ESS bulk restart voltage causing stuck in float

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muddy1 asked Sep 26, '21

ESS bulk restart voltage causing stuck in float

I try not to be too hard on my Lifepo4 batteries so I charge to 56v and float at 53.6v. This worked fine with the MPPT charge controllers, but once I added ESS the problems began. The issue is the bulk reset voltage. On the charge controllers this is float -0.4v so bulk restarted at 53.2v, or around 80% battery capacity which was fine.

With the ESS system, Victron in their wisdom have chosen to set the bulk reset at float -0.8v

Why different ?

This means bulk does not restart until 52.8v. With the flat profile of Lifepo4 this is around 63% battery capacity, which is way too low. Until this point it just sits in float. If you heavily load the system to drop the voltage then it changes over to bulk without any problems, but sitting with a low load you lose a lot of charge time.

Does anyone know a way to adjust this bulk reset voltage ? I know I could float at a higher voltage but this seems a poor solution to the problem.

ESS float

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2 |3000

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Alexandra ♦ commented · Sep 27, 2021 at 08:27 PM

@Muddy1

With ess assistant programmed the mppts go into bulk during the day as they are not dependant on your battery to trigger production? At least all the systems i have do.

So I would say your system is not set up correctly. Do you have a gx device in the system? It is one of the requirements.

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muddy1 Alexandra ♦ commented · Sep 28, 2021 at 06:31 AM

Hi Alexandra

Thanks for your comments. I have Venus 2.80 on my system.

Can you confirm you have ESS installed ?

The ESS manual says the bulk reset is based purely on the voltage.

"Note that these charge-cycle restart-mechanisms differ from the stand-alone MPPT Solar Charger algorithm: they restart the charge cycle every day."

Currently my battery is at 78%, it is early morning, the solar is just starting and I am still in float. I will leave it discharging and see exactly when something changes.

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Alexandra ♦ muddy1 commented · Sep 28, 2021 at 08:00 PM

Yes. I install professionally and have a few years experience.

What does the battery manufacturer recommend as your charge voltages? Or do you have a home built bank?

The other possibility is you have soc drift as well. So some more systeminfo would be helpful here.

In a programmed ess system the mppt activity is load based not battery based. On 100% battery the mppts can produce at full capacity. They do not need to cycle to trigger bulk on the mppt.

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Leslieanne commented · Sep 28, 2021 at 09:53 PM

Hi there,

Perhaps I can offer some perspective. Our system comprises multi 11 48/5000, 4kW of solar AC coupled via a Goodwe inverter on AC1 out, and 1.5 kW solar DC on mppt 150/35, venus GX and BMV 702. Battery is 160Ah 16S Winston LFP cells with zeva BMS using 2-signal communication within ESS, exporting to grid from both AC and DC. Absorb set to 55.2 V, float at 53.6. Optimised without battery life, and 20% SOC floor.

In normal use, it will return to bulk in early evening or occasionally first thing in morning (cooking loads), all exactly as expected. BUT....when we are away from home on holiday and just baseloads running (including refrigerator, small irrigation pump), it will remain in float for a day or two, indeed until voltage falls to 52.8 V. This is usually around 70-80% SOC. Exactly as expected if you think about it, (but I was surprised the first time we were away and noticed it still in float the next day!) Cycling once every 2 or 3 days instead of once (or more) daily. Much easier on the batteries, and still plenty in reserve in case of blackouts. Plus we export all the excess to the grid.

Cheers, Leslie

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muddy1 Leslieanne commented · Sep 29, 2021 at 06:31 AM

Hi @Leslieanne

Thanks for your comments. Your observations are absolutely correct.

My system finally went to bulk at 52.7v and 65% state of charge. Pretty much as the manual says it will.

However 65% is a little lower than I am happy with. It is probably fine in summer when a reasonable amount of daily sunshine can be expected, but in the British winter I want to be able to have every minute of full power charging possible. Several dull days may follow when no energy is available. All my heavy loads are at night so I need to end the day with a good charged.

I think @victron could improve on the ESS software very easily. Clearly no one size fits all. By letting the user set the rebulk voltage, the system would be much more adaptable. Even better would be to allow the rebulk to be set on state of charge. This could be done in parallel with the voltage setting so either triggered bulk.

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Leslieanne muddy1 commented · Sep 29, 2021 at 08:22 AM

Hi again Muddy1,

You may be worrying unnecessarily. However, I am in Australia and our winters are fairly sunny, but we can sometimes get several very dark days in a row! Regardless, I do suspect the following observations might also apply in your case....

I observe that, on the switch to float, the SOC drops rapidly (it even exports battery to grid) from 100% to about 98%, and stays there, so long as sufficient solar is available. A 2% drop is negligible, so basically we always end the day very close to fully charged if there is enough sun. Returning to "Bulk" will not make any significant difference. Note that the mppt, although controlled by the multi, is regulating at a higher voltage, so is always giving all it can, covering any loads and exporting any excess to the grid. Have a look under "solar charger > networked operation" in remote console to see the value. It might scare you!!!

The above is the case when at home, and like you, we use high draw appliances overnight, so it has always switched back to bulk by morning. When there has been minimal load (as when we are away) it will start the next day in float. Then it will only reach about 90% SOC at 53.6V for that day. But that is still plenty of reserve for the low background loads.

Agreed, it would be nice to have more adaptable settings, but at least in our case, the practical advantage would be minimal. In fact, it is likely better for battery longevity to not be brought to 100% each day when unnecessary.

Cheers, Leslie

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