9v ni-mh 7.2, 8.4, 9.6 ?

[john2551]

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[john2551]

The question wasn't "what kind of battery should I use?" The type was already selected. This wasn't a battery application question.

Exactly! No thread busters please!

 

[wptski]

Exactly! No thread busters please!

Can you tell that I'm getting annoyed?

 

[bob_ninja]

The 9.6V is nominal at 1.2V per cell. Off my MAHA charger, the MAHA PowerEx check around 10.4V resting. Hot off the charger, they are higher. No problem using them. I think that I have them in both of my alarms. Use them in clamp amp probes, etc., whatever they fit into as they are a bit fatter than a standard alkaline!

Would you know it, my alarm was beeping last night
So I looked at the 9V NiMH I have, it is 150mAh, 8.4V
(7 x 1.2V = 8.4V)
Now I suppose there would be no harm in going with 8AAs (2 x 4AA holder) as older AAs will have a lower volate anyway, so may end up closer to 8 x 1.1V = 8.8V, which is darn close to 9V.
I suppose my 9V NiMH would be more appropriate for my multimeter which doesn't see extensive use.

 

[wptski]

Would you know it, my alarm was beeping last night
So I looked at the 9V NiMH I have, it is 150mAh, 8.4V
(7 x 1.2V = 8.4V)
Now I suppose there would be no harm in going with 8AAs (2 x 4AA holder) as older AAs will have a lower volate anyway, so may end up closer to 8 x 1.1V = 8.8V, which is darn close to 9V.
I suppose my 9V NiMH would be more appropriate for my multimeter which doesn't see extensive use.

Old or young, all are 1.2V nominal per cell. My MAHA PowerEx are eight cell batteries. Your 8.4V batteries start off at a lower voltage so they get to the cutoff point sooner.

 

[john2551]

Can you tell that I'm getting annoyed?

Yes! I know a few Sgt.'s & Lt.'s that would have handed out a 2 week suspension for behavior like that!

 

[wptski]

Update: Smoke alarm test still works and the battery measures 9.68V. This at least eight months now!

 

[Sub_Umbra]

Great thread.

Much better info than when I asked a couple years ago.

The signal to noise ratio has improved. It's great to hear from people who are already doing it.

 

[john2551]

Update: Smoke alarm test still works and the battery measures 9.68V. This at least eight months now!

Great news! I'm buying the Powerex 9.6v next time, they are better than my iPowerUS 9.6v.

 

[wptski]

Great news! I'm buying the Powerex 9.6v next time, they are better than my iPowerUS 9.6v.

The 9V IPower batteries that I had before were junk. I'm tempted to get one or two of their Li-Poly batteries just to play with but seeing how bad the Ni-MH were, I'm scared!

 

[bob_ninja]

Some time later I actually came accross a 8x AA holder which has the 9V connector, no external wires, no mess. Radio Shack, or now called The Source
I bought a couple of them and moved my old NiMH AA into it, plugged into detector. Voltage was over 10V, but the detector doesn't seem to mind. I even started a fire outside and put detector over it to ensure it works. Worked just fine.

Works for me as these are end of life NiMH AAs while 9V batteries Alkaline or NiMH are very expensive. Also they have a far greater capacity than just about any 9V, so I only need to charge them maybe 2x or 3x / year

For those who worry too much, my device has both audio and visual indications of low power: 1) periodic beep when low power, 2) periodic blinking light when power Ok
That way I can always hear/see if detector is working.

 

[Handlobraesing]

Some time later I actually came accross a 8x AA holder which has the 9V connector, no external wires, no mess. Radio Shack, or now called The Source
I bought a couple of them and moved my old NiMH AA into it, plugged into detector. Voltage was over 10V, but the detector doesn't seem to mind. I even started a fire outside and put detector over it to ensure it works. Worked just fine.

Works for me as these are end of life NiMH AAs while 9V batteries Alkaline or NiMH are very expensive. Also they have a far greater capacity than just about any 9V, so I only need to charge them maybe 2x or 3x / year

For those who worry too much, my device has both audio and visual indications of low power: 1) periodic beep when low power, 2) periodic blinking light when power Ok
That way I can always hear/see if detector is working.

Yeah, but self discharge would more or less deplete the entire charge in about six months.

 

[wptski]

Yeah, but self discharge would more or less deplete the entire charge in about six months.

This is beginning to sound like a broken record again! That's what everybody said, self discharge over and over again. It "hasn't" happened with these newer MAHA PowerEx 9.6V Ni-MH batteries. The battery has been installed over eight months! I think the resting voltage after charging is around 10.4V. Why is this battery so good? I don't know but it is!

 

[Handlobraesing]

This is beginning to sound like a broken record again! That's what everybody said, self discharge over and over again. It "hasn't" happened with these newer MAHA PowerEx 9.6V Ni-MH batteries. The battery has been installed over eight months! I think the resting voltage after charging is around 10.4V. Why is this battery so good? I don't know but it is!

It was in resposne to this guy's idea of using AAs

 

[wptski]

It was in resposne to this guy's idea of using AAs

Oh! You mean that you don't believe that all Ni-MH are the same?

 

[bob_ninja]

Handlobraesing,
I cannot find any info on "self discharge" rate for NiCd and NiMH, or even within the same (NiMH) chemistry for AAs from different brands. Another interesting question is if a steady low power draw (such as from smoke detector) affects self discharge rate either way.
Being in the dark, I may try NiCds next time to see how long they last. For now I will monitor older NiMH and see how they do.
Given the benign environment (inside house, steady temps) I should expect minimum 4 month run, which would require only 3 charges per year. That is much better than my NiMH 9V battery which lasted about single month, or 12 charges per year.

Clearly Bill's 9V Maha is superior to the one I tried (forget the brand, maybe Energizer) and it holds its charge very well. Good stuff It is certainly an excellent choice for detectors. I just didn't want to spend 10 bucks and wanted a useful application for older AAs, retirement duty of sorts.

The "self discharge" issue may be a concern. In fact, another problem could be that one of the AAs goes below 0.9V while detector works just fine due to its low power draw. I'll check 'em out in the autumn (they are working for about 1.5 months now).

 

[Handlobraesing]

Handlobraesing,
I cannot find any info on "self discharge" rate for NiCd and NiMH, or even within the same (NiMH) chemistry for AAs from different brands. Another interesting question is if a steady low power draw (such as from smoke detector) affects self discharge rate either way.
Being in the dark, I may try NiCds next time to see how long they last. For now I will monitor older NiMH and see how they do.
Given the benign environment (inside house, steady temps) I should expect minimum 4 month run, which would require only 3 charges per year. That is much better than my NiMH 9V battery which lasted about single month, or 12 charges per year.

Clearly Bill's 9V Maha is superior to the one I tried (forget the brand, maybe Energizer) and it holds its charge very well. Good stuff It is certainly an excellent choice for detectors. I just didn't want to spend 10 bucks and wanted a useful application for older AAs, retirement duty of sorts.

The "self discharge" issue may be a concern. In fact, another problem could be that one of the AAs goes below 0.9V while detector works just fine due to its low power draw. I'll check 'em out in the autumn (they are working for about 1.5 months now).

You lose about 40% in two months.
http://www.sanyo.com/batteries/pdfs/twicellT_E.pdf

 

[bob_ninja]

Thanks for the PDF. I'll check it out.
Even at 40%/2mos considering the low power draw from detector I still think that 4 months run is doable.

 

[Brighteyez]

Just happend upon this thread and I must confess that some of the arguements gave me a bit of a chuckle.

The way I see this thread is an argument comparing practicality .vs hobby/experimentation.

Concerns that I would have regarding the use of a rechargeable battery would be the rapid drop when a NiCD/NiMH battery reaches the end of it's charge. If the house is not occupied and the battery goes, the warning chirps from the smoke detector may end well before the occupants return home (business or weekend trip, or a longer vacation.) The other thought would be whether it is economically feasible to use a rechargeable .vs the cost of alkaline 9V batteries over say a period of 3-5 years (reasonable estimate for life of a rechargeable battery used in a critical device.) My guess is that the costs of the rechargeable will outweigh the cost of a primary alkaline battery. And that doesn't even include the added inconvenience of recharging the batteries and keeping track of when they need to be recharged.

Given the life of alkaline batteries in smoke detectors, I don't see a need for a lithium battery in this application.

With regards to the use of rechargeable batteries in public safety applications, it's got nothing to do with their reliability, it's pure economic and those uses are in devices where the cost of primary batteries well exceeds the cost of rechargeable over it's useful life. In many cases however, radios that are used for disaster emergencies may well use primary batteries rather than rechargeables because the radios may sit without use for long periods of time and the battery life is considerably longer using alkaline primary batteries. But to replace primary batteries at the end of each shift would be prohibitive compared to the cost of a rechargeable battery that might last 2-3 years.

With regards to flashlight, indeed may agencies do use rechargeable lights like the Streamlight SL20 series or Mag Chargers, for a couple of reasons. The cost of operation is considerably less in daily usage than using disposable primary batteries. Secondly, both of those lights have more lighting capability than any commonly available manufactured light that uses primary batteries, and over the last 20+ years, the producers have been able to provide parts to keep those lights going.

 

[wptski]

Just happend upon this thread and I must confess that some of the arguements gave me a bit of a chuckle.

The way I see this thread is an argument comparing practicality .vs hobby/experimentation.

Concerns that I would have regarding the use of a rechargeable battery would be the rapid drop when a NiCD/NiMH battery reaches the end of it's charge. If the house is not occupied and the battery goes, the warning chirps from the smoke detector may end well before the occupants return home (business or weekend trip, or a longer vacation.) The other thought would be whether it is economically feasible to use a rechargeable .vs the cost of alkaline 9V batteries over say a period of 3-5 years (reasonable estimate for life of a rechargeable battery used in a critical device.) My guess is that the costs of the rechargeable will outweigh the cost of a primary alkaline battery. And that doesn't even include the added inconvenience of recharging the batteries and keeping track of when they need to be recharged.

Given the life of alkaline batteries in smoke detectors, I don't see a need for a lithium battery in this application.

With regards to the use of rechargeable batteries in public safety applications, it's got nothing to do with their reliability, it's pure economic and those uses are in devices where the cost of primary batteries well exceeds the cost of rechargeable over it's useful life. In many cases however, radios that are used for disaster emergencies may well use primary batteries rather than rechargeables because the radios may sit without use for long periods of time and the battery life is considerably longer using alkaline primary batteries. But to replace primary batteries at the end of each shift would be prohibitive compared to the cost of a rechargeable battery that might last 2-3 years.

With regards to flashlight, indeed may agencies do use rechargeable lights like the Streamlight SL20 series or Mag Chargers, for a couple of reasons. The cost of operation is considerably less in daily usage than using disposable primary batteries. Secondly, both of those lights have more lighting capability than any commonly available manufactured light that uses primary batteries, and over the last 20+ years, the producers have been able to provide parts to keep those lights going.

Your just rehashing everything that's been posted already, most of which has nothing to do with the original poster's question which is, what voltage of rechargable to use.