MPPT 150/70 Output voltage versus set voltage incorrect

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k1mgy asked Oct 3, '23

MPPT 150/70 Output voltage versus set voltage incorrect

MPPT150/70 (firmware v 1.61) connected in parallel with a MultiPlus 12|3000|120 and a Orion TR Smart 12|12-30. Installation in a sailboat, with the TR Smart only supplying when the engine alternator is running.

My LiFePo BMS (2 packs, and error occurs with both) have been disconnecting from the charge function due to a high charge voltage condition. As the BMS and an active balancer manage charge and equalization, I have set all three Victron devices to a 14.0 V output. Checking each in isolation, I discovered that only the MPPT 150/70 is producing forcing a charge with > 14.3v.

On the main bluetooth display under the STATUS tab, the device reports a "voltage" consistent to what has been set. But, when I connect the MPPT device to the battery buss, the same voltage display changes to 14.7 volts (sometimes more).

I have disabled the temperature compensation, and have used the victro-supplied profile for LiFePo, changing the absorption and float voltage to 14.0 V. I have also disabled equalization.

For now I've had to keep the MPPT off the battery buss, as this high voltage is not good for my system.

Is this a bug, or a feature? Any way to fix?

MPPT SmartSolar overvoltage

2 |3000

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Answer 1 · 2023-10-03T18:10:54Z

snoobler answered · Oct 03, 2023 at 06:10 PM

It is very common for 12V LFP batteries to have imbalanced cells. If they engage charge protection, chargers may over-volt due to being unable to clamp down on the charge current fast enough.

Recommend you set all chargers to:

Absorption 13.8V

Fixed, 2 hours

Tail current disabled.

Float: 13.5V

13.8V for 2 hours should get your battery to near 100% charge and allow additional time for the BMS to balance the cells. It should also reduce/eliminate over-voltage events.

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k1mgy commented · Oct 03, 2023 at 06:32 PM

Thanks for your suggestion.

The pack has active cell balancing, which keeps everything within a few millivolts (actually quite impressive, this). I'm not worried about cell imbalance.

The BMS disconnects from charging because the input voltage exceeds a safety threshold of 14.3V for the entire pack. Before it drops out, the pack is nearly at 100% charge, but the MPPT keeps on with a high charge voltage anyway.

Everything runs fine with the MultiPlus set to 14.0V. It's the MPPT unit that goes way over the voltage I set for its output. This is what triggers the disconnect.

I tried backing off the output voltage setting to 13.0 V and get the same result.

Seems to me something is broken (?)... maybe?

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snoobler k1mgy commented · Oct 03, 2023 at 06:54 PM

Voltage only equates to balance above 3.40v/cell or 13.6V. Active balancers are a mixed bag. If you can program it to only operate above 3.40v and only if the deltaV is below 20mV, it's probably not a good one and can even be counter productive. The NEEY or the active balancers in JK BMS are pretty good, but most capacitive "dumb" balancers are not worth the cost and can undo a top balance.

14.3V is unnecessarily low cut off. There is no good reason to trigger protection below 3.65V/cell or 14.6V.

Try a a factory default reset.

Would also delete any VE.Smart network to see if behavior changes.

Worth running through this for the MPPT:

https://www.victronenergy.com/upload/documents/Pre-RMA_bench_test_instructions/114199-Pre-RMA_bench_test_instructions-pdf-en.pdf

Might be a defective unit.

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Answer 2 · 2023-10-14T19:43:16Z

k1mgy answered · Oct 14, 2023 at 07:43 PM

A factory reset of the MPPT 150/70 corrected the problem entirely. Apparently there are settings which the factory reset clears which are not otherwise available via the user interface as, following the reset, my settings for output voltage measure and track perfectly at the output terminals.

Relieved I did not have to do the bench testing, although good to have the procedure available should a reset not do the trick.

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