Too low to show?

[BroomJM]

I'm using a couple of 100ah LFP batteries I built 2 years ago to power a small DC fridge. Once the fridge is at temperature, the draw on the batteries is very low, meaning under 5 amps worth of draw. I know from prior experience that the Daly BMS on these batteries doesn't "wake up" for less than 5 amps. What I mean by that is if the BMS is inactive, it takes 5 amps or more to register in the app on my phone.

The problem I'm having, if you can call it that, is one of these batteries will run the fridge for 10-12 days, but the "SmartBMS" app on my phone shows the battery is still at 100%, even when the BMS cuts off due to low (2.5v) cell voltage. When that happens I switch to the other battery and connect the discharged battery to a solar charge controller and bring back up to 14.4 volts. I can't rely on the app to tell me what the SOC is because it basically is showing 99% throughout this entire process. Short of getting a decent shunt or hall effect sensor, is there anything I can do to get a better reading on these batteries?

 

[S Davis]

Same exact problem with my Daly BMS, mine will not register a load below about 3amps. I run a ARB fridge on my work truck and my two 280ah batteries will go out on low voltage before the app shows anything.

I tried contacting Daly for a solution with no luck, the SOC is just about useless on the app if you have small loads.

 

[BroomJM]

Same exact problem with my Daly BMS, mine will not register a load below about 3amps. I run a ARB fridge on my work truck and my two 280ah batteries will go out on low voltage before the app shows anything.

I tried contacting Daly for a solution with no luck, the SOC is just about useless on the app if you have small loads.

Well, that sucks, but thanks for verifying it's not just me doing something stupid.

 

[JeepHammer]

Just an idea...

Would something that draws MORE than 5 amps connected to the battery let the BMS update?

Say a load on a momentary switch? Push the button, the BMS wakes and updates?

This is why I like a BMS with display, once the memory gets top and bottom references, it tracks Watts In/Out, you always know what's in the battery.

Yes, I take A LOT of grief for that... Even with 'Connectivity', I still prefer a way to verify...

 

[Rossman]

You may be better served by just adding a 3rd party shunt and monitor?

 

[JeepHammer]

You may be better served by just adding a 3rd party shunt and monitor?

There are a few BMS units that use a shunt and track charge volume. It requires discharged batteries, whatever you bottom charge/bottom limit is, the charge with the BMS in place so the unit can determine exactly how many kWh moves into the battery.

They are neither particularly expensive, or any more difficult to install than a regular BMS, they just come with a display that shows you battery stats. See about all the big rack batteries currently available.

They HAVE communications ports, you just don't hook them to the inverter so they are invisible to the people updating software, monitoring (and controlling) your inverter.

Bluetooth connectivity with your phone is one thing, wifi connectivity with the internet and being monitored by the manufacturer is another.

The manufacturer MUST follow regulations/laws, so you get screwed. I noticed one of the big hybrid manufacturers stopped asking which state or what your zip code is... The battery connection port is now labeled "DC Input"... (with a charger) instead of "Battery".

Download your software version in you (ganged) inverters so they work together, and they don't ask the question that would be a legal hook for them.

I'm SURE they don't want to get into politics and policing your useage...
(I'll neither confirm or deny a factory tech told me that outright on the phone...)

The smaller inverters, plenty acceptable and affordable, but you might have to jump though hoops to get them passing code, don't ask the question either.

They claim they are 'Economy' inverters and don't have the 'Feature Rich' software and capability to regulate battery usage.
Think the $750-$1,700 versions you see all the time on the DIY videos, mounted side by side for higher outputs...
Connected to non-propritary rack batteries.

 

[RCinFLA]

I know from prior experience that the Daly BMS on these batteries doesn't "wake up" for less than 5 amps. What I mean by that is if the BMS is inactive, it takes 5 amps or more to register in the app on my phone.

Biggest issue is usually the op amp, that amplifies the low level voltage across the current shunt resistors. Cheap units do not have DC offset correction so the zero current point drifts as the op amp's DC offset drifts, mostly due to temperature variations.

The DC offset error can make a small amount of discharge current be counted as a small amount of charging current, or vice versa. Over a long period of time this error builds up in the Columb counter SoC indication.

Higher quality battery monitors have op amps that continuously self-calibrate their DC offset with internal circuitry.

 

[S Davis]

I have found my two Daly BMS don’t show any charge or discharge below about 3amps, this is about what my portable frig uses. Sometimes it will pull just enough to get the BMS attention but most of the time not. I was told this could be changed in the software program but I could never get it to work.

 

[Sharky722]

There is something you can do about this if it is the sinowealth MCU.
Can you connect to the sinowealth software?
If yes, change the dfittercurr setting to 500mah.
It will then read 500ma and above. They are usually set to 3000mah so it won't register anything below that.

 

[S Davis]

There is something you can do about this if it is the sinowealth MCU.
Can you connect to the sinowealth software?
If yes, change the dfittercurr setting to 500mah.
It will then read 500ma and above. They are usually set to 3000mah so it won't register anything below that.

I tried everything to get the BMS to connect to the software so I could change that setting,went back and forth with Daly for a couple months before I finally gave up.

 

[Sharky722]

I tried everything to get the BMS to connect to the software so I could change that setting,went back and forth with Daly for a couple months before I finally gave up.

Does it connect to the pc master software then?
If it does then it has has a different mcu and that setting is not available in pc master.

 

[S Davis]

Does it connect to the pc master software then?
If it does then it has has a different mcu and that setting is not available in pc master.

Yes, they would connect to the pc master but not sinowealth.