Battery charging at less then rated power

Hi, I am having a rather odd problem with my system, a gen 3, 3.6 kw inverter + 5.2 kwhr battery. The combination is rated to charge/discharge at 2.6 kw.

It does discharge at this rated power without any issue. However, i noticed that when using timed charge, or charging from solar, the battery is refusing to charge at a rate above 1.83 kw. BUT when a battery calibration is triggered, the battery has no problem charging at full rate of 2.6 kw.

Is anyone else seeing this kind of behaviour?
in the screenshot bellow, the first charge block before 9pm on the 9th Nov is calibration (full 2.6kw)
subsequent grid charge using the timer at 3 am and 10 pm on the 10th were stuck at 1.83 kw
also between 1230 and 1400, solar was at times > 2 kw, however battery was stuck at 1.83 kw.

if someone can shed some light it would be helpful. if it is a bug in the code, then others on 5.2kw battery should also notice it. problem eiists on both 3012 and 3013 firmware.

if its indeed a firmware issue, given then i am an embedded engineer, i could look for the bug in the code -- does anyone know if the firmware codes are open-source?

How full was the battery when the charging occurred ? The system may throttle the charging rate as the battery gets close gets to full. (That's what cars tend to do, anyway.)

An experiment I'd try would be to reduce the max charging power below that, just to confirm that it is taking notice of that, then set it back to max again.

(What triggered the calibration? Was it a battery firmware upgrade? What firmware is the inverter running ?

I'm sure I've seen this before but can't quite find it.
What does you system page say the battery capacity is in AH. The charge rates in normal are intrinsically linked to AH (for example if you were an installer and set the AH rating of the battery to 10AH it would only allow a max Charge Rate of about 300W)

No the firmware isn't open source. If it was the community may have been able to help the SOC drop stuff.

Also worth checking what the charge rate is set to in the control panel, and maybe change it manually.

But despite my settings being 2.6kW, I find that both of my batteries (9.5 and 5.2) on Gen 1 5kW hybrid inverters will only charge at 2,4kW but will discharge at 2.6kW.

Hi , my battery SoC was < 90 during the tests. All charge rates/percentages are maxed out in the portal.

i did investigate the issue a little, and using givtcp, i matched it up with the battery cell temperature.
it seems charge power gets capped based on the battery cell temperature. i.e. if temp is less than 20 C, the charge is capped at 1.8 kw instead of 2.6 kw. discharge rate is not impacted.

I was wondering if anyone else has been noticing this as well. you will find the battery cell temperature through givtcp. Please mention which battery and how many batteries you are using. My battery is in the garage so i expect it to be sub 20 C most of the year.

I understand that a Li battery can safely be charged from 0 C. and if a battery calibration is triggered when cell temperature is less than 20 C, the battery is still charged at 20 C. so it seems the firmware is choosing to impose a restriction when charging using the timers. I wondering if this is a bug and if it exists when using more than 1 battery or when using battery of higher capacity from gen2

DD

hi
battery calibration was triggered by inverter firmware update to 305. had the same issue on 303 as well. i did try to reduce the max charging power and it does change. setting it back to full power returns the battery to 1.83 kw, and not 2.6.

hoggy
battery is rated at 102 Ah, as it should be

rsarwar87 it seems charge power gets capped based on the battery cell temperature. i.e. if temp is less than 20 C, the charge is capped at 1.8 kw instead of 2.6 kw. discharge rate is not impacted.

I was wondering if anyone else has been noticing this as well. you will find the battery cell temperature through givtcp. Please mention which battery and how many batteries you are using. My battery is in the garage so i expect it to be sub 20 C most of the year.

Certainly seems plausible. I manually limited rate to 1,5kW yesterday since it seemed kinder to charge gently until 3pm rather than fill up quickly by 1pm then export the rest anyway.
I have heard to of people building a small wooden enclosure around the battery, to keep the temperature up in the winter.

Charge rate and estimated percentage can both be affected by temperature, which is why my app shows the estimated percentage, voltage, and temperature on the main screen.
https://play.google.com/store/apps/details?id=uk.rubikcube.invertermonitor

Ah yes, I've been wondering what the logic was on this lower charge.

I think you are right, charge is capped at about 2/3 of full power below 20 C.

Gen 1 + 2.6 - so for me the reduced rate charge rate is about 895W.

Russell_B

are you saying your 2.6 kw battery is capped to 895W? so it is rated at 1.3 kw? I thought it was rated at 2.6 kw. if the logic is correct, then the limit is from the battery, i.e. inverter capacity should not impact it.

and by defination, anyone with 2 or more 5.2 or higher capacity battery should not see the issue, rating should be per battery and i am assuming both batteries are charged at the same time.

rsarwar87 a 2.6 kWh battery should discharge at a maximum rate of 1.3 kW (except perhaps unless almost empty or almost full)

The batteries usually discharge or charge at 0.5 of the capacity. So a 5.2kWh battery would Discharge at 2.6 kW

The units are also quite important! kWh and kW.

If the battery isn't the bottleneck, then the inverter might be (certainly for larger batteries). Older inverters might have a 3 kW limit, some have a 5 kW limit.

But when you're dealing with such a small battery and only one battery, the battery will be the bottleneck.

TX200

may I ask if you noticed your charge rates are throttled due to temperature?
I wonder how the temperature impacts a multi-battery setup. i.e. 2 * 5.2kwhr @ 1.8 kw is 3.6kw?

rsarwar87 I do believe they would slow down the rate if it got too hot. Likewise if too cold could be problems too (especially those outdoors).

Mine never got too hot as I usually charge up slowly when I know there's enough time in the cheap period to do so.

I'm not sure about your maths. I don't quite understand what you mean.

2x 5.2 kWh batteries should be able to discharge at 5.2 kW

But if they are both connected to the same inverter, then the inverter limit is the problem. Thus 3.6 kW might be the limit if that's what the inverter is rated to.

Yes one 2.6kWh battery is max charge and discharge 1.3kW, and as I think we’ve just identified charge at 1.3kW is only above 20 deg C battery temp. If you have two 2.6kWh batteries I believe they can do 2.6kW charge and discharge.

The slower charge will be for the health of the battery. I wouldn’t be surprised if they won’t charge at all below 0. Now I know what the logic is I’m happy! The slower charge in winter tends to work out fine I’m finding, I charge from solar, and any excess on top of what the battery can take gets 15p .. I guess I could build the battery something to keep it warm!

https://givenergy.co.uk/wp-content/uploads/Datasheet-Giv-Bat-2.6-Mar-2023.pdf

It will discharge to -10c

So it might be possible to warm it up by discharging as fast as it will let you, then when warm enough, start charging it.

Alternatively do a slow overnight charge so that it is charging for longer and hopefully doesn’t get as cold as it might do idle.

Plus outdoor batteries and inverters must have a canopy over them to shelter them from heavy rain. Some people have built wooden enclosures around there’s - as long as there is enough clearance around the items and enough ventilation in the summer, then that’s fine.

You could also put additional material around the outside of the battery to keep it warm, then remove that as the weather gets better. Just don’t do that with the inverter!

Ah yes it says on the data sheet min charge temp 0. If it gets v cold I will try to leave a bit in to discharge in the morning to warm it up.

I guess the battery might benefit from a jacket in winter like a hot water tank, but I wonder if that would fall fowl off clearance rules.

Russell_B a few people have "jackets" for them, there was a lot of posts about this last winter and as long as it's removed for the warmer weather it should be ok.