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Leisure battery charge level


Jak
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Hi. I'm new and have recently bought a 1980 47' traditional stern boat. A few things to do, but all working well enough to get out and cruise.

 

I've a very basic 12v system running from a pair of leisure batteries. From reading a couple of posts I'd like to know what charge level I've got (80%, 50%, etc.). Can someone recommend a peice of kit I can buy that would do this?

 

Thanks in advance for any help!

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Anything that will either :

 

1) Measure your charging tail-current (ie ammeter), or

2) Measure the specific gravity of your battery acid (ie a Hydrometer)

 

Both simple and foolproof and do not rely on any complicated maths or interpretation.

 

Edit to add :

 

A voltmeter will give you an approximation, but can only be used after at least 1 hour with nothing 'going in' and 'nothing coming out' of the batteries.

 

post-11859-0-15179200-1477755068_thumb.jpg

 

 

Edited by Alan de Enfield
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Anything that will either :

 

1) Measure your charging tail-current (ie ammeter), or

2) Measure the specific gravity of your battery acid (ie a Hydrometer)

 

Both simple and foolproof and do not rely on any complicated maths or interpretation.

 

Edit to add :

 

A voltmeter will give you an approximation, but can only be used after at least 1 hour with nothing 'going in' and 'nothing coming out' of the batteries.

 

attachicon.gifbattery-state-of-charge.jpg

 

 

The only problem with the SG method is do you want to dip your batteries every day?

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The only problem with the SG method is do you want to dip your batteries every day?

 

Admittedly, not everyone would, but when you are checking your water, header tank, oil levels, belt tension and condition, tightening the greaser and doing an engine 'visual', its not a huge problem to unscrew the battery caps (on the assumption that you have non-sealed batteries and they are located in a 'sensible' place).

 

I know of people who never look at or check the engine from one year to the next, have never done an oil change and just 'mend it when it breaks'.

I prefer to be ahead of the game.

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Thanks for the tips. They are sealed batteries. The voltmeter and table makes sense. But you are crediting me with too much understanding of electrics. How will an ammeter tell me % charge of the leisure batteries?

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Admittedly, not everyone would, but when you are checking your water, header tank, oil levels, belt tension and condition, tightening the greaser and doing an engine 'visual', its not a huge problem to unscrew the battery caps (on the assumption that you have non-sealed batteries and they are located in a 'sensible' place).

 

I know of people who never look at or check the engine from one year to the next, have never done an oil change and just 'mend it when it breaks'.

I prefer to be ahead of the game.

Agree but it wont tell you how well charged they are each day, I top mine up every 250 hours when I change the oil and filter, but I like to know that I an charging them between those times.

Thanks for the tips. They are sealed batteries. The voltmeter and table makes sense. But you are crediting me with too much understanding of electrics. How will an ammeter tell me % charge of the leisure batteries?

I would suggest you lash out and buy a Smartgauge. Most people say its the only meter that gives a reliable indication of percentage charge reading straight from the meter.

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Given the OPs comments, a Smartguage is probably the sensible answer. Easy to fit, and as simple as a fuel guage.

 

With a bit more knowledge, which will be gained with time, the addition of a NASA BM1 or BM2, will add to instantaneous knowledge of how things are working in the battery area.

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A smartguage would be good but if money is tight a cheap volt meter off Ebay will do the job. With the latter you need to make allowances for recently charged batteries and any loads on the batteries but it's not rocket science; easily learned.

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There is only one Smartguage.

 

Example, not a recommendation of seller or anything, link:

 

http://www.cactusnav.com/merlin-smartguage-battery-monitor-p-11874.html

 

Once you have it please read the instructions and manual carefully.

 

It does have one foible (so do all the other meters available) that it is possibly inaccurate when the battery is being charged but accurate when battery is at rest or being discharged.

 

It is the simplest to connect and the simplest to read just a little interpretation and understanding, as with all meters, is required..

 

This link is to the web site of the inventor/designer and will answer all your questions on batteries and charging.

 

You could add an ammeter to actually know when your batteries are 'fully' charged but for now the Smartgauge will be enough..

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As has been suggested, SmartGuage then NASA BM1 or BM2 or other suitable shunted monitor at a later date. I did it in this order and I think I've just about saved myself from ruining my first set of batteries I put in since purchasing the boat.

Edited by discusmaximus
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A smartguage would be good but if money is tight a cheap volt meter off Ebay will do the job. With the latter you need to make allowances for recently charged batteries and any loads on the batteries but it's not rocket science; easily learned.

 

 

Frankly, no it won't.

 

There are so many ways in which one has to do mental gymnastics to interpret the results (and usually get it wrong) that a SmartGauge is the only way to be reasonably sure of the state of charge at any given time. The SmartGauge is actually just doing the gymnastics for you and displaying it as a nice clear number on an LED display.

 

An ammeter such as the BM2, NASA etc will tell the OP when his batteries are fully charged by observing the tail current trajectory, but that isn't what he asked.

 

So my recommendation is a SmartGauge. There really isn't anything else that does the job properly.

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As the link above, I bought mine from Cactus Navigation - cheapest I could find.

 

There was a problem with it, so they asked me to return it and it, (or a replacement), came back and has worked fine since.

 

http://www.cactusnav.com/merlin-smartguage-battery-monitor-p-11874.html

I too bought both my gadgets from them, can't fault them on price and efficiency.

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So my recommendation is a SmartGauge. There really isn't anything else that does the job properly.

Plus, the Sinclair Cambridge display gives a real 1970s vibe to your boat such that hardly anyone will think your 'Jesus Christ Superstar' hair and beard or your loon pants look out of place! Bonus! :D

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Must be a very expensive multimeter if it can accurately show state of charge? If so can we have the make model and most importantly the cost?

 

The above is a bit tongue in cheek but hits the problem with any of the type of meter that uses Amphgour counting to allegedly show a state of charge or time left before needing to charge.

 

Such meters usually have 5 display modes. Amps, Volts, Amphours into the battery (but note this - NOT Amphours actually converted into chemical energy), Amphours out of the battery, percentage of charge, and finally maybe time left before charging. In the case of the first two (amps & Volts) they are accurate so would agree with your multi-meter but just because they are accurate does not mean the other are although pure Amphours in and Amphours out will be but they are somewhat problematical, as for the percentage of charge and time left they are often a work of fiction.

 

The percentage of the amphours into a battery that is converted to stored chemical energy alters hour to hour and day to day as the temperature, charging voltage, and battery condition varies but it will NEVER be 100%. It will also vary from battery type/design to battery type. Just to substantiate this feel some batteries that have been on charge for a while, they will be warm or hot. Where did this heat come from? The answer is the charging current so from that you can deduce that some charge went to make heat, not convert chemicals. Then the fact that the actual capacity of the battery reduces over time means that the meter can not know how much electricity is actually stored in the battery - even if it is 100% charged. Within days or at the most a few weeks it WILL be less that the number on the label.

 

The upshot of the above paragraph is that any display that results from Amphour counting will over record the amount of charge put into the battery and once that is wrong the percentage of charge and time left must also be wrong.

 

The makers try to compensate for this by putting "Fiddle factors" into the algorithms the gauges use to work out the percentage charge and time left.

 

If you have studies the topics here on the subject of charging you will know that when the charging current drops to a very low level - often quoted as 1% of bank capacity - the battery can be CONSIDERED as fully charged. It probably won't be but it will be near enough for practical use. The meter's electronics knows this and at that point resets itself to 100% charged. All that sounds fine and dandy but the meters are not usually set at 1% by the factory. Probably more like 2 %to 3% so they resynchronise early. This causes them to overstate the degree of charge and that in turn persuades many to destroy their batteries by constant and ongoing undercharging. The problems get worse if users do not charge until the current drops to such a low percentage. This is why solar charging has such advantages, it provides many hours at a low charge rate to get the final few percentage back in.

 

If you really understand the limitations in such meters, reset them to synchronise at a very low percentage (known as tail current) AND very regularly charge for long enough to cause them to resynchronise then they will be fairly accurate on all scales but if you do not all you can rely upon is the amps and volts.

 

The basic rule for most boaters with this type of meter is to only use the amps scale while charging and keep going at least once a week until the charge drops to 1% of bank capacity or less, then manually resynchronise the meter. Then you can note the Amphours out and percentage of charge and calculate the current capacity of the bank. e.g. 50Ah out that takes it to 75% of charge tells you the battery bank capacity is 200Ah because 50Ah is 1/4 of the bank capacity.

 

I think it has taken me over half an hour to type that lot and it has all been explained countless times before so we normally just advise that such meters are not accurate and will cause you to destroy your batteries unless you really understand them.

 

Edited by Tony Brooks
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The Smartgauge is probably the only fit and forget device that indicates current SOC of the batteries with any accuracy, not that it is perfect all the time, simply every other indicator dial is simply more flawed.

 

What charging your batteries need is determined by the use that you make of them. An LED light in each cabin would be a small load but a fridge, freezer and auto washer running off an inverter would be a very large load. Your charge cycle must put back the energy that you have used plus some to keep the batteries happy.

 

Despite the most careful use batteries are consumables, if well treated they will last for two or more years, if iltreated batteries can be scrap in two weeks.

 

Protect your starter battery from domestic discharge so that you always have a means to start the engine as one way to charge the batteries.

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Must be a very expensive multimeter if it can accurately show state of charge? If so can we have the make model and most importantly the cost?

 

The above is a bit tongue in cheek but hits the problem with any of the type of meter that uses Amphgour counting to allegedly show a state of charge or time left before needing to charge.

 

Such meters usually have 5 display modes. Amps, Volts, Amphours into the battery (but note this - NOT Amphours actually converted into chemical energy), Amphours out of the battery, percentage of charge, and finally maybe time left before charging. In the case of the first two (amps & Volts) they are accurate so would agree with your multi-meter but just because they are accurate does not mean the other are although pure Amphours in and Amphours out will be but they are somewhat problematical, as for the percentage of charge and time left they are often a work of fiction.

 

The percentage of the amphours into a battery that is converted to stored chemical energy alters hour to hour and day to day as the temperature, charging voltage, and battery condition varies but it will NEVER be 100%. It will also vary from battery type/design to battery type. Just to substantiate this feel some batteries that have been on charge for a while, they will be warm or hot. Where did this heat come from? The answer is the charging current so from that you can deduce that some charge went to make heat, not convert chemicals. Then the fact that the actual capacity of the battery reduces over time means that the meter can not know how much electricity is actually stored in the battery - even if it is 100% charged. Within days or at the most a few weeks it WILL be less that the number on the label.

 

The upshot of the above paragraph is that any display that results from Amphour counting will over record the amount of charge put into the battery and once that is wrong the percentage of charge and time left must also be wrong.

 

The makers try to compensate for this by putting "Fiddle factors" into the algorithms the gauges use to work out the percentage charge and time left.

 

If you have studies the topics here on the subject of charging you will know that when the charging current drops to a very low level - often quoted as 1% of bank capacity - the battery can be CONSIDERED as fully charged. It probably won't be but it will be near enough for practical use. The meter's electronics knows this and at that point resets itself to 100% charged. All that sounds fine and dandy but the meters are not usually set at 1% by the factory. Probably more like 2 %to 3% so they resynchronise early. This causes them to overstate the degree of charge and that in turn persuades many to destroy their batteries by constant and ongoing undercharging. The problems get worse if users do not charge until the current drops to such a low percentage. This is why solar charging has such advantages, it provides many hours at a low charge rate to get the final few percentage back in.

 

If you really understand the limitations in such meters, reset them to synchronise at a very low percentage (known as tail current) AND very regularly charge for long enough to cause them to resynchronise then they will be fairly accurate on all scales but if you do not all you can rely upon is the amps and volts.

 

The basic rule for most boaters with this type of meter is to only use the amps scale while charging and keep going at least once a week until the charge drops to 1% of bank capacity or less, then manually resynchronise the meter. Then you can note the Amphours out and percentage of charge and calculate the current capacity of the bank. e.g. 50Ah out that takes it to 75% of charge tells you the battery bank capacity is 200Ah because 50Ah is 1/4 of the bank capacity.

 

I think it has taken me over half an hour to type that lot and it has all been explained countless times before so we normally just advise that such meters are not accurate and will cause you to destroy your batteries unless you really understand them.

 

But surely the 50Ah is all we can be sure off. Lets not even go into whether it was drawn over 1 hour or 10. The 75% as you previously said is often a work of fiction so you still cannot accurately calculate the battery bank capacity. Or am I missing something? Please do not misunderstand me, I am very interested in this as my MICC regularly under counts as opposed to what you seem to be suggesting is the usual problem of over counting.

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Anything that will either :

 

1) Measure your charging tail-current (ie ammeter), or

2) Measure the specific gravity of your battery acid (ie a Hydrometer)

 

 

A voltmeter will give you an approximation, but can only be used after at least 1 hour with nothing 'going in' and 'nothing coming out' of the batteries.

 

attachicon.gifbattery-state-of-charge.jpg

 

 

 

 

Must be a very expensive multimeter if it can accurately show state of charge? If so can we have the make model and most importantly the cost?

 

 

Perhaps I can just emphasise that measuring a battery's state of charge is one of the most difficult things boaters have to do and why it is so important to get it right.

 

There are only two ways that give a reasonable chance of accurate figures and they both rely on having accurate information from the manufacturer in the first place, the full charge specific gravity (SG) and the full charge rested voltage. Without those everything is guess work.

 

To take a full charge rested voltage takes of the order of 24 hours with the battery isolated from any discharge or charge. Well that does not help boaters turning all the electrics off for a day to know what the state of charge is.

 

To take SG readings needs a little bit of skill and an accurate hydrometer and thermometer and for those with wet (non-sealed) batteries this is a reasonably quick accurate way. But do keep a record of the readings.

 

So where does that leave those with sealed batteries of the various types. Well for one thing do not rely on the green magic eye prevalent on so many batteries today, it just tells you there is a charge in the battery, that could be 100% SoC or 10% SoC.

 

The only reliable way that I know is to measure the tail current using an accurate ammeter. That is the current going to the battery when the charger is in absorption mode. If it has gone on to float mode the reading will be a voltage and current that charger has set. Switch the charger off, count ten and switch it back on and it should after a couple of minutes settle on Absorption mode. Then you are looking for a current (amps) that in my opinion needs to be less than 1/2% of the battery capacity and does not reduce for the next 30 minutes, if it does wait another 30 minutes and check again, when it is stable that is as near as you are going to get to 100% charged.

 

Why all this fuss about fully charging a battery each time. As part of the discharge process of a battery lead and sulphuric acid combine to form sulphate, all part of the process of giving power from the battery. When the battery is charged all of that sulphate has to be turned back to lead and sulphuric acid and if 100% of it is not there is sulphate is left on the plates, the battery is not at 100% charge and cannot give 100% of its power. That sulphate goes hard over time, not that long, blocks the plates so they are not able to react with the sulphuric acid and produce the power you need and gradually the capacity of the battery drops. Once sulphate has gone hard it is not removable without breaking the battery apart. Thus you will hear people taking about sulphated batteries, all it means is that the battery has not been fully charge after each use and the sulphate has gone hard and blocked the plates. I have seen batteries which when opened the plates were in near mint condition with a layer of sulphate stopping the battery working, had they been properly charged instead of lasting a few months they would have lasted several years.

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But surely the 50Ah is all we can be sure off. Lets not even go into whether it was drawn over 1 hour or 10. The 75% as you previously said is often a work of fiction so you still cannot accurately calculate the battery bank capacity. Or am I missing something? Please do not misunderstand me, I am very interested in this as my MICC regularly under counts as opposed to what you seem to be suggesting is the usual problem of over counting.

 

Please read the post and do not miss out a vital few words see:-

 

The basic rule for most boaters with this type of meter is to only use the amps scale while charging and keep going at least once a week until the charge drops to 1% of bank capacity or less, then manually resynchronise the meter. Then you can note the Amphours out and percentage of charge and calculate the current capacity of the bank. e.g. 50Ah out that takes it to 75% of charge tells you the battery bank capacity is 200Ah because 50Ah is 1/4 of the bank capacity.

 

It should be clear that you need to fully (or as near as possible) charge the battery first - then zero it - and only then will the amp hours out be meaningful. As you had just set the capacity to 100% when you re-calibrated the meter the 75% will be 75% of whatever the actual capacity is.

 

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