DIY 200ah LFP underperforming

Luk3jay · Sep 1, 2022

sunshine_eggo said:
This is completely wrong. No way cells at 3.27V are at 90%

Until all cells are above 3.40V, you can't be confident you're at a high SoC.

Good to know. I've adjusted the SOC parameters as follows (i did it before your post) so will see how this goes.

sunshine_eggo said:
Can you produce this chart for your discharge that's draining the battery?

View attachment 109644

Yes. I'm working on it. This chat came from the BT module which isn't normally connected (i have a screen in the van and only use the BT for programming) - i have left the module plugged in to collect data. This is what i have so far:

The big downward peaks are a split second 100a load when the fridge compressor kicks in (powered via an inverter) and then around 6a for a few mins.

I've noticed that the chart seems to have missing or confusing days times as demonstrated below:

I will keep the BT module connected fora few days, especially during use of the induction hob to collect useful data.

Luk3jay · Sep 1, 2022

Luk3jay said:
Yes. I'm working on it. This chat came from the BT module which isn't normally connected (i have a screen in the van and only use the BT for programming) - i have left the module plugged in to collect data. This is what i have so far:
View attachment 109673

The big downward peaks are a split second 100a load when the fridge compressor kicks in (powered via an inverter) and then around 6a for a few mins.

Also a point to mention: the SOC (orange line) jumps around a fair bit on the top left. This is because, as I adjusted various settings, the SOC reading bounced around. Therefore, this chart is probably inaccurate. I'll have to wait until i get a full 100% SOC for any more accurate charts.

Luk3jay · Sep 1, 2022

Browneye said:
If you don't have one already, consider getting a shunt meter. Victron = $$$$ They're really nice. Or something similar like Junctek = $
I have about $40 for mine and it's the coolest gadget, works great. Has a display meter and a BT app. Counts amps in and out and does a great job of keeping track of battery state of charge. You set it at 100% when the battery is 100% charged, then it keeps track of current in and out and let's you know where the battery sits. They're surprisingly accurate, much more so than even a BMS. And you're right - the bms is only telling you the percentage based on what you entered for the state of charge values, and we all now battery voltage is not a real good way of determining state of charge.

Junctek display/meter:

BT App on iOS:

Thanks. This is the exact meter I've been looking at bit I was dubious as I hadn't heard many user examples of them. It looks like exactly what i need, and reading the instructions, it's also possible to integrate it with the smart control system that I'm developing. I'll make an order as soon as I'm home!

One question, van you change the layout of the screen? It looks a little too crowded for me. It's not a deal breaker, but would be nice if it had an option to only show the SOC.

Also, can it show historical data on graphs? Thanks

Browneye · Sep 1, 2022

No, the display layout is fixed.
But you can adjust the voltage scale, and select F or C for the temp reading. The display is a flush mount configuration, and I wanted a surface mount rather than cutting a big hole in the wall. So I sourced a housing box to mount it.

Various shunt amp ratings are available to suit your max system current as well.

You can get just the sending unit wit BT app without the display if you don’t need/want it.

I don’t recall on data logging.

BradCagle · Sep 1, 2022

Sounds like the battery never got fully charged after you ran it down to 0% that first time. Then you went in, and changed BMS settings, which may have reset the SOC to something it's not, like 50% when it was actually 0%

You need to let this battery top off, that probably means not using it for a whole day, or more. You need to see the cell voltages get to 3.45v each, preferably 3.6v

Then you'll know it's actually 100%

Luk3jay · Sep 1, 2022

Luk3jay said:
I've noticed that the chart seems to have missing or confusing data and times as demonstrated below:

View attachment 109674

I will keep the BT module connected fora few days, especially during use of the induction hob to collect useful data.

Okay, scratch that. It turns out that the BT module has no memory, and the log is made on my phone whilst the app is open, which isn't very often. So the app history is basically useless.

DIY 200ah LFP underperforming

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