<span class="highlight">Battery</span> state of charge
Submitted: Tuesday, Sep 23, 2008 at 18:17
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portlester
Hi everyone
I have a 40L Engel wired up in my trailer with the second
battery in the trailer.
I've just set up the Engel inline
battery monitor and its currently reading 12.2V. I was expecting the reading to be closer to 12.8V as the
battery is fully charged (or should be as I have just charged it) and only the fridge (&
monitor) is connected.
Has my L plates in all things electrical got the better of me here? Is the 12.2V what you would expect for a fully charged
battery currently under load & the 12.8V what you would get for a batter not currenlty under load?
I'm doing all this in the hope that I can get a rough idea (obviously it will be dependent upon the fridge temp v outside temp; what's in the fridge; etc) of how long I can run the fridge for without the need to connect back up to the car & take the trailer for a drive when out in the bush.
many thanks in advance - hopefully its not too silly a questions.
Reply By: Member - 1/2A - Tuesday, Sep 23, 2008 at 18:57
Tuesday, Sep 23, 2008 at 18:57
You can't tell a batteries charge state from the voltage. The only correct way to do this is to install a
battery monitor with has an inline shunt to one of the terminals, this measures the current flow in an out of the
battery and then calculates the state of charge.
AnswerID:
326769
Reply By: Affordable Batteries & Radiators - Tuesday, Sep 23, 2008 at 19:08
Tuesday, Sep 23, 2008 at 19:08
What size and type is the
battery ?
12.8V fully charged and no load is OK.
The 40L Engel while running should not drop it as low as 12.2V unless the
battery is small or in poor condition.
AnswerID:
326774
Follow Up By: Affordable Batteries & Radiators - Tuesday, Sep 23, 2008 at 19:17
Tuesday, Sep 23, 2008 at 19:17
Note: What size and length is the cable ?
FollowupID:
593919
Reply By: portlester - Tuesday, Sep 23, 2008 at 19:53
Tuesday, Sep 23, 2008 at 19:53
Thanks for your comments
The
battery is a new 100 a/h which I charged up a couple of weeks back using a CTek smartcharger (its been sitting around since then). It is located in a compartment under the trailer with cables less than 300mm in length from the batter into the trailer proper. The install was professionally done with both fridge cables heavy duty (4mm outside diameter) compared to the other cables to the other power plugs.
What I have subsequently done today is replaced the installed merrit plug for the Engel posifit plug. The inline
monitor is then plugged into this, with the ~1.5m engel fridge lead plugged into that.
When checking the cable lengths just now, noticed that when the fridge is motor is not running
monitor is showing 12.5V then when the motor cuts in it drops to 12.3V.
Thanks again for your assistance.
AnswerID:
326788
Reply By: Member - Mike DID - Tuesday, Sep 23, 2008 at 20:12
Tuesday, Sep 23, 2008 at 20:12
People really need to read the fine print associated with the Voltage-vs-State of Charge tables.
They are only meaningful if there has been no charge or discharge from the
battery for several hours.
AnswerID:
326794
Follow Up By: portlester - Tuesday, Sep 23, 2008 at 20:49
Tuesday, Sep 23, 2008 at 20:49
Which is why I finished my initial question off with "Has my L plates in all things electrical got the better of me here?"
I obviously did not use the best header for my question as I did not mean it to relate to the Voltage-vs-State of Charge tables that you mention, but to whether the 12.2V reading that I have on my inline
battery monitor is what you would expect when the fridge is running.
While trying to search for an answer myself I came across the 12.8V number & that was not qualified with the
battery needing to be at rest.
I would be happy for you to link me to some suitable info (preferably a dummies guide) to the Voltage-vs-State of Charge tables.
cheers
FollowupID:
593944
Follow Up By: Affordable Batteries & Radiators - Tuesday, Sep 23, 2008 at 21:59
Tuesday, Sep 23, 2008 at 21:59
No problem.
Use this one.
Basic-Guide
FollowupID:
593967
Reply By: portlester - Saturday, Sep 27, 2008 at 21:39
Saturday, Sep 27, 2008 at 21:39
Thanks Derek for your link. Also while searching around the net I came across this
battery faq link which I found quite useful as
well.
I've just got around to recharging the
battery again on the CTek & this time got a charge (after the required
battery rest) of 12.8V (last time it was reading 12.5V, so it appears I stuffed up the initial
battery charge I'm guessing. I initially had set the CTek on RECOND thinking that was best for a new
battery ... obviously not however as the NORMAL setting gave the full charge).
cheers
Portlester
AnswerID:
327437