Battery Charging Time

Submitted: Friday, Jan 09, 2004 at 18:51
ThreadID: 9618 Views:1350 Replies:3 FollowUps:5
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Need to charge my deep cycle aux. battery (50 amp hr). It is pretty flat, about 12V. Can anyone advise how long do you charge the battery from a 240V power source? I was going to leave it on overnight (9 hrs), does it matter or will it overcharge? How do you know if it's charged?
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Reply By: Member - Ross - Friday, Jan 09, 2004 at 19:13

Friday, Jan 09, 2004 at 19:13
Jac

If you're using a fair dinkum charger, it won't matter as they have an inbuilt regulator which prevents overcharging the battery.

CheersFidei defensor

Rosco
AnswerID: 42383

Reply By: Eric Experience. - Friday, Jan 09, 2004 at 22:23

Friday, Jan 09, 2004 at 22:23
Jac.
Your battery is 50 amp hour so if you charge for 10 hours at 5 amps or 20 hours at 2.5 amps you will be fully charged. Eric.
AnswerID: 42413

Follow Up By: V8troopie - Saturday, Jan 10, 2004 at 00:23

Saturday, Jan 10, 2004 at 00:23
Eric, that is NOT very good advice you are giving there. You cannot use the batteries discharge ratings as an indication how to charge it.
!0 hours at 5 Amps could boil the hell out of it and it won't be the same battery after that treatment.
One really should use either a voltage regulated power supply or a proper multi stage charger to re charge lead acid batteries.

With just voltage regulated power supplies one has to set the voltage carefully (~13.8V- 14V) or the battery will overcharge and gass off the water.
These take much longer than a multi stage charger for fully recharging. One also has to disconnect the battery after it is full or wind back the voltage to 13.6V for trickle charging.

How do you know the battery is fully charged? Use a hydrometer (the glass tube/float/bulb thingie). Battery is sealed? No problemo, disconnect the charger, wait at least 1/2 hour and measure the terminal voltage with a digital volt meter, 12.6V=full. Why the wait? the plates need to equalise a bit or one measures an artificial higher voltage. The wait also applies to the hydrometer test, to let the bubbles in the acid settle down.

A multi stage charger might push in 20 amps or so for a few minutes, the current will taper off as the battery voltage rises. When the sensing circuit decides the battery is nearly full it starts pulsing the charge to get the last amps in. When full it switches to trickle charge to maintain the battery. With a good multi stage charger you can leave the battery connected indefintely.

Good deep cycle batteries are not cheap, it pays to pamper them with a decent charger.
Klaus
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FollowupID: 304863

Follow Up By: Brett - Saturday, Jan 10, 2004 at 12:29

Saturday, Jan 10, 2004 at 12:29
Good accurate advice Mr V8 Troopy.
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FollowupID: 304897

Follow Up By: Eric Experience. - Saturday, Jan 10, 2004 at 22:49

Saturday, Jan 10, 2004 at 22:49
Klaus.
What you are saying is only half right, what you say about good battery charges is correct but you statement about charge rate and the answer to 'how do you know when its fully charged' is wrong. we know that the battery is dead flat so there is no chance of over charging it if my advice is followed. the method of determining if a battery is fully charged by measureing the voltage is incorect. the battery is a chemical device the output voltage is always 12.6 regardless of charge once over the first few %. the only thing that changes with charge is the internal resistance so measuring the voltage is bad advice because people could have a flat battery and think it was charged if they believed you. In the most critical battery applications like the power supply for a submarine the method of determining the state of charge is to record the charge and discharge current and match them to the AH capacity of the battery. Eric.
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FollowupID: 304938

Follow Up By: V8troopie - Sunday, Jan 11, 2004 at 01:35

Sunday, Jan 11, 2004 at 01:35
Eric, Eric, Eric, I wish you had taken the trouble to check before firing off the remark that a voltmeter is unsuitable to check a battery status.
The internet is such a wonderful resource, especially the 'google' search engine.

I have looked up a reputable deep cycle battery manufacturer - Trojan - to see what they have to say on the subject.
See for yourself at:
http://www.trojanbattery.com/customercare_batterymaint4.html

You'll find they first recommend the hydrometer test, as I also mentioned, but as this is a bit tricky and temperature dependant they also give a table for a voltage check. Note that the difference between fully charged and just about dead is less than a volt. Something a $20.- digital voltmeter has no trouble differentiating - even the cheaper ones read to two decimal places - easy to see if its 12.4V or 12.55V!

What the Trojan suggests as a waiting period after charging (6 hours) before measuring is possibly much better for a true indication of charge but one gets a good idea of it after at least 1/2 hour after disconnecting.

What you say about that a battery measures "always 12.6V" is plain nonsense.

What you say about submarine batteries may have been correct way back when you were presumably in submarines and the digital volt meter was not yet invented.
Note that I said 'use a DIGITAL voltmeter to check the battery charge'
The old analog (pointer) type meters are useless for this.
These days submarines more likely use a sophisticated computer to determine the charge state of their batteries

I happen to know a bit about this subject and still think that just banging in 5 Amps for 10 hours into a dead 50Ah battery is bad advice. You might have gotten away with that on your battery but not all batteries take that kindly.
Best advice I can give is: NEVER let a deep cycle battery become completely discharged - this will drastically reduce its useful life.
Best to keep it above 50% charge at all times while using it and storing it at 100% charge with frequent topping up.
Klaus
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FollowupID: 304944

Follow Up By: Topcat (WA) - Sunday, Jan 11, 2004 at 14:41

Sunday, Jan 11, 2004 at 14:41
I concur with V8Troopie & speak from years of experience in getting the maximum life out of a deep cycle battery. Never let them get below 50% discharge capacity (75% is an ideal working level) & when recharging it is better to charge at low amps over a longer period (known as trickle charging) then doing a rapid charge over a short period. The shallower the charge the longer the life can be obtained.
The recommended charge rate for a 50amp capacity deep cycle battery is 21 hours @ 4 amps. Check each battery cell electrolyte level & make sure each cell is covered with electolyte. If necessary top up with distilled water. DO NOT OVERFILL!!!! About 1/4 inch above the cell is sufficient.
Let the surface charge settle (equalising the cells) & check electrolyte with a hydrometer after the battery has cooled down(below 43degC.Ideal temp should be 26-27deg.C.) The hydrometer average specific gravity should read 1.265 when the battery is fully charged. People might think I'm, bullsh****ting but I have got nearly 8 years life out of a deep cycle battery following this practice & when in storage keeping it fully charged & regularly charging to prevent sulphation of the cells every 3 months. The biggest killer a lead-acid batteries is heat & overcharging!!! Cheers.Have Wheels Will Travel
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FollowupID: 304976

Reply By: V8troopie - Sunday, Jan 11, 2004 at 01:32

Sunday, Jan 11, 2004 at 01:32
Eric, Eric, Eric, I wish you had taken the trouble to check before firing off the remark that a voltmeter is unsuitable to check a battery status.
The internet is such a wonderful resource, especially the 'google' search engine.

I have looked up a reputable deep cycle battery manufacturer - Trojan - to see what they have to say on the subject.
See for yourself at:
http://www.trojanbattery.com/customercare_batterymaint4.html

You'll find they first recommend the hydrometer test, as I also mentioned, but as this is a bit tricky and temperature dependant they also give a table for a voltage check. Note that the difference between fully charged and just about dead is less than a volt. Something a $20.- digital voltmeter has no trouble differentiating - even the cheaper ones read to two decimal places - easy to see if its 12.4V or 12.55V!

What the Trojan suggests as a waiting period after charging (6 hours) before measuring is possibly much better for a true indication of charge but one gets a good idea of it after at least 1/2 hour after disconnecting.

What you say about that a battery measures "always 12.6V" is plain nonsense.

What you say about submarine batteries may have been correct way back when you were presumably in submarines and the digital volt meter was not yet invented.
Note that I said 'use a DIGITAL voltmeter to check the battery charge'
The old analog (pointer) type meters are useless for this.
These days submarines more likely use a sophisticated computer to determine the charge state of their batteries

I happen to know a bit about this subject and still think that just banging in 5 Amps for 10 hours into a dead 50Ah battery is bad advice. You might have gotten away with that on your battery but not all batteries take that kindly.
Best advice I can give is: NEVER let a deep cycle battery become completely discharged - this will drastically reduce its useful life.
Best to keep it above 50% charge at all times while using it and storing it at 100% charge with frequent topping up.
Klaus
AnswerID: 42532

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