Help with aquarium power backup system

[Rickvn]

Hi all. This is my first time here. Please can you help me with the pros and cons of this idea.

I have to set up a backup for my marine aquarium. I live in a rural area and powercuts are pretty regular occurrences. Two weeks ago we were out for 19 hours and I ended up buying a generator to keep my tank alive. We're going on holiday for two weeks and I need to set something up to cover me for that period. I think something that will run for 6 - 8 hours will cover most cuts.

My idea is as follows:
I want to use a deep cycle 60Ah sealed lead acid battery as the power source. To this I want to connect a 300watt inverter. To the inverter I'll connect a 50 watt heater and two pumps (for water circulation) each of about 15 watts. So way less than the 300watts maximum continuous supply from the inverter.

To keep the battery topped up I want to connect it to a trickle charger which will run from mains (grid) power so the battery will be charging when the power is on.

Now here is a bit I'm not sure about.....I want the backup heater and pumps only to come on if the mains power goes out. Essentially a UPS. To do that I thought of building a very simple relay switch. I'd build the circuit on stripboard and put it all in a box with neat plug connectors to hook up the various inputs/outputs. Using a DPDT relay I connect the positive of the battery to the Common. Connect the Normally Closed of the relay to the positive of the inverter. Then connect an off-the shelf mains type plugin transformer that converts to 12v dc to the coil of the relay. So while there is mains power the relay will hold the circuit open and the battery will be charging. During a power outage the relay coil will not be energized and the battery circuit will close and the backup system will kick in. When power comes back the circuit opens and the backup system stops, main aquarium systems resume and the charging of the battery takes over.

Sounds OK to me....but is it?

Thanks for any help & advice

 

[MrAl]

Hello there,

I would not trust my marine aquarium to any automatic life support system unless it had built in redundancy. The fish are too sensitive to changes that could occur so if anything goes wrong, the fish go to that big fish tank in the sky. That doesnt come cheap either as im sure you know.
My advice would be to ask someone to take care of the tank when you are gone or monitor it somehow. If you cant do that then you really do have to have at least two systems where if one fails the other kicks in. Three systems even better.
It would be nice if you could build a 12v heater so you can do the heating more directly rather then need conversion of the battery to AC to drive the commercial heater.

 

[tcmtech]

I would buy a stock UPS unit and add an external battery to it with its own charging system.
That way it does its thing when the power is out but also has the added run time of the much larger second battery as well.

 

[Reloadron]

I have a question about this part:

My idea is as follows:
I want to use a deep cycle 60Ah sealed lead acid battery as the power source. To this I want to connect a 300watt inverter. To the inverter I'll connect a 50 watt heater and two pumps (for water circulation) each of about 15 watts. So way less than the 300watts maximum continuous supply from the inverter.

The heater won't care but if these are AC pumps running on mains voltage they may not care for the modified square wave output of most lower end inverters found in lower end type UPS units. You can buy inverters that deliver a nice clean sine wave but they carry a cost above the everyday flavors. Just something to consider no matter which way you go.

Ron

 

[KeepItSimpleStupid]

Motors, pumps and inverters are always a touchy situation. Aquarium pumps will probably be less touchy. A motor could require 1 to 5x capacity to start. That's why generators and UPS's are rated in VA.

300 Watts for 17 hours is a lot of time. The inverters will probably kick out at 8V or so, so you have to look at the discharge curves carefully.

DIY is kinda tough.

I'd go with the human approach for now. Notification systems when the power goes out could be useful too. A simple technique is to grab an auto-answer modem and place on the phone. Set up a drop out relay. If it answers you have power, if it doesn't then you don't and have to go set it. This can work if your caretaker is far away.

A more permanent solution may be on the order of a solar system or backup generator with an automatic transfer switch where the generator is powered from natural gas. Fuel cell systems do exist too.

For reference, UPS combined with generators have to be special to handle the erratic frequency. Been there. Done that.

 

[Rickvn]

Thanks all for the replies. I know I am just trying to build a DIY UPS but I'm no electronics expert and trying to take apart a commercial UPS to connect a second battery is more daunting to me than connecting a series of off-the-shelf components together to get something working.

I appreciate all the options...but what I'd still like to know....leaving out how long the backup will run for...etc...is....'Will my idea work or will the whole thing just blow up?' (just joking...I'm sure it won't.)

To answer some of the questions and suggestions....
I don't have the option of asking someone to monitor the system for me...it has to be totally self sustained.
I am on a very limited budget so I'm trying to make something work without a huge pricetag.
It will need to supply less than 100 watts total....for about 6 or 7 hours (not 300 watts for 17 hours).
A generator would be great....but once again I don't have anyone to fill the tank if it runs dry and options to autostart them cost more than I have to spend.

So....if someone can tell me if my original idea will work...leaving out other options...I'd really like to know.

Thanks
Rick

 

[Rickvn]

I forgot to mention....I found a pure sine wave inverter for just over £100. I have contacted them and it is a pure sine inverter.

Specifications:
Input voltage range: DC 10-15V
Standby input current: <0.9A
Output voltage: AC 220V~240V
Output frequency: 50Hz
Output power: 300W
Peak output power: 500W
Output waveform: Pure sine wave
Efficiency: >85%
Dimensions: 245(l) x 117(w) x 62(h) mm
Weight: 1.2kg
Protection Features:
Low battery pre-alarm: 10.5V ±0.5V
Low battery shutdown: 10V ±0.5V
Thermal protection: 65°C ±5°
Overload protection: Yes
Short circuit output protection: Yes
External battery protection: Yes
Battery polarity protection: Yes (provided by 2 x 25A fuses)

 

[tcmtech]

Thanks all for the replies. I know I am just trying to build a DIY UPS but I'm no electronics expert and trying to take apart a commercial UPS to connect a second battery is more daunting to me than connecting a series of off-the-shelf components together to get something working.

Drilling a hole in the case and running two wires to an external battery is not a lot of complicated technical work. + to + and - to - and use wire of equal or larger size than what the internal battery uses.

 

[crutschow]

If you want to DIY and not use a commercial UPS, then you might consider just running the aquarium continuously off the battery and inverter, and just get a battery charger big enough to charge the battery and supply the aquarium power at the same time. That way you don't have to do any switching and there's not even a minor interruption in power.

That's the way many commercial UPS units work.

Otherwise the switching relay setup you proposed is not complete. You would want a relay to control the power to the inverter input and a second relay to switch the AC from the mains to the inverter output. You don't want the inverter output connected to the mains. You actually could do both with a single 4PDT relay, but two relays is safer.

You can buy relays with AC coils so you wouldn't need the mains to DC converter.

 

[KeepItSimpleStupid]

Here is a commercial UPS with scaleable run-time. Smart-UPS On-Line - Product Information

The 6 hours of run time is rough.