Bus Volt Fault

[David Yates]

Hi folks,
Long time lurker, first time poster and as often is the case it's when I have a problem!

I have the following setup:
H1-5.0-E-G2 inverter
2x EP5 batteries
11 440w Canadian PV panels

All installed by UPS Solar on 11th December.

All has been well until this morning, when I noticed that the batteries hadn't fully force charged overnight as usual.
Further investigation showed that the inverter logs was showing numerous "Bus Volt Fault" starting at about 01.30 (the force charge period starts at 00.30)

This morning I've done the usual IT first fix attempt of turning everything off and back on again, though I'm not terribly confident this will fix anything and if it does that is a bit worrying!

I've attached a photo of the inverter display showing the error as well as some graphs from my Home Assistant (I'm connected via Modbus to the inverter)

Any advice or guidance would be greatly appreciated!

Thanks
Dave

[Dave Foster]

Hi, that’s reporting a fault condition on the dc bus, at the time it happened it must be battery charging related - the EP5’s are not particularly high voltage batteries - but I have heard a few of these recently which needed a firmware update to correct.

The latest firmware for the H1 G2 is Master 1.31, Manager (ARM) 1.48 - what firmware versions are you running ?

[David Yates]

Thanks for replying Dave.

Master is V1.31
Slave is V1.03
Manager (ARM) V1.48

So from what you've said I'm on the latest firmware version.

I checked the graphing and couldn't see anything anomalous on the battery voltage.

[Dave Foster]

Ok yes firmware is good, I can't tell from your graph but there are those 3 power spikes from approx 4kW up to 5kW were around the time it happened - as you have modbus, do you have the BMS charge rate sensor available you can check to see if that changed... just intrigued as to why the charge power would jump like that.

So probably next best thing to check is the BCU firmware on the EP's - easiest way is in the V2 app, click Device, Battery and click the serial number under the battery image - the BMS version is the one to read off.

[David Yates]

Unfortunately it seems that the three pin reset didn't work, we experienced the same behaviour again this morning.

I've attached screenshots of the BMS firmware version and the BMS charge rate graph from the previous night when this behaviour started.

Seems to me like there's a fault with the inverter most likely, how do I go about getting this resolved?

Thanks
Dave

[Dave Foster]

Ok, I always think if a fault can go away on it's own, it can come back on it's own - and this needs investigating.

Your BMS firmware is almost the latest version (but latest only adds heater function for warm batteries).

If you have a relationship with your installer, you should go through them first as any warranty replacement will need them involved, but you can escalate to Fox service for investigation either in the V2 app by clicking 'Me', 'Contact Us' and click 'Support' - which will let you raise a ticket and attach images etc.. of the problem. Alternatively you can email Fox service at service.uk@fox-ess.com but make sure you include your inverter serial number.

[David Yates]

Inverter battery voltage graphing for the same time period

[Dave Foster]

You sometimes see that when the batteries are float charging if you have a very low charge current set - but given the battery voltage it's unusual behaviour as the state of charge isn't particularly high.

Probably best to keep your service request simple (i.e. repeated bus volt faults) and let them diagnose, complex things get sent to their dev team to investigate.

[David Yates]

Just a brief update for anyone who is interested.

I had the idea to try limiting the force charge power to 3kW which seems to be below the level where the inverter starts tripping out as it's fully charging overnight again.

I have raised the issue with UPS Solar so we'll see what they say.

[Dave Foster]

I wondered about doing that, the BMS is in control of the charge and sets the charge limits so you would expect it to get it right.

The EP5 recommended charge current is 13.5A, you have 2 that’s 27A (in parallel), and a nominal voltage of 192V you should be fine charging at 5,184 watts (although perhaps temperature/soc/battery volts are getting involved)

But good solution - if it works, it works

i’d be interested to hear what you hear back from PS although I suspect most likely it will need Fox dev to investigate.

[David Yates]

Back from the dead with an update!

I heard nothing back from UPS Solar, so got in touch with Fox support directly via email.

They've been very responsive, but seemed to struggle to understand the fault.

After about 20 emails back and forth they identified a problem in that the mode scheduler was enabled at the same time as a charge from the grid schedule.

Why this would cause the symptoms I was experiencing is beyond me. Also I did not enable the mode scheduler, I actually tried to disable it at least twice!

In any case, with just the grid charging schedule enabled it charged the batteries from the grid this morning with no issues.
Having said that, the low temperatures meant that the charge current was limited to 20A anyway so we'll have to wait till warmer weather arrives to find out whether it's actually fixed.

On a similar topic, I can't understand how a 5kW inverter could charge the batteries at more than 20 amps anyway - 250v x 20A = 5000.
Can anyone shed light here please?

Thanks
Dave

[Dave Foster]

Ok, thats an unusual and one to remember in the future, good on Fox that they stuck with it for you

The mode scheduler when in charge / discharge mode takes direct control of the inverter active power registers and i’ve seen it fighting before when you try and change minsoc or workmodes - it doesn’t like anything else to be in control.