DC Backup for aquarium pump

Joined Aug 18, 2017
13
There is also a controller to provide variable flow in the circuit, which is one reason to use a relay instead of just diodes. With a relay, I can connect the battery to the pump directly. If I do that with just a diode, the battery will supply 12V if the controller drops voltage below 12V. I could connect the battery to the controller, but it is 1 more thing that can go wrong if power is out and 1 more thing drawing power off my battery.

Joined Aug 18, 2017
13
My above post is wrong and it is too late to edit. I need to provide power to the controller, it isn't 3-wires positive, negative and ground, but positive, negative and a voltage to control the speed.

So how do I connect this with just diodes? I have 2 wires (positive and negative) from the wall wart to the controller. Without diodes, I'd just hook positive to positive and negative to negative. Do I hook this up the same way with 2 diodes?

Joined Jan 15, 2015
5,720
As long as the pump will start on 12 Volts then in the interest of cost saving a single 12 Volt battery will work fine. A 12 Volt SLA battery from Amazon or similar supplier will run about $20 USD or less. You did mention: The pump draws 40 watts on 24 volts DC. So roughly winging it 40 Watts / 24 VDC = 1.7 Amps and running on 12 Volts and slower the pump will draw less current. Battery "hold up" time will depend on the battery size and pump current draw. As to going with 12 Volts (single battery) or 24 Volts (two batteries) you need to ask yourself how important is what's in the aquarium I guess. Additionally, how often you have mains power failures and for how long? Keeping it real simple, as mentioned, just a single diode would work to maintain the battery and run the pump. Using a relay has its advantages and adds a slight complexity, but not much. Here is an example of a simple battery backup system from within these forums. Keep in mind you would use diodes with a higher current handling rating. Note that a relay is not used, just a few basic parts and that's it. Diodes are relatively inexpensive. Keep in mind the linked circuit is an example. <EDIT> I just saw your last post and did now address what you added. Sorry about that. </EDIT> Ron Thread Starter Brad Bellomo Joined Aug 18, 2017 13 As long as the pump will start on 12 Volts then in the interest of cost saving a single 12 Volt battery will work fine. A 12 Volt SLA battery from Amazon or similar supplier will run about$20 USD or less. You did mention:

So roughly winging it 40 Watts / 24 VDC = 1.7 Amps and running on 12 Volts and slower the pump will draw less current. Battery "hold up" time will depend on the battery size and pump current draw. As to going with 12 Volts (single battery) or 24 Volts (two batteries) you need to ask yourself how important is what's in the aquarium I guess. Additionally, how often you have mains power failures and for how long?
Keeping it real simple, as mentioned, just a single diode would work to maintain the battery and run the pump. Using a relay has its advantages and adds a slight complexity, but not much.

Here is an example of a simple battery backup system from within these forums. Keep in mind you would use diodes with a higher current handling rating. Note that a relay is not used, just a few basic parts and that's it. Diodes are relatively inexpensive. Keep in mind the linked circuit is an example.

Ron
Not sure what the importance of what's in the aquarium figures into the decision, but if it wasn't important, I'd go without a backup. Power outages are rare and usually short. 14 years ago, we had an outage that left many in the Eastern USA without power for days, thankfully I wasn't affected. If civilization ends, that will be the end of my reef tank regardless of what I build. I would expect the same losses running a single PP15 off 12V for a week as going 6 hours with nothing at all, so going to 24V isn't appealing, however I am now starting to wonder if the controller will run off 12V. I know people are running similar pumps half speed off 12V, but I don't know which side of the controller they are connecting DC power to. I might have to try both and see what works.

What are the advantages to using a relay?

Joined Jul 18, 2013
22,018
What are the advantages to using a relay?
1/ No voltage drop.
Max.

Joined Jan 15, 2015
5,720
Not sure what the importance of what's in the aquarium figures into the decision, but if it wasn't important, I'd go without a backup.
I see a backup power system as a form of insurance. If I have several grand invested in something I consider that when I make a plan for backup of anything including power. I have no clue what the value of the occupants of the tank is but that is where I saw the importance.

My suggestion, now understanding this is a reef tank would be using a relay and two 12 Volt batteries in series. Your tank so it's ultimately up to you what you choose.

Ron

Joined Aug 18, 2017
13
I see a backup power system as a form of insurance. If I have several grand invested in something I consider that when I make a plan for backup of anything including power. I have no clue what the value of the occupants of the tank is but that is where I saw the importance.

My suggestion, now understanding this is a reef tank would be using a relay and two 12 Volt batteries in series. Your tank so it's ultimately up to you what you choose.

Ron
I am comparing backup plans the way I would insurance plans. I can either decide how much insurance I need and find the plan that gives it to me the cheapest, or I can decide what I am willing to spend and find the plan that gives me the most insurance. Either way, it is cost-benefit.

Joined Aug 18, 2017
13
1/ No voltage drop.
Max.
Voltage drop should only affect things when running on battery power - if the mains are on, the diodes shouldn't use any power, right? Even running on battery, the diodes shouldn't actually use much power in watts, right? They just reduce pump power but that makes the pump last longer.

I thought the recommendation was to use a diode as protection even if I used a relay. Is this why everyone is suggesting to go to 2 batteries for 24VDC, so I can leave out the diode?

tcmtech

Joined Nov 4, 2013
2,867
I thought the recommendation was to use a diode as protection even if I used a relay. Is this why everyone is suggesting to go to 2 batteries for 24VDC, so I can leave out the diode?

Sort of yes.

Most of it will come down to what your actual power supplies output voltage is. If it's around 24 - 25 volts it would never fully recharge your battery systems if it got run down but the battery would also never sit in a discharged level too low to do harm either.

Up around 25 - 27 volts it would also do no harm and it would give you a fair ~60 - 80% recharge if given enough time. beyond that you would possibly have to consider using a charge control circuit to keep from overcharging the battery in long term standby use.

Joined Jan 15, 2015
5,720
I am comparing backup plans the way I would insurance plans. I can either decide how much insurance I need and find the plan that gives it to me the cheapest, or I can decide what I am willing to spend and find the plan that gives me the most insurance. Either way, it is cost-benefit.
That pretty much covers it. You get the best bang or coverage for the buck. Members here can only make suggestions or suggest what they would do. Ultimately you make the choice based on what works for you.

Ron

Joined Aug 18, 2017
13
I measured 24.6 volts from the adapter. Here is the battery I've been using https://www.amazon.com/Powersonic-PS-12350NB-Battery-Nut-Bolt-Connector/dp/B0010AI3LM with a commercial backup circuit that broke.

What would happen if I bought another battery, and put both batteries in series, then connected the battery terminals to the wall adapter and the pump? Would this work? How much battery capacity would I lose? Any other negatives to such a simple backup plan?