Backyard Aquaponics
A place to discuss aquaponics

Does anyone know of a switch or relay that allows a battery powered 12v pump to be turned on it the power goes out?

I have a large tractor battery that is still in good condition that should run a small 12v pump for a while, but I don't know how to get it to turn on when the power goes out.

Nova

Nova, look in the general album area L.B. has a schemetic of that there. Hope it helps.

Ahh, that helps (link here), but is not exactly what I was after.

I was thinking of a relay type device that switches on a circuit when the mains fails, and then switches it off again when power returns. Must check the Jaycar website and see if there is anything there.

Or maybe I can open up a pc UPS and wire in a big battery instead of the small one they come with. I wonder...

Nova

Just rang jay car and dick smith a neither had anything. That is exactly what I want to do. Someone with some knowhow could probably put it together.

I remember something about this here a while ago, I think it may have been Steve who said something. IIRC all that was said is there are devices like this available.

Nova

Bah, B2b posted a drawing in the hardware album section lets see if i can link to it. Nope dont know how.

Perhaps not the exact thing your were looking for but if you just leave out the battery charger portion you should be good to go.

Here it is.

Really all we need is a 240V NO (normally open) relay that is capable of switching 12v at something less than 20A (50watts is roughly 5A). Too large a pump will flatten the battery too quickly. Wire the relay to the mains so when the power fails, the relay closes and starts the 12v pump. Possibly need something to protect the battery against going fully flat (lead acid batteries don't like that), some sort of valtage cutout switch. A charger as well to charge the battery when the power returns.

Nova

LOL and we have come full circle.

Yes, although we still need to find such a relay.

Nova

Sheez, it must be too late for my brain I was assuming you were looking for how to do it not a specific relay. My humble appoligies, I'll look on this side of the world and see what I can come up with. Should not be too difficult.

Hi Nova:
If you didn't have the battery already it would be easy enough (but spendy) to buy a computer uninterruptible power supply (UPS), which would have an inverter, battery and would switchover when the power goes out. I asked the guy at work if we have any but no. I might end up getting one of those when I have enough investment in fish to worry about it.

I was looking for how to do it but when you pointed me in the right direction I thought doh, of course that is how to do it. I'm not sure how easy it will be to find a ac/dc relay, although I would think there are things like this available for this very purpose.

[edit]
Dave, I have a UPS already (for my firewall), but I don't want to hack it up. I should find out how much grunt the battery has and work out how long it could power my 240v pump for.
[/edit]

Nova

I have made such a device, I will price all the bits that go to make it up, it will come out at about $60.00 If you are interested

Muzza

Not sure if it helps as it looks like Murray has it in the bag, I found a square D relay, part number 8501RS42V24. It's 2PDT and cost for just it is $23.30 US I assume. Thats no base just the relay.
Murray are you sure you don't want to move your shop to Iowa? We have lots and lots of corn fields, not much else to entice though sadly.