AC Powered, Battery Backup CO/Smoke Alarms

[infinity]

Does anyone know how long these types of alarms will operate when they're solely on battery power? A typical battery only smoke alarm will run for at least a year on battery power but what about alarms that use battery backup and are typically run off of 120 VAC?

 

[Redcliffe]

That would depend on how many times it has been activated.

 

[K8MHZ]

That would depend on how many times it has been activated.

Don't 120 volt alarms beep when they lose the 120 volt source? If so, that will wear down a battery, probably faster than just the detection circuitry.

 

[gar]

160430-1025 EDT

infinity:

If this is a single unit device, not a component of a system, then pull the battery out and arrange some way to reconnect the battery to measure battery current. If this uses a rechargeable battery, then you should also be able to see charging current.

Apply AC power for a short time. Measure battery voltage and current with AC power on. If there is a visual numeric display when AC power is on, then note whether that goes off when AC power is removed.

Remove AC power measure battery voltage and battery current. Leave AC power off. Sometime later, possibly 15 minutes, again read battery voltage and current.

Determine whether the battery is a recharagable type or not.

Lookup the battery specifications. In particular the slow discharge capacity in ampere-hours. Use your battery current measurement to calculate an estimated duration of operation for the battery.

Most primary batteries have a long self-discharge rate, like years. Most secondary batteries have much shorter self-discharge times. NiCd can be in the 1 month range. Lead-acid somewhat longer, but some lead-acid are quite a bit longer. Depending upon the load, the self-discharge may be dominate. CMOS memory chips are an example where self-discharge can be domoninate.

I once shipped a system with CMOS memory battery backed up with NiCd batteries. Parameter data was stored in the CMOS memory. The machine was never powered for a year, yet the CMOS data was still good when power was applied. The CMOS only required a few microamps to retain data. Even though NiCd retains a usable charge for only about 1 month there was still enough energy in the battery to retain the CMOS data.

.

 

[iwire]

Does anyone know how long these types of alarms will operate when they're solely on battery power? A typical battery only smoke alarm will run for at least a year on battery power but what about alarms that use battery backup and are typically run off of 120 VAC?

I was able to find a link http://www.brkelectronics.com/pdfs/2008/08/21/smoke-alarm-troubleshooting-guide.pdf that seems to indicate UL only requires the battery to last 24 hours and then be able to sound for four minutes.

Not really an answer to your question but surprisingly short to me.

 

[K8MHZ]

Is there any reason you can't use battery only alarms?

It's recommended to change the battery once a year, but I have had them last several years before they started beeping.

 

[gadfly56]

I was able to find a link http://www.brkelectronics.com/pdfs/2008/08/21/smoke-alarm-troubleshooting-guide.pdf that seems to indicate UL only requires the battery to last 24 hours and then be able to sound for four minutes.

Not really an answer to your question but surprisingly short to me.

Re-read the info at your link. It's 7 days standby and 4 minutes in alarm but they say with fresh batteries it will last 20 - 30 days.

 

[gadfly56]

Is there any reason you can't use battery only alarms?

It's recommended to change the battery once a year, but I have had them last several years before they started beeping.

In older homes in NJ that is perfectly acceptable if the home was never hardwired to begin with.

 

[iwire]

Re-read the info at your link. It's 7 days standby and 4 minutes in alarm but they say with fresh batteries it will last 20 - 30 days.

Actually it says both, I guess it depends on which standard it is listed under.

 

[mgookin]

Don't 120 volt alarms beep when they lose the 120 volt source? If so, that will wear down a battery, probably faster than just the detection circuitry.

And that is a far greater risk than reward.

Imagine a storm knocks power out. Smokes are chirping. How do you abate the nuisance? Pull all the batteries. Meanwhile everyone is reading books by candlelight. Fall asleep and candle catches the house on fire. No smokes working. I can't imagine what brainiac suggested that as a code requirement. I wonder how many dead people they'll find before they change the code and recall all the smokes that have that feature.

/ end rant

 

[infinity]

Is there any reason you can't use battery only alarms?

We have a 700+ unit apartment building where there is a 1000KW optional standby generator to provide power to the refrigerator receptacle, a convenience receptacle and the heat pump with the thought that people could stay in their apartment during an extended outage like in super storm Sandy. The AC/battery backup CO/smoke alarm would need to operate on battery during any outage.

 

[K8MHZ]

We have a 700+ unit apartment building where there is a 1000KW optional standby generator to provide power to the refrigerator receptacle, a convenience receptacle and the heat pump with the thought that people could stay in their apartment during an extended outage like in super storm Sandy. The AC/battery backup CO/smoke alarm would need to operate on battery during any outage.

Is it an AFCI requirement reason that the alarms are not fed by one of the circuits fed by the generator? If not, what is the reason the alarms are not fed by the generator?

 

[JFletcher]

Don't 120 volt alarms beep when they lose the 120 volt source? If so, that will wear down a battery, probably faster than just the detection circuitry.

Yes they do. We have one in the truck right now that was connected to 120V then removed. It chirps every 30-60 seconds... havent timed it exactly. However, I imagine it's the same rate as a low battery alarm, and those can last a very long time before the battery finally gives up the ghost.

 

[curt swartz]

Yes they do. We have one in the truck right now that was connected to 120V then removed. It chirps every 30-60 seconds... havent timed it exactly. However, I imagine it's the same rate as a low battery alarm, and those can last a very long time before the battery finally gives up the ghost.

It must be defective or have a low battery. Are you sure the battery is good and activated?

An AC/Battery smoke alarm should not chirp on loss of AC power. That would defeat the entire purpose of having the battery backup. The purpose of having the battery back up is to allow the smoke alarm to continue working after a power failure, not force the occupants to remove the batteries.

 

[JFletcher]

It must be defective or have a low battery. Are you sure the battery is good and activated?

An AC/Battery smoke alarm should not chirp on loss of AC power. That would defeat the entire purpose of having the battery backup. The purpose of having the battery back up is to allow the smoke alarm to continue working after a power failure, not force the occupants to remove the batteries.

Ill check it Monday to see. Can't imagine a used/old SA got put onto the truck, but stranger things have happened.

I recall several months ago doing a new house where all the SA were chirping; they did not have the plastic shipping shields on the batteries removed (so, had 120V but no backup).

 

[infinity]

Is it an AFCI requirement reason that the alarms are not fed by one of the circuits fed by the generator? If not, what is the reason the alarms are not fed by the generator?

I guess it's a design issue where it's thought that the battery backup in the alarms will last until the power comes back on.

 

[K8MHZ]

I guess it's a design issue where it's thought that the battery backup in the alarms will last until the power comes back on.

So the wire routing was based and installed upon an assumption which posed a question here that should have been asked prior to the design of the routing?

That makes no sense at all, but I don't doubt for one minute that may be the case.

Can you move wires around in the panels to correct the issue? Or would that be a major PITA?

 

[infinity]

So the wire routing was based and installed upon an assumption which posed a question here that should have been asked prior to the design of the routing?

That makes no sense at all, but I don't doubt for one minute that may be the case.

Can you move wires around in the panels to correct the issue? Or would that be a major PITA?

It's too late for any changes now but we've been discussing around the water cooler if this is really a good design or not. If the battery last a week it's probably good enough.

 

[iwire]

I think it would be a huge issue with our local fire departments and the ability to use the property during a outage.