Calling BM1 battery monitor owners, a couple of questions-

[cliffdale]

Following a thread in the practical section, I would like to fit a battery monitor to the boat. There are many suggestions of types. I have looked at them all and favour the BM1 and in particular the read out in hours left on battery drain.

The reason for fitting the battery monitor is I am planning a non stop trip to the Azores and would like to keep a fridge, instruments and sensible use of radar monitored.

The question is, how often do you have to reset the monitor to fully charged batteries?

My concern is on the trip, I will never have fully charged batteries to reset the monitor so it might be quite useless for my needs.

Cliff

 

[Heckler]

Following a thread in the practical section, I would like to fit a battery monitor to the boat. There are many suggestions of types. I have looked at them all and favour the BM1 and in particular the read out in hours left on battery drain.

The reason for fitting the battery monitor is I am planning a non stop trip to the Azores and would like to keep a fridge, instruments and sensible use of radar monitored.

The question is, how often do you have to reset the monitor to fully charged batteries?

My concern is on the trip, I will never have fully charged batteries to reset the monitor so it might be quite useless for my needs.

Cliff

Why do you want to reset the monitor?
Stu

 

[Barry Jones]

You may find this link useful:

http://www.smartgauge.co.uk/sgvahrs.html

 

[Amulet]

Following a thread in the practical section, I would like to fit a battery monitor to the boat. There are many suggestions of types. I have looked at them all and favour the BM1 and in particular the read out in hours left on battery drain.

The reason for fitting the battery monitor is I am planning a non stop trip to the Azores and would like to keep a fridge, instruments and sensible use of radar monitored.

The question is, how often do you have to reset the monitor to fully charged batteries?

My concern is on the trip, I will never have fully charged batteries to reset the monitor so it might be quite useless for my needs.

Cliff

In principle you don't have to reset it. I have one on each of battery banks. One of them once went nuts and said I was drawing 130 amps and recovered by switching on and off. You tell it the battery capacity and it should be able to work out charge state at any point.
Having said that, I would put only modest faith in its "percentage charged", and extremely limited faith in its "hours to run". Much depends on the condition of the battery. However, the ability to see both amps and volts works well for me. I believe that the "smart gauge", much favoured for its price and ease of installation, doesn't give you current amps in or out. I find amps extremely reassuring - it means you know if someone has left something hefty switched on accidentally, and can see what amps charge you get at different engine revs.

 

[snooks]

I believe that the "smart gauge", much favoured for its price and ease of installation, doesn't give you current amps in or out.

I favour it for it's accuracy.

While my batteries were both 110ah at the beginning of their life, having been run down to nothing they have less capacity than they did and this is reflected in the Smartguage's read out...It tells me the capacity (as a percentage) I actually have left, not what it thinks I have left when I set the capacity of my batteries as I installed them.

An amps display would be handy, but it's by no means essential.

It is a double edged sword though, before we got it I lived in ignorance, now I know the SOC at the push of a button, I worry where the power goes

 

[cliffdale]

yes, I like the smartgauge too. I'm half on mind to install them both, one for the accuracy of energy available and t'other for showing how much current draw there is.

I think the state of the electrics is worth investing before the trip.

Cliff

 

[RogerG]

I've been using the Nasa BM1 for about 3 years and find it extremely useful. The Smartguage will give you a much more accurate SOC reading, but I do like the volts/amps in and out on the BM1, especially as I use solar and wind generation.

You really need to reset your battery capacity setting every 3 months or so with the BM1, because with a continuous charge and discharge they will steadily lose their capacity. I reduce the setting by 5% every quarter which will assume a 40% drop in battery capacity over 2 years, which in my experience over the last 7 years is about right. I replace my batteries every 3 years no matter what.

The SOC on the BM1 seems to give me a reasonable guide if I check it before any heavy power use.

Roger

 

[Seajet]

I'd strongly suggest the Smartguage.

I have a BM1, correctly installed & checked a few times, but all I get useful out of it is present status; useless for predicting - I know some people have had more luck.

Especially with the sort of trip you're intending, go for the Smartguage, and whatever kit you use, try to have it fitted in plenty of time to get to know how it reads in various charge situations on your boat.

 

[RogerG]

Just had a thought whilst replying to your monitor query, do make absolutely sure that your batteries are correctly wired for balanced charging and power take off. My own boat which I bought new, had the battery banks wired completely incorrectly by the builders which led to undercharging and early failure of the bank. I simply relaced the batteries not knowing any better at the time and found that they too died after about 12 months living onboard.

After rewiring them correctly, I realised that a number of other liveaboards here also had incorrectly wired banks.

Roger

 

[Georgio]

Hi Clifdale,
I have had a BM1 for a couple of years and it's a great little battery monitor as long as you understand it's limitations. As other have said, the time-to-discharge and % left are best taken with a pinch of salt but provide a reasonable-ish guide. The Amps in/out and voltage is extremely useful. I personally would rather have a shunt-type monitor over the Smartguage.

If you have not done it already fit a smart-charging system to your engine alternator for faster recharging times. With the BM1 you can then watch the Amps drop off as you charge, allowing you to switch off the engine when you get to a certain level to get the most for your diesel/noisy time. At least that what I did for 3000miles this year

I hope you enjoy the Azores, I did the AZAB race this year. Great place that I hope to return to another time and spend a few weeks cruising the islands.

 

[jordanbasset]

Found this on the Nasa BM1 site

"How does it work?
The minimum information required to monitor the state of charge of a battery is the terminal voltage and the charge/discharge current **. The BM1+ measures both these parameters and computes the state of charge using a complex, well proven, algorithm.

A simple and intuitive display shows the service battery voltage, charge/discharge current, state of charge, and time to charge/discharge. The instrument also warns the user when the charge level is too low so that load can be shed or charging commenced to protect the battery. A resettable Amp Hour counter is provided for checking the efficiency of the charging system or keeping a track of power consumption and a second input lets the user monitor the voltage of the starter batter. The simple display format does not mean the internal software is unsophisticated. In fact two separate algorithms are used. One based on integrating amp hours over the charge and discharge cycle, the second based on an adaptive internal mathematical battery model.

A unique feature of the BM1+ is its ability to use information from both algorithms, during the charge/discharge cycles, to continually update its performance. This means that, unlike many other systems that rely solely on amp hour integration, the NASA BM1+ never needs to be re-synchronised with the battery. The algorithm includes Peukert's equation to ensure accuracy over a wide range of load currents.
The BM1+ does all this whist consuming a meagre one and a half milliamps. It is a true battery monitor, easy to install and excellent value for money.

** Some say that they can calculate the state of charge from the terminal voltage only but, as we all know, the terminal voltage falls when the battery is under load and rises when under charge. This fall and rise can be quite substantial, especially when a heavy current is flowing, so how can the terminal voltage be used to calculate anything without knowledge of the magnitude of the current involved?"

Speaking personally fitted one late last year, never needed to synchronise and it appears to work well. Did occasionally check with a stand alone volt meter and it matched up

 

[Sandy]

You may find this link useful:

http://www.smartgauge.co.uk/sgvahrs.html

I love the comment at the bottom of the page, "Website best viewed on a computer of some sort."

 

[Amulet]

You may find this link useful:

http://www.smartgauge.co.uk/sgvahrs.html

Since I have a couple of NASA BM1's, I feel a slight need to convince myself that my money is well spent and point out that they are NOT amps in and amps out counters of the sort criticised on this web site. They use the same same (Peukert) equation as the SmartGauge. This is regarded as unreliable as a way of predicting battery capacity except at constant discharge current. (See: D. Doerffel, S.A. Sharkh, A critical review of using the Peukert equation for determining the remaining capacity of lead-acid and lithium-ion batteries, Journal of Power Sources, 155 (2006) 395–400.)

I assume that, given that the SmartGauge is described more accurate, it does something cleverer than the BM1 to correct for the weaknesses of the Peukert method. The web site does not indicate how. Some of us BM1 users like to describe the BM1 as accurate because of its decimals - which of course could be communicating an entirely spurious sense of accuracy.

 

[RogerG]

You are correct in your assumption that the Smartguage uses additional information to the Peukert equation to give an accurate SOC reading. The designer of the Smartguage and former owner of the company belongs to the same inland waterways forum as me and has frequently explained the maths to interested members. Way over my head, but the large number of IW SG users quite happy to support the claims of accuracy have convinced me.

Personally though I prefer the BM1 for it's wider range of facilities. Even if the SOC of the BM1 is off the accuracy of the SG, I prefer to be able to read the amps going in or out of my batteries at all times, check the drain of individual pieces of 12v gear, instant voltage readout as required and a number of other parameters.

I'm really not convinced that SOC readout is that important, as a fully charged battery is going to show 12.7v and drop at 0.1v for each 10% of discharge, it's not that difficult to see that if you have 12.2v showing you are down to 50% and need to do something about it, even allowing for recovery time. If you can see how many amps you are using and can see the rate of voltage drop, the SOC assessment is pretty simple without the cost of a Smartguage.

The SG website has some superb information on battery wiring, charging, discharging and anything you need to know about batteries.

Roger

 

[snooks]

I'm really not convinced that SOC readout is that important, as a fully charged battery is going to show 12.7v and drop at 0.1v for each 10% of discharge, it's not that difficult to see that if you have 12.2v showing you are down to 50% and need to do something about it, even allowing for recovery time. If you can see how many amps you are using and can see the rate of voltage drop, the SOC assessment is pretty simple without the cost of a Smartguage.

I find my smartguage helpful when charging as it will tell be the percentage, and I know when it gets to 77% it's going to take longer to put the charge back into the batteries. I also know regardless of load the percentage that my batteries are.

Which is something you can't do with a voltmeter

 

[RogerG]

I totally agree with you that the SG is a very good piece of gear, and it gives an accurate SOC percentage. For me personally though, the BM1 at less than half the SG price gives me an accurate enough SOC percentage reading and volts/amps, so that I feel I have a better grasp of what is actually going on in the system rather than just a percentage.

An ideal situation of course would be to have both, funds allowing

Roger

 

[PeterR]

I agree the SG sounds like a good bit of kit if knowing your SOC is your priority. As others have said the figure the BM1 gives for SOC has to be taken with a pinch of salt. However, the ability to see power consumption is invaluable, particularly in checking for kit left on. – in my case usually leaving the radar on standby by accident.

Its rare for power consumption to remain static over a long period when sailing so knowing how many amp hours you have already used a bit of mental arithmatic allowing for future changes in consumption, e,g switching lights or radar on for a known period, will often give a better prediction of remaining battery availability than the capacity remaining calculated from the existing rate of voltage drop.

Being able to see the charge rate of amps going back into the battery when motoring also gives a much better guide as to when it is becoming futile to continue running the engine just for charging purposes than stopping the engine at a particular SOC.

 

[snooks]

However, the ability to see power consumption is invaluable, particularly in checking for kit left on. – in my case usually leaving the radar on standby by accident.

Perhaps you could change your set up to have your radar on it's own switch?

All my switches are the toggle type, up for off, down for on, I have two different switch panel and the chart plotter is on it's own at the chart table.

I have to switch my radar on on my switch panel, (last switch to port and I can switch it on from the cockpit ), then transmit with the chartplotter.

With the exception of the US antifoul, webasto and gas alarm everything has a switch so I can see what's on and what's not

 

[PeterR]

Perhaps you could change your set up to have your radar on it's own switch?

With a Raymarine setup the radar is automatically powered up to standby when the plotter is switched on and you have to remember to switch it off. Breaking into the radar cable to install a switch is asking for trouble.

OK you can get a bit paranoid and become like the crew of Apollo 13 trying to reduce power consumption to a minimum by watching the effect of various changes on the amperage but its actually quite an enjoyable exercise.

If you are on a swinging mooring or on long passages I can see that the more accurate SOC given by the SG may be very valuable. But if you are routinely charging from shore power you know your battery is fully charged when you leave and assuming you periodically carry out a capacity check you should know how many amp hours you have to play with with the BM1.

 

[snooks]

With a Raymarine setup the radar is automatically powered up to standby when the plotter is switched on and you have to remember to switch it off. Breaking into the radar cable to install a switch is asking for trouble.

Ah, doesn't it power down when you switch the chart plotter off? or are you talking about when you are sailing?

And no, breaking the cable would be a bad idea.

My Garmin has a power cable and a data cable so adding the switch was a part in the instruction manual.