Backyard Aquaponics
A place to discuss aquaponics

I'm thinking of getting a second deep cycle battery (75AH) to go with my existing 75AH deep cycle battery that I use for my power backup.

There are 3 reasons for this. One is that the most recent blackout here went for 43 hours. Extremely rare circumstance of course, but all the same something to think about. The second reason is that as I expand my system, I'll need to run more pumps or aerators off the backup and therefore will need more battery capacity if I want to run for the same amount of time as I can now. The third is that the deep cycle doubles as a power source for an electric motor I have for the canoe. I'm planning on getting out more with the canoe, so ideally will still have a battery on the system when I'm using one for the canoe.

So now to the point of the post. My battery is always connected to a smart charger that keeps the battery topped up, switching off when the charge is full. Decent chargers are not cheap ($200 for the one I am using) so naturally I will not want to buy another simply to make sure both bateries are always charged. I'm therefore thinking that the best way to set up my battery backup if I add another battery would be to run the backup as a 24v system, with the 2 batteries connected and to therefore switch the charger to 24V. The disadvantage of this would be that I'd have to run 24V devices, which are less common and probably more expensive than the 12V ones I guess, but bilge pumps are certainly readilly available and this is what I currently run for the backup (albeit 12V ones). Of course if I take on battery off line for a fishing trip - then I'll need to use the 12V pumps again (a pain - so maybe there is a better way).

Any suggestions/ideas - as many of you know electronics and power are not my strongest areas, so I'm sure you'll all probably have some ideas which will totally change the way I'll rig things up.

If you stick with 2 x 12 Volt systems, you get greater redundancy.
Are you using SLA(gell) or wet batteries.?
If you have wet batteries you could get away with a cheaper dual stage charger such as these.
http://www.jaycar.com.au/productView.as ... &SUBCATID=

Thanks Scott.

The deep cycle batteries are wet ones.

I've always liked the idea of a battery charger that switches off altogether when fully charged. I'm sure I read somewhere that trickle charging is not good for the battery.

If I was to run 2 systems as you suggest, to achieve any sort of redundancy then I'd need to have seperate pumps connected to each (meaning twice the pumps). It also means that I'd be running both at once, which doesn't really produce the desired result of being able to run for twice the time.

is it possible to have a 2way charge system?

dunno...I know there are those switches that you can use in cars (or more often 4WDs) to keep a primary and alternate battery charged, but they are kinda expensive.

that is what I was thinking...
maybe a wrecker?

Just connect them in parallel pos to pos neg to neg like they do in trucks

is that called parallel or series?

There is nothing wrong with trickle charging lead acid batteries so long as your charger will drop the voltage when the battery is fully charged.

Not sure if there is a simple (and cheap) solution but there are lots of options...

1) Connect batteries in series and run a 24 volt system.

2) Connect batteries in parallel with a diode in the charge circuit.(will work, but one battery will have a lower internal resistance and will end up doing most of the work). You will not get twice the capacity.

3) Give away your existing battery and buy 2 x 6V batteries of larger capacity.

4) Leave your system as is, purchase a second battery and dual stage trickle charger. You will have to manually change over to the second battery if the first one goes flat.

5) Go for some fancy 4WD change over switch. Remember that most of these systems are designed to run auxiliaries but keep enough charge in one battery to start the engine.

6) Get someone to design a magic box to do the job.

If you want a cheap and easy solution, I would be temped to go for option 4)
Maybe consider a low voltage cutout/alarm on your primary battery.

F&F - that is what I was originally suggesting, though I assumed this would result in 24 volt output. Am I incorrect?

That why I asked 'is that parallel or series knowing the 2 give
different results.
Where is steve???

Not a backup power supply but...and really more for large systems...

Koenders Windmill

These guys Aquasonic Australia list them, but an email sent about 2 weeks ago still hasn't been replied to?

US price is in the > $1000 range - but if they give enough air for aeration and pumping it would be a one off cost that, provided you're in a windy place, would provide another alternative.

Perhaps a smaller version based on something like these: Garden Windmills could be useful for a smaller system?

I charge my bike and mower at the same time by connecting the batteries together.

pos to pos and neg to neg gives 12 volt

parallel