Why doesn't ESS supply the load required from the MPPT controllers (Full battery & EV charging)

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mcwidowmaker asked Oct 26, '20

Why doesn't ESS supply the load required from the MPPT controllers (Full battery & EV charging)

My setup:

Victron Multiplus 48/5000/70

Bluenova 490ah 52v LiFepho4 battery bank

2 x Victron Bluesolar 150/70 MPPT controllers connected over can bus

5kva panels

CCGX running ESS

I am running into an interesting problem. My battery bank is usually fully charged by 11am if we have good sunlight. Once it is fully charged, I plug in the granny lead for my I3 to let the excess power charge the vehicle. What I expect is that the 3.5kw load will be supplied by the MPPT controllers, as there is more than enough sunlight to do so.

What I find however, is that something is throttling the mppt controllers, so that they will only suplly 50 - 60% of the load, even though they have supplied way more than that earlier in the day. Should we have a cloudy morning, they would supply 4kw easily until 3pm, so I know they are capable of supplying the load. So why would they limit their output and draw from the fully charged battery rather than supplying the load from the sun?

ESS

2 |3000

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Answer 1 · 2020-10-26T11:14:42Z

Guy Stewart (Victron Community Manager) answered · Oct 26, 2020 at 11:14 AM

Hi @Mcwidowmaker,

I would suggest running your large load BEFORE your batteries reach 100%, start the large load at 95% instead, OR Enabling PV to export to the grid (if that is allowed).

The reason for this conservation is because when lithium batteries are full, they are really full. Any large and unexpected supply of current at this full charge state can cause system instability.

So imagine that the batteries are totally full, cannot take another 10A, and your very large EV load suddenly switches off. There is a moment where the MPPTs are suppling more current than the batteries can absorb, as there is suddenly no load to consume the power.

This can lead to overcurrent, and over voltage warnings, errors, alarms and eventually system shutdown.

So for this reason, the batteries have some headroom, where they will discharge slightly before allowing full charge from the system again. So if there is any extra power that can't go to the load, it can be safely absorbed by the battery, giving time for the charge controllers to reduce their output to adapt.

This headroom is usually supplied by the batteries themselves, as a current, or voltage limit (set below the the fully charged target voltage). Once the battery is happy that there is sufficient capacity to charge safely, it will raise that target again. This will be communicated to the rest of the system via the GX device.

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Alexandra ♦ commented · Oct 26, 2020 at 06:14 PM

@Mcwidowmaker

I have seen the same as well. We have few systems running the Blue Nova batteries, ranging form the 16K down to the 4K SSS models. We have found setting ESS to keep 95% SOC in case of grid failure helps to work the solar a bit harder. Set with battery life on the system does make sure absorption for balancing is achieved. Usually set the geysers to switch on about 95% and off again around 90% depending on battery banks size.

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