On sunny days, Inverter switches off when DC voltage gets too high?

[GOM BOF]

In December 2022 a local solar company fitted 23 x Trina Vertex S390W panels in two strings. 10 of the 23 panels have optimisers fitted. They connected these strings to a Solis 6KW (rhi-6k-48es-5g) Hybrid Inverter and two Puredrive 5KW batteries. The system is connected to the grid as a producer and consumer of grid electricity.

On very sunny days, between 1100 and 1200 local time, the inverter will switch off for a few minutes recording a “DC input overcurrent fault”. I can see from the graphs available that this occurs when the batteries move from 99% to 100% charged and the inverter DC voltage, spikes from 2x 330v (=720v) to 2 x 387v (=774v). At other times of the day, when the battery reaches 100%, the DC voltage is not as high and the inverter does not switch off. Amps do not rise above 10.3A on each string, at any time.

The technical info for this inverter is:
Input DC (PV side)
Recommended max PV power 8000w
Max input voltage 600v
Rated voltage 330v
MPPT voltage range 90-520v
Full load MPPT voltage range 280-520v
Max input currant 11A/11A
Max short circuit current 17.2A/17.2A

I sense that there is a safety issue here, which will increase as summer develops. Too many volts suggests to me that some component might overheat and ignite, or its electronics burn out, or that the inverter fails completely, as the inverter would not switch itself off if there were no safety issues. I have not contacted the supplier company as the two technical people they had, have both left after completing my installation, having fallen out with the company’s new sales-driven owner. I wonder if I have been sold too may panels or if there needs to be an extra bit of voltage-limiting kit between the input strings and the inverter?
I would welcome your advice as to what I can do, or get done, to sort this problem out.

 

[OzSolar]

he inverter DC voltage, spikes from 2x 330v (=720v) to 2 x 387v (=774v). At other times of the day, when the battery reaches 100%, the DC voltage is not as high and the inverter does not switch off. Amps do not rise above 10.3A on each string, at any time.

Of course, regardless if the original techs are still at the company the company still owes you a resolution.

Some things I gathered from your post:

Overvoltage would likely have already ruined the inverter so I don’t think your inverter is seeing the 774v.

Since you are able to see the amps of each string that tells me they are paralleled at the inverter on their own MPPT channel.

An "Overcurrent error" would mean too many amps, not too much voltage but according to the specs you provided you are under the max amps at Imp. That may indicate that your inverter is seing too high of an Isc but without the module specs that’s just a guess.

One thing I would do is to disable one of the strings and see if the problem persits.

 

[Hedges]

Trina Solar Vertex S TSM-390-DE09C.07 390W Bifacial (Transparent) Black Solar Panel – V O L T A I C O

voltaico.com

Imp 11.54A, which does not include BiFacial aspect.

"Max input currant 11A/11A
Max short circuit current 17.2A/17.2A"

Voc: 40.8V

"23 x Trina Vertex S390W panels in two strings"

Assuming 11 & 12 panels in the strings, 12 x 40.8V = 489.6Voc for longer string.

"Max input voltage 600v"

600V/489.6V = 1.22, which is plenty to avoid over-voltage in cold weather.

Can you confirm how many panels per string?

Your inverter ought to start at zero current, open-circuit voltage, and work down from there. But it may have problems with PV able to deliver more current that it wants. The panel seems less than perfect fit for the inverter but maybe it is OK, just slightly "overpaneled."

https://www.ginlong.com/Uploads/file/Solis_datasheet_RHI-(3-6)K-48ES-5G_AUS.pdf

Why do you say, "2x 330v (=720v)"? Why are you multiplying by two? What numbers are you reading?
What voltage does inverter report for each string?

I think optimizers only reduce voltage and increase current.

It seems like PV panels may be too high a current for that inverter.
Are all panels the same orientation, or are the two strings on different roof faces?
Possibly, if inverter allows its two MPPT inputs to be paralleled, having two strings of different orientation in parallel would keep it within inverter limits. Just a guess, need more information.

 

[GOM BOF]

Thank you OzSolar and Hedges for helping me with this.

All the panels are on one roof face. The roof is about a 45-degree pitch, chalet style roof and faces South-East.

Attached is a document showing the panel layout. I do not know the number of panels in each string.

It also shows the Alarm messages, DC voltage, DC Amps and battery SOC/SOH for yesterday and most of today.

You will see from the charts that at the time of the alarms both strings had a voltage spike and peak, while the amps drop to zero. I have also included a Battery report for the same days, as they show that the batteries hit 100% charge at the same time as the inverter input voltage peaked and the circuits went off.

Talking to a mature electrician doing my neighbour’s extension wiring, he advised me that I should not say that the inverter switches off with these alarms, what I should say is that the two lighting and one sockets power fail backup circuits which are supplied with mains and battery power through the inverter, switch off for the alarm period. The graphs come from my inverter’s internet app. I cannot get to the actual inverter, as my mobility is limited and I am unable to crouch into the side attic where the inverter and batteries are located.

 

[Hedges]

I have also included a Battery report for the same days, as they show that the batteries hit 100% charge at the same time as the inverter input voltage peaked and the circuits went off.

Battery charge suddenly stopping may be the issue.
Graph only shows battery percentage full. Is that lithium? If so, what voltage settings in inverter? In BMS? Is there communication between BMS and inverter?
Try setting to a lower voltage, so it doesn't run up so fast. Maybe then inverter can gradually ease off on PV production.

 

[GOM BOF]

Attached are the graphs for Battery voltage and current, BMS battery voltage and current, and BMS charging and discharging current. These three graphs are the only ones available relating to voltage and/or current in the battery section of the inverter information. The batteries are lithium-iron-phosphate. Also in the attachment is the spec info for each of the two batteries. The inverter comes with a built-in BMS.

 

[Hedges]

Battery has BMS, so I doubt inverter does.
Do they communicate, or does inverter just charge to a volage?
57V max, 3.5625V per cell for 16 cells. That is reasonable, but a cell may start running at that point.
Can you change inverter setting, tell it to stop at a lower voltage like 56V, 55V?

Graph shows charge limit (apparently communication from BMS) 200A, then dropping slightly, then dropping to zero.
You don't want it to drop to zero unless charging has gradually tapered off at max voltage, so I think reduced voltage would help.

Or, maybe cells are imbalanced. Are you able to get a cell by cell voltage report?

If you provided a slower charge (fewer PV panels, or charge from the grid with low amperage limit), that could allow BMS more time to balance.

 

[rpdom]

I've got 8 of those Trina panels, without optimisers, in a single string and had an RHI-3K-48ES-5G inverter which kept tripping out with ILeakPro /1034 Leakage Current Protection. I called my installer and they sent someone to look at it twice. The first time they redid some connections which didn't help. The second time they tested every circuit and eventually decided that the inverter wasn't suitable for those panels.

They replaced the inverter with the newer S5-EH1P3K-L which is rated for up to 15.0A and I haven't had a problem since.

I was also getting the 2015 BMS Alert overvoltage errors on the old inverter. Those have also cleared up since changing the inverter.

 

[GOM BOF]

Thanks rpdom, this is really useful and interesting to know. You obviously had a better supplier than mine turned out to be, as, having made the final payment, I spent five months of chasing different people in the supplying company, including chasing their director, eventually starting legal proceedings before I got my copy of the G99 approval letter, extended warranty certificate, my roof and gutter repairs completed, etc.

I have asked Solis what they recommend the solution should be but have not heard from them yet.

Hedges, thanks again. I don't have access to a cell by cell report. I am looking into how I might be able to set a slower charge rate.

 

[Supervstech]

Every single time I have seen an overvoltage condition it has been a battery issue.
The battery bms is cutting out before the charge controller thinks it is finished.

EVERY time.

So, either the battery has a runner reaching max charge, or the inverter is set to too high a charge voltage.

 

[Hedges]

Hedges, thanks again. I don't have access to a cell by cell report. I am looking into how I might be able to set a slower charge rate.

Are battery terminals physically accessible?
Can you determine BMS make and model?
Is there a documented way to talk to and configure BMS?

Maybe inverter charge settings will let it adjust itself.
If you can get cell voltages, you'll be able to see that in real time.

 

[GOM BOF]

Supervstach and Hedges, thanks for your input. The attached photos may give you more info. Apologies for the quality. Remembering that I am a lay-man, what I am hoping is that you may be able to use these pictures, to tell me which of these parameters I need to be changing, and what value to change it to, in order to reduce the charge voltage and to avoid the battery running up to max charge.

There is no separate BMS unit. The Solis hybrid inverters will only work with a few named types of hybrid lithium storage batteries. According to the manual, the BMS type settings are automatically set by the inverter for a specific battery type except for the Overcharge SOC and Forced charge SOC, which are manually set.

 

[Hedges]

"Equalizing Charge" is a lead-acid term, but the 58V specified is 3.625V per cell for 16 cells, reasonable for LiFePO4.
That is the one I would reduce, at least temporarily, to see if it allows BMS to complete balancing.

"Float" 53.5V is 3.344 per cell.

Over-voltage 60V is 3.75V per cell, seems reasonable. Maybe I would use 3.65V per cell, at least, that is what people often charge individual cells to, one time, for "top balancing" then subsequent charging lower. But I think some battery brands say that is max voltage for daily cycling.

Doesn't say how long it holds "Equalize" before dropping to "Float", but that hold time, and the charging time approaching equalize, is when balancing occurs.

I suggest trying "Equalizing Charge" 3.5V per cell (56V) for maybe 10 cycles, then step up 0.5V at a time until you get back to 58V.
See if that holds without tripping; if not, back off to a lower voltage where it doesn't trip.

Imagine you're filling 16 wine bottles with a hose that splits into 16 hoses. The bottles have different amounts of water in them initially. As one gets near full, level starts rising rapidly in the narrow neck. Imagine there is a pipe tapped off all the bottle necks that gradually equalizes level between them. If you pour in too much too fast, some overflow. If you slow down or stop and hold before the first one overflows, there is time for them to be equalized.

(Some BMS equalizers actually transfer charge between cells, others just bleed off charge through a resistor.)

 

[Daddy Tanuki]

Every single time I have seen an overvoltage condition it has been a battery issue.
The battery bms is cutting out before the charge controller thinks it is finished.

EVERY time.

So, either the battery has a runner reaching max charge, or the inverter is set to too high a charge voltage.

Supervstech is right...i had this same issue on my system a couple of years ago. took some fiddling with the settings to get everything to play nice.

 

[GOM BOF]

Every single time I have seen an overvoltage condition it has been a battery issue.
The battery bms is cutting out before the charge controller thinks it is finished.

EVERY time.

So, either the battery has a runner reaching max charge, or the inverter is set to too high a charge voltage.

Thanks for this. I am a non-tech homeowner and solar novice. Given that, what actions would you recommend that I take to remedy this inverter/BMS problem? If I need to change some settings, which exact settings should I change and what value should I change them to? The attached pictures show how things are currently set.

 

[GOM BOF]

"Equalizing Charge" is a lead-acid term, but the 58V specified is 3.625V per cell for 16 cells, reasonable for LiFePO4.
That is the one I would reduce, at least temporarily, to see if it allows BMS to complete balancing.

"Float" 53.5V is 3.344 per cell.

Over-voltage 60V is 3.75V per cell, seems reasonable. Maybe I would use 3.65V per cell, at least, that is what people often charge individual cells to, one time, for "top balancing" then subsequent charging lower. But I think some battery brands say that is max voltage for daily cycling.

Doesn't say how long it holds "Equalize" before dropping to "Float", but that hold time, and the charging time approaching equalize, is when balancing occurs.

I suggest trying "Equalizing Charge" 3.5V per cell (56V) for maybe 10 cycles, then step up 0.5V at a time until you get back to 58V.
See if that holds without tripping; if not, back off to a lower voltage where it doesn't trip.

Imagine you're filling 16 wine bottles with a hose that splits into 16 hoses. The bottles have different amounts of water in them initially. As one gets near full, level starts rising rapidly in the narrow neck. Imagine there is a pipe tapped off all the bottle necks that gradually equalizes level between them. If you pour in too much too fast, some overflow. If you slow down or stop and hold before the first one overflows, there is time for them to be equalized.

(Some BMS equalizers actually transfer charge between cells, others just bleed off charge through a resistor.)

Hedges, thanks for this. May I just check that I have understood this correctly. My understanding of what you are suggesting is that I manually change the Equalising Charge from 58v to 56v. Then let this run for about 10 days but that this period must include some very sunny days. If the system does not alarm on those sunny days, then repeat the exercise at 56.5v, then 57v, etc, until the system again alarms on sunny days. Having found the lowest voltage at which it alarms, go back 0.5v to the highest equalising voltage that did not alarm on sunny days and then leave it on that setting. Have I understood this correctly?

 

[Hedges]

Yes, that's exactly what I meant.

If you settle on some voltage lower than 58V for operation without alarm, you could repeat the exercise in the future, after it has had more cycles. Maybe then it can reach 58V.

The batteries are lithium-iron-phosphate. Also in the attachment is the spec info for each of the two batteries.

Actually, the page you included says, "Max charge voltage 57V", which is 3.56V per cell.

Getting it to charge successfully to some higher voltage 57.5V or 58.0V we'll call "top balancing", with the BMS balancer helping to do that over some cycles. Then you could back off to 57.0V for future operation. That is meant to provide some margin in operation so it doesn't trip protection.

I'm not sure what spread between top balancing voltage and operating voltage people usually use (I haven't used these batteries myself.) I know the forum members normally top balance to 3.65V per cell (with cells wired in parallel before assembling the series pack) and stop when charge current has tailed off to maybe a couple percent of what they were charging at. I understand that held forever at that voltage it would continue to charge slowly. What I'm less sure of is what operating voltage they prefer, and how long they hold at that voltage before dropping to float.

The parameters you showed included a float voltage. After some time your inverter will reduce voltage to float, which seems good.

 

[SeaGal]

Maybe I'm having a (another) blonde moment ?‍, but I don't see why this thread is focussing on battery over-voltage when the OP reported the alarms as a "DC input overcurrent fault", which I understood refers to PV DC and not battery DC. He also says the battery reaches 100% at other times of day, without any alarms being raised, so I don't immediately see that (without more data) it being a battery / BMS related issue.

In my view, the issue is that his installers have put 23 * 390 W = 8970Wp of panels on a 6000W inverter that states "Recommended max PV power 8000W".

With those panels all facing South-East then, late morning, when they are at their peak, the battery reaches its capacity. The Solis will have been (presumably) exporting a large chunk of power to the grid and the rest into the battery at whatever rate the PureDrive's BMS is allowing. Once 100% is reached, the Solis is no longer able to charge the batteries and will, for a few seconds, have 8900W of PV being drawn on its DC input, which it will need to ramp down (as it is only a 6000W inverter). My guess is that, before it can ramp down generation (which from my experience of my Solis can take a few seconds), the voltage on the DC PV input will go up, the current will go up and 'hey-presto' a" DC input overcurrent fault" is triggered.

 

[Ampster]

Once 100% is reached, the Solis is no longer able to charge the batteries and will, for a few seconds, have 8900W of PV being drawn on its DC input, which it will need to ramp down (as it is only a 6000W inverter)

I agree with your overall logic with the following nitpick exception. I do not think 8,900 Watts will be drawn by a 6,000 Watt inverter. It may be a timing issue as the charging shuts down. I do think lowering the charging voltage might be worth a try to see if that resolves the timing issue.

 

[SeaGal]

I agree with your overall logic with the following nitpick exception. I do not think 8,900 Watts will be drawn by a 6,000 Watt inverter. It may be a timing issue as the charging shuts down. I do think lowering the charging voltage might be worth a try to see if that resolves the timing issue.

The Solis Hybrid's rating is for delivery to house / grid export... Mine is a 3680W version and that is the max it will output as AC. However it can also charge the battery via DC over and above that power rating, up to the max it handles on the PV DC side.

For example: I have a 3.6kW Solis which, on a sunny day, will take 5.5kW from my (over-panelled E-W) PV, sending up to 3.6kW to the house and still charge batteries with the remaining 1.9kW.

So I assume the 6kW Solis may be able to take up to 8kW from PV, deliver 6kW to the house and 2kW to the batteries... so a timing issue, as you say, when the batteries suddenly stop taking charge! ?

I'll suggest @OzSolar 's suggestion of...

An "Overcurrent error" would mean too many amps, not too much voltage but according to the specs you provided you are under the max amps at Imp. That may indicate that your inverter is seing too high of an Isc but without the module specs that’s just a guess.

One thing I would do is to disable one of the strings and see if the problem persits.

.. would be best to try first.