Backyard Aquaponics
A place to discuss aquaponics

Hey Guys have Designed a Battery Backup unit.

Will concist of a

- 300w Inverter
- 12v Car Battery (Charged From Mains)
- a Control Cirtcuit

The Control Circuit:

will have 3 relays and 2 timers

What will happen when mains drops, the inverter will be powered up instantly and one of the timers will activate, after 60 Sec a Relay will Switch the Inverter 240 Supply to my Pumps.

Once the power comes back on, The inverter will power down, also the relay will drop the 240v from the inverter. a 60sec timer will be activated and after this the MAINS 240 Supply will be sent back to my pumps.

the idea with the timers is to give them some grace time between switching sources.
the circuit is designed to never allow both mains and inverter to be on at the same time.


This allows me to use the same pumps as iv got now, saving the need for more plumbing or cost in pumps etc.

Cost of system:

Relays and timers $110
Inverter $70
Battery $30 (Second hand)
Charger: $15 Supercheap special


i build Switchboards for a living so im going to build a small one to house it all
will be putting an RCD Plug on the mains side so if anything gos wrong its off.

i have ordered the stuff and will keep pics coming as i do it.

Here is a Very Messy Schematic if anyone can read it/understands electronics

The charger will fry the battery and kill it, meaning there will be no battery backup.

Your design is sound and it will work fine, but you need either a smart charger, or a charge controler, which are around $30 on ebay.

Nice cheap setup, could be something you can sell to members if its reliable.

Hmmm so these battery chargers dont switch themselfs off??

bloody Automatic Charger my Ar$e

well i'll have to look into some other charger.....

not into sales, design is free to use for all members, but if someone does use it to sell them i want my 10% hahahahahah

Is my system going to damage my battery then

I have a 4 amp battery charger (not a smart charger) which trickle charges a large deep cycle battery (like you would put in a 4X4 for camping) with a 600w inverter constantly drawing off it to run a 240V otto air pump which is 4 watt from memory.

On the setting I have the air pump on it seems to draw the currant from the battery at the same rate it is replaced by the charger on trickle. The charger always indicates the battery is 75% full while the air pump is running but if I turn it off the charger displays 100% battery charge with in 2 seconds.

I usually run the battery down to 25% charge one a month by switching the charger off and letting the air pump run off the battery for 48 hours.

I believe this is similar to the back up OBO was running on his home system.

Am I doing any thing wrong? Do I need a charge controller?

Depends what voltage the charge is maintaining it at with the additional load as well.
For standby use 13.5-13.8v is normally safe (depending on battery) and can be left on permanently. Pretty much all alarm systems and a lot of other equipment are have a current limited DC supply set to that voltage.

For cyclic use its better to have a smart charger that charges to 14.4-15v then once the battery is full drops back to the standby voltage.

Most of the cheaper car chargers however charge at 14.4-15v permanently and your supposed to remember to disconnect it.
Permanently charging it at 14v+ will cause degassing and shorten the lifespan considerably.

why run the pump off the inverter at all times?? the would only cause wear to the inverter??

sounds like you need this kind of switching device

Thinking this could work ok, we used to use these on the Auto Gate operator setups would love to put a 20AH SLA in there but its a bit expensive

http://www.altronics.com.au/index.asp?a ... m&id=M8528

Yeah the cheap chargers killed two of my batteries before i realised. They seem to be charged and fine, but put some load on them for more than a few minutes and they fail.

Got the timers and relays on fri!

Now need to build a small switch board to house it all, get the battery and Inverter over the next few weeks.



These timers are $125 Each hahahahaha i near died when he told me Oh well.....




I guess using Commercial Grade Switch Gear should leave less room for failure, then a mate who is a sparky also told me i should have got an old UPS System, taken the 7AH Batts out of it and stuck it onto a Car Battery, remove the buzzer and presto Battery backup system.

however not as Efficient as mine, i think with the Mains Being used for the whole time and it only dropping over when a powerout is on is the best setup.

Will post more as it happens and will show Amps used etc and how long it will run for.

if anyone out there has 12v Pumps and Air Pumps as backup can you please post how many amps it draws off your battery for a comparison to Inverting upto 240v... if it is more efficent to run a smaller 240v Pump maybe this could be better for solar??

look for "projecta" or "ctek" chargers. I have them for all my bikes and i leave them on 24/7/365... one bike has not been ridden for over 8 months. these units charge and maintain, thats it... they are brilliant bits of gear. look around as pricing will vary ... i know REPCO sell them as do AUTO 1 .. both differ in price. you should only need a small one and they come with alligator clips OR the flylead to bolt up to your battery.

check them out

+1....I have one that was for my old harley.....hadn't ridden it in 3 yrs.....but it would start everytime

+1 for Projecta chargers. Expensive, but three year guarantee and are smart.

i have a 900mAh, which i have used on my cars when i have left them for any length of time

Yep projecta real good gear also look on ebay i picked up a 2400 watt inverter for $199 it will start a 9 in angle grinder

Will definatly get one of these as a trickle charger, and want to setup another timer (an cheaper one than the omerons) to give the batterys a good 6-10A of charge for a while after a power out, incase its only back on for an hour or two then off again. call me paranoid