Off Grid Chalange

[Bendesa1962]

Problem:
Off Grid Systeem:
Morningstar SureSine inverter 48 VDC 2500 Watt
Morningstar Tristar TS 45 Charge Controller
Battery bank 4S2P 8 x 12V 200Ah VRLA Gel batteries
4 x Longhi 550-Watt Solar Modules
System load:
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The system is located at Pulau Rote in Indonesia.
After it was installed in March of this year the client did ad a huge fridge/freezer to the system.
Specs of the fridge freezer:

• Fridge/freezer: Samsung RS61R5001M9
• Rated power: 270 W (220 V / 50 Hz)
• Normal running power: approx. 120–150 W
• Compressor startup surge: approx. 1000 / 1500 W (very brief)

The system runed fine for 5 months and then problems occur. During the night the Morningstar inverter does an automatic Low Voltage Disconnect which means the whole system went off. After a while, sometimes 30 minutes but mostly several hours in the night the system recovers but it’s possible that after a while during the night it switches off again due to a low voltage disconnect of the inverter.

When they disconnect the fridge freezer verything is smooth

I tell the client that this extra fridge was not in de design demands and they do understand that but they also ask how it is possible that it did run fine for 5 months. I think it has to do with SoC of the battery bank and the surge power of the fridge freezer. What do you guys think about the situation. And how could it be repaired?
Many thanks for participating
Kind regards

[organic farmer]

How frequently have they been performing an Equalize Charge?

We must assume that the individual batteries are going to be out of sync, we must pay strict attention to holding them in sync before we can expect them to hold a charge through the night.

[Bendesa1962]

Hi organig farmer, thanks for your reply.

I'm confused to be honest because I found this info on the web:

Equalize Charge and VRLA Gel Not recommended: A classical equalize charge (with increased voltage and gas formation) must not be applied to VRLA Gel batteries.

Reason: Gel batteries are sealed and equipped with a valve. They are designed to allow internal oxygen recombination.

During an equalize charge, excessive gas formation occurs → this cannot escape or be mixed as in flooded batteries.

Consequence: Pressure buildup, drying out of the gel, cracking of the separators, and permanent capacity loss.

Manufacturer guidelines: Virtually all manufacturers (e.g., Sonnenschein, Exide, Trojan) explicitly state that equalizing is prohibited for Gel and AGM batteries.

[organic farmer]

I am using Exide Lead-acid batteries and they need a monthly equalize charge.

When they are not equalized the symptoms sound just like the OP.

[SunEagle]

I am using Exide Lead-acid batteries and they need a monthly equalize charge.

When they are not equalized the symptoms sound just like the OP.

I agree. I also am not sure how those 8 batteries are wired. If they are in parallel at all then some are not getting an equal charge

[MichaelDK]

A couple of observations. In my own personal experience with the region, Pulau Rote is going to be equatorial jungle hot the year round, but the weather might change a bit temperature-wise during the monsoon season.

Those LongHi panels may be the ones with a Vmp of 41V, and a Voc of ~50V. The TriStar controller is an older PWM controller, so most likely the four panels are wired in parallel. What I suspect is happening here is that the panels are wired in parallel, and getting only marginal charging with batteries that need a charging voltage close to the Voc. What might be happening here is that the batteries were marginally charging during somewhat cooler weather, but got pushed over the edge with a combination of a higher load, and hotter weather that pushed the panel voltage down.

I think the best single option is to replace the TriStar with a MPPT controller, so the panels could be wired at least 2S2P. An additional two solar panels wouldn't hurt either. That area is going to be plagued by constant partial cloudyness, so I would de-rate the panel output down to ≤80%. Assuming a 400Ah battery bank with optimal charging around 1/8th of C, to get an honest 50A of charging current you'd need (50A X 50Vcharging)/0.80 = 3125W of panels.

So, I'd replace the charge controller first, and then add more panels. With four panels wired 2S2P, a 50A/150V controller would work. With three in series, then a 60A/200V controller.

BTW, I used to be MichaelK!, but something was wrong with my account, and I had to re-register.