Batteries: What's going on here?

[Jim Batty]

We have a 460Ah sealed battery bank about 8 months old.

 

Our electric audit for a typical day's use is 26Ah (That is: 12v fridge = 20Ah/day; 4 LED lights on for 6hrs = 4Ah/day; two pumps with sporadic use = 2Ah/day tops).

 

Occasionally, like two days ago, we hook up to an electric point at a marina and fully charge the batteries through an inverter charger. A number of hours after shutting the engine down (say 4 - 8hrs later) my multimeter usually shows about 12.75v - 12.85v. Nice. Fully charged. (That's what they've shown from brand new fully charged by this multimeter method).

 

24 hours later, though, my multimeter shows about 12.10v - 12.20v (indicating the batteries are down to 50% charge), which seems way down considering only 26Ah has been used out of the 460Ah available.

 

What's going on here? Or am I missing something?

[mrsmelly]

We have a 460Ah sealed battery bank about 8 months old.

 

Our electric audit for a typical day's use is 26Ah (That is: 12v fridge = 20Ah/day; 4 LED lights on for 6hrs = 4Ah/day; two pumps with sporadic use = 2Ah/day tops).

 

Occasionally, like two days ago, we hook up to an electric point at a marina and fully charge the batteries through an inverter charger. A number of hours after shutting the engine down (say 4 - 8hrs later) my multimeter usually shows about 12.75v - 12.85v. Nice. Fully charged. (That's what they've shown from brand new fully charged by this multimeter method).

 

24 hours later, though, my multimeter shows about 12.10v - 12.20v (indicating the batteries are down to 50% charge), which seems way down considering only 26Ah has been used out of the 460Ah available.

 

What's going on here? Or am I missing something?

 

Is it switched on..............

[Jim Batty]

Is it switched on..............

Is what switched on?

[Bob18]

You've only "surface charged" the batteries, or they are already dead - let's hope the former...

 

Why? Each charge cycle is only replacing part of the use not all of it.

 

What voltage were they at before you started the charge cycle? - somewhere around 12.10v I'd guess.

How long are you running the engine for?

What is the charge voltage while the engine is running?

How long were you on the shore line for?

What alternator do you have?

What charger do you have?

Are you charging via a split charger of some sort? (If so what make and type?)

Are all the connections between the alternator, the battery and the inverter/charger in good order and with correctly sized cables?

 

The batteries may be sulphonated, in which case they may recover if given a "de-sulphonation" charge - which is at a higher voltage than a normal charge, and needs to be watched carefully to make sure you don't boil them - how to do this depends on your inverter/charger, some will do it "automagically", others need to be told to do it - I guess in your situation it will be better to do it under manual control.

[dor]

Your battery's symptoms are typical of sulphation, resulting from not getting fully recharged on a regular basis. You might have a 90A alternator, but it will still need to be run for anything between 10 & 20 hours to get the batteries back from say half charged. The reduction in capacity due to sulphation is progressive.

 

I have recovered batteries which were in a similare state to yours to about 70% of their new capacity by giving them several days of float charge, followed by about 8 hours at 15.5 - 16V. The capcity is still limited, but the saving grace is the solar panel which as we only use the boat 3 or 4 days a week, generally gets the batteries back up to full charge over three days.

[WotEver]

And some folk say "What's the point of a SmartGauge?"

 

Tony

[ditchcrawler]

We have a 460Ah sealed battery bank about 8 months old.

 

Our electric audit for a typical day's use is 26Ah (That is: 12v fridge = 20Ah/day; 4 LED lights on for 6hrs = 4Ah/day; two pumps with sporadic use = 2Ah/day tops).

 

Occasionally, like two days ago, we hook up to an electric point at a marina and fully charge the batteries through an inverter charger. A number of hours after shutting the engine down (say 4 - 8hrs later) my multimeter usually shows about 12.75v - 12.85v. Nice. Fully charged. (That's what they've shown from brand new fully charged by this multimeter method).

 

24 hours later, though, my multimeter shows about 12.10v - 12.20v (indicating the batteries are down to 50% charge), which seems way down considering only 26Ah has been used out of the 460Ah available.

 

What's going on here? Or am I missing something?

Is that your measured consumption or estimated, I would expect the fridge to be higher than that, maybe twice as high.

[Ark Right]

I would like to know the make of your fridge you have if it only consumes 20Ah per day. I would suggest a fridge is at least 3.6Amps per hour, on for 50% of the time. Over double your audit value.

[alan_fincher]

I would like to know the make of your fridge you have if it only consumes 20Ah per day. I would suggest a fridge is at least 3.6Amps per hour, on for 50% of the time. Over double your audit value.

It's of the order of what I'd say Shoreline claim for their smaller models, even if their advertising doesn't really seem to fully understand the concept of amp hours.....

 

Avg Amps per Hour (12V): 0.91

 

Shoreline linky

[dmr]

Hello

 

I find exactly the same, my batteries are almost always at 12.2 to 12.3volts.

But, measuring voltage only gives a good measure of capacity if there is nothing switched on, and nothing has been switched on for quite some time.

So when you measure the voltage 24 hours later do you have anything turned on???

Turn off everything that can be turned off, go for a walk with the dog, or a few pints, or whatever, and a couple of hours later measure the voltage again. I bet it will be about 12.5volts.

(if you have solar panels then you need to do this test when its dark)

After this experiment do remember to turn the fridge back on or there will be big trouble.

 

I suspect that Smartguage actually works by watching how the voltage goes down and back up as various things are turned on and off, which is much safer than turning off the fridge!!!!

 

.......Dave

[Jim Batty]

You've only "surface charged" the batteries, or they are already dead - let's hope the former...

 

Why? Each charge cycle is only replacing part of the use not all of it.

 

What voltage were they at before you started the charge cycle? - somewhere around 12.10v I'd guess.

How long are you running the engine for?

What is the charge voltage while the engine is running?

How long were you on the shore line for?

What alternator do you have?

What charger do you have?

Are you charging via a split charger of some sort? (If so what make and type?)

Are all the connections between the alternator, the battery and the inverter/charger in good order and with correctly sized cables?

 

The batteries may be sulphonated, in which case they may recover if given a "de-sulphonation" charge - which is at a higher voltage than a normal charge, and needs to be watched carefully to make sure you don't boil them - how to do this depends on your inverter/charger, some will do it "automagically", others need to be told to do it - I guess in your situation it will be better to do it under manual control.

 

Thanks. Lots of good questions here, which I will think about for a bit. Let me tackle some of the other thoughts here.

[Jim Batty]

Your battery's symptoms are typical of sulphation, resulting from not getting fully recharged on a regular basis. You might have a 90A alternator, but it will still need to be run for anything between 10 & 20 hours to get the batteries back from say half charged. The reduction in capacity due to sulphation is progressive.

 

I have recovered batteries which were in a similare state to yours to about 70% of their new capacity by giving them several days of float charge, followed by about 8 hours at 15.5 - 16V. The capcity is still limited, but the saving grace is the solar panel which as we only use the boat 3 or 4 days a week, generally gets the batteries back up to full charge over three days.

 

Our batteries don't get fully recharged all the time. We continually cruise, cruising one, two or three days every week or two, with engine-runnings every three days when not moving. That's why we try to pull into a marina every month or so and plug in to the 240v supply overnight to recharge the batteries. This is done via our inverter/charger. As I said, after 12 - 16hrs of this recharging, my batteries read 12.75v - 12.85v (after a settling down time). Which I take to be fully charged as that is what they read when I first got them. The inverter/charger is set specifically to charge our sealed batteries and their total Ah capacity, so I assume it is doing its job properly.

 

I also understand that we'd have to cruise 16 hours or something mad like that to near fully charge the battery bank via the (70A) alternator.

 

Are you saying that recharging via shore power for 12 - 16 hours and giving the above reading (12.75v to 12.85v) is not enough to fully recharge them? That it is only 'superficially' recharging them? When you say 'float charge', is this the same as plugging in to shore power using our charger ... and you are suggesting we should do this for three days?

 

I would like to know the make of your fridge you have if it only consumes 20Ah per day. I would suggest a fridge is at least 3.6Amps per hour, on for 50% of the time. Over double your audit value.

 

Hi Ark, Alan

 

Our fridge is a new, small Shoreline specced with an average load of 0.8Amps. This is a 24hr figure supplied by Shoreline. Multiply this by 24hrs = 19.2Ah/day. Given that it has been quite cool at night where the fridge is located, and that it is set very low (set at <1), this should be about right. Even if it were double this, surely we shouldn't be losing battery power at the rate outlined in my OP. Or, again, am I missing something?

[WotEver]

Are you saying that recharging via shore power for 12 - 16 hours and giving the above reading (12.75v to 12.85v) is not enough to fully recharge them?

Quite possibly. What was the charging current at the end of the 16 hours?

 

The voltage can only be relied upon after a number of hours off charge - and in your case it's showing that the batteries weren't fully charged.

 

That it is only 'superficially' recharging them?

It's called a 'surface charge'. So called because the charge is initially only sitting on the surface of the plates. Once the batteries have been left for a while for the charge to even itself out throughout the plate the charge then appears lower (because it is).

 

When you say 'float charge', is this the same as plugging in to shore power using our charger ... and you are suggesting we should do this for three days?

Yes, and yes. When I first got a 'proper' charger and plugged our boat into shore power it took nearly a week for the charge current to drop enough to show that the domestic battery was fully charged.

 

Tony

Edited November 15, 2011 by WotEver

[Jim Batty]

Hello

 

I find exactly the same, my batteries are almost always at 12.2 to 12.3volts.

But, measuring voltage only gives a good measure of capacity if there is nothing switched on, and nothing has been switched on for quite some time.

So when you measure the voltage 24 hours later do you have anything turned on???

Turn off everything that can be turned off, go for a walk with the dog, or a few pints, or whatever, and a couple of hours later measure the voltage again. I bet it will be about 12.5volts.

(if you have solar panels then you need to do this test when its dark)

After this experiment do remember to turn the fridge back on or there will be big trouble.

 

I suspect that Smartguage actually works by watching how the voltage goes down and back up as various things are turned on and off, which is much safer than turning off the fridge!!!!

 

.......Dave

 

Ah, this is interesting. No, I don't turn the fridge (or pumps) off before measuring. So, I need to make sure the batteries are completely and utterly inactive for this period of time.

[WotEver]

Ah, this is interesting. No, I don't turn the fridge (or pumps) off before measuring. So, I need to make sure the batteries are completely and utterly inactive for this period of time.

Yes, but a couple of hours should do it, particularly if you firstly switch a load on for a minute or so (like the tunnel lamp) before resting them.

 

Tony

[Bob18]

The number of "engine runs" is almost irrelevant, its how long you run the engine for, and what voltage is being applied to the battery during that time.

 

A 12-16 hour recharge, with a multi-stage charger will do some good, but it will not "cure" the sulphonation, for which you need a significantly higher voltage than the normal 14.5ish you get off an alternator at full chat.

 

Float charging is a very long term activity, many charging systems don't go into float until at least 12 hours of bulk and saturation charging have taken place. You might find, and I understand that this may not be possible to achieve until this year's big freeze with you tied up in a "nice warm marina", that by charging via your inverter continuously for more than 24hours will get the batteries back to a better state of health than they are in just now.

[WotEver]

.. that by charging via your inverter continuously...

I know you mean 'charger' and you know you meant 'charger' but I thought I'd point it out here just in case anyone gets confused

 

http://www.batteryfaq.org says the following:

 

A surface charge can be eliminated by one of the following methods after recharging a lead-acid battery:

 

Allow the battery to sit (or rest) without discharge or charge for between two and eight hours at room temperature, if possible, to allow for the surface charge to dissipate. (Recommended method.)

 

For deep cycle batteries, apply a load that is 33% of the amp-hour capacity for five minutes and wait at least ten minutes.

 

Tony

[LoneWolf]

I know you mean 'charger' and you know you meant 'charger' but I thought I'd point it out here just in case anyone gets confused

 

http://www.batteryfaq.org says the following:

 

A surface charge can be eliminated by one of the following methods after recharging a lead-acid battery:

 

Allow the battery to sit (or rest) without discharge or charge for between two and eight hours at room temperature, if possible, to allow for the surface charge to dissipate. (Recommended method.)

 

For deep cycle batteries, apply a load that is 33% of the amp-hour capacity for five minutes and wait at least ten minutes.

 

Tony

 

hey even i knew he meant charger

 

Sadly, i dont understand how to apply the last bit in practice. Do you mean 33% of the capacity of the bank? Or of the capacity of each battery.

[WotEver]

Sadly, i dont understand how to apply the last bit in practice. Do you mean 33% of the capacity of the bank? Or of the capacity of each battery.

The capacity of the bank.

 

So if you had a 300Ah bank (see, I'm making the maths easy) then you'd apply a 100A load for 5 minutes, wait 10 minutes (or more) and check the voltage. For a 100A load you could draw 10A from the inverter.

 

Tony

[Pretty Funked Up]

I'd agree the power audit is probably quite alot off. so double it to be on the safe side.

And you havent been charging often enough. three days without any power going in is a bit harsh on 'em. Time is a major factor in the quantity of damage. Get some charge into the batteries every day, solar panels are great for this (in fact they should just be called battery nannies not solar panels).

 

Remember the quicker you get the batteries back up to 12.8v after using them the longer they will last.

[LoneWolf]

The capacity of the bank.

 

So if you had a 300Ah bank (see, I'm making the maths easy) then you'd apply a 100A load for 5 minutes, wait 10 minutes (or more) and check the voltage. For a 100A load you could draw 10A from the inverter.

 

Tony

 

And if i had 220Ah and no inverta I could get 72amps by turning on the fridge & charging both computers? I will do some sums. thanks

[dmr]

I would not worry too much about getting rid of surface charge.

If you can monitor current (amps) during charging then this should tell you when the batteries are fully charged,....the charge current will fall to a very low value (maybe 4 or 5 amps). The more important issue is not too assume that the batteries are half empty just because you measure 12.2volts. This figure might rise quite a bit if you turn everything off for an hour or so.

 

On the subject of Salar Panels....I can not imagine getting our batteries fully charged using Solar, the best they do is slightly reduce the rate at which they discharge, but we are liveaboards. Unless you have a huge solar array they will only ever charge the batteries if you leave the boat with everything turned off.

 

.........Dave

[Bob18]

Charging current is only a guide, useful during the early stages of charging, but when you get into the long tail of float charge it is of no use at all, this is particularly true when using a "modern" multi-stage charger which do all sorts of clever things like current limitation at high voltage to break suplphonation - during which time the apparent charge current may only be a few amps, but the voltage is being forced higher.

Battery voltage tells you a lot more about the state of the battery than charger current. You need to know what the voltage was just after you stopped charging, The a few minutes later, then an hour or so later (with no loads on)

 

Unless your batteries are one of the "strange" low voltage types then 12.2v is pretty close to 50% discharge, and getting into the realms of this battery is in serious need of charging.

 

 

Solar panels need to be of adequate size, expecting a 2w "window panel" to maintain a 400Ahr battery is, how shall we say it, er - "stoopid"? You need a panel and controller combination that is going to supply enough amps at times of poor light availability, a panel could be down to bellow 50% of quoted output for less than 6 hours a day on a typical gloomy mid winter's day. Do your sums on that sort of figure and you will be pleased in summer, and not so worried in winter.

 

And don't forget that lead-acid batteries self discharge, so you might leave them fully charged, but come back a few weeks later and they will be a log way down the discharge curve - how fast depends on the type of battery, but even then there are quite marked differences between manufacturers so its a case of reading the literature to find out what the self discharge rate is for a particular battery (under ideal conditions of course)

[alan_fincher]

And if i had 220Ah and no inverta I could get 72amps by turning on the fridge & charging both computers? I will do some sums. thanks

No,

 

Unless your fridge or chargers are very very unusual, you will draw more like 7 amps than 72 amps, I'd say.

[LoneWolf]

No,

 

Unless your fridge or chargers are very very unusual, you will draw more like 7 amps than 72 amps, I'd say.

 

i think i would have to turn everything on then