Wednesday, August 8, 2012

Shindig Volt Meter

This blog post will attempt to describe an instrument that I designed to monitor batteries on board.  Beware.... there is a lot of geek speak below.

One of the big challenges on Shindig is managing and monitoring all 13 batteries on board.  My DC system consists of 4 battery banks:
  1. Domestic Bank - 8x 6 volt AGM
  2. Engine Start Bank - 2x 12 volt AGM
  3. Bow Thruster Bank - 2x 12 volt AGM
  4. Generator Start - 1x 12 volt AGM
There is one Xantrex Amp/hour meter(Link 2000) that indicates battery health for the domestic and engine start banks.  While this meter is great for monitoring the amps in and amps out it doesn't tell me anything about the health of the individual batteries that make up the 24 volt banks.   Shindig only has one big bank (domestic) for operating all the onboard electronics, refrigeration, etc.  It is important that I keep a close eye on the health of this bank.

The purpose of the Shindig Volt Meter is to monitor the individual batteries that make up the system so that I can get an early warning if one is failing.  This will give me a chance to address the problem before a bank gets out of balance and impacts otherwise healthy neighboring batteries in the bank.

The meter is now installed and has already helped me identify a few batteries that were not pulling their weight.

The "Shindig Volt Meter" is based around the Arduino micro controller platform.  The Arduino is a popular hobbyist package that I started playing around with a few years ago.  It uses an Atmel micro controller that has all the digital and Analog to Digital (A/D) IO pins needed to do the job.

The input circuit multiplexes battery voltages through a resister ladder to voltage levels that the micro controler is happy with.  The Arduino controls a multiplexor to select the specific battery voltage to be read and then converts the analog voltage input to a digital value.  Once all the voltages are sampled they are compared to warning and alarm presets and output to the LCD.  The LCD is updated every half second as are the status lights.

Bread boarding the components for proof of concept

Placement of Arduino, voltage regulator, chip sockets and edge connectors
Back side of main board with LCD mounted

Final version installed on the boat.  This is showing the summary info screen for all 4 battery banks.

The red button allows you to scroll through different screens of information.
The two toggle switches are for on/off and LCD back-lighting.
The Green light indicates and all is well.
The Yellow light indicates that 1 or more of the 13 batteries voltage is below normal.
The Red light indicates that 1 or more of the 13 batteries is critical.
The alarm buzzer will sound if any one battery is in the red for more than 120 seconds.  It is common for batteries to bounce into the red under high loads(bow thruster, big inverter load, etc).  This is why I wait for 2 minutes before alarming.

Summary screen

Domestic bank details.  Port and Starboard 6 volts X 8

Engine bank detail.  2 X 12 volt

Thruster bank detail.  2 X 12 volt

Generator start battery.  12 Volt

Firmware version, threshold settings and "on" timer

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