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Topic: automating lead acid battery protection - low voltage cut off (LVC) (Read 922 times) previous topic - next topic

simplesimon10

Hi there,

I'm new to the board (excuse the pun) and need some help from someone who know how I might put together some arduino hardware and code to achieve the following (diagram is attached):

Basically, I need a simple automated solution that turns on and off my inverter (via a arduino relay controlling  low voltage serial data rs232 port) based on the current (again excuse the pun) voltage of my 24v battery array.

So basically when the arduino reads 22v or below, the relay will kick on and, via the serial connection, the inverter will turn off. When the battery array is charged back up to 24v or above the arduino will read this voltage and the relay will kick off, and via the serial connection, the inverter will turn back on. 

It seems like it should be pretty simple thing to build but I just can't seem to find anything out there to help me put this thing together.

I've attached a JPG image of the proposed system that may help explain things better.

Thanks in advance Simon




jackrae

You don't need an arduino for that.  A simple opamp comparator with hystresis will do the trick

weedpharma

As jackrea said, use a comparator.

Lm311 is a cheap common comparator with plenty of info. Use the output to drive a transistor and relay.

You may need to change the +/- connection to get the right output.

Weedpharma

simplesimon10

Oh ok thanks. I googled it and it seems pretty complex (not being an EE). Would it allow me configure some logic variables and conditions (based on the updated diagram I've attached)?

I figure that given the solar system is configured as primary source supplying a steady AC load on the AC transfer switch, in the event that over time the load draw depletes the battery array to the point that its voltage drops to 20v or less, the arduino will:

1. Turn off the inverter, (causing the AC transfer switch to automatically fail-over to the secondary grid power source).
2. Wait until the following condition are met before turning the inverter back on:
  a. The DC battery voltage rises to say... 26v, AND
  b. say...30 minutes have passed
3. The inverter now back on will cause the AC transfer switch to automatically switch back to the primary solar power source


THanks
Simon

jackrae

Now that you've advised of increased complexity (time delay with a rising voltage coupled with lack of "comfort" in designing your own circuit) you probably will be better off using an arduino.  This also gives you the advantage of being able to "see" the variables in real time and permit tweaking the settings to suit actual, rather than theoretical, conditions.  A simple potential divider to give you a 5v measured input voltage and conditional logic programme should meet your needs.

simplesimon10

uhh well yes thats right and why I was asking for help on an arduino based solution on an arduino forum.
so now that we're back to square 1, any ideas on how to put this together using a mega board and a relay?

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