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Thread: Battery monitor

  1. #11

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    Quote Originally Posted by hairydog View Post
    It depends what you want to monitor. Monitoring the voltage is easy, but pretty useless on its own.

    The voltage of a battery is only an indication of its remaining charge if no current has flowed in or out of the battery for the last hour or two. Which makes it an impractical measure, even though many people on WC seem to think it tells them something.

    In theory you can calculate the state of charge by measuring both the voltage and the current, but the reality is that this is never accurate either, even with fancy calculations involving Peukert's formula.

    The only worthwhile way is to monitor the current going in and out and try to keep track. This is fairly reliable as long as the battery is charged right up to the top fairly often, or run right down flat (not recommended!) However accurate they are, small errors can build up, so getting up to 100% from time to time helps keep them accurate.

    As far as I can see, the Victror 712 is one of these, with the addition of a bluetooth bit to provide connectivity to an app.

    The one I use (which works brilliantly, and has done for many years) looks exactly like DC Battery Monitor Positive Negative Current +/- 30A Voltage 120V Car Volt Meter 754610748905 | eBay which costs less than 15. But if you would rather pay more than ten times as much to be able to open an app instead of looking at a display, that's fine by me!

    [Later] Mine must be a bit different because it measures charge currents way over 30A. Perhaps mine is a 50 or 60 amp one. I don't remember, to be honest. It was installed many years ago.
    Amp hour counters such as the Victron are excellent for measuring the amounts of power used by the batteries or received by them from a charger over time. However they aren't very accurate for measuring the state of charge of batteries even when using modifications to the calculations for Peukert's formula (as does the Victron). I use a Smartgauge which is from experience the most accurate readily available instrument for measuring the state of charge of a battery. It does this without the need to install a shunt. However it does not perform the other functions of an amp hour counter for which I have a separate unit. For a detailed explanation why the Smartgauge is better for measuring the state of charge please have a read of this webpage. SmartGauge Electronics - SmartGauge compared to Amp Hours Counters

  2. #12

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    I've not used a smartguage, but although I accept most of their criticisms of amp counting meters, I consider their smoke and mirrors calculations to be dubious at best.
    Far better to accept that no battery monitor is 100% precise, and to try to get the batteries up to (and past) 100% full on a regular basis. That way the "counting meter" resets itself and is far more accurate than the smartguage which is only guessing.
    Of course, the capacity of your battery bank is an unknown in the first place. Yes, each battery may be.nominally 100Ah, but that will only be when it is brand new, at a temperature of 25c and a discharge current of exactly 5A, and subject to production line variations.
    Those conditions cease to apply as soon as it is installed and/or used. You have to use an informed guess to decide what your battery bank's capacity is. You could never be 99% accurate in that, so their quibble that ammeters can often be 1% out is silly.

  3. #13

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    Quote Originally Posted by hairydog View Post
    I've not used a smartguage, but although I accept most of their criticisms of amp counting meters, I consider their smoke and mirrors calculations to be dubious at best.
    Far better to accept that no battery monitor is 100% precise, and to try to get the batteries up to (and past) 100% full on a regular basis. That way the "counting meter" resets itself and is far more accurate than the smartguage which is only guessing.
    Of course, the capacity of your battery bank is an unknown in the first place. Yes, each battery may be.nominally 100Ah, but that will only be when it is brand new, at a temperature of 25c and a discharge current of exactly 5A, and subject to production line variations.
    Those conditions cease to apply as soon as it is installed and/or used. You have to use an informed guess to decide what your battery bank's capacity is. You could never be 99% accurate in that, so their quibble that ammeters can often be 1% out is silly.
    In fact, when it comes to leisure batteries, most sellers publish the C100 Rating for the battery as being the 'nominal' capacity and not the C20 one - so assuming a 2A discharge current. So when configuring the monitors, you end up using a value that is lower than the 'headline' value (so my AGM batteries are advertised as 110Ah units, but that is the C100 value. For the Victron BMV, I entered their C20 value (95Ah).
    And of course no one draws exactly 5A or 2A or anything anyway, so the theoretical available capacity is constantly varying. I pull anything from 1.5A minimum to 180A+ maximum in my setup.

    I find the Victron BMV very good in the way its algorithm works out the SOC percentage. I can look at the data in the VRM portal, see precisely how much power has been used, the Ah drawn and when looking at a chart of Discharge current as a 'C' level, the SOC drop looks spot on for that 'style' of usage (be it just a few Amps with the fridge running, or a heavy draw when the Induction Hob or Water Heater is on.
    Once I had done that a few times to confirm the data, I no longer need to worry about if the SOC value displayed is correct as I am confident it is - and I occasionally check that by seeing how much net power is going in to get the battery bank upto 100% again.
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  4. #14

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    Despite all the complicated stuuf

    We have a simple voltmeter connected to the LB

    We only have a 85AH battery and we only use vehicle in the summer

    A) The meter shows to over 13V and even 14V mid morning if it is sunny
    B) Evening it goes down but never below 12.6 V

    For us it does the job 5

    I sometimes use an inverter (150Watt) off the EB
    The onboard meter for the EB is a lighted lozenge display
    I only star to use the inverter when all 5 lozenges are showing..once is goes down to 3 I switch the inverter off and wait..
    On a moderately sunny day the solar recharges the EB up to 5 lozenges at which point I can use the inverter again
    This is a sunny day only procedure...BUT IT WORKS
    It I want extended use of the inverter I do so whilst travelling as the alternator and the solar will keep both batteries fully charged.

    You do not need anything fancy..Except common (electrical) sense
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  5. #15

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    Quote Originally Posted by wildebus View Post
    In fact, when it comes to leisure batteries, most sellers publish the C100 Rating for the battery as being the 'nominal' capacity and not the C20 one - so assuming a 2A discharge current.
    I'm sure you are right. To be quite honest, I wouldn't buy a "leisure" battery in the first place. Normal batteries tend to be a far better buy, if you can't afford Deep Cycle.
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  6. #16

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    Quote Originally Posted by hairydog View Post
    I'm sure you are right. To be quite honest, I wouldn't buy a "leisure" battery in the first place. Normal batteries tend to be a far better buy, if you can't afford Deep Cycle.
    I use the term "leisure" battery to distinquish between Starter Batteries and Traction batteries and the ones targetted to the RV & Marine industries rather than a specific subset.
    I don't blame the makers as it is one of these things where people generally compare by price and size and if one company used the C20 rating they would appear less competative for what might well be a better quality battery. The only company that comes to mind that quote the C20 by default is Victron.

    (I have a feeling that in the US, the standard measure when Ah are quoted is the C20 rating - but they also have this obsession of quoting batteries by their 'group', which makes things a bit confusing as the capacities within a group can vary a fair bit)
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  7. #17

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    Quote Originally Posted by hairydog View Post
    I've not used a smartguage, but although I accept most of their criticisms of amp counting meters, I consider their smoke and mirrors calculations to be dubious at best.
    Far better to accept that no battery monitor is 100% precise, and to try to get the batteries up to (and past) 100% full on a regular basis. That way the "counting meter" resets itself and is far more accurate than the smartguage which is only guessing.
    Of course, the capacity of your battery bank is an unknown in the first place. Yes, each battery may be.nominally 100Ah, but that will only be when it is brand new, at a temperature of 25c and a discharge current of exactly 5A, and subject to production line variations.
    Those conditions cease to apply as soon as it is installed and/or used. You have to use an informed guess to decide what your battery bank's capacity is. You could never be 99% accurate in that, so their quibble that ammeters can often be 1% out is silly.
    I had a read of the Smartgauge link. I've never used one either and felt the write-up was heavily biased towards a "we're great, the rest is rubbish" angle and was hardly impartial. I would like to read an independent review on the product.

    The write-up reminded me of the Charles Sargent video I watched last year talking about running AC fridges via inverters and how his inverter jobby is 10 times better than every other one on the market.
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  8. #18

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    Quote Originally Posted by hairydog View Post
    .....

    The one I use (which works brilliantly, and has done for many years) looks exactly like DC Battery Monitor Positive Negative Current +/- 30A Voltage 120V Car Volt Meter 754610748905 | eBay which costs less than 15. But if you would rather pay more than ten times as much to be able to open an app instead of looking at a display, that's fine by me!

    [Later] Mine must be a bit different because it measures charge currents way over 30A. Perhaps mine is a 50 or 60 amp one. I don't remember, to be honest. It was installed many years ago.
    This looks the same as yours, but with a higher 150A current rating
    DC 0-120V 0-150A Volt Amp Watt Meter Capacity Percent Battery Monitor Test Meter 754610748950 | eBay

    And one with a 500A Rating!
    DC 0-120V 0-500A Dual Voltage Current Capacity Power Watt Meter Battery Monitor | eBay

    They all LOOK the same - I guess it is just the shunt that is different about them. They do look very neat I have to say and at the price could well be worth a punt.

    Here are some other options which in price and/or features sit between a basic voltmeter and a NASA Marine or Victron BMV unit:

    As far as other meters/monitors go, I tried these in-line on some Solar Panels so I could monitor what has happening
    Digital Monitor LCD Watt Meter 60V/100A DC Ammeter RC Battery Power Amp Analyzer 712190256203 | eBay
    They worked as expected but ... when I took it apart to check the innards the quality of the build was not very good. if the metal case was slightly pressed it would touch the the solder blob (rather than joint) on the positive connection and short.

    These are good units which used a fair bit on general monitoring and solar panel monitoring
    AC80-260V 100A LCD Digital Volt Watt Current Power Meter Ammeter Voltmeter BI507 4894663039127 | eBay
    The one above is an AC monitor - there are identical ones for DC and for different maximum current limits
    I'm using one of these (DC version) in my van on the input to the Victron inverter which is on 24/7 so I can see how much power that (and the stuff connected to it) is using.
    It is great for that kind of specific job but the one Hairydog has is better featured if monitoring a battery.


    Once which looks very interesting and I am going to get to see how the info matches my BM-712 is this device
    https://www.ebay.co.uk/itm/Wireless-.../142637245664?
    It doesn't use a shunt, you simply route the battery -ve cable though the sensor. It looks promising, would be very easy for anyone to install I suspect, and is cheap for what it promises. (just like HDs one, there are different options with different current ratings at slightly diffrent prices). There are monitors identical to the one above that DO use a shunt however, so need to check carefully if you want one type over the other.


    (PS. None of the links and sellers are anything to do with me.)
    Last edited by wildebus; 29-11-2018 at 11:01.
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  9. #19

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    I bought one of the units above to test and compare to my Victron BMV

    This is the Unit I am checking out:

    Battery Monitor w/Hall Sensor
    by David, on Flickr

    And the Victron BMV-712 BT Screenshot

    BMV-712
    by David, on Flickr

    The Voltage is quite a bit different - that is my error really as I am getting the voltage from the top device from a different pickup and AFTER some heavy cable loading.
    The Current reading is a wider variation then I would have expected - 173.2A vs 180.0A - so around 5% difference. It could be down to the voltage but it really shouldn't matter for current.
    The Wattage is different, but that WILL be down the different voltage reading (P = V*I).

    I do like the info on the top monitor - the Ah in the battery counts down in use and the very visual battery gauge is nice as well.
    Overall, I think it is a nice unit and worth the 30 odd it costs
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  10. #20

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    So to top things off 90% of folk on here are battery gauge watchers rather than go out play,if mine die i buy new ones,but im still going out to play,na na na na.
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