battery monitoring

[destinyjon]

Hi all.

Before i start embarking on what appears to be an emotive topic to some(!), i have read a number of threads on the forum regarding this subject, but being a novice with boat electrics and a relatively new boater, i have found a lot of threads somewhat overwhelming! (no disrespect to any forum members)

Having been on my boat for 8 months or so, i have managed so far by charging regularly either by engine power generating or my external 2.6Kw kippor generator. I would consider myself not to be a high power consumer, no toasters, electric kettle, etc.

The system charges through a sterling charger, which indicates when battery bank is either in fast charge, absorbtion or flood. I think the only issue with this approach is uneconomic regarding fuels, ie, would like to know the battery state before having to charge.

 

Therefore, i would like to install a battery monitor and probably do it myself, in order to keep the cost to a minimum!

The system comprises of a bank of 3 batteries (110ah i think!) and 1 engine battery. Additionally, one solar panel.

My primary requirements are:-

Ease of use and not necessarily over complicated

Ease of installation

Cost.

Many thanks all.

 

 

 

 

oh, should say, the two i am looking at are the smartgauge and the victron bvm 602.

thanks

[nicknorman]

Hi all.

Before i start embarking on what appears to be an emotive topic to some(!), i have read a number of threads on the forum regarding this subject, but being a novice with boat electrics and a relatively new boater, i have found a lot of threads somewhat overwhelming! (no disrespect to any forum members)

Having been on my boat for 8 months or so, i have managed so far by charging regularly either by engine power generating or my external 2.6Kw kippor generator. I would consider myself not to be a high power consumer, no toasters, electric kettle, etc.

The system charges through a sterling charger, which indicates when battery bank is either in fast charge, absorbtion or flood. I think the only issue with this approach is uneconomic regarding fuels, ie, would like to know the battery state before having to charge.

 

Therefore, i would like to install a battery monitor and probably do it myself, in order to keep the cost to a minimum!

The system comprises of a bank of 3 batteries (110ah i think!) and 1 engine battery. Additionally, one solar panel.

My primary requirements are:-

Ease of use and not necessarily over complicated

Ease of installation

Cost.

Many thanks all.

 

oh, should say, the two i am looking at are the smartgauge and the victron bvm 602.

thanks

Emotive? Yes!

 

For me it would be the smartgauge. This tells you the actual State of Charge and, bearing in mind it is generally considered best not to go below 50% actual State of Charge it tells you when you should start charging. It is also fairly good at telling you when to stop charging, but not perfect. It tells you the SoC and voltage of the domestic battery, only the voltage of the engine battery. It doesn't tell you current. It gives you a good idea of whether your batteries are / remain adequate for your needs since if you routinely find the SoC getting quite low in the morning, presuming they were properly charged the previous day this is a good indication that the batteries are dying.

 

Its very easy to install.

 

BMV: Tells you voltage, current and has a SoC readout that presumes the actual battery capacity is the same as that you put into the system. So you have to adjust it from time to time as the battery capacity decreases, although it can be hard to know what to adjust it to. It is the best way to know when to stop charging because that is when the current falls to say 1% of the bank's capacity.

 

Its main weakness is the unreliable nature of the SoC indication once your batteries start to depart from perfection - unlike the smartgauge it doesn't give you the hint that your batteries are dying, you have to work it out for yourself, which can involve batteries going flat etc.

 

It is harder to install than a Smartgauge

Edited January 20, 2016 by nicknorman

[Graham.m]

I get the impression that you want to know when your batteries are charged rather than when you need to charge them. To an extent it depend on whether you have flood batteries (you can top up the water) or sealed batteries where you cannot top them up. Do you know which you have?

 

Looking at telling whether the battery is fully charged or not.

 

The Smartgauge has a problem and tends to get to it 100% reading before the battery is fully charged and that last bit is a bit of an unknown

 

The BMV602 or the BMV702 (which I would recommend) allows you to see what current is going in or out of the battery all the time. Thus when you can see the actual charge going into the battery, It is generally accepted that once that current drops to 1% of capacity (with 3 x 110Ah batteries 3.3A or less in your case) (this is called the tail current) the battery is as near fully charged as make no difference. That does of course require nothing else to be drawing current at the time.

 

There is another two ways

 

On the Sterling charger there are two displays the left volts and the right amps and viewing that will again show the current (amp) being supplied to the battery and hence the tail current can be read there, again so long as nothing else is drawing current. I am naughterly assuming a Sterling Pro charger

 

If you have flood batteries then a small £17.00 reticule hydrometer (I am sure Nick will post a link) can easily read the batteries specific gravity and tell you exactly what is going on within the battery. Specific Gravity (SG) is the measurement of the density of the electrolyte in the battery. When a battery is used (discharged) the sulphuric acid is taken up by the chemical reaction and leaves the electrolyte and the density SG drops. When the battery is charged that sulphuric acid is released and the SG rises until it reaches the fully charged level. You will appreciate the above is simplified. Thus by measuring the SG you can check the state of charge of the battery both while charging and discharging.

 

Now discharging the BMV602 and the 702 record the current drawn from the batteries and give you a reading of Ahs used and give to me a very acceptable idea of when I need to charge my batteries. I would suggest for best battery life you limit discharge to 25% of capacity.

 

There is a problem I believe with measuring State of Charge (SoC) electrically. How do you define it, it has not bottom because the capacity of a battery depends on so many factors as Nick has eloquently post in the past.

 

So first the need is to know what batteries sealed or flood?

Edited January 20, 2016 by Graham.m

[nicknorman]

The Smartgauge has a problem and tends to get to it 100% reading before the battery is fully charged and that last bit is a bit of an unknown

 

No this is incorrect. It is not particularly accurate on indicating fully charged but it may be a little ahead or a little behind depending on various things including the alternator power and voltage, battery condition etc. But typically the error is pretty repeatable. In reality, since there is no definition of "fully charged" it is close enough, there is more variation caused by the decision whether to stop charging at 4%, 2%, 1% etc tail current..

 

As an example, in my case the Smartgauge will be reading within 1 or 2% of the indication on the correctly set up amp-hour counting gauge as their indications are in the high 90s.

 

Something like a BMV602 or 702 will read 100% when the conditions you specify are met, these can be anything you like within reason in terms of tail current, voltage and time, and as such it is no more accurate than a Smartgauge, and worse if you set it up wrong (the Smartgauge doesn't need any setting up except for battery type.)

[nicknorman]

It is generally accepted that once that current drops to 1% of capacity (with 3 x 110Ah batteries 3.3A or less in your case) (this is called the tail current) the battery is as near fully charged as make no difference.

I don't disagree with you, but it is interesting that the BMV series has 4% as the default value. That makes it quite a poor indicator of fully charged out of the box for someone intimidated by adjusting the settings.

[Graham.m]

No this is incorrect. It is not particularly accurate on indicating fully charged but it may be a little ahead or a little behind depending on various things including the alternator power and voltage, battery condition etc. But typically the error is pretty repeatable. In reality, since there is no definition of "fully charged" it is close enough, there is more variation caused by the decision whether to stop charging at 4%, 2%, 1% etc tail current..

 

As an example, in my case the Smartgauge will be reading within 1 or 2% of the indication on the correctly set up amp-hour counting gauge as their indications are in the high 90s.

 

Something like a BMV602 or 702 will read 100% when the conditions you specify are met, these can be anything you like within reason in terms of tail current, voltage and time, and as such it is no more accurate than a Smartgauge, and worse if you set it up wrong (the Smartgauge doesn't need any setting up except for battery type.)

 

I believe that it is commonly accepted that the Smartgauge has problems following a charging battery and I believe the published spec give an accuracy of +/-10% while charging.

I don't disagree with you, but it is interesting that the BMV series has 4% as the default value. That makes it quite a poor indicator of fully charged out of the box for someone intimidated by adjusting the settings.

 

The BMV is adjustable and can be set to whatever the client requires between 0.5% to 10%.

[Phil.]

Hi all.

Before i start embarking on what appears to be an emotive topic to some(!), i have read a number of threads on the forum regarding this subject, but being a novice with boat electrics and a relatively new boater, i have found a lot of threads somewhat overwhelming! (no disrespect to any forum members)

Having been on my boat for 8 months or so, i have managed so far by charging regularly either by engine power generating or my external 2.6Kw kippor generator. I would consider myself not to be a high power consumer, no toasters, electric kettle, etc.

The system charges through a sterling charger, which indicates when battery bank is either in fast charge, absorbtion or flood. I think the only issue with this approach is uneconomic regarding fuels, ie, would like to know the battery state before having to charge.

 

Therefore, i would like to install a battery monitor and probably do it myself, in order to keep the cost to a minimum!

The system comprises of a bank of 3 batteries (110ah i think!) and 1 engine battery. Additionally, one solar panel.

My primary requirements are:-

Ease of use and not necessarily over complicated

Ease of installation

Cost.

Many thanks all.

 

 

 

 

oh, should say, the two i am looking at are the smartgauge and the victron bvm 602.

thanks

You have posted this just for some afternoon sport haven't you.

 

In all seriousness though if like me you not a techno expert who understands electrical equations then opt for a smartgauge. Cheap, simple to instal simple to use and read. I charge batteries to 90% on the engine then let the solar panel finish them off. Job done.

Edited January 20, 2016 by Phil.

[nicknorman]

I believe that it is commonly accepted that the Smartgauge has problems following a charging battery and I believe the published spec give an accuracy of +/-10% while charging.

The absolute maximum error is indeed quoted as 10% during charging. With our very large alternator to battery ratio I find that the AH counter can be 10% ahead of the Smartgauge mid-charge, but repeatably they come together toward the end such that as I mentioned, they will be within a couple of % in the high 90s. Of course if I had a BMV and installed it "out of the box" it would indicate 100% very prematurely.

 

Anyway the point is that if you want to stop charging at say 80% SoC, the Smartgauge is not good for that. If you want to stop charging at 100%, which is what most people want, it is fine.

[Paul C]

If you think an amp is something that sits on top of a pair of Marshall cabinets then buy a Smartgauge. If you know that an amp is a unit of current and want to know all about where they hide on the boat, then buy a Victron BMV700. If you don't believe one is better than another, or are worried about accuracy, or want to know more than average, buy both. (There is merit in having both, and intelligently interpreting the results).

 

All IMHO of course.

[Graham.m]

The absolute maximum error is indeed quoted as 10% during charging. With our very large alternator to battery ratio I find that the AH counter can be 10% ahead of the Smartgauge mid-charge, but repeatably they come together toward the end such that as I mentioned, they will be within a couple of % in the high 90s. Of course if I had a BMV and installed it "out of the box" it would indicate 100% very prematurely.

 

Anyway the point is that if you want to stop charging at say 80% SoC, the Smartgauge is not good for that. If you want to stop charging at 100%, which is what most people want, it is fine.

 

 

mmmm I am sure I have seen it said to people on the forum charging once they get to 100% to keep going for an hour or so because of that inaccuracy.

[WotEver]

 

I believe that it is commonly accepted that the Smartgauge has problems following a charging battery and I believe the published spec give an accuracy of +/-10% while charging.

Unless you are being deliberately obtuse you should have noted numerous reports from users of SmartGauge that after a few cycles the SoC indication when fully charging is generally within 5% of actual. The 10% figure is a maximum figure which, unlike other monitoring solutions, is also self-correcting. Hence it gets more and more accurate over time.

 

Tony

 

A good addition to SmartGauge would be a cheap ammeter which, if correctly positioned, can accurately show tail current.

Edited January 20, 2016 by WotEver

[nicknorman]

mmmm I am sure I have seen it said to people on the forum charging once they get to 100% to keep going for an hour or so because of that inaccuracy.

 

I think i can remember someone saying that, probably depends on the specifics of the battery/alternator, and of course with some types of battery it is recommended to continue charging after nominally fully charged to stir the electrolyte, but I think it boils down to the fact that there is no definition of fully charged. Charging for a bit longer is better than charging for a bit shorter.

[Graham.m]

Unless you are being deliberately obtuse you should have noted numerous reports from users of SmartGauge that after a few cycles the SoC indication when charging is generally within 5% of actual. The 10% figure is a maximum figure which, unlike other monitoring solutions, is also self-correcting. Hence it gets more and more accurate over time.

 

 

I think you have miss the flow of the thread. We are talking about charging and while charging of a running instrument we have not got to the part of the Smartgauge's shall we call it running in nor the settling down after a charge.

[Graham.m]

If you think an amp is something that sits on top of a pair of Marshall cabinets then buy a Smartgauge. If you know that an amp is a unit of current and want to know all about where they hide on the boat, then buy a Victron BMV700. If you don't believe one is better than another, or are worried about accuracy, or want to know more than average, buy both. (There is merit in having both, and intelligently interpreting the results).

 

All IMHO of course.

 

I think Paul has hit the nail on the head, both have imperfections there is no such thing as a perfect battery monitor.

 

Personally I believe it is important to be able to accurately measure the battery voltage and current that the BMVs do.

Unfortunately the gauge does not read current and on a 12 v unit only shows the reads of volts to 1 1/2 decimal places i.e. 12.1, 12.15, 12.2

on the 24V box it only reads to 1 decimal place.i.e. 24.1, 24.2 etc

[nicknorman]

I think Paul has hit the nail on the head, both have imperfections there is no such thing as a perfect battery monitor.

 

Personally I believe it is important to be able to accurately measure the battery voltage and current that the BMVs do.

Unfortunately the gauge does not read current and on a 12 v unit only shows the reads of volts to 1 1/2 decimal places i.e. 12.1, 12.15, 12.2

on the 24V box it only reads to 1 decimal place.i.e. 24.1, 24.2 etc

OP says "being a novice with boat electrics" and "Ease of use" I am wondering what he would do with voltage and current information when what he actually wants is SoC information. It would be like a car fuel gauge showing not only how full the tank was, but also the instantaneous fuel flow and injector common rail pressure. Interesting to the fanatic but not normally considered appropriate for a non-enthusiast. Edited January 20, 2016 by nicknorman

[Graham.m]

OP says "being a novice with boat electrics" and "Ease of use" I am wondering what he would do with voltage and current information when what he actually wants is SoC information. It would be like a car fuel gauge showing not only how full the tank was, but also the instantaneous fuel flow and injector common rail pressure. Interesting to the fanatic but not normally considered appropriate for a non-enthusiast.

 

OP is considering the gauge and the BMV I think he already has an idea of what they do.

[Tony Brooks]

He may well have an idea, from marketing bumph, about what they do but does he know just how easily they can lead to ruined batteries IF they are not correctly set up and regularly synchronised?

 

I would suggest the setting up and regular synchroniser tends make the BVM more complicated, e specially if you are not sure what you are doing. In any case can anyone state with confidence what capacity the OPs domestic batteries have NOW. If not a BVM used for Ah counting is never likley to be correct.

 

For simplicity of use and installation I would go for Smartguage.

 

For reading volts and amps and the extrapolating the SOC I would go for a BVM.

[ditchcrawler]

 

I think Paul has hit the nail on the head, both have imperfections there is no such thing as a perfect battery monitor.

 

Personally I believe it is important to be able to accurately measure the battery voltage and current that the BMVs do.

Unfortunately the gauge does not read current and on a 12 v unit only shows the reads of volts to 1 1/2 decimal places i.e. 12.1, 12.15, 12.2

on the 24V box it only reads to 1 decimal place.i.e. 24.1, 24.2 etc

I think you have to consider that not everyone has you electrical knowledge and not all are able to interpret amp ah and volt to give an indication as to what there batteries are doing. My wife will happily pop up and tell me the Sterling battery monitor is reading zero. to her the batteries are charged, to me they are well on the way there.

[WotEver]

One thing that an Ah counter cannot do, which is one of the most important features of SmartGauge, is to tell the user 'either start your charger now or at the very least stop discharging your batteries'.

 

I would suggest that for novices, particularly if they don't have much electrical know how (the majority, it would seem), the above is the single most important discipline for them to learn.

 

Tony

[Graham.m]

He may well have an idea, from marketing bumph, about what they do but does he know just how easily they can lead to ruined batteries IF they are not correctly set up and regularly synchronised?

 

I would suggest the setting up and regular synchroniser tends make the BVM more complicated, e specially if you are not sure what you are doing. In any case can anyone state with confidence what capacity the OPs domestic batteries have NOW. If not a BVM used for Ah counting is never likley to be correct.

 

For simplicity of use and installation I would go for Smartguage.

 

For reading volts and amps and the extrapolating the SOC I would go for a BVM.

 

 

Think you missed that I did not say used the BMV to measure SoC. I said measure the Ahs used on it, different I think you might agree

[nicknorman]

Think you missed that I did not say used the BMV to measure SoC. I said measure the Ahs used on it, different I think you might agree

It is a different thing, of course, but I question its use unless one knows the actual capacity of the bank. If you have both those pieces of information then you can work out the SoC and thus when to recharge. Alternatively look at the single piece of information on the smartgauge to get the same thing.

[Graham.m]

One thing that an Ah counter cannot do, which is one of the most important features of SmartGauge, is to tell the user 'either start your charger now or at the very least stop discharging your batteries'.

 

I would suggest that for novices, particularly if they don't have much electrical know how (the majority, it would seem), the above is the single most important discipline for them to learn.

 

Tony

 

I think you might need to read up on the BMV 602 it has high and low voltage alarms so charge now etc s covered, it also has the capability to start and stop generators etc

It is a different thing, of course, but I question its use unless one knows the actual capacity of the bank. If you have both those pieces of information then you can work out the SoC and thus when to recharge. Alternatively look at the single piece of information on the smartgauge to get the same thing.

 

It depends on what is being defined as 100% SoC

 

I think that is where SG measurement comes in.

 

BTW can you post a link to those hydrometers?

Edited January 20, 2016 by Graham.m

[nicknorman]

I think you might need to read up on the BMV 602 it has high and low voltage alarms so charge now etc s covered, it also has the capability to start and stop generators etc

Both devices allow starting and stopping of generators. The SG does it on SoC or voltage. I don't know if the BMV does it on SoC, but I'm not too convinced I'd want the genny starting up for 5 minutes because the battery voltage dropped when I put the kettle on. If it is done in voltage, how does it know when to stop the genny?

 

What the SG lacks is an ability to limit the time of day when the genny is running. Does the BMV cater for that (don't think so)?

Edited January 20, 2016 by nicknorman

[smileypete]

I think i can remember someone saying that, probably depends on the specifics of the battery/alternator, and of course with some types of battery it is recommended to continue charging after nominally fully charged to stir the electrolyte, but I think it boils down to the fact that there is no definition of fully charged. Charging for a bit longer is better than charging for a bit shorter.

Oh dear Nick!

 

Hate to nitpick, but there IS a definition of fully charged, and it can be found in The Battery FAQ:

 

http://jgdarden.com/batteryfaq/carfaq9.htm#charged

http://www.batteryfaq.org/

 

'9.5. How Do I Know When My Battery Is Fully Charged?

 

In descending order of accuracy and depending on the battery type, one or more of the following three methods is normally used to determine if a battery is fully charged:

According to IEEE 450-2002 Annex B Recommended Practice, "The pattern of charging current delivered by a conventional voltage-regulated charger after a discharge is the most accurate method for determining state of charge. As the cells approach full charge, the battery voltage rises to approach the charger output voltage, and the charging current decreases. When the charging current has stabilized at the charging voltage, the battery is charged, even though specific gravities have not stabilized." It should be less than two percent of the capacity (C/50) at the manufacturer's recommended temperature compensated absorption charging voltage level of the battery. For the average sized wet Low Maintenance (Sb/Ca) car battery (BCI Group 24) at 80° F (26.7° C), that would be less than two amps at 14.4 VDC with the cells gassing (bubbling) freely and evenly.'

 

Short answer I think is that if you want a simpler life then fit a Smartgauge, but just be aware that it's not a panacea.

 

cheers, Pete.

Smpt

Edited January 20, 2016 by smileypete

[Graham.m]

Both devices allow starting and stopping of generators. The SG does it on SoC or voltage. I don't know if the BMV does it on SoC, but I'm not too convinced I'd want the genny starting up for 5 minutes because the battery voltage dropped when I put the kettle on. If it is done in voltage, how does it know when to stop the genny?

 

What the SG lacks is an ability to limit the time of day when the genny is running. Does the BMV cater for that (don't think so)?

 

Ah we are back to the 200A kettle lol There is a delay on the BMV not sure of the length but pulling a battery voltage down to a need to charge value should sound alarms etc the aim is to preserve the batteries.

Edited January 20, 2016 by Graham.m