MPPT has stopped fully charging 48v bank

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padamson1 asked Jul 25, '22

MPPT has stopped fully charging 48v bank

I've had a MPPT 150/45 hooked up to 48v bank which two banks of two 100Ah 24v LFPs (400Ah capacity) functioning fine for 7months. The MPPT would increase voltage until absorption (58.6v) about every other day this month and properly drop to float.

Starting last week, right after a firmware upgrade from my phone, the MPPT output voltage never goes above 53.9v. Battery temp is 33c so it is not a thermal shutdown. It slowly gets to 53.9v and just stays there, pumping in 500-750W for the rest of the day. The SmartShunt reports 100% at 53.9v which is different, but if I manually reset the SmartShunt SoC to 90% using Victron Connect it will go to 100% at 53.9v even though voltage hasn't gone over 57v. Looks like the SmartShunt is just measuring current flow into the battery for SoC.

No wires have changed since this weirdness started, only firmware. I also have a 24v bank connected to different MPPT 150/45 which functions as before and goes above 27v as soon as the batteries are 26.8v (according to Smart battery readings) and the voltage continues to climb until absorption (28.6v).

The strange thing is the firmware version on the 24v MPPT says v3.10 on the Product Info page, but the 48v MPPT says v1.59 (and that it is the latest version). If I click update, it says that I have the latest version. Huh? Why is one version different than the other?

Anyone have thoughts on what is limiting the MPPT output voltage to 53.9v?

MPPT Controllers

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Answer 1 · 2022-07-25T12:14:29Z

nickdb answered · Jul 25, 2022 at 12:14 PM

There are different hardware revisions which run different firmware, so the versions won't match between models and ages of product.

Have you double checked none of the settings were overwritten by the update and that charger settings are as you expect them to be?

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padamson1 commented · Jul 25, 2022 at 12:50 PM

Yes. I only used the switch settings. So 48v, 45a, and switch position 7. The load output is on battery life. However I now remember being forced to enter a value when I first brought up the MPPT pages after the upgrade, but I can't remember what it was and don't see anything I new on any of the settings pages.

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Answer 2 · 2022-07-25T13:08:06Z

JohnC answered · Jul 25, 2022 at 01:08 PM

Hi @padamson1

v3.10 is for a CAN port equipped mppt. You could check, but these updates are very reliable.

The real clue here is that the batts are still accepting charge. Possibly a phantom load, or to heat (that'll be noticeable). The most likely scenario is that the Smartshunt is incorrect. The batts should reach 100% when they can't accept charge at Absorb V. Maybe accumulated drift or regular premature syncing. Can you screenshot it's settings? For now, assume that it's wrong.

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padamson1 commented · Jul 25, 2022 at 03:01 PM

Somehow my response seems to have disappeared.

Below is the settings for the SmartShunt. The SoC can be ignored b/c I manually set it yesterday when the 48v MPPT clipped at 53.9v to see if the Shunt was causing the the clipping. Knocking the SoC down to 90% increased the consumed Ah but the voltage did not move past 54v on the MPPT.

Right now the 24v MPPT output is 27.05v and the batteries read 26.75v (on VictronConnect), but the 48v MPPT output flutters betweem 53.8 and 53.9 while the batteries read 26.8 That small differential on the 48v MPPT seemd too low to get current into the 48v batteries to me.

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screenshot-20220725-094517.jpg (214.4 KiB)

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JohnC ♦ padamson1 commented · Jul 26, 2022 at 04:30 AM

Thanks for the screenpics @padamson1

The first thing (and I apologize for not spotting this earlier) is that you only really have 200Ah of batts at 48V. The 400Ah setting will grossly overestimate SOC.

The 4% Tail is a default setting, and too high in my view. What it means is (assuming a 400Ah capacity) that the shunt will sync to 100% when 4% of 400Ah (ie. 16 Amps) can't be reached at the Charged V (for the set 3 minutes). That 16A is a lot of power at 48V. A 1% Tail would be better until you refine it even further.

For now, I'd continue to charge your batts until you reach Abs V. Then you can watch the Amps taper quickly. Only then will your SOC be 100%. You could then set it to 100% manually or let the Tail do it itself. Ignore SOC completely until you see this at least once.

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