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12V Battery Alarm

12V Battery Alarm

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2 replies to this topic

#1 OFFLINE   SnowStorm


    C-Max Hybrid Member

  • C-MAX Hybrid Member
  • 959 posts
  • Region:U.S. Southern Atlantic
  • LocationVirginia
  • My C-MAX's Year:2013
  • Current Vehicle:C-Max SE

Posted 09 September 2014 - 11:14 PM

Here is my alarm for the 12 volt battery.  A makeshift affair at this point but low cost.  Parts used are:

  1. Voltage monitor with LED and audio (beeper) alarm functions.  Bought it here from New Harbor because it shipped from the US (it came in like two days).  It is made for monitoring batteries in model aircraft so you know when to land!  There are all sorts of things like this out there.
  2. Cable to connect to it easily - here's the link.  Also from New Harbor.
  3. Three 470 ohm 1/4 watt resistors.
  4. A 1/2 amp fuse (do not connect anything to the battery without a fuse!)
  5. Red and black clip leads

The monitor looks like this (the two black thing on the left are beepers):


It can monitor up to 6 lithium cells at about 3.5 volts each.  So I use the resistors to make it think its connected to a 3 cell battery with about 4 volts on each cell.  You can set it to alarm (lowest cell) anywhere from 3.00 to 4.00 volts in 0.05 volt steps.  Mine is set at 3.60 which, with my crummy resistors, should alarm at about 11.2 volts on the car battery.


Here is the whole mess connected to my camping battery - monitor/alarm, resistors, fuse and clip leads:


The display cycles through total voltage (shown above), largest delta between "cells" (don't care about that), and each "cell" voltage.  The lowest one is important since it will trip the alarm.


It is now connected under the hood all stuffed in a plastic bag near the grille and duct tapped in place (don't know if it can stand the heat).  The beepers are quite loud so I should hear it out in the garage if I'm awake and in the main living area of the house.  Asleep is another story but a $15 audio only baby monitor should solve that problem.


The battery monitor draws 27 mA.  The current goes to an average of 60+ with the alarm going off.


I hope this is all a waste of time!

  • JAZ, ptjones, obob and 1 other like this

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#2 OFFLINE   SnowStorm


    C-Max Hybrid Member

  • C-MAX Hybrid Member
  • 959 posts
  • Region:U.S. Southern Atlantic
  • LocationVirginia
  • My C-MAX's Year:2013
  • Current Vehicle:C-Max SE

Posted 23 May 2015 - 10:20 PM

Not a waste of time!


Had our third "dead" battery problem this morning but, thanks to the alarm, it was only down to 8.1 volts instead of 2 or 3.  Heard the beeper going off when I got up.  Door unlocked OK but there were no dash/display lights and outside/courtesy lights were dim.  Car started OK and I let it run to charge battery.  We had driven 4+ hours the day before and without rain.  A few short trips today were no problem and seems to be holding OK at 12.4 volts.  This instance highlights again how you can have "the problem" without knowing it because the battery is still high enough to "start" the car.  But 8 volts is beyond "fully discharged".  Last dead battery was 16 months ago!


15B04  - here we come!

  • obob likes this

#3 OFFLINE   Ponypower


    C-Max Hybrid Member

  • C-MAX Hybrid Member
  • 106 posts
  • Region:U.S. Great Lakes
  • LocationTinley Park
  • My C-MAX's Year:2014
  • Current Vehicle:Ford C-Max

Posted 24 May 2015 - 06:41 AM

Awsome, why can't Ford do this and make it a gauge.

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