Battery holding charge issue....

Dervis Garip

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Feb 17, 2012
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Guys thanks for help advice. One thing I forgot to mention is voltage charge sometimes reverts back to normal being tested today with AC on at 14.1 volts.

Bottom line I’m thinking the alternator is charging right and yet most time times not.

Planning to visit the auto electricians next week for get to the bottom of this issue.
 
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PeterLC

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Lead acid batteries have a huge problem with leaving them discharged, i.e. at a low voltages, under 11V. Sulfatation occurs while at low voltage. The sulfate crystals end up on the bottom inside the battery and create a shortcut inside a cell. However it is a slow process so if your battery gets discharged and you recharge it immediately, no harm will be done. That might explain why some of us see this more as a problem then others, it is just a matter of how long the battery remains discharged.
One bad cell in a battery can ruin its performance. The internal resistance will go up and the starting current will be drastically reduced. If you have a 24V starting system, there are 12 cells in series, 6 from each battery so a single bad cell in any one battery ruins the starting performance. And vice versa, it will inhibit charging.
About the problem at hand, I tend to agree with Firewout and many others. Even a small alternator will end up charging batteries as long as it delivers more current than the vehicle requires and you drive it long enough. 80A is a lot. The best way to check is to measure with a voltmeter : alternator output voltage and all individual battery terminal voltages once the vehicle is started. There shouldn't be a big difference between any of them at any time and the voltage should rise towards 14,2V or 14,5V. If not all voltages are more or less equal, check cabling and relay contacts, urgently. Worse case, these kind of faults may cause fire.
If the alternator charges intermittently, this points in the same direction.
The alternator has an S terminal. It opens a ground circuit as soon as the alternator starts working. If this is used to drive the relay that connects the third battery, you avoid discharging this battery while starting. Unless you have very thick cables running to the rear battery, that would be much safer.
 

Towpack

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My third battery in the back connects to the charging circuit via a relay which operates 10 secs (adjustable) after turning on the ign. This avoids any cranking current being drawn from it.
 
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Dervis Garip

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Guys after a few days of testing everything looks good now. The alternator is charging well all three batteries. The only thing that needs investigating further is how much power draw my Engel 40 liter has leaving it on every day from the 100 amp car battery. On the net is says 2.5 amps per hour that seems a lot!!
Does anyone have any idea?

Thanks
 

PeterLC

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What you are looking for Dervis is the energy use of your fridge. That will be expressed in Ah (ampère hours) at 12V. You can compare that to your battery's capacity of 100Ah. Looking at the Engel datasheets, the 2,5A that you mention is the current draw of your fridge when it's running. Mutiply it by 12V and you get the power draw. To convert power or current to energy or running time you will need to know how much of the time your fridge is running. Mine is a Waeco 30l, it runs 30% time unless the car is parked in the sun or we have just bought some hot six-packs. So 30% of an hour x 2,5 A = 0,75Ah. Now you can compare it to your battery size. Remember that the effective capacity of a lead acid battery usually is only half the rated capacity (50%DOD).
 
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Dervis Garip

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Peter running the fridge for 12 hours over night the reading of my gauge was 13.3v to start and 12.4v after. So roughly looking at 0.9-1.0v. Would this be 2.0v per day?
Trying to get an idea of the limitations of my setup and roughly should I turn the fridge off if not using it / driving the vehicle everyday?

Thanks
 

Mick W

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Guys today finally got round to getting the alternator out. It appeared to have a weak Diode set fitted last time. Perhaps not as good as was on the alternator from stock.
Is the new rectifier a Toyota part? They are almost the cost of a complete alternator. Sorry I might have misled you at the beginning due to my haste in replying. Should have known better as I work in electrical engineering
 

Dervis Garip

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Is the new rectifier a Toyota part? They are almost the cost of a complete alternator. Sorry I might have misled you at the beginning due to my haste in replying. Should have known better as I work in electrical engineering
I doubt it TBH Mick, a generic one not sure of the make. Easier to repair here in Cyprus than ordering one from overseas. This setup is temporary now as if I’m in Cyprus for next season will probably be transitioning into a trailer / caravan set up with solar and taking out the fridge & accessories.

Thanks
 
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PeterLC

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Well Gervin, that's only part of story. After a charge, at first your voltage will drop really fast from 14,5V to 12,8V, even with very low load. After that you can use this graph to get an estimate of the state of charge. Note that these points are measured at no load, which is may not be what you did, your fridge might have been running. The voltage is influenced by the load too.

1596299338117.png

One thing that you could do is make a note of the voltage, say every hour. Assuming your energy requirements are constant (fridge running same number of minutes per hour) you will see that the voltage drop during the first hour is bigger than the one during the last hour (if you started with a full battery). That will allow you to extrapolate more accurately.

If you want a good view on your energy consumption out of your battery, consider a coulomb counter. It will count how many ampère-hours you used and you can compare that to your battery's capacity. They come with voltage, ampère and ampère-hour displays. You won't need to get up at night every hour. An additional advantage is that you will get a good idea of how your battery ages : the voltage of an aged battery will be lower at the same DoD.
 
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Dervis Garip

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Thanks peter that’s idea I’m more serious about looking into because when I start the truck all the charge is being send to the fridge battery.

Also considering to plug in to the mains electric from the truck to the fridge whist it’s parked up and try this out next week. This takes the hassle and load of the battery and don’t have to be too concerned if the trucks driven often enough.
 
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goodoldboy

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maybe a Ctek charger would be the solution ? V is a pretty crude way of measuring battery capacity. A battery should be at rest -neither being charged or discharged - for at lest 1 hour before measuring voltage will give an accurate reading.The rate of discharge also affects a batteries capacity Peukert's law - Wikipedia - [Leaving Land Cruiser Club]
 

Dervis Garip

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Guys after a long drive home the fridge gauge was reading 13.1v and so decided to plug the Engel into the mains for power. Only thing kinda new to me was that had to unplug the 12v lead. Kinda a hassle unknown to me. Guess both leads are designed that way as mains power cannot be detected to override the 12v system?

Giving this a go to see how this works out and test the condition the all batteries this way.
 
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