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larry asked

Best ESS settings for backup with limited PV

I am using ESS mainly for backup, but have 1000W of solar as well and want to use it effectively. I have feed-in disabled and don't want to feed the grid. I have a grid limit of 300W set to minimize overshoots that feed the grid. My lowest normal consumption is 350W at night, average is about 600W and peak can be around 4000W. I am using mode set to "Optimize w/o BatteryLife", but have also tried it with BatteryLife. I have tried Peak Shaving set to "Always" and also "Above SOC". I have tried minimum SOC settings of 90, 95 and 100%. I am currently using 100%. To avoid hitting the battery limit, I have my SmartShunt set so that 54.0V is 100% SOC. I do not have BMS. These settings seem to work well except for one major issue... I have had a number of "Low battery" and/or "High DC Ripple" alarms, and two that shut down the output. These come with no warning, and with nothing dynamically happening with the load. The battery was above 53V in both cases, and generally always is. I checked all my cabling and everything seems fine. Any suggestions on the best way to utilize the PV and still keep the battery charged would be welcome. It doesn't have to 100% charged. I only tried that setting because of the low battery alarms when set lower, but it didn't improve things in that regard.

ess settings
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Alexandra answered ·

@larry

You don't mention your inverter and battery combo.

DC ripple can be caused by loose connection/bad crimps. (That you have checked). DC cable that is too small. A battery that is too small. Or a battery they is being overcharged. Or a battery whose BMS is trying to refuse charge or discharge since it is above its ability.

So how is is being charged? Does it fit in with the battery manufacturers specification?

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larry avatar image larry commented ·

MultiPlus II-3000. Battery is EG4 LifePower4 - 5.1kWh server rack battery. It has built in BMS, but the BMS is not connected to the MPII because it's not a supported protocol. Cables are factory built 2/0... 3 ft. for positive, 2 ft. from battery negative to 500A Smartshunt, and from Smartshunt to inverter. I try to keep the voltage in the 53.0V to 54.0V range, which it seems to do. It is being charged from the inverter and Victron MPPT. I have not seen any alarms on the battery itself. Is it possible that this could be a comms issue with the VE.Direct cable between the Smartshunt and the Cerbo? Should I try monitoring the battery using the internal monitor in the inverter instead? BTW, I used this same battery with an EG4 6500EX-48 inverter for several months with no issues. I did not use the BMS cable in that case either.

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Alexandra avatar image Alexandra ♦ larry commented ·

@larry

Yeah not many inverters monitor for DC ripple. So saying another inverter didn't have the problem could also mean there was no monitoring for it.

No it is not a Comms issue it is a physical one.

If you have an MK3 adaptor you can use the ve bus and ve configure to see what the ripple voltage being measured actually is.

Or do it the old fashioned way and use a good DMM and measure it yourself.

Look up the book wiring unlimited by Victron, it has a section there on DC ripple.

Page 10 section 2.9

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larry avatar image larry Alexandra ♦ commented ·
I don't think that DC ripple is the cause, I think it's the effect. In the last two days with my current setup, I only had one DC ripple warning and it lasted 1 second. It coincided with a low battery warning, but the battery was 99% charged. I think something else is going on, but not sure what it could be. I'll read the article in your link just in case.
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Alexandra avatar image Alexandra ♦ larry commented ·

A warning might mean you are hovering just under the limit. Gotta do the work and check.

With the low battery combo it is likely the battery is disconnecting or the BMS is shutting down. Signs that the battery is unhappy.

What are your dynamic cut off set to in the ESS assistant, that can also trigger low battery warnings since it is a voltage related to load.or c rating of the discharge.

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Alexandra avatar image
Alexandra answered ·

@larry

Looking at the manual for the EG4...

1. Make sure in DVCC the max charge is set between 30 to 50A. That is the max charge current from all sources.

2. Set bulk/abs to 56v. Float to 54v. Absorption 1 hour. Make sure the lithium profile is active. Check if the system is measuring it correctly. Compare with a meter. If there is a difference adjust the charge voltages accordingly. check under system set up that the shunt is being used for the measurements (I assume you have it as close to the battery as possible).

3. Low DC cut off for ESS start at 47v. If the voltage dips lower than that at a 4k load maybe adjust then down a bit more. According to the manual it can go down to 44v but that assumes the cells are in balance, so best to shut down the Inverter before then

4. Maybe as one ore thing limit the inverter power to about 4000w. To prevent over discharge from the battery when power assisting.

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Alexandra avatar image Alexandra ♦ commented ·
Are your smart shunt settings ok, so your SOC is right?
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larry avatar image
larry answered ·

I'm not using DVCC. I thought that it was not recommended without CAN bus BMS, but after watching a video, I see that it can be. So I can use DVCC to limit charging voltage and/or current from the MPPT. Does this affect AC charging, or does the "Limit Charge Power" setting still control AC charging? Do the AC and DC charging limits interact? I assume that when I hit all my limits... AC charging power limit, DC charging Voltage and/or Current limits and Grid Power limit, that the system throttles back the MPPT. Is this correct?

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