BrianK Posted January 22, 2020 Share Posted January 22, 2020 I'm-re-installing habitation batteries following a bodge by the last owner and have purchased one of the monitors at the links below. I fully understand that all negative connections must go through the shunt but lose it a little where the connection is made from shunt to the circuit board. The out and about article is clear enough to follow but will connecting in this way give me all of the capability of the monitor? I find the instructions on the PDF (second link) more confusing and don't really get the benefits/difference of the 3 different layouts. For a cheap little monitor this has plenty of capability, I just want to make sure I can get the maximum info out of it. https://www.outandaboutlive.co.uk/motorhomes/articles/practical-advice/motorhome-advice-how-to-fit-a-multi-function-battery-monitor https://www.hisse-et-oh.com/system/assets/000/093/889/original/ELITE_-_Amp-Volt-Ah_metre.pdf?1411106362 Thanks for any help anyone can offer. Link to comment Share on other sites More sharing options...
spirou Posted January 22, 2020 Share Posted January 22, 2020 ridiculously complicated wiring :-D But anyway, just wire the same way as in the OAL link and you should be fine. The crucial thing with all battery monitors is that no negative bypasses the shunt. I can't imagine where you'd have external power supply for this system, maybe in a grid connected house? Link to comment Share on other sites More sharing options...
Derek Uzzell Posted January 22, 2020 Share Posted January 22, 2020 As I understand the instructions for the Elite DCM120100C unit, an external power-supply will be required only if the voltage being measured exceeds 90V. 50A to 1000A versions are advertised here https://www.amazon.co.uk/Digital-Voltmeter-Ammeter-Capacity-Percent/dp/B0788MQ74N and some 2015 comments are here https://forums.ybw.com/index.php?threads/cheap-chinese-battery-monitors.418949/ This 2018 forum thread might also be of interest https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Nasa-Battery-Monitor/48563/ Link to comment Share on other sites More sharing options...
plwsm2000 Posted January 22, 2020 Share Posted January 22, 2020 Although I have not used this particular unit, it is probably similar to others that I have used. My comments therefore come with a bit of a health warning. It appears that the monitor uses a separate 12V input (marked +Vext) to power the unit and another input (Vin) for the actual voltage measurement. The way that it has been wired in the outandabout article and the "Discharge - two wires" option in the datasheet (+Vext and Vin linked together) means that it gets its power from the same power source as the one it is trying to measure. The return power supply current goes through the GND pin back to the battery (black wire). The displayed current DOES NOT include the actual current drawn by the module itself. With its LED display, this is likely to be around 20-30 milliamps (0.02 - 0.03 Amps) and although not that significant, you probably don't want to leave it on continuously. The "three wire" option just allows you to use a separate supply to power the unit rather than the voltage you are measuring. In your case just use the outandabout article method. For the current measurement, as the resistance of the shunt is very small (just a few milliohms), the voltage across it will also be very small even with several amps through the shunt. To get any level of accuracy, the voltage across the ISNS and AGND terminals (green and blue wires) must be exactly the same as the voltage across the shunt so you cannot have any current flowing in these two wires (not even the 20-30milliamps for the module). Basically make sure you link the AGND (green) and GND (black) wires at the shunt and not on the module connector block. In the outandabout article (photo 7), I noticed there is another (brown?) wire on the actual battery negative terminal in addition to the thick black wire going to the shunt. I am confused about this wire as any current in it will bypass the shunt and not be measured. If it is the chassis ground connection, I cannot see how the monitor will measure the charging current from the alternator and therefore read a very inaccurate remaining battery capacity. I would have expected to see this brown wire on the right hand side of the shunt. Link to comment Share on other sites More sharing options...
BrianK Posted January 22, 2020 Author Share Posted January 22, 2020 Thanks for the input everyone. plwsm2000 - 2020-01-22 2:40 PM It appears that the monitor uses a separate 12V input (marked +Vext) to power the unit and another input (Vin) for the actual voltage measurement. The way that it has been wired in the outandabout article and the "Discharge - two wires" option in the datasheet (+Vext and Vin linked together) means that it gets its power from the same power source as the one it is trying to measure. The return power supply current goes through the GND pin back to the battery (black wire). The displayed current DOES NOT include the actual current drawn by the module itself. With its LED display, this is likely to be around 20-30 milliamps (0.02 - 0.03 Amps) and although not that significant, you probably don't want to leave it on continuously. The "three wire" option just allows you to use a separate supply to power the unit rather than the voltage you are measuring. In your case just use the outandabout article method. For the current measurement, as the resistance of the shunt is very small (just a few milliohms), the voltage across it will also be very small even with several amps through the shunt. To get any level of accuracy, the voltage across the ISNS and AGND terminals (green and blue wires) must be exactly the same as the voltage across the shunt so you cannot have any current flowing in these two wires (not even the 20-30milliamps for the module). Basically make sure you link the AGND (green) and GND (black) wires at the shunt and not on the module connector block. The first thing that occurred to me when I read this was whether a connection to the starter battery could be used to power the display as I will have that in the vicinity anyway but on the other hand I’m wondering if this draw is insignificant enough to just ignore. plwsm2000 - 2020-01-22 2:40 PM In the outandabout article (photo 7), I noticed there is another (brown?) wire on the actual battery negative terminal in addition to the thick black wire going to the shunt. I am confused about this wire as any current in it will bypass the shunt and not be measured. If it is the chassis ground connection, I cannot see how the monitor will measure the charging current from the alternator and therefore read a very inaccurate remaining battery capacity. I would have expected to see this brown wire on the right hand side of the shunt. I also wondered about this brown wire, although if you see the link below it seems a lot of people do make the mistake of not realising ALL LOAD negatives need to be connected to the opposite end of the shunt to the batteries. https://marinehowto.com/installing-a-battery-monitor/ Link to comment Share on other sites More sharing options...
BrianK Posted January 23, 2020 Author Share Posted January 23, 2020 Another question after reading the instructions again if you would chaps: Under Calibration of Zero and High Voltage Readings and Calibration of Zero and High Current Readings it says to 'just short Vin and GND' and 'just short ISNS and AGND'. Do they mean LITERALLY short them?! Link to comment Share on other sites More sharing options...
plwsm2000 Posted January 23, 2020 Share Posted January 23, 2020 BrianK - 2020-01-23 12:48 AM Another question after reading the instructions again if you would chaps: Under Calibration of Zero and High Voltage Readings and Calibration of Zero and High Current Readings it says to 'just short Vin and GND' and 'just short ISNS and AGND'. Do they mean LITERALLY short them?! Yes but you need to disconnect other wires first (temporarily) To get zero voltage, disconnect Vin from +Vext and then link Vin to GND. If you don't, you will short out the 12V supply (on +Vext) and blow the fuse. To simulate zero current, temporarily remove the wire on ISNS and then link the ISNS terminal to AGND Link to comment Share on other sites More sharing options...
Alanb Posted January 23, 2020 Share Posted January 23, 2020 Regarding the brown wire mentioned above, I suggest that, as the author of the article mentions adding a second battery, it is most probably the negative connection to this second battery. The earth connection to the batteries is often made at the 12V distribution board. In support of my suggestion, the connecting lug for the brown wire at the battery looks too large for the single 6 sq mm brown wire. It seems probable that the original brown load wire has been removed from the lug, and diverted to the load side of the shunt, which would then monitor the current flowing to both habitation batteries. Alan Link to comment Share on other sites More sharing options...
BrianK Posted January 23, 2020 Author Share Posted January 23, 2020 plwsm2000 - 2020-01-23 9:27 AM BrianK - 2020-01-23 12:48 AM Another question after reading the instructions again if you would chaps: Under Calibration of Zero and High Voltage Readings and Calibration of Zero and High Current Readings it says to 'just short Vin and GND' and 'just short ISNS and AGND'. Do they mean LITERALLY short them?! Yes but you need to disconnect other wires first (temporarily) To get zero voltage, disconnect Vin from +Vext and then link Vin to GND. If you don't, you will short out the 12V supply (on +Vext) and blow the fuse. To simulate zero current, temporarily remove the wire on ISNS and then link the ISNS terminal to AGND I know I'm probably being a numpty but presumably you have to make sure NO lives are connected at all whilst doing this? Link to comment Share on other sites More sharing options...
BrianK Posted January 23, 2020 Author Share Posted January 23, 2020 Alanb - 2020-01-23 9:51 AM Regarding the brown wire mentioned above, I suggest that, as the author of the article mentions adding a second battery, it is most probably the negative connection to this second battery. The earth connection to the batteries is often made at the 12V distribution board. In support of my suggestion, the connecting lug for the brown wire at the battery looks too large for the single 6 sq mm brown wire. It seems probable that the original brown load wire has been removed from the lug, and diverted to the load side of the shunt, which would then monitor the current flowing to both habitation batteries. Alan Extremely good point Alan and embarrassed such a simple explanation didn't occur to me *-) Brian Link to comment Share on other sites More sharing options...
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