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  • Voltmeter connected to wifi or ethernet.

    I have been searching on internet for a voltmeter which can connect to the LAN or WAN so that I can see the voltage on the batteries (lead Acid 24v) without having to actually go to the batteries .

    Surely there must be a big demand for this?

    There is nothing available to buy even on Amazon and ebay.

    The only thing I have found is this which is way overpriced at over $250
    A modified rasberry pi.

    https://shop.enerserve.eu/262/smartp...mber=100029.34

    It would be cheaper to look at my charge controller through a wifi cam.

    Or get a cheap charge controller that has ethernet or wifi.

    Is there anyone else who would like to know how many volts there are in a battery without actually having to go and look or anyone who knows where to buy or make such a device?















  • #2
    If u have data port on charger add Wi-Fi bridge to monitor your system

    Comment


    • #3
      I still haven't found what I am looking for but I did find a very expensive module starting at $273.
      https://www.redbusbar.com/Wireless-Voltmeter.html

      Yesterday I wasted a couple of hours looking at arduino and raspberry pi you tube videos of wireless voltmeters.
      They all looked really complicated.


      The best solution I have found so far is a bluetooth voltmeter which send signal to a smartphone.
      This would be good enough if the batteries are near.
      http://www.batbot.net/

      I suppose I could leave a dedicated smartphone next to the batteries and then look at the smartphone over the internet using airdroid or similar app.

      I am surprised that nobody knows a good solution to to problem.

      I thought that this was the age of "the internet of things"
      Not in my experience.

      By the way I have been getting more useful results on duck duck go than on google.





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      • #4
        Here's a pretty simple project, with a schematic and all the code you'd need:
        https://community.blynk.cc/t/power-m...r-ina219/10297

        But if you just want a pre-built product, here you go:
        https://ebay.us/BPuVXo

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        • #5
          I agree with you cortijo, the market seems to lack cost effective IoT devices that you describe.For my needs, I plan to use an Arduino with a simple voltage divider. I plan on building one when I get time, hopefully shortly. Just google "arduino voltage divider" for lots of information. There are online sketches available.For wifi, you can use an ESP8266 board or an arduino with integrated wifi. I bought some ESP8266 boards for about $1.20 each, and will stick everything into a $2 plastic 2-gang switch/outlet box to keep jumper wires contained. I don't have a need for displays or serial monitors and instead use MQTT packets going upstream to an RPi or other data collection system.

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          • #6
            I used these with a voltage divider. They are ESP modules but easy to work with https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
            With the ESPEasy firmware you can send the data to Thingspeak or a bunch of other options https://www.letscontrolit.com/wiki/i...?title=ESPEasy

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            • #7
              I had looked a few years ago for something similar to remotely monitor my portable generator. I just wanted a simple device to monitor CT current per leg (voltage and frequency would also be nice) so that I could monitor the load on my generator remotely when running during a power failure to balance the legs, prevent overloads, etc. All of the devices I found were designed for power consumption monitoring. No would just tell me (or better yet log) the instantaneous current on each hot leg. They all wanted to tell me how many KWh I was using.

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              • #8
                These have potential. Not sure all of what they capture / display / log.

                https://www.amazon.com/dp/B07R11H2Q2/?tag=uid705600-20

                https://www.amazon.com/Eyedro-EHEM1-...=fsclp_pl_dp_3

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                • #9
                  I tried a simple voltage divider that should work for any battery size. I selected pins 1 and 12 on the Leaf's left side wiring harness which was 42.97v (no sense wire on left side terminal) on a roughly 47v pack. Selecting other pins will get you different voltages if that matters. With a 10kOhm resistor and 1kOhm resistor, I got 3.88v out, which is about where I'd expect. 42.97/11 ~= 3.91 or within about 1%, +/-, which is good enough for me. The 3.88v (brown wire) will be input into an Arduino ADC pin. I'll try it on an Arduino when the wifi modules arrive.
                  voltageDivider-min.jpg
                  Attached Files

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                  • #10
                    Originally posted by HollySprings View Post
                    I tried a simple voltage divider that should work for any battery size. I selected pins 1 and 12 on the Leaf's left side wiring harness which was 42.97v (no sense wire on left side terminal) on a roughly 47v pack. Selecting other pins will get you different voltages if that matters. With a 10kOhm resistor and 1kOhm resistor, I got 3.88v out, which is about where I'd expect. 42.97/11 ~= 3.91 or within about 1%, +/-, which is good enough for me. The 3.88v (brown wire) will be input into an Arduino ADC pin. I'll try it on an Arduino when the wifi modules arrive.
                    What was the SOC of that pack when you took those measurements? 3.88 volts per cell looks on the low side of that chemistry. At least by my charts it is less than 30% SOC.
                    9 kW solar. Driving EVs since 2012

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                    • #11
                      Ampster, it's a gen 1 battery, and it is a little low. Lithium Manganese Oxide. Per battery university, the "typical operating range 3.0-4.2V/cell"
                      https://batteryuniversity.com/learn/...of_lithium_ion

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                      • #12
                        Originally posted by HollySprings View Post
                        Ampster, it's a gen 1 battery, and it is a little low. Lithium Manganese Oxide. Per battery university, the "typical operating range 3.0-4.2V/cell"
                        .....
                        I also have Gen 1 batteries and I would be careful about believing everything you read on Battery University about generic chemistries. My testing of these batteries show a distinct knee of the discharge curve beginning at 3.6 volts per cell. It gets pretty steep after that. See the attached graph (not my own)
                        I have my low voltage cutoff set at much higher than 3.6 volts so that the weakest cell never has a chance to get to the knee of the curve. These are six year old batteries and have lost some capacity. There is not enough capacity between 3.6 volts and 3.0 volts to take the risk of reversing a cell. There is no right or wrong and each of us can choose where we want to be on the risk/reward line.
                        Leaf Discharg curve.jpg
                        Last edited by Ampster; 01-16-2020, 05:56 PM.
                        9 kW solar. Driving EVs since 2012

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                        • #13
                          Ampster, thanks for that. To date, our small Leaf packs (14s2p) have been lightly charged/discharged and we tend to stay between 3.67v to 4.17v since that's the SI-6048-US config (44-52 volts for the pack.) I am still waiting (after multiple emails) for the SMA interface spec I requested a few months ago, but I'm not sure what it will provide as far as ability to adjust charge/discharge.

                          Anyway, it seems a good metric to 'see' where the battery is on the curve is voltage. In the context of this topic, I am already deploying Arduinos, and have space for a voltage divider to a dedicated to one of the six analog inputs. I know ground from an analogRead call results in 0 and from 5v results in 1024 (10 bits of 1s). The plan is to map from 3.5v to 4.2v input to a 0..1024 value that will represent, essentially, a 'voltage remaining' value. For current, I'm ordering YHDC company's SCT-013-030 (30A) and SCT-013-020 (20A) CT clamps from our distributor. The parts are a few bucks (quantity 10), but hopefully I can use the data going forward to 'see' the curve.

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                          • #14
                            There are those that will argue that because the discharge curve is flat that voltage is not a good estimate of SOC. I have two different coulomb counters on my pack, one in the BMS and the other in the inverter. They often vary by as much as 30% so I often rely on voltage myself to give myself another measure of the status of the pack. I think that is what you mean by the term, "voltage remaining value".

                            On another note I think I understand that you will have two 14s batteries connected in parallel, each with their own BMS. Is that correct? I started this journey using Prismatics in an EV I built and applied those principles of buddy pairing those cells into a pack with one BMS. As my Leaf pack ages and I assess the need for more storage capacity, I am considering using Tesla modules. That will imply using multiple BMSs if I want more capacity than two modules in series. So I hope you continue to update us on your progress for my benefit. As more and more batteries become available, others may also benefit.
                            9 kW solar. Driving EVs since 2012

                            Comment


                            • #15
                              Regarding the 14s2p packs, I am migrating to 12s2p (6 leaf modules), keeping the car's three battery packs intact and reusing the existing sense wiring. The end system will be 8 x 12s2p, so yes, I'll run parallel 48v (6 modules in series) batteries. My BMS hardware count will be higher than someone running parallel packs in series. There are tradeoffs either way, but scaling the energy storage system (e.g adding incremental storage capacity) was a given -- it's a high priority requirement. I will split packs 4 and 4 initially between the two Sunny Islands, and figure out over time in L1 or L2 needs more energy storage support. I can change to 3 and 5, 2 and 6, or even 1 and 7 if necessary.

                              I wasn't good with the terminology in the prior post. Without hijacking the OP's post, I'll try to stay on point relative to the topic at hand: "Voltmeter connected to wifi or ethernet." As a function of SOC, I'll adopt the generally accepted premise that 1) the graph Ampster presented is a reasonably accurate depiction of the battery system, and 2) that voltage, time, and cumulative current are material to SOC. The graph shows a roughly 3hr, 10 minute discharge. The consumed amps are ~63A which is about the 2p total module capacity (2s2p module, 8v at ~66A nameplate capacity.) The load on the graph is close to a constant ~20A. I plotted sole key points on the graph, which is listed below, and looked at the delta-mAmpHour (dmAh) to delta-Voltage (dV) number.

                              2020-01-17 (5).png

                              My metric for dmAh/dV (the first derivative) is that values over 50 show a healthy state of charge, those under 50 not so much. The only thing I'd change from the chart is the unit of time measurement, which I'd change to 15 minute (900 second) intervals. That's my prejudice from prior life in telecom and RFC MIB days.

                              Putting this all together, the SOC for me will be expressed as f(v, t, a) with instantaneous values where v=voltage, t=time, a=amperage as seen by an Arduino. Calculating the voltage will be via a voltage divider as above with reference voltage from the battery pack (A..H). Calculating amperage will be via SCT-013-020 current sensor from Shenzhen Xiangyangwei Electronics (Quantity 10 or 50... still discussing) The parts costs are $0.01 for the voltage divider, the SCT-013-020 is $2.60 w/o shipping, so I expect about $4US per part, the arduino Uno is about $11, and the ESP8266 is $1.20. I've not used the ESP8266, but youtube shows it may use quite a bit of power. So add in a small (<$1) heat sink just in case. And add in a $2 plastic 2-gang box. $20 or so?

                              All theory for me at the moment. I'll post more when I get parts.

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