using a 12v 5ah battery as power backup for dvr.

Thread Starter

Parmjit_sparky_singh

Joined Feb 29, 2020
15
Hi first post here and I did try and search for this and found a few posts but not with the information I'm looking for, basicly I want to know if I were to connect a 12v 5a transformer to a 12v 5ah battery and the run a live and neutral from the battery to an inline 1 amp fuse and then to a barrel connector, will this work as a backup when there is a cutout for a dvr or possibly anything that requires 12v 1a, I'm aware that any power sources wired in parallel doubles voltage but when it is a battery and a wired power source will that cause the same issue? would I need to connect a 6v power supply and a 6v battery in series for this to work? And is any of this even feasible or will it go all explodey? Thanks
 

oz93666

Joined Sep 7, 2010
737
, I'm aware that any power sources wired in parallel doubles voltage
No ...voltage stays the same ....

You need to be more exact .... A 12v supply wont charge a 12V battery ... the voltage is the same , so no current will flow ....

What is the exact voltage of the supply , with no load , and the voltage with 1A flowing ...

What type of battery ?? lead acid?
 

Thread Starter

Parmjit_sparky_singh

Joined Feb 29, 2020
15
No ...voltage stays the same ....

You need to be more exact .... A 12v supply wont charge a 12V battery ... the voltage is the same , so no current will flow ....

What is the exact voltage of the supply , with no load , and the voltage with 1A flowing ...

What type of battery ?? lead acid?
So the supply voltage would be coming from a power brick plugged into the wall, the dvr is rated for 12v 1a for supply I was going to get a 12v 5ah power brick and use that for the supply.

The battery would be lead acid.

Oh and thanks I always mix up series and parallel
 

MisterBill2

Joined Jan 23, 2018
9,025
Adding a battery backup arrangement to a DVR is not so simple as your description. There is a lot more than just a transformer that goes between the mains connection and the 12 volt battery. Next, and this is a guess, is that the DVR does not have a barrel connector for it's 12 volt external power supply connection. If it does already include one then the project becomes a lot simpler. The good news is that adding a second supply correctly does not double the voltage.

If the DVR only has a mains power cord connection, then probably the power supply inside provides multiple voltages, and so a single battery backup will not be that simple.

So please let us know about the existing power hookup for that DVR. Then we can provide useful answers. Until then the best you can get are guesses.
 

Thread Starter

Parmjit_sparky_singh

Joined Feb 29, 2020
15
Adding a battery backup arrangement to a DVR is not so simple as your description. There is a lot more than just a transformer that goes between the mains connection and the 12 volt battery. Next, and this is a guess, is that the DVR does not have a barrel connector for it's 12 volt external power supply connection. If it does already include one then the project becomes a lot simpler. The good news is that adding a second supply correctly does not double the voltage.

If the DVR only has a mains power cord connection, then probably the power supply inside provides multiple voltages, and so a single battery backup will not be that simple.

So please let us know about the existing power hookup for that DVR. Then we can provide useful answers. Until then the best you can get are guesses.
So the cameras have their own power supply and the dvr has it's own, it uses a barrel connector for supply and doesn't run anything externally connected to the dvr
 

MisterBill2

Joined Jan 23, 2018
9,025
So the cameras have their own power supply and the dvr has it's own, it uses a barrel connector for supply and doesn't run anything externally connected to the dvr
First let me thank you for the prompt response and answer.
OK, given those conditions then the project can be done, and it will be less complex than I had been anticipating.
For the maximum battery life and the longest possible operation time when the power fails, you will need a float charging voltage to keep the battery fully charged without over charging it. This means that you will need to have an accurate voltmeter to do the setup of the charger. The very neatest arrangement can be if you can get a second Barrel Connector pair like the one on the DVR and it's power supply. Is that possible?
The really simple arrangement would be to have the battery and the power supply directly in parallel, with the power supply voltage adjusted to the recommended "float charge" voltage for the battery. Then, when the power failed, the DVR would keep running from the battery power. When the power returned the battery would slowly recharge. The only problem would be if the power failures were frequent and longer, so that the slow chatging would not have time to completely recharge the battery. That is why many battery backup systems use a higher voltage that will recharge very quickly but greatly shorten the battery life,often to less than a single year.
 
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Thread Starter

Parmjit_sparky_singh

Joined Feb 29, 2020
15
First let me thank you for the prompt response and answer.
OK, given those conditions then the project can be done, and it will be less complex than I had been anticipating.
For the maximum battery life and the longest possible operation time when the power fails, you will need a float charging voltage to keep the battery fully charged without over charging it. This means that you will need to have an accurate voltmeter to do the setup of the charger. The very neatest arrangement can be if you can get a second Barrel Connector pair like the one on the DVR and it's power supply. Is that possible?
The really simple arrangement would be to have the battery and the power supply directly in parallel, with the power supply voltage adjusted to the recommended "float charge" voltage for the battery. Then, when the power failed, the DVR would keep running from the battery power. When the power returned the battery would slowly recharge. The only problem would be if the power failures were frequent and longer, so that the slow chatging would not have time to completely recharge the battery. That is why many battery backup systems use a higher voltage that will recharge very quickly but greatly shorten the battery life,often to less than a single year.
Hi thanks for the answer, and yes I have access to terminal barrel connectors, also where i live in the UK we only have 1-2 blackouts per year that only last about an hour each
 

MisterBill2

Joined Jan 23, 2018
9,025
Hi thanks for the answer, and yes I have access to terminal barrel connectors, also where i live in the UK we only have 1-2 blackouts per year that only last about an hour each
OK, then a float battery arrangement can work out quite well. I will attempt to deliver a sketch of the circuit when I can access a different computer. Presently it is 4:40 AM here and I could not sleep, so I was answering questions.
 

Thread Starter

Parmjit_sparky_singh

Joined Feb 29, 2020
15
OK, then a float battery arrangement can work out quite well. I will attempt to deliver a sketch of the circuit when I can access a different computer. Presently it is 4:40 AM here and I could not sleep, so I was answering questions.
Thank you very much I appreciate the help and I completely understand not being able to sleep I posted this at 2:30in the morning for the same reason.
 

Dodgydave

Joined Jun 22, 2012
10,035
A 13.8V psu across the sla battery and feed that into your dvd player, this will keep the battery charging and feed the player too.

Any laptop charger will give out 19V, use a regulator to drop down to 13.8V.
 

MisterBill2

Joined Jan 23, 2018
9,025
I would suggest an adjustable power supply, and setting it to the manufacturer's recommended float voltage. I am thinking that 13.8 volts is too high.
 

Thread Starter

Parmjit_sparky_singh

Joined Feb 29, 2020
15
So essentially it would be from the charger to the battery and then from the battery to the 1amp fuse then into a barrel connector? And possibly a regulator before the barrel connector?
 

Tonyr1084

Joined Sep 24, 2015
6,077
On a Lead Acid battery, the recommended float charge is 2.3 volts per cell. A 12 volt battery should be maintained at 13.8 volts float. That's the low end of the float charge. But it's important to understand the term "Float Charge". You don't "Charge" a battery at 13.8 volts, though it will work. You Charge it at up to 14.4 volts to about 70% of its capacity. After that you soak it at 13.8 volts to bring it up to a full charge.

A 12 volt battery at rest (not being charged or discharged) should be 12.6 volts. That's the sign of a good strong battery. 12.2 volts indicates age and suggests a possible replacement soon. I've seen batteries as low as 12.0 volts still be able to start a car. But we're not talking about a car battery, we're talking about an SLA battery (Sealed Lead Acid). The same voltages basically apply, but the battery is considerably smaller. Still, keeping it at 13.8 volts at all times won't harm the battery.

My concern would be for the DVR. It's designed for 12 volts. I have a DVR with security cameras about the property. I DON'T KNOW that a DVR will handle 13.8 volts without issue.

Another concern is the cameras. How will they fare with a higher voltage? Also, if the cameras are not on a backup power source then during a power failure the DVR (with battery backup) will continue recording, but if the cameras are not also on backup then they will shut down. At that point - what are you recording? Blank screens?

A better solution (my opinion) would be an Uninterruptable Power Supply (UPS). Plug all the cameras - or just the critical camera(s) into the UPS along with the DVR. May be a little more expensive, but it should protect the DVR and the cameras. Plus, the UPS will (should) also provide surge protection. But that's just my opinion.
 

Thread Starter

Parmjit_sparky_singh

Joined Feb 29, 2020
15
On a Lead Acid battery, the recommended float charge is 2.3 volts per cell. A 12 volt battery should be maintained at 13.8 volts float. That's the low end of the float charge. But it's important to understand the term "Float Charge". You don't "Charge" a battery at 13.8 volts, though it will work. You Charge it at up to 14.4 volts to about 70% of its capacity. After that you soak it at 13.8 volts to bring it up to a full charge.

A 12 volt battery at rest (not being charged or discharged) should be 12.6 volts. That's the sign of a good strong battery. 12.2 volts indicates age and suggests a possible replacement soon. I've seen batteries as low as 12.0 volts still be able to start a car. But we're not talking about a car battery, we're talking about an SLA battery (Sealed Lead Acid). The same voltages basically apply, but the battery is considerably smaller. Still, keeping it at 13.8 volts at all times won't harm the battery.

My concern would be for the DVR. It's designed for 12 volts. I have a DVR with security cameras about the property. I DON'T KNOW that a DVR will handle 13.8 volts without issue.

Another concern is the cameras. How will they fare with a higher voltage? Also, if the cameras are not on a backup power source then during a power failure the DVR (with battery backup) will continue recording, but if the cameras are not also on backup then they will shut down. At that point - what are you recording? Blank screens?

A better solution (my opinion) would be an Uninterruptable Power Supply (UPS). Plug all the cameras - or just the critical camera(s) into the UPS along with the DVR. May be a little more expensive, but it should protect the DVR and the cameras. Plus, the UPS will (should) also provide surge protection. But that's just my opinion.
I know I could buy a ups, and for my clients that's what I would always recomend (im an electrician that works on high voltage systems not low voltage the most I do is networking, alarm systems and cctv) but this is for me to mess around with for home project and to help expand my knowledge of the electronic field, i got the idea for this from the telecom veritas alarm panels as they have an SLA as a backup
 

ElectricSpidey

Joined Dec 2, 2017
1,762
The crux of the issue here really is can the DVR handle the 13.8 float charge and then going below 12 volts when the power is off.

Most "12" volt systems that use a 12 volt battery to provide backup can actually operate below and above 12 volts, for example from 9 to 15.

Backing up a system that can only tolerate 12 volts with a 12 volt battery becomes problematic at worse, complicated at best.
 

Thread Starter

Parmjit_sparky_singh

Joined Feb 29, 2020
15
The crux of the issue here really is can the DVR handle the 13.8 float charge and then going below 12 volts when the power is off.

Most "12" volt systems that use a 12 volt battery to provide backup can actually operate below and above 12 volts, for example from 9 to 15.

Backing up a system that can only tolerate 12 volts with a 12 volt battery becomes problematic at best, complicated at best.
Right I see what your saying, it's about if the dvr can take the fluctuation, is their a way of using a voltage regulator to bring it back to 12v like dodgydave suggested? I might just rig this up to test it out and see if I can get a reliable 12v supply if not then I'll just buy a UPS as I said this was more of a home project so I can get hands on with electronics
 

djsfantasi

Joined Apr 11, 2010
7,763
Where does the DVR get its video feed? Does it have a built-in digital receiver and tuner? Or is it connected to cable?

My question is what’s providing backup power to those devices?
 

Thread Starter

Parmjit_sparky_singh

Joined Feb 29, 2020
15
Where does the DVR get its video feed? Does it have a built-in digital receiver and tuner? Or is it connected to cable?

My question is what’s providing backup power to those devices?
The dvr is an oynx falcon dvr it receives the video signal only through bnc connectors the cameras are powered individual using an 8way psu which includes a battery backup
 

ElectricSpidey

Joined Dec 2, 2017
1,762
If you use a regulator to bring the 13.8 down to 12, it will only function for a short time during discharge, until the voltage drops below the regulators dropout voltage.

A buck/boost module may work between the battery/supply and the DVR but there are a few things to consider.
 
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MisterBill2

Joined Jan 23, 2018
9,025
My comment about the float voltage is based on what the manufacturer has printed on some of the cells that I have seen. Typically I try to pay attention to what a manufacturer says about their product. And now with the last remarks from the TS it is clear that we are not talking about some entertainment toy DVR. So probably none of the concepts relative to a toy are applicable.
 
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