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I want to build a multi voltage monitor for checking BMS balancing protection boards functionally - Page 2 — Parallax Forums

I want to build a multi voltage monitor for checking BMS balancing protection boards functionally

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  • Actually, as I understand the above schematic that represents @msrobots idea, the muxes are connected to eight cells, but in such a way that P2 would measure only one cell at a time.

    That's correct. It's also correct that the power supply for the CD4051 should be isolated from that of the Prop. It can be whatever voltage is necessary to accommodate the output from one cell, plus a margin of error.

    I neglected to include the "inhibit" pin in my schematic. It may make sense to use it during transitions on the S0 - S2 lines.

    -Phil

  • If you just want to measure the voltage across each cell, then why not just use Op-Amps configured in differential mode? The Caveat is that the Op-Amps need to be powered from the highest voltage potential, but the output from each Op-Amp will never be more than the individual cell.

    https://tinyurl.com/ygnuqglu

  • sam_sam_samsam_sam_sam Posts: 2,263
    edited 2021-08-06 21:34

    Okay

    Now question is what differential Op-Amp would be a good candidate that is a through hole device for this project one note the voltage need to go as high as 4.2 voltage between battery cells is that going to be a problem

    There seems to be a problem with the simulation on Op-Amp because the one OP-Amp in the middle is different from the other two if the other two are working correctly then I get just of how it works

    I do have a question how much current would the Op-Amp draw from the charging/discharging in either mode

  • "Now question is what differential Op-Amp would be a good candidate" - differential is the way it is configured and used. A QUAD LM324 would do the job as long as the total voltage did not exceed 32 V. In the example I only used 3 cells ... how many cells would you have in your design?

    The middle should respond the same way as the others. If you right click on the battery symbol, you can change the voltage in the simulator to whatever you want. The total voltage in the case of the example "11.1" volts but for your 4.2 Volt requirement it would read 12.6 Volts.

    In this configuration the inputs are current limited with a 100k resistor ... for each battery essentially a 21 micro amp load to measure the battery voltage status

    Note: With the LM324 QUAD Op-Amp you could go up to 7 cells, but you would need TWO of the LM324's with one Op-Amp not used. 7 x 4.2 = 29.4 Volts

  • Now my next question is can I power it from the battery voltage or do I need to power the Op-Amp with a +15 and -15 volt power supply

  • You can power it from the battery voltage, but it should be slightly higher than the total battery voltage. The current just needs to be enough to suffice the LM324's. You DON'T need a negative supply. See attached schematic PDF ....

  • Thank you for all your help with this project request I will have to order the parts and put it together and try it out

    Can use two diodes in front of the power supply so that the power supply is slightly higher than the battery voltage will ever be or is there another way that would be better

  • msrobotsmsrobots Posts: 3,459
    edited 2021-08-07 05:50

    Actually @"Phil Pilgrim (PhiPi)'s circuit shows 8 Batteries, one mux connected to the low side of each cell, one to the high side.

    He basically showed what I intend to build (thank you Phil) but - as usual - he is one step ahead of me, I did NOT thought about the insulation between power for P2 and power for muxes. But he is absolutely right there.

    By varying the resistor divider at AOUT for the ADC pin and varying the power supply for the muxes one can adjust it nicely to different battery/voltage levels. And the CD4051 muxes can handle up to ~15-20?V.

    So I need to order some opto-isolators(?) too, together with a bunch of CD4051's any tips on what part would suit?

    But this forces the next question, I know I can isolate a circuit using AC and a transformer. Are there components out there to allow me to isolate it without going back to AC?

    -EDIT found them> Isolated Module DC DC Converter.

    Another thing I could not figure out is how much current the CD4051 can handle. Ideally I not just want to measure the voltage, but charge also.

    Mike

  • frank freedmanfrank freedman Posts: 1,853
    edited 2021-08-07 07:31

    I could be wrong on this one but,
    I see one possible problem as drawn if the supply to the 4051 is 3.3V.
    The data sheet maximum ratings state:
    DC Input Voltage –0.5 VDD + 0.5 V
    If VDD to the 4051s is 3.3 then any input exceeding 4V will likely kill the 4051s

    Another possibility:
    Use four lines demuxed to battery count +1 to turn on SSRs
    Use battery cell count +1 of CP1017N OptoMos solid state relay. 60 volt 4pin SOP package,
    Feed into a differential op amp (LM348 looks like about $0.25 at DigiKey) each cell by selecting the appropriate OptoMos switch to select the + and - side of a cell and take the reading with a single ADC channel.
    Power the op amp with a small DC/DC converter.

    Mike,
    As to charging, you would need a separate circuit with a very low series resistor in the battery charging circuit and another op amp across the resistor to measure the current in the battery circuit. I in max for 4051 looks like 18uA.

  • sam_sam_samsam_sam_sam Posts: 2,263
    edited 2021-08-07 12:02

    @msrobots said:
    Ideally I not just want to measure the voltage, but charge also.
    Mike

    I would think that each battery cell would have the same current but you have brought out an interesting question does each cell take the same exact amount of current for each battery cell this would be an interesting investigation to find out but how would to go about doing this would be the question

    One thought would be to use a very low resistor in series between each battery cell but this would add up by the time you got to the last battery cell for the total resistance to the hole circuit

    Versus a battery pack with no current sensing resistance add to the circuit

    This might be another reason why the BMS balancing protection board that is very picky to match batteries for this might be the other issue that the current for each cell is some what different

    But the question is how much difference is there between each battery cell in the amount of current is drawing or passing through the the battery cells

    The battery on charge they do heat up a little bit which is normal but this is still current loss in term of heat it nominal amount 1* to 2* F ( this depends on how much current you are using for charging a battery cell )

    But I could be completely wrong in my thinking

  • I see one possible problem as drawn if the supply to the 4051 is 3.3V.

    It's not 3.3V. It can be much higher than that, since it's not the same supply that powers the Prop.

    -Phil

  • @"Phil Pilgrim (PhiPi)" said:

    I see one possible problem as drawn if the supply to the 4051 is 3.3V.

    It's not 3.3V. It can be much higher than that, since it's not the same supply that powers the Prop.

    -Phil

    Thanks Phil, the drawing appeared to have 3.3V going to supply the 4051s. I think the TI one I looked up was able to have up to 20V supply.

  • msrobotsmsrobots Posts: 3,459

    @"frank freedman",

    what you wrote is way above my level of understanding, but I will look for the parts you mentioned.

    You AND @"Beau Schwabe" are talking about OP-Amps. this makes me feel stupid because I sort of know you are usually right , I just do not see the picture.

    @"Phil Pilgrim (PhiPi)"'s Diagram shows the brute force variation I try to build. And the Idea is that the 'analog' part with them CD405xB as well as them optocouplers are driven by the expected Battery voltages, in my current case below 5V, so I will feed this with 5V. But could be higher, say 12V depending on the opto-couplers voltage range and desired battery voltage.

    The other side of the opto's will be switched with 3.3V by the Propeller. And the opto's will protect the propeller pins from mishap happening on the 'analog' side. If I understand this correctly.

    Except my Analog measuring Pin which gets protected by a resistor divider and a zener, so my guess.

    I am not a EE at all, forgive me

    I did found a bunch of HCPL2630 in my boxes it is a dual open-connector opto-coupler, kind of old but will do for experiments.

    GND between Prop and Analog GND will be constant connected (maybe with big resistor) and switched to the low side of each cell in turn. And the analog output of the mux goes over a resistor divider into the P2 ADC pin.

    So that is the plan for measuring Voltage of each cell.

    If I now would use another opto-coupler to PWM the analog supply between resistor divider and mux IO (going to the + side of the cell) I should be able to charge the cell and measure the current while doing so.

    But I will need to find out how much current the mux can handle at say 5V.

    I have some trouble understanding the Datasheet of the CD405xB.

    in 6.1 Absolute Maximum Ratings it states:

    DC Input Current Any One Input –10 10 mA - that sounds like the digital inputs for selecting. Or not?

    in 6.5 Electrical Characteristics it states:

    Input Current, IIN (Max) 18μA - that sounds awful if this is for the switched channel, but is it? Or is it the max current on the digital selector pins?

    in 9.2.2 it states:

    1. Input/output current consideration: The CD405xB series of parts do not have internal current drive circuitry and thus cannot sink or source current. Any current will be passed through the device.

    confused,

    Mike

    I have 12 of them on order at Digi-Key so I can break a couple finding out.

  • @msrobots
    @"Beau Schwabe" and @"frank freedman" are talking of just another approaches.
    What I see in the schematic @"Beau Schwabe" has attached is he just measures the battery cells differentially using op amps in a voltage follower mode (the voltage of the battery is present on the output of a given op amp, referenced to ground) and "posts" these to the eight prop ADC pins - no mux required. You can then take a voltage measurement all at once - all eight cells. It's just a front-end where you do not have to switch anything.
    Another possibility, if you only have one ADC pin is to combine the two solutions but you will not need to switch ground in this case - just the ADC input. It will be a bit more complicated but should also work.
    That's how I see it.

  • sam_sam_samsam_sam_sam Posts: 2,263
    edited 2021-08-08 13:51

    @"Beau Schwabe" said:
    You can power it from the battery voltage, but it should be slightly higher than the total battery voltage. The current just needs to be enough to suffice the LM324's. You DON'T need a negative supply. See attached schematic PDF ....

    LM324*** Dip package and specifications which one would be the choice for this application

    Digikey has several options

  • msrobotsmsrobots Posts: 3,459

    OK, Guys

    not being a EE I did some crude experiments and, YES the basic circuit @"Phil Pilgrim (PhiPi)" gave me, with some added capacitors as of Datasheet for the mux did work.

    But I did not listen to what to what our member of the @Yanomani tribe said. I mean I did, just not careful enough.

    My thinking was to isolate one cell for measuring. switching my measuring ground to that cell. But Henrique is perfectly right, that just works as long as those 8 in serial connected cells do not exceed the maximum voltage of the CD405xB - and that effed it up a bit.

    But basically, YES switching Propeller Ground and Measurement Pin from one cell to the next does work fine.

    In order to have say 8 cells connected at the same time the mux(es) itself needs to handle the complete range of voltage provided. And that is about 20v they can handle. The chip offers pins to supply bias voltages, basically, but to cascade this to more then 8 cells would be a nightmare for me.

    I think I need to go the other way around, first, starting with small devices attached to the needed places.

    Mike

  • YanomaniYanomani Posts: 1,306

    Hi Michael, thanks for the kind reference! :smiley:

    I'm not an EE, nor any rainmaker, from any tribe; there are too many others way better than me, just at the forums.

    Since that connection is not mentioned at the diagram posted by Phil Pilgrim (#25), I just need to know if pin 7 (VEE) of each mux got connected to pin 8 (VSS) of the same mux, or left floating?

    Brazilian indians "Rain Maker Stick" (Pau de Chuva):
    https://youtu.be/8_-Oow_EaCk

  • YanomaniYanomani Posts: 1,306
    edited 2021-08-19 04:28

    P.S. 2: just scratch it: they'll not work, just the way it's described ahead, because each mux would still be 'seeing" (7 x 4.2) V; yet some magic smoke, at the horizon.

    But the general idea "can" work, if each CD4051B is replaced by associating two CD4052B (4:1 MUXES) in series, but now, the whole circuit will need to be re-designed, including the optocoupler block (you'll need multiple instances of this block), and each pair of CD4052B outputs would need further re-thinking (perhaps by adding another pair of 2:1, CD4053B muxes, ahead).

    Just another tought:

    In order to avoid too differing solutions (smt/hard to find), like the one I refered before (#27), I was trying to immagine other scenarions:

    - Since those CD4051B muxes doesn't consume almost any appreciable current while working, perhaps its just possible to connect both in series, so, the topmost GND (VEE + VSS) would be routed to the lowermost PWR (VDD) pin, configuring an "intermediate" CENTER node, while the topmost PWR (VDD) and the bottommost GND (VEE + VSS) stays routed to the nodes they already are represented .

    The "CENTER" node don't needs any further connection, provided, of course, that you had at least two ceramic caps, connected between PWR and GND of each mux.
    Sure, then you'll need to have two groups of optocouplers; one providing control inputs to the upper mux, and the other, routed to the lower one.

    Each group of optocouplers would be connected to PWR and GND ot the respective mux they control.

    Hope it helps.

    Henrique

    P.S. Note that the mux themselves will be working "in series", but this is more than usual, at the analog realm.

  • YanomaniYanomani Posts: 1,306
    edited 2021-08-19 14:02

    Two new guys on the block, from TI, one of them able to withstand 60 V, and the other, 44V.

    Only one is available thru distributors, but it's just the one that has a TSSOP package readilly available (the other is only directly from TI, and has only its a QFN version, not any thru-hole, at all).

    Will need a bit of study, in order to verify ensure any of them would fill the bill, without too many mods at the original circuit.

    https://ti.com/product/TMUX7208

    https://ti.com/store/ti/en/p/product/?p=PTMUX7308FRRPR

  • msrobotsmsrobots Posts: 3,459

    Yeah, as I said it will be a nightmare and I need to find a complete different solution.

    The problem is that the 'trend' goes to higher voltages in solar systems and cars. because higher voltage means smaller and lighter wires.

    Enjoy!

    Mike

  • sam_sam_samsam_sam_sam Posts: 2,263
    edited 2021-08-19 22:25

    What do you think of this device to isolate the battery cell voltage

    https://www.electronics-lab.com/project/optically-isolated-analog-input-module-for-arduino/

    To the micro controller inputs

  • Hi

    I thought I would add my 10 cents (for better or worse)

    It seems to be generally accepted that a fully charged lipo is 4.2v and a fully discharged lipo is 3.0v, and that charging or discharging outside of these limits will damage the cell.
    A stack of cells wired in series has to be treated with respect. Since each cell will have a slightly different capacity, the pack as a whole is only as good as the weakest cell. So only measuring the voltage of the stack of cells to determine its charged or discharged state is dangerous. Remember the capacity is measured in milli-amp hours and since each cell is wired in series, each cell HAS to deliver the same current- it can't be avoided.
    Suppose the weakest cells capacity is 1900 maH and the strongest 2100 maH. If you discharge at 1 amp the weakest cell will be flat after 1.9 hrs and the strongest after 2.1 hrs. (114 mins / 126 mins) You should stop discharging after 114 minutes if you do not want to damage the weakest cell. There is NO WAY to maximise the energy from the entire pack! Fact of life! Some cells will never be asked to give their full capacity if the pack as a whole is expected to survive.
    So how DO you discharge safely?
    Either continuously monitor each cell individually when discharging and stop when ANY cell drops below 3.0v; or stop discharging when the whole packs voltage drops to a voltage safely ABOVE the expected [number of cells times 3.0v]. What margin to allow- that is the question!

    Of course exactly the same applies when charging. However when charging intelligently, each cell can have the charging current by-passed once it's reached its full voltage, preventing the cell from overcharging.

    So I don't see how you can ever get the FULL energy out of EACH cell as long as you wire them in series and then put a load across them.

    But if you want to monitor the charge/ discharge process, just measure the voltage at each cell junction and do the math. A potential divider at each junction to earth to give a suitable range of voltages for the a/d's, calibrate in software and do the math and display the results.

    You've got my juices flowing so I'm going to give it a test. However I don't have enough lipo's so I will use Ni-MH's of which I have plenty. Packs of those can suffer the same fate as I've proved in electric r/c aircraft. When using a pack and repeatedly discharging till the motor slows noticeably I wondered why the packs had such a short life- one day I measured each cell after discharging and found one cell reverse voltaged!! Amazingly it survived a few more uses but then was useless.

    Phew!!

    Dave

  • msrobotsmsrobots Posts: 3,459

    interesting.

  • sam_sam_samsam_sam_sam Posts: 2,263
    edited 2021-08-20 07:25



    @tritonium said:
    Hi

    I thought I would add my 10 cents (for better or worse)

    It seems to be generally accepted that a fully charged lipo is 4.2v and a fully discharged lipo is 3.0v, and that charging or discharging outside of these limits will damage the cell.
    A stack of cells wired in series has to be treated with respect. Since each cell will have a slightly different capacity, the pack as a whole is only as good as the weakest cell. So only measuring the voltage of the stack of cells to determine its charged or discharged state is dangerous. Remember the capacity is measured in milli-amp hours and since each cell is wired in series, each cell HAS to deliver the same current- it can't be avoided.
    Suppose the weakest cells capacity is 1900 maH and the strongest 2100 maH. If you discharge at 1 amp the weakest cell will be flat after 1.9 hrs and the strongest after 2.1 hrs. (114 mins / 126 mins) You should stop discharging after 114 minutes if you do not want to damage the weakest cell. There is NO WAY to maximise the energy from the entire pack! Fact of life! Some cells will never be asked to give their full capacity if the pack as a whole is expected to survive.
    So how DO you discharge safely?
    Either continuously monitor each cell individually when discharging and stop when ANY cell drops below 3.0v; or stop discharging when the whole packs voltage drops to a voltage safely ABOVE the expected [number of cells times 3.0v]. What margin to allow- that is the question!

    Of course exactly the same applies when charging. However when charging intelligently, each cell can have the charging current by-passed once it's reached its full voltage, preventing the cell from overcharging.

    So I don't see how you can ever get the FULL energy out of EACH cell as long as you wire them in series and then put a load across them.

    But if you want to monitor the charge/ discharge process, just measure the voltage at each cell junction and do the math. A potential divider at each junction to earth to give a suitable range of voltages for the a/d's, calibrate in software and do the math and display the results.

    You've got my juices flowing so I'm going to give it a test. However I don't have enough lipo's so I will use Ni-MH's of which I have plenty. Packs of those can suffer the same fate as I've proved in electric r/c aircraft. When using a pack and repeatedly discharging till the motor slows noticeably I wondered why the packs had such a short life- one day I measured each cell after discharging and found one cell reverse voltaged!! Amazingly it survived a few more uses but then was useless.

    Phew!!

    Dave

    The output voltage can be changed 5 volts I got in touch with the company that made this device and there response was just two resistors that need to be changed R6 and R7 which controls the gain of the circuit

    They also told me that they could make a version that would work like this what ever voltage from 0 to 5 volts the output voltage would be 0 to 5 volts

    They also told me that the minimum order request would have to be 8 of them

    You are forgetting the hole purpose of this project was to determine weather or not the batteries that are going to be used with a BMS balancing protection board that if you see battery voltages all over the place that the battery cells are not matching each other

    I have a BMS balancing board that is extremely picky about how close the battery charging and discharging curves are if they do not match exactly the battery charging is greatly effected the discharging is not quite as bad but if the discharge curve is not very close you have the same exact problem

    What I want to do is monitor the battery voltage on each cell as accurately as possible so I can match each as close as possible for for the best results from this BMS balancing protection board or determine that there is an issue with the BMS balancing protection board and that it can not correctly control the balancing function of the battery cell voltages

    Here is what I did when I first got this BMS balancing protection board I have battery testing machine that is very good at showing you the charging and discharging curves of battery that is under testing and you can match them very close but what I noticed was that after a few charging and discharging of this battery pack was that a few of the cells were not even close to each other as they had been when charging them individually
    However when I recharged these batteries in question they results came back to what they had been in testing of the batteries in the first place

    So this is the issue with trying to matching battery packs cells and BMS balancing protection boards

    One note that the batteries in question are from a brand name new battery pack
    They are LG brand batteries so are very good batteries because I used this battery operated soldering iron station from this tool battery pack and get very good results

    But the hole reason I bought this battery operated soldering iron station was how small it is and the batteries are also in the case but BMS balancing protection board issue with this device because the company does offer this device with the batteries it is in a kit form

    I know that it is possible to match batteries to each other because I bought four of the the other 3 battery packs only are BMS protection boards from Battery Hookup that have a BMS balancing protection board on one of the battery packs

    I have done some battery testing on this battery pack and the battery are very closely matched to each other the difference between cells are only 0.01 volts from each other I have charge them and discharge them several times these are medical battery packs that are changed out every few years or after so many cycles

    The only problem with using these battery packs in the battery operated soldering iron station is the BMS balancing protection board only is 16.80 the battery operated soldering iron station is 24 volts and the BMS balancing protection board will not fit in the device case

    Also Battery Hookup does not have any more of these battery packs in stock right now and they do not know if they will be getting any more of them

    I still have to test the other two battery packs for how close the battery cells are to each other in the other two battery packs ( the configuration of this battery pack is 4c2p )

    I have been thinking about splitting this battery pack apart and using on the battery pack BMS balancing protection board which poses a problem which is as follows

    This BMS balancing protection board on the board operated soldering iron station is set up like this it has two ports of three battery cells each if one port charges faster than the other port it shuts down the charging cycle

    Use the first three cells and use the same three cells that are under first set and see how well this works and hopefully this will work

    Now I found out there is a way to use the SkyRc IMAX b6 battery tester to monitor the battery voltage on each cell however you have to sit and monitor the battery voltage on each battery cell because the software does not have this function capability
    ( plotting the results over time ) unfortunately I wish it did but this another story

    One note is if you plan on doing this your self use the battery charging cycle not the BMS balancing function that would defeat the purpose of checking the BMS balancing protection board under test

    If anyone is interested in how to hook this up and how to hook up the balancing wires to the SkyRc IMAX b6 battery tester I will be glad to explain to you

    You could also test nicad batteries this way but you have do three cells to one battery balancing input wire not prefect solution to see if batteries are matching each other but you check a battery pack that is giving you problems but it would limit you to the following voltages 1.25 + 1.25 +1.25 = 3.75 which is very close to 4.0 you could use the battery type that only charges to 4.11 volts or you could also use the battery type that charges to 4.21 volts

  • @tritonium said:
    ..
    I thought I would add my 10 cents (for better or worse)

    ... There is NO WAY to maximise the energy from the entire pack! Fact of life! Some cells will never be asked to give their full capacity if the pack as a whole is expected to survive.
    So how DO you discharge safely?
    Either continuously monitor each cell individually when discharging and stop when ANY cell drops below 3.0v; or stop discharging when the whole packs voltage drops to a voltage safely ABOVE the expected [number of cells times 3.0v]. What margin to allow- that is the question!

    Of course exactly the same applies when charging. However when charging intelligently, each cell can have the charging current by-passed once it's reached its full voltage, preventing the cell from overcharging.

    So I don't see how you can ever get the FULL energy out of EACH cell as long as you wire them in series and then put a load across them.

    But if you want to monitor the charge/ discharge process, just measure the voltage at each cell junction and do the math. A potential divider at each junction to earth to give a suitable range of voltages for the a/d's, calibrate in software and do the math and display the results.
    ...
    Dave

    I'm glad you said that as I was a bit hesitant in doing so.... :smiley:

  • @Maciek said:

    @tritonium said:
    ..
    I thought I would add my 10 cents (for better or worse)

    ... There is NO WAY to maximise the energy from the entire pack! Fact of life! Some cells will never be asked to give their full capacity if the pack as a whole is expected to survive.

    I would have to agree with you on this point

    So how DO you discharge safely?
    Either continuously monitor each cell individually when discharging and stop when ANY cell drops below 3.0v; or stop discharging when the whole packs voltage drops to a voltage safely ABOVE the expected [number of cells times 3.0v]. What margin to allow- that is the question!

    I personally would not use this method because if the individual battery cells are way out from each other voltage wise

    Of course exactly the same applies when charging. However when charging intelligently, each cell can have the charging current by-passed once it's reached its full voltage, preventing the cell from overcharging.

    Where do you find a BMS balancing board that would work that way

    So I don't see how you can ever get the FULL energy out of EACH cell as long as you wire them in series and then put a load across them.

    This is a great point

    But if you want to monitor the charge/ discharge process, just measure the voltage at each cell junction and do the math. A potential divider at each junction to earth to give a suitable range of voltages for the a/d's, calibrate in software and do the math and display the results.

    Just how accurate would this approach be for each battery cell voltage monitoring

    ...
    Dave

    I'm glad you said that as I was a bit hesitant in doing so.... :smiley:

  • sam_sam_samsam_sam_sam Posts: 2,263
    edited 2021-09-18 15:58

    I just want everyone to know that I have found a work around for the issue with not being able to watch the battery voltage on each cell when testing a BMS balancing protection board the battery charger tester that I have talked about will work not do exactly what I wanted but thing I have to do when the battery cells reaches near the 4.00 volts on each battery cell is when I have to watch the screen to get the information that I need for how balance the battery voltage is for each cell it not the ideal way to do this like I mentioned earlier in this post if I knew programming better I do i would tailor the software that is for this charger more for what I would like to have it do

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