only use electricity when there's a fire, so they should be left wired into the system.

Fire Walks

When the panel quits working, that's when you need to use people to replace the panel's fire detection function. Someone or several people will have to walk through the whole place every half hour looking for possible fire.

Check with the fire marshal in your area about how the fire walks are supposed to be implemented, and to indicate what documentation is needed to show that the fire walks were performed.

Fix the Breaker

Fixing the breaker is the easy way to get the fire alarm system back to normal. It really is recommended that you get the failed breaker fixed right away, no waiting for estimates.

Douglas Krantz
Thanks Doug, you basically confirmed exactly what I was thinking. My boss is not the most tech savvy guy, big surprise, so your answer to my question worked out great. I have our alarm company/electrician coming in today to get us back online. Hopefully no surprises, though, I'm sure you know how Fridays can be. Fingers crossed.

Thanks very much, A W

Based on his electronics training, and his understanding of Life Safety, Douglas Krantz has compiled his knowledge of Conventional Fire Alarm Systems into the book Make It Work - Conventional Fire Alarms. The book covers the basics of the Conventional Fire Alarm System, and shows how Life Safety and internal supervision affects the fire alarm system.

Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

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