Second Battery

Submitted: Saturday, Oct 30, 2004 at 16:04

ThreadID: 17425 Views:2354 Replies:4 FollowUps:1

This Thread has been Archived

pauls

Is my second battery on the way out.

I started with a fully charged battery reading 12.65v which is normal for this battery. I ran a 60w electric light through an inverter and a 12v light (13 watts) for 2 hours. I then checked the battery terminals after 2 hours and was down to 11.6v. After switching everything off, the battery immediately read 12.16v. Would this rate of discharge for the load signify an unhealthy battery. It is 4 yrs old.

Thanks

Back Expand Un-Read 0 Moderator Share

Reply By: Member -Dodger - Saturday, Oct 30, 2004 at 16:35

Saturday, Oct 30, 2004 at 16:35

An inverter uses power in its own rite.
The sums go something like this, divide the 60w by 12 = 5amps per hr then 13w by 12 = 1amp add them together = 6amps per hr x 2 = 12 amps. Take the 12amps off the total batt amps & it will give you what is left. Running inverters always works a batt hard and if the batt is a fair age then this will even be harder on the storage.
However if you had used an inverter type light EG. a Versa light which only draws 1amp per hr then the battery would probably hardly notice 2hrs running.
These type of lights are usually = to a 75watt incadesant bulb.
However having said all that your batt is getting near its usefull life. You can always get it checked by a auto elec.

I used to have a handle on life, but it broke.

Cheers Dodg.

Lifetime Member
My Profile Send Message

AnswerID: 82327

Reply By: Member - Collyn R (WA) - Saturday, Oct 30, 2004 at 16:45

Saturday, Oct 30, 2004 at 16:45

Depends on size and type of battery but seems due for retirement.

Assuming it was a 100 A.hr battery - by four years its likely to have lost about one third of its nominal capacity. That brings it down to about 66 A.hr.

You say it was 'fully charged' but it's close to impossible to fully charge a battery without a three-step charger or its solar equivalent. Without that type of charging the battery is more likely to be 70-75% charged (and your measurement of 12.6 volts confirms this).

The battery is thus likely to be charged to the equivalent of 45-47 A.hr - to about half it's nominal capacity.

Your load was about 15 A.hr. This dropped the battery to about 30 A.hr - ie to about 33% of its nominal capacity. Off-load voltage at that level of charge is likely to be 12.1 -12.2 volts - which was much what you had.

I think it's trying to tell you something!

Trust this helps
Collyn Rivers

AnswerID: 82328

Reply By: Magnus - Saturday, Oct 30, 2004 at 20:59

Saturday, Oct 30, 2004 at 20:59

Check out this site for a downloadable comparison of State of Charge tables.

SOC Tables

They may help you establsih where your battery is at.

Cheers

Magnus

AnswerID: 82344

Reply By: Member - Collyn R (WA) - Sunday, Oct 31, 2004 at 11:13

Sunday, Oct 31, 2004 at 11:13

Magnus
Am quite puzzled by some of the columns in that battery chart. I have just checked against half a dozen charts, plus my own (my were derived by averaging ten typical readily-available batteries). All are in agreement within 5%.

But the voltages quoted in 'SOC' are, in some columns, just HUGELY lower than typical. I suspect they may be for batteries that are on heavy load - or there is a major spread-sheet error?
Collyn Rivers

AnswerID: 82369

Follow Up By: Magnus - Sunday, Oct 31, 2004 at 18:33

Sunday, Oct 31, 2004 at 18:33

Collyn

Nope. They were downloaded from the sites just as is. I find the variances a bit dis-concerting myself. The only site that seems to make a distinct difference between standard Lead Acid batteries and the Valve Regulated Sealed Type is the Bill Darden site.

I tend to just use an average and make sure I don't drop much below 70 %. Have tried graphing them and fitting a trend line.

In the end, decided I was chasing a mist and gave up.

I use solar when camping and just stay close to between 12.35 and 12.5 when in camp as measured by a digital voltmeter first thing in the morning. Not right I know, but at least any error will be reasonably constant. If the readings get lower than 12.40 I start to get worried, maybe panic even, and then reduce my consumption that night.

I probably undersized my battery. It is an 80 amp hour. Should have gone for 150 or so, but was working to a budget and budget didn't stretch that far. Such is life,

At home, I use a three stage charger for the battery (a Deep Cycle Delkor) , a Projecta MC 121045 that is rated at 4.5 amp constant current for the bulk charge tapering during the absorption down to a float charge of way less than .5 amp. That works fine. Just put it on a week before we go away to make sure it is fully charged. We camp frequently so it doesn't get a chance to self discharge.

As you have said before, finding some reliable info on the net that lines up is difficult. These SOC tables are just an example. You have to use them with some with caution, at least this set you do!!

It really would be nice to find at least three or four SOC tables that were within a whisker of each other for the same battery type, preferably a deep cycle.

So, unless I screwed up in reading the sites where I got the SOC's from (and that is certainly possible), then the SOC's are just as I downloaded them.

Makes life interesting. But so far I have managed to get by without ever running out of power. Nearly 4 years now. Probably as much luck as good management!!

Cheers,

Magnus

FollowupID: 341490