Calculation of amp-hours for hydroponic system

Discussion in 'General Electronics Chat' started by SPQR, Jan 1, 2013.

Nov 4, 2011
379
48
Me again.
I'd like to confirm some calculations for my new project.
I'd like to be able to control a series of six water pumps for a hydroponic system with a microcontroller, and have a backup battery system in case main power goes out.
Each pump draws a MAXIMUM of 0.5 amps, but I'll assume 1 amp each.
I assume that the relays/triacs and the microcontroller will draw a total of 1 amp.
Diagram below:

Up to the point of the relays/triacs, I assume a total of 7 amps or 840 watts.
Assume the inverter/converter is 80% efficient, therefore up to that point I need 1,008 watts.

Assuming deep cycle 12V batteries, I would need to deliver 84 amps of current via the batteries. So to last for 10 hours I would need 840 amp hours or about six 125 amp hour batteries.

Is this a correct way to think about the project?

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2. takao21203 Distinguished Member

Apr 28, 2012
3,578
463
might be cheaper to buy a small diesel generator, only drawback is you need to start these manually.

Anyway, plants won't be dead immediately from lack of water.

3. Jaguarjoe Active Member

Apr 7, 2010
770
90
Many small engines can be retrofitted with a geared flywheel and starter motor. Those parts were \$79 from an engine distributor for my 5kw generator. I kicked in the solenoid, the battery and the rest of the 2 bit parts.

4. ErnieM AAC Fanatic!

Apr 24, 2011
7,442
1,628
Are you growing weed? Just askin' as it would explain some of your numbers.

Unless you only want this to work a few very occasional times you need to use batteries with much more capacity so you only drain them 25 (typical) to 50% (maximum) as fully drained batteries will last for much fewer cycles then partially cycled.

Nov 4, 2011
379
48
That's actually VERY funny, for a variety of reasons - I joke about that all the time
When I go into the local hydroponics store, I'm the oldest one there, and I'm the only one growing tomatoes!!!

I'll give you a larger view of the issues.

There are many hydroponic methods. Over the last two years I've started to migrate from "ebb and flow" (intermittent use of a pump) to "nutrient film technique" (NFT). The NFT technique requires low, constant flow through a long series of "pipes". If it is off for more than an hour or two - toast.

I was on vacation a couple of weeks ago, a GFI tripped, and we had a large scale mass extinction. It's not a big deal - I lost a few heads of lettuce, maybe eight tomato plants and some basil.

In the past, I wanted to make a control system for the fun of it, and now, the mass extinction has galvanized me to put it together.

My goals are to try to cycle the pumps to minimize "on time", yet keep the plants healthy. And if there is a power-down, there is a way to keep things going for a time (I'm thinking about other ways to handle "power out").

So I've over-engineered it (in reality, the largest pump draws 0.5 amps, the smallest 0.07), and would like to get the theory right, before I start making PC boards.

I'll be posting other questions about control systems, but I wanted to get the concepts of amp-hour conversions between various voltage levels.