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Battery Status - does anything work?

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I've used both a Xantrex Link 2000, and a Mastervolt MICC to monitor battery status and they're both useless. Both of these devices count amp hours, but they quickly become out of sync with the actual status of the battery. Right now the Mastervolt MICC reports 25.5v and a 33% state of charge! I always end up using the morning voltage when there is very little current draw as the indicator of battery status but I know that's also not very accurate. I have a 24v 1,000 ahr battery bank that is charged from solar, wind and the engine alternators which can bring it to 80-90%. About once a month it gets fully charged and topped up via shore power. I came across a "not counting amp hours" solution at Does anyone have experience with this device, or with any other device that accurately tracks battery charge status?

24 Replies

  • If you have a NMEA 200 bus, Maretron's DCM100 is interesting. It has a SoC reading that is much more sophisticated than just looking at amps used. (But you also will need their DSM250 display to see the data...)

  • OK, I'll follow up on that. Does anyone have experience using it to monitor battery status?

  • Hi, regarding the amphour counting: all of these battery monitors, including ours (Victron Energy), read and count amphours. Actually it is not done by just counting the amphours, but they take the Peukert exponent, battery temperature and also charge efficiency factors in account as well. To my knowledge, the above mentioned Xantrex and Mastervolt products do this too.

    First some background:
    It is important for all this type of monitor that it is 'synchronised' on a regular basis. To be workable, this synchronisation should be automatic. The battery monitor will synchronise itself when the battery is charged up to 100%. The reason behind this is that the monitor can only accurately deduct State of Charge (SoC) from its inputs (amps and volts) when a battery is full. Synchronisation works with simple logic: if the voltage is high, and at the same time there is not a lot of current going into the battery, the battery will have to be full. So the monitor resets its SoC back to 100% and the monitor is accurate again.

    Now, all monitors have parameters for this, we called them Charged Voltage and Tail current. SoC is reset to 100% when the voltage is higher then the specified Charged Voltage threshold and the amps going into the battery are below the Tail Current. The lower you set your tail current, the more accurate your battery monitor will be (on a theoretical basis). The battery monitor will reset to 100% when the battery is completely full. The problem is that batteries are seldomly completely topped up, and therefore these parameters are very seldomly met.

    The most simple solution is to loosen up the Tail Current setting. For example, set it to 5% of your battery bank capacity (or even a bit higher when necessary in your specific application). This way the battery monitor will synchronise more often. The drawback is that you'll get a SoC that might be a bit optimistic, but hey, it will be much better then the SoC you see at the moment! And, it will be stable.

  • JAnwyl - I looked at the Marteron documentation and it appears to be counting hours also, just with a Hall effect sensor instead of a shunt. Unfortunately the Hall effect sensor maxes out at 200a, and I've got 300a of alternators. Other than putting the data on the N2K bus, I don't see any advantage in the Maretron over the Mastervolt MICC.

    Matthijs - I'll try changing the tail current setting and see if that triggers the sync more often. But of course we know we're just tweaking a flawed solution.

    Battery technology has to be very well understood by this point. Is there really no way to accurately monitor battery status?

    Has anyone heard of the Smart Gauge solution or have an opinion on it's accuracy?

  • I have found my Link 20 to be accurate ... BUT, it didn't start that way. It was installed incorrectly in three different ways, and was really tough to debug.

    There cannot be any neg battery path, none whatsoever, that bypasses the shunts. It's amazing how many small things get connected directly to the battery. They seem not to matter, but then they become a way for volts consumed or charging to get registered partially against the wrong battery bank.

    Look everywhere, is your starting battery directly grounded to the engine ? Bilge pumps ? Inverter ? Nothing can bypass that shunt ... or your readings are useless !

  • After researching and installing many of these units I have come to conclude, in my opinion, that the Victron outperforms the Xantrex and others and is less problematic. But the initial setup at installation is critical to get accurate information from any of them. Chuck

  • I have both the Maretron DCM100 and a SmartGauge fitted to my boat. The first DCM100 I had has given some problems and I have now received but not yet installed a replacement instrument, so I don't have a great deal of experience with this device. The main limitation of the DCM100 is the Hall Effect current sensor. This is limited to 200 amps and if it's typical, will only have a +/-2% accuracy which means it's not very good for monitoring small currents.

    The SmartGuage is highly regarded amongst the UK canal boating fraternity. Although I don't have any experience of this type of boating, it appears that most canal boats use engine alternators for most battery charging, shore power hook-ups are not very common, so state of battery charge is a very important measurement.

    As I posted in the main blog, I believe that the SmartGauge uses AC conductivity measurements to obtain information on the state of battery charge. See for more information on this technique.

    My own experience of the SmartGauge is limited at present - due to not using the boat very much - roll on summer - but so far it seems to do what it claims.

    The owner of SmartGauge is Chris Gibson. He is a well respected member of the canal boating world and frequently posts under the name Gibbo on the Canal World forum, His posts make entertaining reading at times - a person with strong views on some topics!

  • Kees: Sorry for the confusion, the Link2000 was on my previous boat, a Swan 44 Mk II. The Mastervolt MICC is on the current boat. The problem is the same, they both become out of sync fairly quickly.

    The MICC has a 500a shunt and I'm fairly certain that nothing bypasses it. I know that the wind, solar, refers, heater, etc. do not bypass it, but I'm checking on anything else. However, it is so far out of sync that some smaller items just can't account for the difference in hours reported.

    I look forward to hearing from anyone who has actually used the Smart Gauge. I'll also look into the Canal World forum as suggested by OldLimey.

  • I found that the measurements get out of sync quite unproportional to the size of the "small item".

    Look out for bonding wires and funny connections at the "neg off" switch if your boat has one ... on my boat there was one bonding wire that escaped my attention and drove me nuts.

    To make the rewiring easier ... I ran 8 gauge black wire from the common lead on the shunt (I have a two bank shunt) to a post I mounted near each battery bank, to which I moved all the misc. ground wires (stereo memory circuit, DC panel battery test, bilge pump, bonding wire, etc.). Now even when I run something direct to the batteries (2nd bilge pump etc., I can run the wires to one location)

  • I installed a Xantrex XBM monitor before the last season.

    I've been very happy with it. We keep a 24V/500 hour bank charged with propulsion engines, generator/charger and occasional shore power when we cruise.

    The main benefit of the monitor was being able to manage and plan charging (e.g. let the batteries run a little low if shore power or a long engine run was planned for the next day) and we only ended up running the generator a couple of times in 2 months solid cruising.

    I have a DC distribution panel modeled after the Mastervolt DC panel. This keeps all primary DC connections in one enclosed panel. The monitor shunt is also in the enclosure so the monitor connection is simple and safe.

  • One upshot of this interesting thread is that Chris Gibson is sending over a SmartGauge to try out in the lab. He wrote that if I didn't like it, I can "smash it up"!

    I've always fancied chartering a canal boat one day, but now that I've wandered that forum a bit (pity the fellow who asked about bow thrusters), I am not so sure. Rough bunch.

  • That's great news. The challenge is to see how it performs over at least 30-60 days with a daily mix of charging and discharging, but without a complete shore power top up; this is where the amp hours counting systems fail miserably.

    I look forward to reading the results.

  • Ruse wrote "fail miserably" ??

    I guess your not buying the possibility you have a wiring problem? My beneteau sailboat has a much simpler electrical system and it took many iterations to find every ground path that bypassed the shunt.

    I have some faith in the link20 after using it at length to measure and chart my power system to prove back to my dealer I had a charger issue that was damaging the batteries. (the manufacturer had placed HVAC ducts over the charger, the 100+ lb HVAC unit against that, and then a shelf on top of the whole thing making the charger unaccessible directly)

    After I got all the bugs out of my link 20 to boat wiring, I had good results. The link 20 measurements were also verified by putting a fixed load on the batteries and looking up the voltage on a decay chart.

    The issue went on for five month, during which I would go periods of months without using the charger because it was cooking the batteries (wrong switch settings)

  • I checked with the builder and they are pretty confident that nothing goes around the shunt. The shunt is right next to the battery so any other wiring will be pretty obvious. Next week we'll take a closer look.

    That said, the ahrs counting strategy ignores Peukert's equation and Mastervolt will not publish the Peukert's exponent for the batteries they sell, the tell me to derive it myself with a high load / low load test. I don't have the time or facilities to do that. This makes no sense to me since these batteries are mass produced and should be fairly consistent. They recommend using 1.27 which based on my reading is too high for a gel cell. Mastervolt does use Peukert's for predicting the time remaining, but this is based on the last 30 minutes of consumption which is fine if you're running a fairly constant load, but useless when the load varies widely over 24 hours.

    All of Mastervolt's data is oriented to high loads over short periods of time. This is good data if you're backing up a cell site, but not relevant to my boat where it takes 5-10 days to use half the capacity.

    In any case we know that Peukert's equation means that a very low drain on the battery effectively results in a larger battery My calculations say that with an average load of about 2.5a, using a Peukert's coefficient of 1.27 yields a battery capacity about 2.7x the rated capacity. Yet the ahrs counting systems always treats it like a fixed capacity. With the 1,000 bank, use 350 hours and you're at 65%. They totally ignore whether I pulled out the 350ahrs in 3 hours or 72 hours. How can such a system accurately report my state of charge?

    I'm very curious about what Ben will find with the SmartGauge. I hope he'll run it in parallel with an ahrs counting system and compare the results. They should coexist on the same system without any problem. But will they report the same SOC?

  • Russ, I think the battery monitor testing could work out well on the boat I'm very close to buying. It has a Xantrex Link 1000 and Freedom Marine 25 already installed, along with a 560ah house bank, and engine and generator start batteries. The boat will be living on a Camden float without shore power, and I'll be aboard quite a bit fiddling with electrical/electronic stuff. When we cruise/test locally it will be mostly to anchorages.

    Besides the SmartGauge, I also have a Maretron DCM100 to try, and can probably borrow other gear. Getting on top of electrical use and battery state is one of my highest priorities, particularly because I'm pretty ignorant on the subject. I'm hoping to expand my knowledge by visiting the Victron office in Thomaston soon.

    Long range I'm hopeful that better and more reasonable monitoring, batteries, solar collectors, lighting, and air handling could render this boat's generator and dual CruisAirs obsolete. But I may be dreaming, especially if she goes south!

  • Ben: Sounds great!

    I'm "south" (17N) without a genset and haven't run the AC in a couple of months. It's possible!

  • Kees / Dan - OK, today I verified that there is nothing connected between the battery and the shunt. It's a 500a shunt, more than sufficient to handle all the current from consumption or charging.

  • Kees & Dan: We verified yesterday that there is nothing connected to the battery before the shunt. The shunt is literally inches from the negative battery terminal and there is nothing between it and the battery.

  • Ben - any progress on reviewing the SmartGauge or the Maretron unit?

  • Sorry, didn't see your post from April !

    If it's wired correctly and the sync function isn't working, I think pretty much it is game over. The sync function is necessary, because some of the other math that goes on (the faster you draw power from a battery, the higher the loss), is in exact.

    If the sync function is working, then the next place to look is to run a test of the Ahr function. Run a load thru it in both directions, say 1/4 amp for 10 hours, each way, then 10 amps (or the maximum your VOM can measure) for 10 hours. If those results are bad, then you can further debug to determine if you have a bad shunt, a voltage drop between the shunt and the panel (will cause an underreporting of amps) or an issue in the panel that is something solid to chase Mastervolt on.

    If the test above checks out, then I am out of ideas. For what happens in the panel you are at the mercy of sloppy programming for syncing or applying power factors (Pxxxxx something, right ?) correctly for your batteries, or not having the right power factor ... and really no capability to resolve either.

    The Link 20 has been effective at re-syncing on my boat, and has proven extremely effective at measuring and tracing down even small power issues. It makes me a believer in the approach of measuring Ahr to understand how much capacity is left.

  • Ben - I don't know how those entries got duplicated, I only did the first one.

    Dan - It could be the Mastervolt MICC, I'm on the second unit.

    Or there could be some wiring that I haven't discovered, though it's not between the shunt and the battery.

    I've verified the voltage readings, the MICC is reporting the correct voltage.

    I don't think there is any reason to doubt the shunt itself as the current readings on the MICC are also very much what is expected at any point in time. The wire from the shunt to the MICC is probably 8-10' so there is certainly some voltage drop there, but it shouldn't be material to the measurements.

    I'm tracking a 1,000ahr/24v battery, if it was even within 20ahrs I'd be thrilled. The last cycle before we connected to shore power it was reading -1009ahrs and 24.4v!

    The CEF is supposed to be computed automatically, and the Peukert's exponent is only used for calculating time remaining, which I never use anyway.

    I'll take another look at the wiring when I get back onboard.

  • Hi,

    Just found this article and am interested in what the results were. Did the SmartGauge work? Did you also try to use it with the SmartBank?



  • Bryce, I feel very guilty about the SmartGauge as I still haven't tested the sample I got so many years ago!

    But I can tell you that Balmar now sells and supports it, which is a great validation:

    I believe that I also heard Nigel Calder say good things about it, though I can't find anything online.

  • Ben,

    I recently finished nearly 4 months of testing the Smart Gauge. Pretty cool product that removes a lot of the programming and wiring issues that are associated with traditional Ah counters. The article is a bit detailed, but it had to be, because the testing was a bit complex and I felt it had to be explained....

    Smart Gauge

    RC Collins
    Compass Marine Inc.