Daly BMS gone crazy..Update Opinions

time2roll will you use a DC to DC charger in your set up?

What size is the bank you are replacing? Chemistry?

BFL13 wrote:
My question has not been answered-- how does the Smart BMS know what the SOC is while the inverter is running the battery down and the voltage is the loaded voltage? How do you know you are as low as you dare to go towards the lower knee?

The BMS I see cuts you off at 10 volts and you are well into the lower knee.

The chances are virtually zero that your usage will match full capacity just as the recharge starts. No different than running your vehicle fuel to zero and expect to coast into a fuel station as it sputters out of fuel. (happened by chance once in my mustang... used 2nd gear and the starter to get me 100 feet to the pump) You will never get exactly maximum range in real usage. If you aim for 60 %, tolerate 80% and allow 100% DoD all you can hope is the solar or generator activates before power is cut.

Same for FLA. If you aim for 50% max you might find yourself charging at 70% to 40% discharged depending on conditions and timing of the entire event.

Only way to get max DoD is to have an autostart generator with no time restriction.

BTW... ordered some lithium from China today. May take a month+ for the DIY to come together. Will post details as it comes together. So far it is looking like 300 Ah for $700 + assembly.

The charging profile in the graph here -scroll down to "charging LFP"
does not show that. The voltage curve upper knee is earlier and then holds for Vabs. I am unclear when the balancing act occurs on this profile.

https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/

Even if the "full" is not an issue so zeroing the AH counter is not needed, you still use AH for knowing where you are for SOC while operating. Besides the voltage being too flat for that, you have loaded voltages.

If the Smart BMS uses voltage per SOC, and you allow that it can use the flat voltage for its SOC (Trillium's only gives an approx SOC "window" or bandwidth idea for its SOC display), what about loaded voltages?

You can look at the battery voltage while a load is running and see it does not represent SOC, but the AH counter still does. Does the Smart BMS use show an AH count?

My question has not been answered-- how does the Smart BMS know what the SOC is while the inverter is running the battery down and the voltage is the loaded voltage? How do you know you are as low as you dare to go towards the lower knee?

Itinerant1 says he plays it safe and stays well above the knee. He foregoes using the extra AH he could use by going lower. He can, because he has 500AH to play with.

If you bought your single LFP, believing the ads that say you can use 100% of its capacity, and you want to get your money's worth doing that, but then find out about the lower knee so you can't/shouldn't, then you will want to get as close to the knee as you can get away with. Now you need a way to tell when you are as low as you can go and get away with it. (unless you know you have a 120AH rated at 100 so your 0 is really 20 DOD--but what about the voltage/real SOC? Is the 10v for 20 DOD and not 0 like it says?)

Say you are watching TV at 10 amps for a few hours on inverter, from your 100AH LFP. 3 hours is 30AH which is a lot from 100. If your knee is at 10% DOD, then you need to start at 40% DOD to get your three yours in. If the BMS is reading loaded voltage from that 10 amp draw (not so much drop with LFP, which helps some) it will call 10% too soon before your 3 hour movie is over. If you go past the knee at all, voltage will crash so you need to stop quickly before the BMS shuts down. You really need accuracy as with the AH counter when skating on thin ice like that, and the loaded voltage while the inverter is running the TV isn't going to do it AFAIK.

LFP is different from FLA to know it is full. Once LFP gets into the upper shoulder for voltage it is full. It just is every single time. This is different from FLA where you are trying to remove those sulphur ions from the lead and you are never quite certain if you have them all. So you push and push and push scrubbing harder and harder until you give up and call it full. A very different chemical process.

LFP is like filling a tank and when the voltage runs over it is full. Charging FLA is like draining the tank where you keep shaking it and shaking it to get every drop of sulphur out. Maybe even go in and wipe it with some equalization voltage.

Different paradigm, no need to apply the same rules.

I wonder how it calculates the capacity

It does read voltage and it does read amps, but does it do AH? Does it do auto-reset of AH count whenever it thinks the batts are full (however it defines that)? Can its AH count get out of whack by doing that auto-reset? (if it does AH count at all)

IMO you want to cross-check your "meters" to see they "agree", and that is why you want to measure SOC by some other means than just what the monitor says. Looks like the "smart BMS" is nifty in providing lots of info like a monitor does, but what is the means to cross-check it?

We have had folks on here who believed their monitor's or their charger's read out of SOC saying the batts are at a high SOC while in fact the batts were nearly dead. The big lesson is not to believe just the one meter.

IMO with the money at stake with LFP, you would want to be even more paranoid about what any one "meter" says, even if it is the "smart BMS" in the LFP. Actually- especially the battery's own BMS! Some independent "meter" would be my choice.

It seems the lower knee is the most critical. With the rapid drop off past the knee, you don't have much time to reverse course and not have the BMS shut you down with no 12v for anything.

And since one of the LFP advantages you paid for is to operate to lower SOCs, that means you will be pushing your luck going to that lower knee, so you want to have accurate SOC info.

I don't pay much attention to indepth details of the dropins but pay a little more to lifeblue (I always claimed if I were to buy a dropin it would be them). Here is from there site.

LiFeBlue Battery is smart...VERY SMART. Each LiFeBlue battery has a wireless Bluetooth® BLE transmitter that let's you communicate with the Battery Management System (BMS) using our free software called Smart Connect. For LiFeBlue Battery owners, it's a simple software download for your compatible IOS or Android phone or tablet. The BMS in each LiFeBlue Battery protects against many conditions and will communicate through Bluetooth® any fault or event.



With SMART CONNECT you can check the battery capacity or State of Charge (SoC), voltage, temperature, charge or discharge current simply by opening the application on your compatible smart phone or tablet. No internet connection is required. This feature can save you hundreds of dollars as it replaces the need for a separate battery monitor like the Trimetric, Magnum BMK or Blue Sky Energy IPN Pro remote or others.


SMART CONNECT will even keep track of how many cycles your battery has experienced. Each time you remove and replace a total of 80% of the batteries stored energy, 1 cycle is added to the count.

BMS most certainly reads the amps in/out as it has protections for over current.

With the BMS reading cell voltage and getting the SOC from that, how can it tell when the cell voltage is a lower loaded voltage and the SOC is actually higher? The AH counter doesn't get fooled by that.

Some dropin don't needa monitor if they have bluetooth which shows all the battery details, not all dropin have that then you need a monitoring device.

Those that have bluetooth with soc and other info the bms does the reset of full after getting to what voltage the manufacturer says it needs... it seem 14.4v is their resetting/ ballancing point. I read of one person using lifeblue battery and trying to work in psoc for a long period of time without going to the recommended voltage and his capacity % was out of wack, trying to get long life using a lower voltage doesn't work so well with dropins. Recommended voltage needs to be applied at times more often.

The BMS does not control charging, you do. As Itinerant1 has warned several times, the BMS is the last ditch stand when all else has failed.

You need a monitor so you can do your part, and that monitor has to be zeroed often enough to stay accurate.

I am unclear if that Victron automatic "syncing" (what they call zeroing) will do it right. Could do if the settings are chosen properly?

I am suspicious of that because I don't like how my Trimetric auto reset works as designed. I have that disabled and do manual AH counter resets when I decide to.