Sunday, 20 January 2013

And so it begins

And so it begins.... this is an attempt to build an Open Source battery monitor for my motorhome. So why do I want to do this? Several reasons: cost, flexibility, and... just for interest.

The idea is to build something akin to the NASA BM-1 battery monitor. This is a unit that retails in the UK for around £95 incl VAT. So I'm wanting to build something that is cheaper than that.

Three specific things I want to be able to do with this unit, which you can't with the BM-1:

  1. Output the voltage, current and temperature readings real time via a serial port (so it can interface with another general motorhome control project I'm working on)
  2. Record the voltage, current, and temperature to some kind of storage (an SD card most likely) every few seconds so that the data can be subsequently graphed on a computer to get a better idea of battery performance.
  3. Be able to set the meaning of 'empty' for the battery. The BM-1 tells you what the state of charge is as a percentage, but with lead acid batteries you don't want to take them down below 50% state of charge regularly. So when the BM-1 says 50% left, does that mean 50% until the battery is half empty, or 50% until the battery is at 0% and damaged.
I'm going to be building this on top of an Arduino-based system. No doubt there will be mistakes along the way and this might end up costing me more than a BM-1 in the process of learning, but hopefully the end result will be something that can easily be replicated by anyone else.

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