Tomthumb62
Solar Wizard
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- Sep 25, 2022
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How to measure state of charge with lifepo4?
- Thread starter Gueyog8a7
- Start date
I totaly agree…well said…
peace …and results …well worth the little bit extra ya pay for it.
…
Hi guys can the bmv be suitable for me if I don't want bluetooth or apps and all that? Seems I could just use the screen or am I wasting money for that for many features I would not use? The display looks unoffensive but does it light like a christmas tree when not in use?
Also which one to buy if I may want to buy more batteries in future?
I just saw that victron have made an unnofficial linux app. That is encouraging indeed however I still prefer hardware monitoring really, less points of failure.
Ok so is it 700 for 1 battery only, 702 for 2 and 712 for multiple?
Or...can the 700 be for multiple if they are a 'bank'?
The aili doesn't seem available in the UK except from amazon...which I don't use.
Also which one to buy if I may want to buy more batteries in future?
I just saw that victron have made an unnofficial linux app. That is encouraging indeed however I still prefer hardware monitoring really, less points of failure.
Ok so is it 700 for 1 battery only, 702 for 2 and 712 for multiple?
Or...can the 700 be for multiple if they are a 'bank'?
The aili doesn't seem available in the UK except from amazon...which I don't use.
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Reading the output of the mt50 does the same as this right?Simple voltmeter does work at the critical points. ebay has them with 2 or even 3 decimal accuracy.
Easy to see if battery is down at 12.9 the solar is not keeping up and a manual charge is needed.
Likewise if the voltage stays at 13.2+ battery is good all day long.
With a 2 to 3+ day battery this works fine. With a 12 hour battery some additional monitoring is needed. Maybe even an alarm.
Just need to get used to the loaded vs resting values to interpret correctly.
Mine sits at 13.1-13.3. Does this mean I am still at around 90% oh my 105ah lithium? Also fogstar state 105ah but Mike says only 100ah and I saw something like that on the technical sheet. Why do they state 105ah then? Is it not false advertising?
The cheap one I linked earlier is a hull sensor rather than shunt. Is that worse or neutral for my lithium battery?
I found this video which goes in to depth on it.
If this little thing would do the job I like the simple bare bones design and do not see the justification for paying 3-6x the price for victron flashiness that I would not use 90% of anyway.
I found this video which goes in to depth on it.
If this little thing would do the job I like the simple bare bones design and do not see the justification for paying 3-6x the price for victron flashiness that I would not use 90% of anyway.
rodrick
Free energy enthusiast
Watched some of the video and the way he has to change cable makes me wonder if it’s only going to track one direction so it may give you power used but not what you put in thru charging added back to charge level
if it doesn’t track both ways it’s worthless
the other thing is some of the comments on the video say there units smoked not good and others said inaccurate readings personally I wouldn’t buy one
As far as dead on accurate voltage readings? My hand held volt meters (fluke and others) is the only thing I have that actually gives perfect readings voltage wise.
1 being dead accurate and higher being worse.
1. Fluke and other hand held dedicated volt meters.
2. Victron smart shunt
3. My inverter when it isn't using power from the battery of course.
4. Renogy shunt and display.
5. Generic shunts I bought off amazon.
6. 4215bn charge controllers.
Of course the batteries being a perfect "rest" is the only way to know what the charge really is via voltage readings.
But for me a shunt is still a better state of charge tool in real life.
1 being dead accurate and higher being worse.
1. Fluke and other hand held dedicated volt meters.
2. Victron smart shunt
3. My inverter when it isn't using power from the battery of course.
4. Renogy shunt and display.
5. Generic shunts I bought off amazon.
6. 4215bn charge controllers.
Of course the batteries being a perfect "rest" is the only way to know what the charge really is via voltage readings.
But for me a shunt is still a better state of charge tool in real life.
Over time if you keep a eye on the batteries voltage during operation, and when loads cycle off, I find that you can generally have a good idea of SOC. You begin to get use to voltage load droop and also end charge readings.
13.300 is close to 90%. 13.100 would be somewhat lower.
if the battery is currently charging the 12.9 could be 13.3 and if it is currently discharging the 13.3 could be 12.9 (just as an example)Simple voltmeter does work at the critical points. ebay has them with 2 or even 3 decimal accuracy.
Easy to see if battery is down at 12.9 the solar is not keeping up and a manual charge is needed.
Likewise if the voltage stays at 13.2+ battery is good all day long.
With a 2 to 3+ day battery this works fine. With a 12 hour battery some additional monitoring is needed. Maybe even an alarm.
Just need to get used to the loaded vs resting values to interpret correctly.
so you're half the battery capacity off in your readings just by if you're simply charge/discharging currently..
It's worse as the batteries aren't always that exact voltage.
So that is why knowing the full capacity of the battery and using a shunt to see how much has been taken out / put in is the only accurate way.
If you need to know where it's at in the middle of this without a shunt you can guess with the voltage. but fully charging or fully discharging then monitoring the input/output of it is only way
This is true. However in my experience if I am charging I am charging and the capacity does not matter. If I reach 14.2 at some point on solar the battery is full and good for a couple days. If I hit 14.2 on generator it is time to quit. In practical use it never seems critical to me. If the exact charge level at every hour really matters so much maybe the battery is too small.
Otherwise yes the simple voltmeter does require a bit of interpretation at times. The monitor just dumbs down the process. I actually enjoy the thinking part. Monitor can always be added later if desired.
So is there much point getting a dedicated battery meter rather than just using this graph other than convenience of having a tidy number?Simple voltmeter does work at the critical points. ebay has them with 2 or even 3 decimal accuracy.
Easy to see if battery is down at 12.9 the solar is not keeping up and a manual charge is needed.
Likewise if the voltage stays at 13.2+ battery is good all day long.
With a 2 to 3+ day battery this works fine. With a 12 hour battery some additional monitoring is needed. Maybe even an alarm.
Just need to get used to the loaded vs resting values to interpret correctly.
If this is generally accurate I don't see much advantage. I seem to be getting an idea of the voltages now from day to day. It was at 13.2 for ages but now it seems stuck in 13.0 to 13.1 land. Haven't been able to break back up to 13.2 consistently.
I think my battery is generally at rest as I don't have anything constantly running and only run the heater or fan for a little so that means it is at rest the other times right? Or solar counts as not at rest? Anyway the figures seem the same even when it is dark so the numbers should be accurate?
I know that battery meter does other stuff like say how much load is currently going in and out but again what really is the benefit of that over knowing the state of charge via the volts? If you know what % you were at one day and then see the volts have dropped then you can infer that you used x amount of amps in the meantime.
If there was a great reason to get one other than just having easy mode statistics I will get it but if the volts on this chart are generally accurate I don't see that it is worth it.
13.0 to 13.1 is getting rather low on the chart. Need more energy into the battery. Need 2x the solar or 2x the charging time if a plug in charger is used.
Best to see 13.8 / 14.2 at some point each day to ensure a top charge. A monitor saying 25% or a reading of 13.0 says the same thing, need more power in.
Best to see 13.8 / 14.2 at some point each day to ensure a top charge. A monitor saying 25% or a reading of 13.0 says the same thing, need more power in.
For an in use aka connected to loads system a shunt is the only way to go.
Voltage readings are about useless for one simple reason and that is because you can apply enough load to make the voltage readings show anywhere between 13 point whatever volts and 9 volts just by varying the load applied to the battery. But the shunt setup is going to show what actually has been drawn from the battery or charged back into the battery.
Its just the only way to run a real system.
Voltage readings are about useless for one simple reason and that is because you can apply enough load to make the voltage readings show anywhere between 13 point whatever volts and 9 volts just by varying the load applied to the battery. But the shunt setup is going to show what actually has been drawn from the battery or charged back into the battery.
Its just the only way to run a real system.
Now that the concept is understood the voltage sag under high load should not fool you.
Will if you have a real world system with multiple devices going about their business. Without a shunt you have no idea how much actual load is being applied at any given time. Things are turning on and off and going about their business. So trying to measure what is left in the battery without knowing the actual load on the system makes measuring it via a voltage reading useless.
I can fire up my connection to a camera I have that monitors my renogy shunt at 3am to see how things are going. Just looking at the voltage reading it will change based on how many heaters are running.
But I can see on that same display ah remaining and actual load drawing from the batteries which tells me instantly the state of charge and how well I'm doing. If I could only see the voltage part I might see a well charged system or drained battery depending on how many heaters were on and such.
A shunt is the only way to really manage it all.
In my opinion, it's very difficult to determine state of charge through voltage alone.
13.6-14.4 = about full
13.2-13.3 = still have some juice left
13-13.1 = going dead
Under 13 = about to die
That's about as accurate as you can get with a multimeter, especially if testing while under any sort of load.
As mentioned before, a shunt is really the only way to know exactly how much power you have left. I got one for under $20 off of Amazon that is incredibly accurate, it matches my fluke within about a milliamp or two. It's even more accurate than some of the expensive shunts.
13.6-14.4 = about full
13.2-13.3 = still have some juice left
13-13.1 = going dead
Under 13 = about to die
That's about as accurate as you can get with a multimeter, especially if testing while under any sort of load.
As mentioned before, a shunt is really the only way to know exactly how much power you have left. I got one for under $20 off of Amazon that is incredibly accurate, it matches my fluke within about a milliamp or two. It's even more accurate than some of the expensive shunts.
I agree. However that is about all that is needed for many people. If every percent is critical I would call poor design. For example I want a minimum two day battery to have time to intervene. I plan to be sleeping at 3am where nothing is critical if there is enough battery to begin with.
Warpspeed
Solar Wizard
Have to agree.
The fuel gauge in my car has a scale:
E .......... F
And I have never run out of fuel yet.
The fuel gauge in my car has a scale:
E .......... F
And I have never run out of fuel yet.
scubadoo
New Member
I have a $60 400A Juntek and 500A Victron SmartShunt with dedicated old android phone monitoring our battery setup.
While being a long time a Victron user I must admit that the Junctek is my GOTO unit for day to day use.
Either both are inaccurate or I can rely on the numbers. They always agree within 1 or 2% SOC.
Click to enlarge
While being a long time a Victron user I must admit that the Junctek is my GOTO unit for day to day use.
Either both are inaccurate or I can rely on the numbers. They always agree within 1 or 2% SOC.
Click to enlarge
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