How to measure state of charge with lifepo4?

[Gueyog8a7]

As people have mentioned that looking at mt50s volts reading is inaccurate. I have read smart shunt. Is that the only or main way? What are the options?

I would prefer not have to buy another expensive piece of equipment if there is a cheap way to do it which might not be as efficient. Measuring the charge is important though in order to gauge effects of charging or can it be done indirectly? For example you know it is full when SCC stops charging right? Are there other circuitous ways to get fairly accurate gauges without pricy gadgets?

 

[rodrick]

Shunts are the only real accurate way

 

[time2roll]

I use the BMS state of charge data output to the phone app. Close enough for my needs.

Otherwise the battery voltage can be used but it will be a bit granular between 40% and 90% charged. Probably good enough if there is sufficient capacity and gain some usage experience. Can always add the shunt/monitor later if needed.

 

[Gueyog8a7]

I use the BMS state of charge data output to the phone app. Close enough for my needs.

Otherwise the battery voltage can be used but it will be a bit granular between 40% and 90% charged. Probably good enough if there is sufficient capacity and gain some usage experience. Can always add the shunt/monitor later if needed.

Oh yes I recall my fogstar drift having some app. I don't use a smartphone though so I wonder if it will work for computer too. I doubt that since I use linux and will be extremely unlikely they have written software for it!

 

[Gueyog8a7]

Shunts are the only real accurate way

Ok I should have said I will get the additional equipment if it is clearly the best option. Do they cost a lot? I shall look now but are there better ones and worse ones? I know victron has been mentioned more than once and they are the creme de la creme it seems in the solar game.

 

[time2roll]

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.

 

[Tomthumb62]

Oh yes I recall my fogstar drift having some app. I don't use a smartphone though so I wonder if it will work for computer too. I doubt that since I use linux and will be extremely unlikely they have written software for it!

I too use the smartphone app for my Bluetooth enabled battery. It’s not as accurate as an expensive shunt, but the app saved me from buying such a piece of equipment. It’s good enough. And far more accurate than by voltage alone.

You don’t need a smartphone. Just find a friend who has an old one and connect to WiFi to download the app. No cell or data connection needed and no money needed for a plan. A good friend may be happy to just give it to you, glad that it’s getting a second life.

Once you’ve downloaded the app and installed it, you can turn off WiFi on the phone. You can also keep Bluetooth turned off most of the time, except when you want to connect to your fogstar battery.

****
EDIT: I have read threads where users compared accuracy of the Bluetooth BMS psuedo-shunt (they are a shunt but lower quality) and the popular Victron Smartshunt. The results I read from a couple of different batteries was the Bluetooth BMS one was pretty darn accurate. But the BT BMS route is a very very simple thing, whereas the Smartshunt has tons of bells and whistles. One of those bells is the Smartshunt (someone correct me if I'm wrong), will track more of the history of the battery, whereas my BT BMS simply shows me a graphical SoC along with how many Ah are left in the battery. For example, it current tells me that I have 44Ah out of 199Ah. The battery is a 200Ah battery and the 199 simply means that the cells are a bit out of balance...I can live with a 0.5% loss of capacity. Yes I paid slightly more for the Bluetooth battery, but I saved over $75 by not needing to buy a Smartshunt.

Now, I really want a Smartshunt! I want a really good excuse to buy one. But because the BT battery shows everything need, then I have no good excuse to buy one!

 

[rodrick]

Ok I should have said I will get the additional equipment if it is clearly the best option. Do they cost a lot? I shall look now but are there better ones and worse ones? I know victron has been mentioned more than once and they are the creme de la creme it seems in the solar game.

The victron we're about 130 US dollars there are some cheaper ones on eBay running from 35 to $40 us up

 

[littleharbor2]

One thing I don't like with the Victron meter is the tiny readout. Sure you can monitor it other ways but there's something nice about walking into the garage, or wherever you place it, and seeing a bright, good sized readout on a Tri Metric meter.

 

[Tomthumb62]

One thing I don't like with the Victron meter is the tiny readout. Sure you can monitor it other ways but there's something nice about walking into the garage, or wherever you place it, and seeing a bright, good sized readout on a Tri Metric meter.

Just for clarification, you're talking about the readout on the Victron BMV-712 or 702? Yeah, those look small. But since we were talking about the Victron Smartshunt, it has no physical readout and you use a smartphone app (Victron Connect, it's free and has an awesome demo library) to view the readout.

To my knowledge, the Victron battery monitors like the BMV-712 can also be viewed on the app as well as the screen. I don't think the 702 can, though, someone correct me if I'm wrong.

 

[littleharbor2]

Just for clarification, you're talking about the readout on the Victron BMV-712 or 702? Yeah, those look small. But since we were talking about the Victron Smartshunt, it has no physical readout and you use a smartphone app (Victron Connect, it's free and has an awesome demo library) to view the readout.

To my knowledge, the Victron battery monitors like the BMV-712 can also be viewed on the app as well as the screen. I don't think the 702 can, though, someone correct me if I'm wrong.

I believe you're all right. Yes, I was referring to the BMV shunt based monitors

 

[mikefitz]

fogstar drift having some app. I don't use a smartphone

Get a SH phone or tablet and take advantage of the Fogstar app, it connects via Bluetooth. It will show battery volts and SOG. More importantly it will show the voltage of the cells and give an indication of how the battery is performing. The app will show any protection issues such as cell imbalance. You realy need this.
I have assisted some Fogstar battery users that were having issues that became apparent via the app.
Monitoring the battery via the app is top priority .

looking at mt50s volts reading

The volts are perhaps not too accurate in calibration but give a useful indication of state. Unloaded, no charge, over 13.3 volts is full, below 13 volts time to charge, at 12 volts practically empty.

 

[Gueyog8a7]

I too use the smartphone app for my Bluetooth enabled battery. It’s not as accurate as an expensive shunt, but the app saved me from buying such a piece of equipment. It’s good enough. And far more accurate than by voltage alone.

You don’t need a smartphone. Just find a friend who has an old one and connect to WiFi to download the app. No cell or data connection needed and no money needed for a plan. A good friend may be happy to just give it to you, glad that it’s getting a second life.

Once you’ve downloaded the app and installed it, you can turn off WiFi on the phone. You can also keep Bluetooth turned off most of the time, except when you want to connect to your fogstar battery.

****
EDIT: I have read threads where users compared accuracy of the Bluetooth BMS psuedo-shunt (they are a shunt but lower quality) and the popular Victron Smartshunt. The results I read from a couple of different batteries was the Bluetooth BMS one was pretty darn accurate. But the BT BMS route is a very very simple thing, whereas the Smartshunt has tons of bells and whistles. One of those bells is the Smartshunt (someone correct me if I'm wrong), will track more of the history of the battery, whereas my BT BMS simply shows me a graphical SoC along with how many Ah are left in the battery. For example, it current tells me that I have 44Ah out of 199Ah. The battery is a 200Ah battery and the 199 simply means that the cells are a bit out of balance...I can live with a 0.5% loss of capacity. Yes I paid slightly more for the Bluetooth battery, but I saved over $75 by not needing to buy a Smartshunt.

Now, I really want a Smartshunt! I want a really good excuse to buy one. But because the BT battery shows everything need, then I have no good excuse to buy one!

I do not use a smartphone in principle not through lack of money. I will sooner buy a dedicated device than get a free smartphone.

I am seeing there are some reasonably priced battery monitors though. I only want a basic one which would be equivalent in design to like the mt50 solar charge monitor.

I don't want an app for the shunt for same reasons as above or the other bells and whistles. Just a simple way to see state of charge. I prefer to buy a simple device than have to use volt meter or suchlike suggested previous. So money is not the issue but rather simplicity and not paying for bells and whistles I don't want.

I saw this yesterday. Looks nice and simple. Looks like it might even just be a raspberry pi.

Also saw aili is another option though looking at a review I don't like how it would flash when battery is charging. I don't like unnecessary lights and bought an expensive blueseasystems dual usb port just because it was the only one I could find without an intrusive charge light.

Any other recommendations for a simple state of charge device without obnoxious flashing lights when not using it?

 

[Gueyog8a7]

Get a SH phone or tablet and take advantage of the Fogstar app, it connects via Bluetooth. It will show battery volts and SOG. More importantly it will show the voltage of the cells and give an indication of how the battery is performing. The app will show any protection issues such as cell imbalance. You realy need this.
I have assisted some Fogstar battery users that were having issues that became apparent via the app.
Monitoring the battery via the app is top priority .


The volts are perhaps not too accurate in calibration but give a useful indication of state. Unloaded, no charge, over 13.3 volts is full, below 13 volts time to charge, at 12 volts practically empty.

I don't use windows and have no intention of going back to it or getting a smartphone. I will be happy to pay for a dedicated device though.

 

[Tomthumb62]

I don't like unnecessary lights and bought an expensive blueseasystems dual usb port just because it was the only one I could find without an intrusive charge light.

Yeah I almost bought that one for the same reason. But ended up with an excellent one for $13. I put a slim piece of black electrical tape over the LED light and it blocks the light 100%. Where it’s mounted you simply can’t see the tape.

 

[Tomthumb62]

Any other recommendations for a simple state of charge device without obnoxious flashing lights when not using it?

I looked for one as well. Haven’t found one yet.

Which is why I prefer the app. There’s no lights or whistles when the phone screen is turned off. It’s the simplest method I’ve found yet.

Maybe you could design one? If it’s price competitive, I’d consider buying it.

 

[TacomaJoe]

The backlight on my AiLi monitor is adjustable. I have it turned off in my trailer because it was distracting at night. This one is a 350A shunt that I bought a year ago. I have a couple of 100A shunts but they don't have the backlight adjust feature. Not sure if it is a new feature (the 100A shunts are 4 years old) or if it is the current rating. I do like the at a glance SOC.

 

[JRH]

Just for clarification, you're talking about the readout on the Victron BMV-712 or 702? Yeah, those look small. But since we were talking about the Victron Smartshunt, it has no physical readout and you use a smartphone app (Victron Connect, it's free and has an awesome demo library) to view the readout.

To my knowledge, the Victron battery monitors like the BMV-712 can also be viewed on the app as well as the screen. I don't think the 702 can, though, someone correct me if I'm wrong.

 

[Tomthumb62]

The nice thing about the 712 is you can mount its round display near your system ( or 30 ft away ) but you don’t have to pull out or have your phone to see what you’re wanting to see.

If you hold down the the( - button ) for exactly 4 seconds on the front of the round display it will make it scroll through each setting (speed is adjustable) and so is the brightness ….you can adjust the backlight light to stay all the time if you wish…the display is a huge benefit for a piddling 60 bucks more than the smart shunt.

The phone app is amazing to help with trouble shooting stuff and monitor whats up from afar…very strong blue tooth range. I have like 9 Victron devices and this has the strongest BT signal by far…
This critter is the best 200 bucks one could ever spend on their solar system for info collection and adjusting gear.
The Menu and options are huge ….and extremely accurate …
I cannot imagine not having mine , regardless of the cost …

J.

Oh I agree completely, except my use case is for a camp trailer we use at most a few months out of the year. It just not an expense I can quite justify…yet!

If I was in an off grid home, it would be my next purchase.

 

[JRH]

Oh I agree completely, except my use case is for a camp trailer we use at most a few months out of the year. It just not an expense I can quite justify…yet!

If I was in an off grid home, it would be my next purchase.

Basically all I was saying was how well the 712 did on about everything one could want and more… that thing is one of the true “feel good purchases” in solar gear…

thx J.