Three Way Charging / Mixing Old and New Tech

[SquirrellCook]

How does the BMV detect charge current ?

I'm not as posh as you I'm only using Bluetooth.
The Shunt is a precision resistor and the BMV measures the voltage across it.
From ohms law the current can be calculated flowing through it.
The BMV has to learn what is fully charged based upon the numbers you gave it about the battery.
You can see the voltage on a second battery using the mid point connection, but it will only read voltage.
Are you trying to monitor all 3 batteries with one Shunt?

Before I bought the Victron BMV I had played with some other charge meters that used an inductive connection. A bit like a current clamp.
I got very frustrated trying to get what I considered to be real world number out of it.
As with all computers and sometimes me, they are stupid. They just do as they are told based on the information and programming given to them.
The BMV must know what Zero current looks like and also what fully charged looks like.
Capacity of the battery is a bit like believing a politician. You want to believe it, but it's seldom true.
Based on state of charge with reference to no load voltage you could learn the batteries true capacity using the BMV to measure power in and power out. If you think it's not telling the truth, change your battery capacity numbers.
Just don't fiddle with it every day. Let it go through a few charge discharge cycles first. It might take months if you have an older battery.

 

[wildebus]

The Victron BMV is not a 'learning' device.
You put in the Battery Capacity in Ah at the C20 Rating; you enter the Peukert Factor and Charge Efficiency parameters and then it does what it does.

Current is read via the Shunt
Voltage via the connection in the Shunt
Watts data is based on Current read x Battery Voltage at the time.
Ah data is a calculation of Current with a time factor applied
SOC is Ah data, modified by the Peukert Factor (so if you double the Amps pulled, for example, you more than double the % taken out out the battery as the theory is as you pull a greater load, the actual battery capacity is reduced)
Charge Efficiency is factored in the other direction. I haven't looked at this in detail on the BMV but I think it takes the current going into the battery (so a charge) and applies the efficiency adjustment (default is 0.85? so of every 1A into the battery, 0.15A is wasted in the charging process) to work out the increase in the SOC%
Yup, all done via maths as that is how this is all worked out with batteries.

So accurate use of the BMV relies on accurate input from the battery data sheets. And where the learning bit comes in is reviewing the info the Battery Monitor is telling you and tweaking the parameters from your own observations (so essentially not the BMV learning, but you adapting it)


Robert, you KNOW the Battery is not 100% as it did the default reset, so saying it is inaccurate compared to the inverter control display is a silly thing to conclude.

You also don't have to ensure it is at 100% before you fit the BMV as otherwise it will never be accurate. That is not the case.
If it is reset to 100% prematurely (as in your case), as charge continues to go in, the SOC does not go to 101%, 102%, 103%, and so on. it is capped at 100%. As soon as the battery bank it is monitoring is fully charged, the SOC info will start to have meaning (assuming the parameters are set right).
Also, like so many battery state light systems, the lights on the Edecoa are purely a translation of voltage - light display - it is a very rough approximation. Useful quick indication but certainly not an accurate way to monitor a battery.

All Battery Monitors need a starting point to start the calculations from. You can't just plug something in and it magically "knows" the battery level of charge. You don't need an intelligent charger to work with a BMV, but you DO need to charge your battery fully to give you a calibration start point. Some Meters work by having the Batteries full to start. Others want the batteries totally empty as a start point (I am not keen on those personally as don't really like to totally drain a battery).
It is like fitting a new random fuel gauge into a car tank. you wouldn't expect it to instantly tell you how much fuel was in the tank would you? you would need to find the empty point and the full point and calibrate it.

I have found the BMV extremely accurate in terms of predicting the SOC, but you do need to do some tweaking for your own setup. I still have a little adjustment to do after changing my battery bank months ago - the BMV goes to 100% when certain parameters are identified (voltage level and current over a certain time period) and my parameters are not quite right so my battery is never at 100% according to the BMV, but is stuck at 99.9% maximum (not a massive problem so not got round to sorting it out)

Also I'm not sure how you would clear all collected data, say after doing an upgrade. Under those conditions it would be nice to start fresh.
I have some rubbish info on my first BMV from when I was trying to figure it out.

There is a Reset all History option on the BMV. From memory, you have to go into this from the buttons on the unit and cannot use the Victron Connect App. See here on how to: https://community.victronenergy.com/questions/21646/reset-history-on-bmv-712.html

 

[wildebus]

Here is a handy video from Victron which explains how to initially setup the BMV (and how you need to take account of a system with Solar Charging)

and a short update applicable to Lithium Batteries

 

[RAW]

That's really helpful, it's all starting to make sense....
Many thanks

 

[RAW]

OK so more on this now
At the front of the Van the Voltage on the Leisure Battery Old after a Day more charging is reading 13.2 Volts

This is how the LEOCH looks from the battery monitor

18:27 Yesterday	10:56 Today

So maybe the Old LabCraft Charger will fully charge the LEOCH AGM, however it is taking a very long time....

The other issue I have now is that I have plugged the MPPT back into the Raspbery PI but now the VRM portal & Pi think it is a new device ?

I guess I will just delete it, however seems odd that it's seen as new ?

 

[wildebus]

OK so more on this now
At the front of the Van the Voltage on the Leisure Battery Old after a Day more charging is reading 13.2 Volts

This is how the LEOCH looks from the battery monitor

18:27 Yesterday	10:56 Today
View attachment 1869	View attachment 1870

So maybe the Old LabCraft Charger will fully charge the LEOCH AGM, however it is taking a very long time....


The other issue I have now is that I have plugged the MPPT back into the Raspbery PI but now the VRM portal & Pi think it is a new device ?
View attachment 1871
I guess I will just delete it, however seems odd that it's seen as new ?

The Battery Monitor and the OLD Solar Charger have the same ID number (288). As a guess, I would say you used the same VE.Direct Dongle on both and the new/current Solar Charger is using the 2nd VE.Direct Dongle you bought?

It is not unusual for the Devices to end up being recognised as new if they get disconnected and reconnected even though no apparent changes made. I got that a lot with my Multiplus conencted to the Raspberry Pi via a VE.Bus-USB Mk3 Dongle. At one time I had 5 or 6 (maybe more!) different (but the same) Multiplus Devices listed. It was quite frustrating TBH when reviewing the download info for comparisions as the spreadsheet columns kept changing. I still got this happening when I changed from the Pi to the GX, but not as much It seems - although may have been due to me fiddling around more when I had the Pi in use? (as it happens, I got a "old device" thing with the Multiplus in the last few days but it was the same ID number and I was doing 'stuff' so I just deleted the old device without consequences)

I've still got 3 showing in the VRM List as individual product data is kept for 6 months.

All the VE.Bus Systems (261, 290 and 291) are the same device seen at different times. I am expecting 290 to disappear in a couple of weeks and 291 around an hour after that, leaving me with just 261 by 5th December (261 has been the current one since 5th June)

If the new device has the same ID as the old device, then you can just delete the old without consequences. If it is a new ID then the historical graphs can be akward to use when looking at an individual product (the Summary ones are unaffected though)

If you go into the VRM and select widgets for both 288 and 289 and do a view over say 2 or 3 months, you will see something like the above, where data is in one graph and suddenly moves to the other. (like I said, it is only device drill down affected though. Summary Info is not, so look at say SYSTEM Solar Yield rather than the indivdual DEVICE Solar Yield and it will show "both" controllers in that).

 

[RAW]

The Battery Monitor and the OLD Solar Charger have the same ID number (288). As a guess, I would say you used the same VE.Direct Dongle on both and the new/current Solar Charger is using the 2nd VE.Direct Dongle you bought?

Actually I used the newest VE Direct Cable from Victron on the Charger, rather than the one that was used before.
They are made slightly differently I noticed, First one is like this:

Second, newer one I was sent, is like this:

They both came from https://www.onboardenergy.co.uk/

It is not unusual for the Devices to end up being recognised as new if they get disconnected and reconnected even though no apparent changes made

I think then I will just delete the Old device

Cheers
Robert

 

[wildebus]

that is what I meant - you used a different cable, "rather than the one that was used before"

 

[RAW]

Isolated Battery Alpha AGM on BMV shows a Voltage drop of 0.21V in 3 Hours yet Battery is still at 100% SOC
Is that correct ?

 

[wildebus]

Isolated Battery Alpha AGM on BMV shows a Voltage drop of 0.21V in 3 Hours yet Battery is still at 100% SOC
Is that correct ?

it's a drop, but what is the actual voltage? it might be a high voltage due to the surface charge which has now naturally decayed.

What was the current drawn in those 3 hours? the SOC is based on current draw, not voltage levels.

 

[wildebus]

Logged on to VRM today and noticed the following which shows how using a voltage level to determine a battery state of charge can really give the wrong picture ...

So Clarence's Battery is at 12.84V and is at 96.3% SOC
But LxxxxM's Battery is at 13.36V but only 85.4% SOC?

Reason is simple - Clarence is actually using Battery energy, whereas LxxxxM is recharging from its Solar, hence the 'reversed' battery levels. It is only when a Battery is disconnected (and has been for some time), the Voltage level can be used as a capacity indication.

 

[wildebus]

This talk about the BMV resetting to 100% if power removed ..... There is a setting to not do that - which I have set. But this evening I rerouted the -ve cable from my battery bank (removing for a few minutes in the process) and so the BMV lost its ground and has reset to 0% instead! Grrrr!

Annoying as I am in the middle of doing a battery test and really wanted to have a record of the Used AHs and SOC so I knew my starting point! (not a total calamity as that info would have been logged on the VRM, but still blooming annoying)

 

[RAW]

Yes, annoying indeed, it would make sense if the BMV had some sort of backup battery in it to keep settings in memory, I looked at the datasheet here and it appears it does not

 

[wildebus]

Yes, annoying indeed, it would make sense if the BMV had some sort of backup battery in it to keep settings in memory, I looked at the datasheet here and it appears it does not

What I would do next time if I had to disconnect and didn't want to loose the data would be to rig up a little battery to take over. It is a rare occurance that a meter is disconnected in reality. (FWIW, I have a master disconnect from my battery to the "services", but also have a 'secondary' supply out the battery to a little fusebox for the key but very low current devices I want to always have running such as Victron Venus, the BMV, lighting in the garage area to work in the battery area when the disconnect is off, etc).
But to sort out my testing, had to recharge the battery bank back to full, and then start my drain again (had a 500W oil heater on since 11pm last night)

 

[RAW]

Sounds good. 500W Oil heater, interesting idea. How many AH is the battery bank powering that ?
Just a question on your graph here, which is higher up the thread.

You have some nice icons as Green Battery; Blue Voltage; Orange Solar whereas I do not have them just a Dull Grey one on SOC and nothing else

Any ideas ?
TIA

 

[RAW]

Sounds good. 500W Oil heater, interesting idea. How many AH is the battery bank powering that ?
Just a question on your graph here, which is higher up the thread.
View attachment 1883
You have some nice icons as Green Battery; Blue Voltage; Orange Solar, whereas I do not have them just a Dull Grey one on Battery SOC and nothing else
View attachment 1884

Any ideas ?
TIA

 

[wildebus]

Just a question on your graph here, which is higher up the thread.
View attachment 1883
You have some nice icons as Green Battery; Blue Voltage; Orange Solar whereas I do not have them just a Dull Grey one on SOC and nothing else
View attachment 1884

Any ideas ?
TIA

Not noticed that, but just had a play and it is down to the browser mode. When in mobile mode, you get the coloured icons and on a desktop you don't
I put my [firefox] browser into 'responsive' mode so it changes depending on screen size ....

Mobile style size

And when I make the screen wider ...

Sounds good. 500W Oil heater, interesting idea. How many AH is the battery bank powering that ?

How many Ahs? well that is a good question. All depends on the C-Discharge rate for Lead Acid according to Peukert. According to the Battery makers discharge table, at C20 (which means at a constant rate discharge you would have a dead battery in 20 hours), each battery is 214.6Ahs (if you go down to 1.80V per cell), so I have put 645Ah into the BMV (3 x 215 as 3 batteries).
as it happens, the heater seems to be a 420W heater not 500W when looking at the data, and when on actually pulls current close to a C20 rate for my bank (pulls 38A, C20 rate for my bank is 32.25A), but for some reason I don't know but is a characteristic of this heater, it has a 50% duty cycle and so is really only a 210W heater when taking that into account.
With that low wattage, I am still waiting for the batteries to drop where I want them to go (around/below 50%) ...

After 13 hours on the heater on, still at over 60% aand will be a few more hours yet until it hits 50%.
I'm running the heater as a load, but what this has actually told me is that I would not be adverse to switching it on as a silent overnight heater if I knew sometime the next day I would be getting a good charge back in (EHU site or driving) or I was heading home so remaining charge not important

 

[Nabsim]

Some interesting remarks about the BMV. I never bothered one until I went Lifepo4 but find it invaluable now keeping track of SOC. Although it is annoying when you update or do anything to lose power I don’t find it too much of a problem, I hook the genny up and run til I know the onboard chargers will have them at 100%.

Not sure why going off your comments but I only seem to lose SOC in these circumstances, not lost parameters I have changed from default to date. I have a BMV700 with Bluetooth dongle but that shouldn’t make a difference