NFU Mutual Smallholding Insurance

Author Topic: how do i tell how much charge is in a 12v battery  (Read 2958 times)

lynnandrob

  • Joined Jan 2013
how do i tell how much charge is in a 12v battery
« on: February 16, 2013, 09:18:22 pm »
Hi,

How do I find out how much power is in a 12v/80ah battery.
At the moment I have a 12v/80ah battery connected to a security camera system but would like to measure the power as it dissapates.
I have a standard multimeter which can handle 10amps max so I know I can not just bridge the terminals.
ive read that you shouldnt let the battery drop below 50% before charging it,and so need to find out how long the system can run before i need to recharge.

Thanx.
Voss Electric Fence

lachlanandmarcus

  • Joined Aug 2010
  • Aberdeenshire
Re: how do i tell how much charge is in a 12v battery
« Reply #1 on: February 16, 2013, 09:44:23 pm »
Some electric fence energisers have built in meters, might be able to borrow one? Mine is a speed rite one from rappa. Doesn't show exact amount left but does show proportion left in series of green/ red lights

fl206

  • Joined Feb 2013
Re: how do i tell how much charge is in a 12v battery
« Reply #2 on: February 16, 2013, 09:46:29 pm »
From http://en.wikipedia.org/wiki/Lead_acid_battery#Voltages_for_common_usages

If it's a lead-acid battery, fully charged would be measured as 12.6V with only your multimeter attached to the battery. Bridging the battery with your multimeter is fine if you're measuring voltage as opposed to current.

50% discharge should be around 12V.

bazzais

  • Joined Jan 2010
    • Allt Y Coed Farm and Campsite
Re: how do i tell how much charge is in a 12v battery
« Reply #3 on: February 17, 2013, 01:48:17 am »
Use a hydrometer if its lead acid.

If its a dry cell - run it till it runs out then the next time take it to charge it a day earlier than that ;)

bazzais

  • Joined Jan 2010
    • Allt Y Coed Farm and Campsite
Re: how do i tell how much charge is in a 12v battery
« Reply #4 on: February 17, 2013, 01:50:38 am »
Security camera should last for ages unless it has lights, IR, wireless or on a huge 100m bnc cable up to the sheds.

mab

  • Joined Mar 2009
  • carmarthenshire
Re: how do i tell how much charge is in a 12v battery
« Reply #5 on: February 17, 2013, 08:04:54 pm »
yep, hydrometer is by far the best way to measure state of charge, unless it's a sealed battery.

you can measure current drawn by the load and multiply by time the load has been on.

if in doubt; recharge.

lynnandrob

  • Joined Jan 2013
Re: how do i tell how much charge is in a 12v battery
« Reply #6 on: February 20, 2013, 05:48:47 pm »
using a digital battery analizer ( sealey BT2002 )
i can see the health of the battery and the charge from 100% to 0% which are  shown in bars and percentages,you can also whatch the volts as they drop on the screen

 

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