MidNite Solar Battery Capacity Meter

SparkletronSparkletron Solar Expert Posts: 71 ✭✭✭✭
MidNite Solar has a new voltage-based battery capacity meter. Thoughts?

I don't see it as being significantly different from other voltage-based meters, which means it will suffer from the same accuracy shortcomings. When charging a bank, voltage readings will be artificially high; when discharging (under load), readings will be artificially low. Any readings during this time will be inaccurate. After you isolate the bank from everything and let it rest for a while, the meter can take a reading, and in that narrow range of voltage, the meter can try to divine the SOC. But even then, every bank is different; the same voltage measured from one bank to the next may correspond to significantly different SOCs. Only a meter that profiled a bank through an entire deep cycle would have any chance at useful accuracy. And even then it would be limited to "at rest" readings--very inconvenient.

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter

    that meter is geared like idiot lights on a car are geared. there isn't any voltage meter there, but the leds will light at predetermined voltage setpoints and reads in terms of % in increments of 10.
  • SparkletronSparkletron Solar Expert Posts: 71 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter
    niel wrote: »
    that meter is geared like idiot lights on a car are geared. there isn't any voltage meter there, but the leds will light at predetermined voltage setpoints and reads in terms of % in increments of 10.

    Well that's fine actually--if it was accurate. But due to the reasons I mentioned, I think you'll see the meter hop around a lot as you add/remove significant loads. Going from 100% to 70% back to 100% just because you decided to use a microwave would not inspire much confidence.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter

    loads will pull a battery's voltage down and even a digital meter will show a lower voltage under load. just as is the case with a dmm the at rest condition should be gone by. this means after 3 or 4 hrs for a good reading. even this is a very remote indicator of a battery's condition, but is not always good to go by.

    to get a better idea of a battery's condition, one should consider amps in to amps out like some of the higher priced meters do. even with these meters one should weigh in all factors that could give a battery's condition such as temperature, battery efficiency, and specific gravity to name a few.
  • boBboB Solar Expert Posts: 980 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter

    The MNBCM was originally designed (by request) for use in small out in the middle of nowhere village huts in Africa... It has other uses too, though and has become a fairly popular item.

    That meter simply looks at the time the battery spends at, or above the typical (and jumper selectable) Absorb charge voltages and lets the user know that the batteries have not had a charge in a while (a week (or two)... (the usual timed Absorb voltage because current is not known) After that, it looks at the voltage and watches it drop, which can give an idea of SOC. No, it's not as good as knowing the current out of the battery, of course. But on the average, battery voltage and its drop is a pretty good indication of SOC or specific gravity. Voltage is a better indication of SOC if the current draw isn't huge relative to the size of the battery or for long periods of time. For things like golf carts, fork lifts, small weekend cabins and the like, at $69 list, the BCM fits the bill pretty well most of the time.

    Of course, if you want the best SOC metering, then a Tri-metric or some other Coulomb counting (Amp-Hours IN/Amp-Hours Out) meter is THE way to go, that is if it is designed correctly. (the Bogart is very good) Of course those cost more and are harder to install because of the shunt, etc. The BCM is not intended to replace metering for a full day to day, off grid living installation where the discharge currents and surges are large and can last a long time as I believe, Sparkletron is referring to.

    boB
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: MidNite Solar Battery Capacity Meter

    Also the MidNite meter gives you an indicator of when the battery's where last full. This is very you can at a glance see if the battery's have been charged fully in the last few days.
  • SparkletronSparkletron Solar Expert Posts: 71 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter

    The standard of measure I use to compare and evaluate all voltage-based SOC meters is... a voltmeter. It's not quite the at-a-glance meter that mounts attractively to your wall and beams at you with happy green LEDs. But it's way more accurate--IF you've profiled your bank.

    Determining your bank's 100% SOC voltage reading requires nothing more than a voltmeter with 0.01 resolution. You can acquire a multimeter that will do this (and so much more) for about $15.

    If you're using sealed batteries, determining the all-important 50% SOC voltage requires something that can count coulombs. For those of you who use a RIGrunner, I recommend a TURNIGY watt meter. At $20 or so it's hard to beat. The only caveat is that the counter resets at 65Ah. Not a problem; simply add 65 every time that happens.

    Profiling with a Kill-A-Watt is also possible although not as accurate, because it only displays KWH to a resolution of 10W, and it's only measuring what comes out of the inverter--not what goes in. So you'll have to factor in your inverter efficiency and do some math to convert to Ah.

    Note that the point of all this is not to create a poor man's Trimetric, but merely to profile your bank so that you can convert voltage readings to SOC, and do so more accurately than any voltage-based meter on the market. Many of us already have multimeters and Kill-A-Watt meters so the cost is a bit of time and patience.
  • boBboB Solar Expert Posts: 980 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter

    A simple volt meter won't tell you if the battery has had a full charge (gone through an Absorb cycle).

    Your batteries will sulphate and be dead early if you don't charge them.

    boB

    PS. Voltmeter with 0.01 what resolution ? percent ? 10 millivolts ? Why ?
  • SparkletronSparkletron Solar Expert Posts: 71 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter
    boB wrote: »
    A simple volt meter won't tell you if the battery has had a full charge (gone through an Absorb cycle).

    True, and neither will a simple voltage-based SOC meter. The fact that the MNBCM has measured 14.2v for one hour (on the AGM setting) and now shows you the happy green LED does not mean that the bank has been fully charged.
    boB wrote: »
    Voltmeter with 0.01 what resolution ? percent ? 10 millivolts ? Why ?

    That would be volts. As in 12.75v as opposed to 12.7v or 12v. Why? Because that's the accuracy you need if you want to convert a narrow range of voltage readings into a useful SOC estimate.
  • boBboB Solar Expert Posts: 980 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter
    True, and neither will a simple voltage-based SOC meter. The fact that the MNBCM has measured 14.2v for one hour (on the AGM setting) and now shows you the happy green LED does not mean that the bank has been fully charged.
    .

    Sure it will. That's how chargers (without finishing Amps) have been used for many many years now. What do you think Absorb Time is for ? It may well need to be longer than 1 hour though. 2 Hours or more is better.

    BTW, 12.7 V vs. 12.75 V is 50 millivolts not 10 mV. You will want to err on the high side way more than 10 mV anyway (charge V higher than spec due to battery temperature.) Although in Africa, it might be assumed that the batteries are warmer rather than cooler so even less of a problem You just gotta watch the water level if it's a vented Lead Acid.

    boB
  • SparkletronSparkletron Solar Expert Posts: 71 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter
    boB wrote: »
    Sure it will.

    Of course it won't. The MNBCM has no idea if a charger went through its bulk cycle, or how long that bulk cycle was. Did you use the correct charge profile? The MNBCM certainly doesn't know. It has no idea how many amps the charger put out. It has no idea if a charger was even the source of those volts. All it knows is that it measured 14.2v for one hour. But unless you counted coulombs going in, you can't say that you know the bank is fully charged. A simple charge profile does not fit every bank, any more than a simply table of voltage set points will accurately tell you the SOC.
  • boBboB Solar Expert Posts: 980 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter
    Of course it won't. The MNBCM has no idea if a charger went through its bulk cycle, or how long that bulk cycle was.

    Doesn't really matter as long as the Absorb time was greater than some minimum amount of time. Just have to make sure the Absorb time is longer than necessary and not shorter.

    A larger Amp-Hour battery bank generally needs a longer Absorb time but the small-ish systems the MNBCM is intended for have small batteries.
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: MidNite Solar Battery Capacity Meter
    Of course it won't. The MNBCM has no idea if a charger went through its bulk cycle, or how long that bulk cycle was. Did you use the correct charge profile? The MNBCM certainly doesn't know. It has no idea how many amps the charger put out. It has no idea if a charger was even the source of those volts. All it knows is that it measured 14.2v for one hour. But unless you counted coulombs going in, you can't say that you know the bank is fully charged. A simple charge profile does not fit every bank, any more than a simply table of voltage set points will accurately tell you the SOC.

    Well simply put the MidNite meter works the same as most all the charge controllers and Inverters ever built it looks for a set voltage for a period of time. I would say it is quite obvious by the price this is a simple meter and obviously nothing you are interested in purchasing so I will leave it at that.
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: MidNite Solar Battery Capacity Meter

    Sparkletron

    It seems that you are judging our little battery meter without any real experience with it. We would like to offer you the opportunity to play with one at no cost provided you tell us what you think when you are done. Keeping in mind this is a simple to install $69 list price voltage based meter. The meter has some logic built into its processor that a lesser expensive DVM would not have. Most people find this logic to be useful and a fairly good representation of what state the batteries are really in.

    If you are interested contact me via PM and I will make the arrangements.


    PS it also looks cool mounted on the wall :)

    Ryan
  • SparkletronSparkletron Solar Expert Posts: 71 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter
    halfcrazy wrote: »
    It seems that you are judging our little battery meter without any real experience with it.

    True, I've never used the MNBCM, and my comments are in no way a specific review or evaluation of this product. I've simply pointing out that, unless you've done something innovative to address the inherent issues that exist with *all* voltage-based SOC meters, then all you've really accomplished here is to--if you'll pardon the expression--put lipstick on a pig.

    Your meter's certainly attractive and not too expensive, and if I were looking for a sexy low-maintenance meter then I might take you up on your offer. But I'm looking for the most accurate meter I can get for my rapidly devaluing dollars--even if that meter is uncomely by comparison. I'm looking for brains--not beauty (although it's always a pleasure to have both).

    I'm no engineer but here's an idea you can take back to biz and and get shot down. If it was possible for a customer to take the MNBCM and manually adjust at least two of the fixed set-points (100% SOC and 50% SOC), such that the remaining values would adjust themselves accordingly, then you will have just advanced the state-of-the-art in voltage-based meters. Would it be worth all the extra R&D? Would it make a profit? No idea; probably not. But producing the most accurate voltage-based SOC meter in the industry would certainly give you marketing props, grow the brand, differentiate yourselves from the competition, build up your reputation as leaders and innovators, etc.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: MidNite Solar Battery Capacity Meter

    let's not make this into a battle here as the meter may well suit some and not others. some may look upon it as just what they were looking for as they know little of using dmms or other available electrical equipment. it may put it into the equivalency of idiot lights on a car for those that aren't up on the mechanical symptoms and needs of a car. that doesn't mean they shouldn't drive anymore than someone not electrically inclined shouldn't have a solar setup as the meter with its lights may suffice for their needs. i agree it isn't for everybody, but even those that can read better meters may like it.

    the one i have lets somebody like my other half see where empty really is as she would be inclined to continue to use the power as long as everything still works.:cool:
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: MidNite Solar Battery Capacity Meter
    niel wrote: »
    the one i have lets somebody like my other half see where empty really is as she would be inclined to continue to use the power as long as everything still works.:cool:

    Niel
    That is so true of my house as well. Glad to realize I am not alone. I do not know how many times I have heard "But the Light still turns on". :(
  • BB.BB. Super Moderators, Administrators Posts: 31,338 admin
    Re: MidNite Solar Battery Capacity Meter

    I believe Smart Gauge (UK) has gone through a bunch of modeling of battery banks to run their voltage monitoring product (no current shunts) state of charge predictions.

    Has anyone here tried their product? Is is accurate enough to protect the battery bank from poor charge/load control?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: MidNite Solar Battery Capacity Meter
    BB. wrote: »
    I believe Smart Gauge (UK) has gone through a bunch of modeling of battery banks to run their voltage monitoring product (no current shunts) state of charge predictions.

    Has anyone here tried their product? Is is accurate enough to protect the battery bank from poor charge/load control?

    -Bill

    'Smart Gauge' does a lot more than just match voltage profiles. It looks like they use a simple form of Impedance spectroscopy measurements for SOC profiles.

    http://www.buchmann.ca/article25-page1.asp
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