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Protecting batteries from over discharge ?


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7 hours ago, CompairHolman said:

What kind of device would cut off my feed from the leisure battery bank so that they are never damaged by over discharging ?

 

I have 480w of solar so there is always some charge going in , so they would at least maintain the minimum voltage until I could charge them again.

 

And how much would it cost ?  

Please don't take a-fence but I think you need to understand battery technology a little better.

 

Summary - If you use any part of a battery capacity it is reducing its life, &, if you do not recharge it immediately it is further damaging it by sulphation.

You could take you battery down To 50% SoC and leave it standing for a week and it is 'damaged'

You could take it down by 10% to 90% SoC and leave it standing for one day and it is 'damaged'

 

Leaving a battery at ANY state of discharge 'until you can get around to re-charging it' is slowly 'killing it'.

 

Batteries really need to be considered as disposable items and replaced when 'empty' - just like a gas cylinder (but one that with care will last a little longer)

The care needed to maximise a battery life is to re-charge it every time it has been 'used'.

Just think about how long a starter battery lasts - 5 years, 10 years, more ?. This is because only a small amount is used from it and it is re-charged immediately it has been used.

 

A second issue is your perception that solar is 'always' giving some charge, unless your electrical usage is virtually zero in the Winter 4 or 5 months then Solar (of almost any size) will fall way behind - how many Wh have solar given you in the last couple of weeks ? - enough to run a single light maybe ?

 

Don't buy 'gadgets' to do the job you can manually do, but, by all means buy monitoring equipment so you know when to start the engine (most days possibly) to re-charge the batteries.

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What Allen said, spend your money on monitoring equipment and some time in learning how to get optimum battery life and performance. When you get that equipment ignore any percentage or Amp hours left reading because it is most likely a lie.

 

If you are off the boat with the batteries turned off then even 60 watts of solar will recharge them during the winter given time. If you are on the boat and using electricity then fully recharging them frequently is far more important than not discharging them to any given degree.

 

 

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4 minutes ago, CompairHolman said:

What does the optimum charging regime look like then ?

 

Discharge right down then a big charge once a week, or always keep them above a specific voltage ?

 

 

 

 

The general advice is to not deplete the battery more than 50% and recharge daily.

 

It may take several hours per day to recharge depending on your usage, which is why you need to do an energy audit.

 

If you recharge once a week you will be buying new batteries (probably) every 4 months or so.

 

I repeat what I said above in post #4

10 hours ago, Alan de Enfield said:

Leaving a battery at ANY state of discharge 'until you can get around to re-charging it' is slowly 'killing it'.

 

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At the moment I can only visit the boat once a week. While I'm there I switch on the inverter and do a few odd jobs lowering the batteries down to about 65%. I then put the generator on for a couple of hours and that leaves the battery bank at around 98-99%. I read in the masterlink monitor manual that the final green led comes on when the battery bank is full (96-100%). So I had assumed that this was OK. A month ago when I returned to the boat the solar would have returned the bank to 100% but lately it is still at 98% a week later. 

11 hours ago, Alan de Enfield said:

You could take it down by 10% to 90% SoC and leave it standing for one day and it is 'damaged'

 

Leaving a battery at ANY state of discharge 'until you can get around to re-charging it' is slowly 'killing it'.

Having read this I'm now concerned I am actually killing the batteries slowly. Should I not leave the boat till the monitor shows 100% and the bank voltage is around 12.65 V. Or is 98% OK.? 

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37 minutes ago, Felshampo said:

At the moment I can only visit the boat once a week. While I'm there I switch on the inverter and do a few odd jobs lowering the batteries down to about 65%. I then put the generator on for a couple of hours and that leaves the battery bank at around 98-99%. I read in the masterlink monitor manual that the final green led comes on when the battery bank is full (96-100%). So I had assumed that this was OK. A month ago when I returned to the boat the solar would have returned the bank to 100% but lately it is still at 98% a week later. 

Having read this I'm now concerned I am actually killing the batteries slowly. Should I not leave the boat till the monitor shows 100% and the bank voltage is around 12.65 V. Or is 98% OK.? 

The monitor is almost certainly lying to you, percentages are normally way out and get worse every cycle. You must have very small batteries or using hell of a lot of power to drop you batteries to 65% unless you are staying all weekend and not charging while you are there

 

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4 minutes ago, ditchcrawler said:

The monitor is almost certainly lying to you, percentages are normally way out and get worse every cycle. You must have very small batteries or using hell of a lot of power to drop you batteries to 65% unless you are staying all weekend and not charging while you are there

 

Wouldn't that depend on what he was running from his inverter? I've got a 450 a/h bank but I could easily bring it down from fully charged to 65% SoC pretty quickly if I run the microwave, a vacuum cleaner or switch on the immersion heater from the inverter.

Edited by blackrose
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41 minutes ago, Felshampo said:

At the moment I can only visit the boat once a week. While I'm there I switch on the inverter and do a few odd jobs lowering the batteries down to about 65%. I then put the generator on for a couple of hours and that leaves the battery bank at around 98-99%. I read in the masterlink monitor manual that the final green led comes on when the battery bank is full (96-100%). So I had assumed that this was OK. A month ago when I returned to the boat the solar would have returned the bank to 100% but lately it is still at 98% a week later. 

Having read this I'm now concerned I am actually killing the batteries slowly. Should I not leave the boat till the monitor shows 100% and the bank voltage is around 12.65 V. Or is 98% OK.? 

You cannot test the battery voltage until (a minimum of) one hour after you have stopped charging.
if you test immediately after stopping the charging and get 12.7, 12.0 or even 13.0 volts this is just a 'surface charge'. It takes and 'hour or two' to 'soak in' before the voltage you are reading is actually the voltage 'in the battery'.

 

Your 'voltage monitor' will not show you when the battery is charged, you need to monitor the 'charging tail current' at a voltage of (around 14/4v).

The battery is charged when the charging voltage is around 14.4 volts AND the charging current is 1% (or close to) the value of the battery, so :

 

A single 110ah battery is charged when the charging current is 1a to 1.5a

A battery bank of 4x 110Ah is fully charged when the charging current is between 4a and 6a at a voltage of 14.4 volts.

 

You need to be able to measure BOTH CHARGING VOLTAGE & CHARGING CURRENT.

1 minute ago, blackrose said:

Wouldn't that depend on what he was running from his inverter? 

In part - Yes, but it could also mean

 

1) he only has a single small battery.

2) the battery bank is already sulphated and being slowly made worse by undercharging.

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1 hour ago, Felshampo said:

At the moment I can only visit the boat once a week. While I'm there I switch on the inverter and do a few odd jobs lowering the batteries down to about 65%. I then put the generator on for a couple of hours and that leaves the battery bank at around 98-99%.

Start the genny as soon as you get there - don't discharge the batteries first and then start charging them if you are only there a few hours.

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40 minutes ago, Alan de Enfield said:

You cannot test the battery voltage until (a minimum of) one hour after you have stopped charging.
if you test immediately after stopping the charging and get 12.7, 12.0 or even 13.0 volts this is just a 'surface charge'. It takes and 'hour or two' to 'soak in' before the voltage you are reading is actually the voltage 'in the battery'.

 

Your 'voltage monitor' will not show you when the battery is charged, you need to monitor the 'charging tail current' at a voltage of (around 14/4v).

The battery is charged when the charging voltage is around 14.4 volts AND the charging current is 1% (or close to) the value of the battery, so :

 

A single 110ah battery is charged when the charging current is 1a to 1.5a

A battery bank of 4x 110Ah is fully charged when the charging current is between 4a and 6a at a voltage of 14.4 volts.

 

You need to be able to measure BOTH CHARGING VOLTAGE & CHARGING CURRENT.

In part - Yes, but it could also mean

 

1) he only has a single small battery.

2) the battery bank is already sulphated and being slowly made worse by undercharging.

OK so I have 5x 160ah batteries. That means the charging current is around 8amps and 14.4 volts. So this will be at the end of the absorption phase of the charger? 

4 minutes ago, TheBiscuits said:

Start the genny as soon as you get there - don't discharge the batteries first and then start charging them if you are only there a few hours.

Right. I can do that. 

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20 minutes ago, Felshampo said:

OK so I have 5x 160ah batteries. That means the charging current is around 8amps and 14.4 volts. So this will be at the end of the absorption phase of the charger? 

Yes - at that voltage and current your batteries will be fully charged (as near as you will get them anyway)

It may take 3 or 4 hours to get from 95% to 100%

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?Some solar controllers have a load output with over discharge protection. This could be used to charge an old smartphone, which would send a text when the charge source is disconnected, using the app 'E-Robot'.

 

So when the batteries get over discharged while you are away you get a text message from the boat. ?

 

Happy Christmas everyone!

  • Greenie 1
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