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understanding my batteries ???


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Sorry, its another battery thread,

 

I've read loads on here about looking after batteries including "Wotever's" battery primer thread several times and I think I'm getting my head round things.

Does the following make sense ?

 

We've been on hook up in the marina for the last two months but started to get a bit "marina crazy" so have gone out cruising for a few days and decided to try and analyse the state of our batteries.

We have a nominal 520ah bank and I turned the engine off at 7.45 last night with the mastervolt panel showing a 5.3 A charging current, making them fully charged from what I've read.

 

This morning (7.45) so a full 12 hours later, the voltage was at 12.45v so battery bank at 75% with mastervolt panel saying we had used 52ah.

 

Some simple maths suggests that total bank capacity is now 208ah, i.e. 52 x 4 assuming the 52ah used is 25% of the capacity. 

The boat was new to us last march so have no idea how old the batteries are or how they have been treated in the past. 

 

My musings from the above is that the batteries are on their way out but as we will be back on hook up for the next two months, its not a issue at the moment and I might be able to squeeze another summer out of them when solar starts working again. 

Does the above sound about right or is there a fundamental flaw in my thinking ?

 

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9 minutes ago, waterdog said:

Sorry, its another battery thread,

 

I've read loads on here about looking after batteries including "Wotever's" battery primer thread several times and I think I'm getting my head round things.

Does the following make sense ?

 

We've been on hook up in the marina for the last two months but started to get a bit "marina crazy" so have gone out cruising for a few days and decided to try and analyse the state of our batteries.

We have a nominal 520ah bank and I turned the engine off at 7.45 last night with the mastervolt panel showing a 5.3 A charging current, making them fully charged from what I've read.

 

This morning (7.45) so a full 12 hours later, the voltage was at 12.45v so battery bank at 75% with mastervolt panel saying we had used 52ah.

 

Some simple maths suggests that total bank capacity is now 208ah, i.e. 52 x 4 assuming the 52ah used is 25% of the capacity. 

The boat was new to us last march so have no idea how old the batteries are or how they have been treated in the past. 

 

My musings from the above is that the batteries are on their way out but as we will be back on hook up for the next two months, its not a issue at the moment and I might be able to squeeze another summer out of them when solar starts working again. 

Does the above sound about right or is there a fundamental flaw in my thinking ?

 

Possibly correct but what used the 52 Ah over night? Does this tally with your power audit?

You need to work out how long it takes to get back to fully charged, if in fact you ever get there.

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7 minutes ago, rusty69 said:

What was the voltage when charging at 5.3A?

 

Was the 12.45V reading achieved with no load on the bank? 

 

hi, voltage was 14.1v and 5.3A just before switching off. 12.45v taken First thing this morning, 240v fridge and freezer running via inverter.

8 minutes ago, Boater Sam said:

Possibly correct but what used the 52 Ah over night? Does this tally with your power audit?

You need to work out how long it takes to get back to fully charged, if in fact you ever get there.

240v fridge and freezer running overnight plus we had 4 hours of TV after the engine went off. A 5.3A tail current before engine off suggests fully charged ??

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Just now, waterdog said:

hi, voltage was 14.1v and 5.3A just before switching off. 12.45v taken First thing this morning, 240v fridge and freezer running via inverter.

 

I don't think your reading tells you anything useful then. 

 

The tail current needs to be down to 1 or 2% of actual capacity and also noted when charging at 14.4v, not 14.1v. 

 

The resting voltage reading needs to be just that too. Taken with no load having been on the batteries for an hour or two or three.

 

 

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Or, you could just accept that you got up this morning with plenty left in your batteries. You therefore have sufficient capacity for your usual daily usage so you haven't taken them too low as to damage them and you know it's best to recharge them fully now. You're ahead of the game!

 

The only thing I'd say is that you may be able to get more charge in. The  voltage looks a bit low to me and I think the tall amps would have come down more if you'd kept cruising. Experience will show you just what violets and amps is normal for your set up.

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6 minutes ago, Mike the Boilerman said:

 

I don't think your reading tells you anything useful then. 

 

The tail current needs to be down to 1 or 2% of actual capacity and also noted when charging at 14.4v, not 14.1v. 

 

The resting voltage reading needs to be just that too. Taken with no load having been on the batteries for an hour or two or three.

 

 

ok, makes sense, I'm not sure about turning fridge and freezer off for three hours is feasible though, the beer might get warm :)

 

6 minutes ago, Sea Dog said:

Or, you could just accept that you got up this morning with plenty left in your batteries. You therefore have sufficient capacity for your usual daily usage so you haven't taken them too low as to damage them and you know it's best to recharge them fully now. You're ahead of the game!

 

The only thing I'd say is that you may be able to get more charge in. The  voltage looks a bit low to me and I think the tall amps would have come down more if you'd kept cruising. Experience will show you just what violets and amps is normal for your set up.

This is kind off where I'm at, will think about replacing the bank when they can't cope overnight or when engine running gets excessive. Just want to know if my basic thought process is along the right lines.

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41 minutes ago, waterdog said:

I'm not sure about turning fridge and freezer off for three hours is feasible though, the beer might get warm :)

Sure it is, the freezer will keep its temp. If you are worried turn it to max for a couple of hours before switching off, or use a freezer pack in the fridge. 

 

Assume you have flooded lead acid batteries. 

48 minutes ago, Sea Dog said:

Experience will show you just what violets and amps is normal for your set up

Good advice seadog,though not sure what violets have got to do with it. 

Edited by rusty69
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17 minutes ago, rusty69 said:

Good advice seadog,though not sure what violets have got to do with it. 

Yeah, it's a shame they no longer feature as SI units, but they really ought to as they smell so much nicer than Volts (according to my phone's smell checker anyway)! ;)

 

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If your battery bank does indeed have a capacity of 520Ah, then 5.3A tail current is 1% of capacity and represents more or less fully charged. But if the battery capacity is down to 208Ah, then you should be aiming for a tail current of around 2A.  That would suggest that your batteries weren't fully charged, and that the capacity is down (but not necessarily to 208Ah).

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8 minutes ago, David Mack said:

If your battery bank does indeed have a capacity of 520Ah, then 5.3A tail current is 1% of capacity and represents more or less fully charged. But if the battery capacity is down to 208Ah, then you should be aiming for a tail current of around 2A.  That would suggest that your batteries weren't fully charged, and that the capacity is down (but not necessarily to 208Ah).

Good point, we're just about to set off so will give it a good run today and see how low the charge rate goes.

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13 minutes ago, waterdog said:

Good point, we're just about to set off so will give it a good run today and see how low the charge rate goes.

If the charge voltage is only reaching a maximum of 14.1v with virtually no load on the alternator, this is not enough to fully charge modern calcium-rich leisure batteries. If the boat has spent a lot of time on shore power, probably the charge voltage was much higher but if you intend to break free from the marina and spend a lot of time "off grid", new batteries are going to get sulphated rapidly. Before getting new batteries (which will be rapidly destroyed) I would find out why the charge voltage is so low.

 

Firstly, I would measure the voltage actually coming out of the alternator using a digital voltmeter (be careful of moving belts and pulleys!). If the alternator voltage is 14.1v when the batteries are well charged / current down to a few amps, you will need to replace the alternator regulator with something with a set voltage of at least 14.4v, preferably 14.6v.

 

The other possibility is that the alternator is producing a higher voltage but there is a diode split charge system that is dropping 0.6v or so, but looking at the voltage that seems unlikely (it would be lower than 14.1v).

 

Also just to mention that when you are measuring the voltage to assess SoC, you need to have zero current drain and let it rest in that state for quite a while.

 

Otherwise, your thought processes / calculation is correct.

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30 minutes ago, David Mack said:

If your battery bank does indeed have a capacity of 520Ah, then 5.3A tail current is 1% of capacity and represents more or less fully charged.

 

Not really, as the charge voltage had only risen to 14.1.

 

The jury seems to be out on whether this ought to be 14.4v or 14.8v

 

 

 

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2 minutes ago, Mike the Boilerman said:

 

Not really, as the charge voltage had only risen to 14.1.

 

The jury seems to be out on whether this ought to be 14.4v or 14.8v

I don’t think it much matters if it’s 14.4V, 14.6V, or 14.8V. 14.8V would probably require you to keep a close eye on water levels. 
 

I think that OP’s biggest problem was not measuring the batteries properly at rest. The voltage could easily have been depressed by 0.1V or more by the inverter load. 
 

As others have said, check out why the alternator is only supplying 14.1V to the batteries but in the mean time just enjoy boating as there’s plenty of power for his usage whatever the actual capacity might be. 

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7 minutes ago, rusty69 said:

Just to add.I am sure it is obvious but the at rest voltage includes no input from solar charging (if you have any):unsure:

Indeed. The phrase ‘at rest’ has a clue in the name...

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39 minutes ago, WotEver said:

Indeed. The phrase ‘at rest’ has a clue in the name...

Easy to forget though, particularly glancing at the voltmeter at 0745 on a dull Winters day.

 

ETA.Looks like OP may have 1.2KW of solar, so unless disconnected, this may have had some influence at 0745 this morning. Was it still dark?I dunno I was asleep.

 

 

I made the mistake of installing our voltmeter next to a digital clock.It was very confusing at elevenses!

 
Edited by rusty69
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ok, I kept a close eye on the figures whilst cruising today (about 4.5 hours)and the voltage did get up to 14.4, 

 

started the engine again at 5.30 to give it another couple of hours charging and again saw 14.4v on the mastervolt display. however when I went to check just now the volts had dropped to 14.2 and 8A current.

 

I've turned the travelpower on to run the charger and the voltage is up to 14.6v with the charger going into absorption mode within 5 minutes. Will leave it for another hour and see what the amps drop to.

 

Is all this pointing to a potential alternator / adverc issue? I will get in engine bay tomorrow with a meter and check the alternator output.

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2 minutes ago, waterdog said:

s all this pointing to a potential alternator / adverc issue? I will get in engine bay tomorrow with a meter and check the alternator output.

Start the engine ay 08:00 tomorrow and run it until 21:00 and see if you can get the battery(s) fully charged, it looks to me as if you have not yet managed to get them properly charged.

Then turn off everything and connect up a known load (old-style 55w car headlight bulb is good) run the load until the battery drops to 12.1 volts disconnect the load and battery should recover to 12.2 volts. How long did it take to get from 'full' to 12.2 volts ?

What was the 'known load' wattage ?

 

Keeping doing 'a couple of hours' is not achieving anything as you are still using 'leccy in the interim so we don' know what you are actually getting to.

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8 hours ago, rusty69 said:

Easy to forget though, particularly glancing at the voltmeter at 0745 on a dull Winters day.

 

ETA.Looks like OP may have 1.2KW of solar, so unless disconnected, this may have had some influence at 0745 this morning. Was it still dark?I dunno I was asleep.

 

 

I made the mistake of installing our voltmeter next to a digital clock.It was very confusing at elevenses!

 

yes I do have 1.2kw solar but it was doing nowt at 0745 this morning, in fact it did the best part of bu**er all, all day :0

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1 minute ago, Alan de Enfield said:

Start the engine ay 08:00 tomorrow and run it until 21:00 and see if you can get the battery(s) fully charged, it looks to me as if you have not yet managed to get them properly charged.

Then turn off everything and connect up a known load (old-style 55w car headlight bulb is good) run the load until the battery drops to 12.1 volts disconnect the load and battery should recover to 12.2 volts. How long did it take to get from 'full' to 12.2 volts ?

What was the 'known load' wattage ?

 

Keeping doing 'a couple of hours' is not achieving anything as you are still using 'leccy in the interim so we don' know what you are actually getting to.

Thanks Alan,

 

We've been on shore power the last 2 months so the batts were fully charged 24/7 with the charger sitting on float the majority of the time.

We will be back in the marina tomorrow so will run the suggested checks then. 

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30 minutes ago, waterdog said:

yes I do have 1.2kw solar but it was doing nowt at 0745 this morning, in fact it did the best part of bu**er all, all day :0

Not surprising - even f you had 12Gw of solar panels you get now unseful power in this country, at this time of year...

It's as if you had a 200HP car - whic doesn't produce that amouf of OOmph =- if you don't start it...

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