Automatic battery backup

[DrRob]

Hi everyone, I'm trying to work out how to do something that, on the surface, looks very easy, but I'm looking for advice on how to make it as neat, cheap and safe as possible.

I have a fishtank, which relies on constant power for the filter to stay alive amongst other things. In the near future we'll be rewiring, which is likely to involve several prolonged periods of power outage, on top of that, being as rural as we are, we're quite prone to power cuts, getting short outages about once a week during the day while we're out at work and often at night.

For the timings involved a whole generator set with automatic switch seems overkill. I'd considered a computer UPS but don't really need the quality of waveform (and therefore cost) to drive a pump.

My next thought was a battery with inverter for the short periods involved. I know I can run automatic switching for this with relays but can't fine anything proprietary and would prefer the safety of something properly made.

The final option, which appeals to me most, is a separate 12v inline pump (which I already have one of), with a battery, the advantage to this being that it can run if the primary pump fails as well as as a power fail backup.

My last question is, is there an easy way to add in an automatic system that both detects power outage and will also kick in if the primary pump stops drawing power (i.e. fails)?

Hopefully I haven't asked anything too badly explained.

Thanks in advance for any advice.

 

[Taylortwocities]

You are much better looking on Google for specific advice.

I found this interesting thread http://www.everything-aquatic.com/2010/03/uninterruptible-power-source-ups-test.html

by Googling "uninterruptible power supply fish"

 

[sparkticus]

My last question is, is there an easy way to add in an automatic system that both detects power outage and will also kick in if the primary pump stops drawing power (i.e. fails)?

Hopefully I haven't asked anything too badly explained.

The DC pump is a good idea. You can use the NC contacts of a "current sensing relay" to detect the drop out of AC power. So the pump would energise as soon as the AC failed. You may also want to add a charger to the NO contacts so that battery is automatically charged when the AC is on.

http://www.serelays.com/time_delay_sensor_relays.php


You could put the relay into a low cost enclosure such as a plastic shower consumer unit, wire it up along with a battery charger. When AC power is on the DC pump will be off, the AC pump would be on, the bat charger would be on. When AC power is lost the DC pump would be on, the AC pump would be off, the bat charger would be off.

 

[DrRob]

You are much better looking on Google for specific advice.

I found this interesting thread http://www.everything-aquatic.com/2010/03/uninterruptible-power-source-ups-test.html

by Googling "uninterruptible power supply fish"

Thanks for that. I'd actually seen that one, but he starts with 2 UPS devices which costs a lot more than some of the alternatives I was hoping for.

 

[DrRob]

The DC pump is a good idea. You can use the NC contacts of a "current sensing relay" to detect the drop out of AC power. So the pump would energise as soon as the AC failed. You may also want to add a charger to the NO contacts so that battery is automatically charged when the AC is on.

http://www.serelays.com/time_delay_sensor_relays.php


You could put the relay into a low cost enclosure such as a plastic shower consumer unit, wire it up along with a battery charger. When AC power is on the DC pump will be off, the AC pump would be on, the bat charger would be on. When AC power is lost the DC pump would be on, the AC pump would be off, the bat charger would be off.

Thanks Sparktitus, that's pretty much what I was looking for. Without needing an inverter I'll get a lot more from my battery as well.

 

[JohnW2]

http://www.serelays.com/time_delay_sensor_relays.php

There are some very interesting and potentially useful relays mentioned on that page, some of them I could have made good use of of many occasions in the past, had I been aware of them. However, a quick look seems to suggest that availability over here is fairly limited, and they are far from cheap (in the £30-£70 range from one source I found). Do you use them and, if so, where do you obtain them from?

I'm particularly intrigued by the fact that many of them have 'universal' input volltage (12V-240V, AC or DC).

Kind Regards,John.

 

[big-all]

12v pump/lights heater supplied from a car or traction battery with a 12v charger no mains just the 12v but charged from the mains

 

[viewer]

I made up a mains failure switch for next door's central heating. Used 2 relays, 12V battery and inverter. Also put solar panel on chimney. Now been working for 3 years without a hitch and has switched on reliably whever power went down. Total cost was about £40 plus the battery. The C/H pump is quite happy with the output from the cheapest Screwfix inverter.

 

[timtheenchanter]

12v pump/lights heater supplied from a car or traction battery with a 12v charger no mains just the 12v but charged from the mains

I was going to suggest that, use a CTek or similar "intelligent" charger and you won't cook the battery,
I have no idea what is avaliable in the 12V line of pumps etc, I used to use an inverter, so it was charger - Battery - Inverter - Pump/heater.

mainly because I already had an appropriate battery and inverter.

 

[bernardgreen]

Measuring the current to the pump will not be a reliable way to detect pump failure. The pump might even take more current if it stalls.

A flow switch in line with the primary pump would detect any type of failure in the main pump and that could then start the DC pump running on 12 volts from a trickle charged battery.

Put the DC pump in a pipe bypassing the main pump and with non return valves in both pumps ( or pipes ) and you have a near fail safe system.

 

[DrRob]

Measuring the current to the pump will not be a reliable way to detect pump failure. The pump might even take more current if it stalls.

A flow switch in line with the primary pump would detect any type of failure in the main pump and that could then start the DC pump running on 12 volts from a trickle charged battery.

Put the DC pump in a pipe bypassing the main pump and with non return valves in both pumps ( or pipes ) and you have a near fail safe system.

Now that looks like a neat solution. Thanks for that thought.

 

[westie101]

12v pump/lights heater supplied from a car or traction battery with a 12v charger no mains just the 12v but charged from the mains

The simplest system following the KISS principle, this will work with no complications.
The biggest expense will be the battery

 

[slup]

I would have thought the simplest and cheapest solution would in fact be a computer UPS?

I know you said you didn't want one, but if you look into the cost and compare it with the hassle of a home-brew solution, I expect you'll find it's not worth it...

 

[westie101]

I would suggest that the UPS solution for "extended running" would be very expensive, especially given the additional losses that would occur in an inverter

 

[DrRob]

That's why I was going for 12V. The inverter will eat through the battery at a rate of knots.

Now I'm trying to source a sensibly priced flow switch or current sensing relay.