charging a 9 volt battery question

Thread Starter

corvairbob

Joined Mar 31, 2023
26
i have a device on my main power panel that when we lose power it will alarm to tell me the power returned. i have a generator also and when i have the generator running that alarm will also alert me to the power returning. however the 9 volt battery ran down this time and it did not alert me when the power returned. fortunately i was outside when they repaired it and i was able to do a good test and it failed because the battery went dead. i replaced the battery and it sounded. i want to put a 9 vdc power supply in the outlet next to this device, and have that keep the battery charged when the generator runs. will a 9vdc power supply work or will i have to get a 9 volt battery replacement unit like i have for my grandfather clock? what is the consensus
thanks
 

Ya’akov

Joined Jan 27, 2019
8,973
You can’t safely charge an ordinary 9V battery. There are NiMH 9V batteries for applications like this, but if the device doesn’t have a charging circuit, you aren’t going to be able to charge it in place.

In theory, it would be easy to work up some arrangement, but I think a board like this one is a much better option.

1699017250938.png
 

Thread Starter

corvairbob

Joined Mar 31, 2023
26
thanks i forgot to mention that the 9 volt battery i would use would be a ni-mh battery 9V Rechargeable Battery 9 Volt 6F22 Ni-MH and it sounds like yours telling me the power supply i have is not a real good option. this would only be used during the generator use but may still be a bad choice. maybe i can find a 9 volt battery backup device like i have for my grandfather clock. on the clock i have a battery backup that has a space for the aa cell battery and that is a ni-mh battery but that is a 24-7 situation it is real hard to set that clock so that is why it has that setup on it. i even hate tiem changes as it takes days to set it to spring time but fall time i can unplug it and take out the battery for an hour. anyway i will see if i can find a 9 volt battery backup device then thanks
 

schmitt trigger

Joined Jul 12, 2010
843
Yes, you could add an external power supply instead of the battery. But…from where are you going to power up this supply during the blackout period? By blackout period I mean the time from where the mains fail to the time the generator is running. Your supervisory circuit may reset.

I once had a similar problem and solved it with a low self-discharge NiMh battery which was trickle charged with a small solar cell.
Make sure you purchase rechargeable batteries suitable for smoke- detector duty, like these:
1699018632654.png1699018632654.png
 

Thread Starter

corvairbob

Joined Mar 31, 2023
26
finding a 9 volt battery backup is hard to find so i will just get a 9 volt battery recharger it is the same thing in a different term.
 

Thread Starter

corvairbob

Joined Mar 31, 2023
26
you missed where i said i have the backup generator running and can plug the power supply into the wall and keep the 9 volt battery charged. i did some looking and i found what you posted and that is exactly what i will get. then when i have the device turned on it will alert me to power returning and when the generator is on it still will alert me but also recharge. i run the generator for a few hours in the morning to reheat the house and then shut if off when it is light outside so we can see. then at night i run it again from dark till bedtime at bedtime i reset the mains to the outside power just inc ase the power returns and then if so the night lights tell us power came back. but what happened this time was the alert device was on for 3 days during the day and off at night but it did not recharge. i did not know it took that much power.

anyway thanks for that post and i found some on ebay for 16$ a bit steep but i may find them cheaper as i look thanks

1699019689656.png
 

Thread Starter

corvairbob

Joined Mar 31, 2023
26
this is what i may get it does the same thing for like 4$ i can wire the battery connector into the alert device and then plug the battery into this when i run the generator and unplug it when the power is on. thanks

1699019946751.png
 

Ya’akov

Joined Jan 27, 2019
8,973
thanks i forgot to mention that the 9 volt battery i would use would be a ni-mh battery 9V Rechargeable Battery 9 Volt 6F22 Ni-MH and it sounds like yours telling me the power supply i have is not a real good option. this would only be used during the generator use but may still be a bad choice. maybe i can find a 9 volt battery backup device like i have for my grandfather clock. on the clock i have a battery backup that has a space for the aa cell battery and that is a ni-mh battery but that is a 24-7 situation it is real hard to set that clock so that is why it has that setup on it. i even hate tiem changes as it takes days to set it to spring time but fall time i can unplug it and take out the battery for an hour. anyway i will see if i can find a 9 volt battery backup device then thanks
Did you miss the board I linked?
 

Thread Starter

corvairbob

Joined Mar 31, 2023
26
no i did not but that board requires another battery to run it. then an enclosure. that battery posted does the same thing and is ready to go thanks
 

dl324

Joined Mar 30, 2015
16,684
i found some on ebay for 16$ a bit steep but i may find them cheaper
This seems like it would be a viable option. You could put a USB charger on them indefinitely and can use them while they're being charged.

I have some of this type of battery and just tried putting a 33 ohm load on one that was dead before I put it on a charger.

Don't expect these batteries to have much shelf life. The ones I have self-discharged in a few months, so they're not much good for anything without frequent recharging.

You can get them for a lot less than $16, but the concept is flawed and they're not useful for most 9V applications.
 

Ya’akov

Joined Jan 27, 2019
8,973
no i did not but that board requires another battery to run it. then an enclosure. that battery posted does the same thing and is ready to go thanks
I think you might misunderstand what that board is.

It will let you take a 5V-12V power supply and a LiPo cell and provide an uninterruptible 9V. The arrangement is much better than cobbling together a NiMH 9V battery and a supply. It’s made to do what you want, it’s cheap, and the LiPo cell can be quit high capacity if you want a long offline run time (easily many times more the 9V runtime).

It would be my choice in your situation.

But, it’s your situation, so good luck with whatever you choose.
 

Thread Starter

corvairbob

Joined Mar 31, 2023
26
ok makes sense what do you think of this then it looks like what you posted and i can put one of my 5 vdc power supply units at the input end and then park a 3.7vdc battery of which i have lots of, and then the output then to the device. and not actually use a 9 volt battery then am i correct in that? this way the power supply keeps the 3.7 volt battery charged and then when i need the 9 volts i can then just turn on that alert device and let this power it for the duration of the outage. is that what your saying? as for the 3.7 volt battery i can install it during the outage and then plug in this device and have it keep that power alert powered for the duration. ebay link and select the single uninterruptible unit? let me know if i'm thinking of this correctly then


https://www.ebay.com/itm/193719446351?
1699027724945.png1699028351396.png
 

Ya’akov

Joined Jan 27, 2019
8,973
Sounds like you‘ve got is right and that board seems to be equivalent.

You should also get a 9V battery snap to make the connection to the device.
 

Thread Starter

corvairbob

Joined Mar 31, 2023
26
yes your correct just in case i wind up having to use a 9 volt battery. anyway i will gather the parts and set this up. thanks for the idea and the help. when i get this done i will post what i have and let you all know how it works. thanks much for all the ideas.
 
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