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| Q20: Victron BMV 712 monitor Begin with the hardware hook up. Cut the copper plate, and leave separated. A common problem is all negative wires must be separated. The power leaves the -ve end of battery and ALL of it goes via the shunt, and comes back to all your -ve wires that need returning power. Power enters the shunt by two negative leads. The patch lead goes to the house via a stainless steel cable, to the PMV 712 monitor. The big negative cable goes to all the negative cables on the copper plate bus. A small power lead is required for driving the shunt, so the monitor gets a know reading through the shunt. The BMV 712 monitor requires manually charging the batteries to 100 % SOC. (state of charge) All three are blue solar and DO NOT sychronize as one. However they do work OK. A smart controlled would have been a better choice. The current on all three MPPT boxes is about 5 amps, its early in the morning and the batteries are on bulk, and no loads are switched on. The cable going to the house, in the kitchen. The BMV 712 monitor in the wall of kitchen. To manually clear the data on your APP smart phone for Victron devices, On the BMV 712 monitor, (1) Turn off all loads to your battery bank and allow MPPT to fully charged the bank to reach FLOAT at 0.0 amps coming into battery. This must occur for all three MPPT boxes, on float, with 0.0 amps coming in. (2) This point is called 100% SOC. On our system we had 9100 watts over one and a half days (10am). The final reading of energy was 9100 watts. Our batteries are supposed to hold (24 x 500 ) 12,000 watts. So something is wrong? I suspect the battery bank is 370 Amp hour, but I did turn the float from 29.2V to 29.0 V, thus reduces our theoretical SOC. Also at 19 Volts about 20% of power remains and is unusable. So at this stage my useful battery reserve is around 370 Amp hours, but this assumes 100 charging efficiency. With 85% efficiency, I suspect we have a 300 Amp Hour Battery. Several day later, an update. I think my calculations are right and wrong. Consider a 12,000 watt battery, at 80% this is 9600 watts, roughly what I got. The APP that runs with the MBV712 is nice, but offers few parameters, easily understood. To manually set up for NiFe batteries: Run the APP for Victron devices, Like so Click on the cog gear icon, and choose battery setting:- battery setting Next click relay settings:- And for low SOC relay Choose (edit) between 80% and 99% I will discuss why these values later. Update: seems setting battery capacity to 200 amp/hr allows the monitor to work on the SOC best? Update: I have set battery capacity to 300 amp/hr allows the monitor to work best? I have upgraded the system with Smart Solar MPPT boxes, so will test this for the first time with a manual charging and zero load. First I have to see if they work accurately for two weeks. Update: Hmm? Not sure about SOC calculations? Does anybody know how Victron SOC is precisely calculated? Victron says to manually set your batteries to SOC 100% every 2 weeks. So getting these parameters right is iffy. The accuracy drifts over time. It's now 11:30 am, some 90 minutes since the manual reset to SOC 100%, and all three MPPT boxes are on float. The status on the BMV 712 is showing negative 3 amps and 99% SOC. This is nice, why the float allows a negative drain on the battery now and than? Hmm? On a water pump load, fridge, freezer and washing machine load, the current drain can be 40 amps, the available amps coming in is over 80 amps, but the float reads negative 10 amps, so drains the battery, rather than topping it up? Now ... let's watch this monitor for the next two weeks and see how my 300Amp hour battery goes into the night loads with no solar energy coming in. Its night time, I checked the APP ran the BMV712 monitor and noticed 900 w coming out. Odd I thought, why so much? Switched off the fridge and freezer loads, but still 26 amps leaving battery. Something on I said to the wife? Oh she forgot to turn off a tap while feeding the chooks. Going off grid, means to watch your night loads. Update: On another day I noticed my night load was too low. Hmm? Odd? Discovered the next day, the freezer tripped safety switch, malfunction or short in compressor. So looking at your monitor daily is a useful thing is seems. All our freezer stuff had to be moved else where. The simplest solution to this problem seeing my biggest loads are the water pump (20 amps) and the bore pump (20 amps), is to install daylight switches, so they are turned off automatically after 3 pm (dim light). And will not turn on until (8am) with more light entering the power room. Update: Do you know how impossible it is to purchase a daylight switch that switches ON, not OFF, when light hits the photocells? I have not been able to find any....so will have to build such a device? I will have to install a 24V pump for the house so we have bore water 24 hours. Such things as 24V DC pumps run on a sniff of an oily rag. So the BMV monitor says right now:- This is correct ( 500 - 161 / 500 = 70%) And time remaining is 48 hours (500- 161 / 6) = 48 hours) Only thing I don't like is the voltage so low when 340 Amp hours is still in the battery, and we have 60amp hours useful power left. Something not right here? At 19 Volt the SOC should be 20 %. The monitor is too theoretical. I notice if I change the battery capacity to 239 amp hour, I get the SOC at 26% and 2 hours remaining, which looks better. Now when the sunshine hits today, will my battery reflect only 230 amphrs? Answer no. To fully charge the battery, took 9,100 watts, or 9,100 x 0.65 / 24 = 246 Amp Hr. Let's try 85% efficiency 9,100 x 0.85 / 24 = 322 Amp Hr. So this 500Amp hour batteries I bought, after 12 months of age, are really it seems turning out to be 300Amp hour batteries. Update: Not so easy measuring battery capacity, I will leave my older comments so readers gain experience, often learning means throwing out our old ideas? I think we still have 500Amp hr batteries, with perhaps 300Amp hr of useful power in them. As for device calculations the battery capacity for 400 Amp hr seems OK for now? "Yes that's a reasonable assumption if you have no better info. You could possibly try to contact the battery manufacturer. Also note that the Ah rating varies for the same battery depending on the discharge rate, the battery capacity @ the 20h discharge rate should be entered into the BMV (some battery manufacturers quote Ah at the 100h rate, which can make their batteries appear better)." I place a scholarly remark from Virtron Forums, so readers learn fancy terms, etc. Personally it's all stuff none of us really knows, and I write things easier for readers like myself. The truth is we never know all things about power, and it would be nice if Victron told us the computer code on how the SOC is precisely calculated for those of us wanting manual changes to parameters. What is confusing is the voltage rises when the loads reduce. When the fridge turns off the Volt age rises to 21V. When you buy a battery from the shop, they only tell you it's theoretical battery storage in amp hours, the light blue coloured area, under the voltage curve for 1 hour, adding up all the amps stored there, right down to zero, therefore they say it's a 500 amp hour. So you get 300 amps for one hour, or larger amounts (500 amp hr) over a longer time period. Here in a typical good manufacture data test, the Amp hour capacity of a battery ranges depending upon the number of hours and discharges the battery is exposed to. In short your battery has a sticker than means nothing about it's amp/hr capacity. Therefore, the practical amps stored, the darker blue area under the curve, shows power stored to 19 volts, which for NiFe batteries is around the maximum before permanent damage is done to the chemistry of the metal plates. This is a practical amount of 300 amps stored. What I learned is using 9,100 watts of power to charge this bank to 0.0 amps coming in, (no loads) we can assume a fully charged battery, means I have an efficiency of possibly 79%. (9100 x 0.79 / 24 ) = 300 Amp hr storage. Yes but add this 300Amp hour to the 200 amp hour we can't use, because it's below 19 Volts, and we get 500 amp hours in theory? But again this is a guestimate because we don't know for sure the efficiency of the battery chemistry. I will run this for today and test the monitor during charging at this battery storage value. What the monitor says right now at 7:00 am Sunshine coming in, giving us 5amps, at 28 Volts already, when in theory we have a dead flat battery. You could not achieve this with Lead Acid batteries. For 200 amp hr in a lead acid you would require at 90% SOC as a minimum, you would need a 2,000 amp hour battery storage, costing you over $20,000 and that is assuming it lasts the 10 years on the warrenty date. Update: When topping up the battery cells this week, with my usual 500ml per cell, I noticed the electroly te is not changing black anymore and remaining colourless in most cells. It's nearly 8:00 am, the power from my panels is 16 amps coming in, the monitor says 12 amps coming is, because 4 amps is going to the fridge, going out. So the monitor doesn't give you all the details, only the net total. In reality my 12 hall effect ammeters give you far better details, I have the current for all major leads, going in and going out, I have the bulk, absorb and float LED on the blue boxes, so I don't really need a BMV 712 monitor, it's all theoretical hype. Update: But does tell you if your freezer goes dead, LOL In fact all I need is the LED lights on my MPPT to tell you what is going on. The blue bulk LED light tells you, your battery is LOW. The absorb LED light tells you, your battery is OK. The green float LED light tells you, your battery is fully charged. I think the extra electronic devices are unneccessary waste of money. Update: The monitor only adds to your stress levels. My wife thinks the off grid stuff is a waste of time. So sadly I can't talk much to her, all alone with my thoughts and understanding of electrical battery technology. If the process helps you too look after your batteries every day, it is money well spent. But as a link I posted here, if the monitor remains poorly programmed , the monitor may cause you to believe your batteries are fine everyday and so the monitor actually helps you to destroy your battery health. Please watch your discharge loads, and the most important factor is your voltage when the batteries run down. I am beginning to also think if my batteries are now 300 amp/hr, than the charging process should reflect this. That means I should reduce the incoming charging current to 60 amps, rather than 100 amps for 500 amp hr battery. This might be the reason for excessive water loss? One is so lucky to be with Ni-Fe technology, because overcharging them is not critical. However it seems within 12 months of use, my capacity is around 300 amp/hrs. Further update: I used only the BMV 712 monitor, to guage my battery bank discharge rate, to ascertain if my batteries are in fact 500amp hr in total. Now I am not sure? If you discharge them little, say 3 amps/hr for 150 hours, you might reach that figure. But if you discharge them moderately, say 20 amps per hour, you seem to affect the capacity chemistry, and this seems to shorten the capacity when measured by the monitor? I am not sure about this idea? Once your system is working, you don't need a monitor at all. I got one only as a diagnostic tool only. Rarely I use it anymore. Shalom The sychronize of the MPPT's is not all that neccessary either. Though I wonder if one being on bulk and the other two on float is uneccessarily over charging the batteries, wasting my distilled water? Update: However I decided to upgrade them to Smart MPPT's. I hope this helps with overcharging?? Experience costs money, so I hope the readers are learning to save thousands of dollars? So results from my reading and in simple terms for learners like me:- Peukert factor, is a curve of the decay or increase of power during charge or discharge. This curve can be a straight line (Set Peukert factor to 1.00) or you can create a sigmoid curve by setting the value between 1.07 to 1.19, so I choose a conservative curve at 1.12. This value under estimates the SOC so you get a little under what your SOC might be. Tail current. The float current value when fully charging exists, as a percentage of the total storage. I set mine to 1%, which means the float current is 5 amps, for 500Amp hr, in practice my meters show 0.0 amps on float. Charged detection time = the minutes on float, when the monitor sees your battery fully charged. Better with 10 minutes, to ward off cloud blanket affects on reading your current. So solar panel set up, if the charging voltage is met, and the tail current met, both for 10 minutes, it is assumed the SOC is now 100%. Set your charging voltage 0.3 V under your bulk voltage. Which is the highest voltage your charging MPPT will go to. This stops cloudy day and rainy overcast days spoiling the monitor from guessing the SOC. Make sure your batteries are fully charged at least once a week, every day is better, so you reach the correct estimate of your SOC. For example if your monitor says your SOC is 95%, you would expect all the MPPT boxes to be on float, or close to float LED display. Hmmm? Mine is not showing this, I have 87 amps coming off the MPPT's but only 37 amps going to batteries, all on bulk, at 97% SOC, with water pump and other loads removing the other current coming in. This is going to be a learning curve, and I place all the comments here as experience for readers. I suggest you play with parameters and learn your own experience. Set your battery synchronize to OFF, for NiFe is best. LOW SOC relay: This I think is the range of power available from your battery , the monitor calculates for. For NiFe, we can go as low as 18V and as high as 28 V at night, so your low SOC relay can be "80% to 99%". Discharge Floor: - The bottom level of useful power in your system, in NiFe that is 18 to 19 Volts, or about 20% of your battery storage. There are cheaper MPPT and monitor systems out there, but few, except Victron allow manual adjustments, and NiFe requires manual adjustments to lots of parameters. Problem this morning. So is my battery bank really 150 Amp/hr? Not happy Jane :( If that is the case, why does it take so long to charge to 100 % SOC? I will reset my data to zero and check the sunshine coming in. To reach float should take more than 9,000 watts again, if not, than it's an issue of battery loading when voltage falls, a chemistry problem. Today I used 100 amps last night and the voltage is 27V. SOC at 50% (200-100/200= 50% SOC ) is correct. So my theory 500 Amp hr battery is really :- 200 amp/hr battery. I will test this over a few days at confirm. Update: I have reset the battery capacity to 300 amp/hr amp/hr. Another question: Why if there is plenty of sunshine doesn't the MPPT on bulk charge at the charging voltage set, ie 33.0 volts? 33.0/20 = 1.65 Volts per cell for optimum charging, but I do not get this from the MPPT? The MPPT has over 70 Volts DC to play with and heaps of current, (10 amps), so there should be scope to bulk charge correctly? Today at 7:30 am I have 10 amps on the batteries but only 24 volts, the water pump is loading I notice, so maybe the MPPT cannot overchange the loading of the batteries at the same time? Update: I tested each cell of my battery bank to ascertain the charging voltage. I got roughly 1.45 to 1.46 per cell. This is roughly the low end of being fully charged, some say at 1.65 per cell. So I suspect the battery is almost fully charged, and will confirm this with another manual charging test. So charging voltage can vary between 1.46 to 1.55 per cell. Today at 7:30 am I have 23 amps coming out the batteries but only 13 amps coming in, while on 23 volts, the water pump is loading I notice, with 50% SOC? We consumed 104 amp/hr last night, so that is (200-104/200=48%) roughly correct for my monitor. Another statistic I notice is discharged energy and energy was 5.5 and 6.6 KW/hr, so subtraction means 1,100 watts went into the battery. Hmm? 1100/24 = 45 amps. Something not right here, on bulk we get 60 amps for over 2 to 4 hours, ie something like 120 amps. Not sure if the monitor say anything useful, as the theory doesn't add up? However it is working OK with battery capacity on 300 amp/hr . Found this really useful in depth study into calculating SOC, bit beyond the average reader, so I will make some comments later:- It is as I thought, calculating SOC in a battery is like hitting a moving target. It is difficult to achieve and your battery capacity decreases over time. Hence mine after just one year of use might be 300 amp/hr . Maybe with new electrolyte, I can get my rated amp hour capacity back or partially improved? Monitor BMV 712 -"time remaining" = nanm, I quote from a Victron community writer:- It seems that you have the setting to start synchronized turned off. You have to manually synchronize the SOC to 100% when fully charged Oh, so that means nothing much, as I prefer the auto monitor device turned OFF. The long life of NiFe is over 30 years, gives us peace of mind. Shalom all ye learners of " off-grid technology". Next we look at upgrading from Blue Solar MPPT to Smart SOlar MPTT ........... |
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