Open circuit voltage

[ImJustARegularJoe]

I posted a message last week about some issues that I was having in while on vacation in South America. I am back home and want to understand better what happened so that the next time I go there I can take the right equipment with me and hopefully have better luck.

In short, I was migrating from lead to LiFePO4 and the batteries (3x Huawei 48150b1) kept tripping because of overvoltage shortly after turning on the PV panels (~1200W). It appears that the BMS checks what the open circuit voltage is before getting into charging mode and trips if it's over 58V. I had the charge controller (Epever up5000-m8342) set to only charge up to 56.4V, but it appears that the open circuit voltage that it exposes is higher than that, which makes sense to me and in the world of acid was completely inconsequential.

I also have a wind generator, which doesn't even have a charge controller (I have a diversion load). I didn't try it, but I would totally expect to see the same issue there.

Since I have plenty of time before I go back, I am trying to figure out what my options are.

1.- Are there charge controllers that give more control over the open circuit voltage that gets exposed to the batteries? I understand that every charge controller worth its salt will enable me to stop charging at certain battery voltages, but it appears that that's not what's triggering my batteries.
2.- If not, I will attempt to replace the BMSs. There are a few videos (none in English) of people that ended up having to do that with these same batteries.

I could of course use different batteries, but they were a pretty large investment that I'd like to salvage, especially since getting stuff delivered so remotely is a pain.

 

[MisterSandals]

(3x Huawei 48150b1) kept tripping because of overvoltage

Is this battery over voltage or cell over voltage? If the latter, then your battery(s) may be the issue.

 

[Mattb4]

The SCC should not expose the DC charging bus to PV Voc (assuming it is not a PWM type and you have minimal panel Voc). If your batteries BMS trip due to a cell reading going high it is possible to see a higher DC charging bus voltage than is recommended since no battery on the bus to moderate it. For instance you could see 62vDC

First off you connect the batteries to the SCC so that it can properly adjust DC bus voltage for charging since many SCC auto detect battery voltage. Than the Panels can be connected and energized.

You might try a conservative charge voltage such as 56vDC. If you can prevent BMS trips your battery may eventually start to balance. Although if as you mention the type of battery you have is noted for faulty BMS's no SCC setting can help.

 

[ImJustARegularJoe]

Thank you for the replies.

I honestly do not know the condition that tripped the batteries. I am assuming that it's battery overvoltage, but it could be something else. I am assuming that it's battery overvoltage because all three batteries tripped at the same time (they were connected in parallel but there was no data connection to each other) and because it happened consistently a few seconds after switching the PV panels on.

A few additional tidbits:
- The PV panels were connected to a SCC/inverter that had been connected to the batteries for a while before I switched on the PV panels.
- There were no issues with the batteries when I did not connect the PV panels. Notably, I connected the SCC/inverter/charger to a portable generator to charge the batteries and it charged them fine.
- I tried setting the boost/float charge voltages very conservatively and it did not make a difference. The batteries still faulted, all at once, shortly after switching on the PV panels.

 

[Mattb4]

When you say the batteries tripped or faulted how was this manifested?

 

[MisterSandals]

I am assuming that it's battery overvoltage, but it could be something else

Cell overvolt is more likely based on my 100:0 experience with quite a few batteries.

 

[ImJustARegularJoe]

The red ALM (alarm) led on each battery turned on and the batteries disconnected for about 10 seconds.

 

[MisterSandals]

Does your manual say what that means?
Can you post a link to your batteries?

 

[Mattb4]

It would seem that if the inverter/charger, when operating as a charger, does not cause the battery fault, but the SCC part of your unit does, that the SCC portion is doing something unusual. I would not think it was high voltage as long as your batteries were connected because they would resist higher bus voltage. At least until they became fully charged. Is it possible there is a maximum amperage your batteries will accept and the SCC is putting out more?

As Mister Sandals mentioned it would help to know a bit more about this alarm condition.

 

[ImJustARegularJoe]

I have not found a freely available online copy of the manual in English that I can post here, but I'll keep looking.

Unfortunately, there is a large number of conditions that can trigger the alarm. Copy/pasting from the manual: "Cell voltage sampling fault, cell temperature sampling fault, charge converter output short circuit, relay coil short-circuit, charge low temperature protection, discharge low temperature protection, charge high temperature protection, discharge high temperature protection, power module internal overtemperature protection, discharge converter output short circuit, input reverse connection, BMU anti-theft lock, overload lockout due to component failure, serial number conflict, input/output discharge overvoltage lockout, and discharge overcurrent lockout".

The battery alarm was triggered even relatively late in the afternoon when the panels would not be producing more than a few hundred watts. That is much less than what the generator was producing when the batteries were charged.

As you pointed out, everything seems to point to the interaction between the SCC and the batteries and the only thing that I can think of is the Voc that that SCC is exposing. I understand that the batteries should resist the voltage, but it almost sounds like the BMS is checking what the Voc is before starting the charge and thus resisting the voltage. Is that completely farfetched?

 

[MisterSandals]

I just reread from the top and recall the Epever voltage spike issues:

Search results for query: Epever voltage spike

diysolarforum.com

 

[ImJustARegularJoe]

That's a fantastic find, thank you.

Is there a tried-and-tested charge controller that you would recommend for 48V and a ~150V/1500W array?

 

[MisterSandals]

Victron 150/30 or more

 

[ImJustARegularJoe]

Excellent. Thank you so much for your help again.

 

[Mattb4]

.. I understand that the batteries should resist the voltage, but it almost sounds like the BMS is checking what the Voc is before starting the charge and thus resisting the voltage. Is that completely farfetched?

The BMS detects voltages at the cells. Once wired into a charging circuit the cell voltages and the charging circuit voltages are in parallel. So no the BMS does not detect Voc. BMS's are not chargers.

Think of it like paralleling two batteries one of 12.2vDC with another at 13vDC. Apart the voltages of each is measured but when in parallel you will find that the combined voltage will be somewhere between the 2 amounts depending on the lower batteries ability to accept current.