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Laurens D avatar image
Laurens D asked

Charge curve

Hey guys,

I have a Seplos BMS directly connected to the multiplus II GX 48/3000; so it can retrieve data directly from the BMS; I thought that was worth mentioning before asking stuff.

I have a 58v lifepo4 battery but it continues to charge until it reaches the point of 'total voltage overvoltage protection' which is 57.6 volt; In this case the BMS decides to shutdown the charging as it should and allow only discharge.

I was expecting it to continue to charge it with 56.8v and then keep it at 54v (100%)

When looking at the settings, I have this setup.

1678793519285.png

Am I getting something wrong here? because I wasn't expecting it to force it to continue until the BMS gives an cut-off message.



battery chargingESS
1678793519285.png (20.9 KiB)
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5 Answers
kevgermany avatar image
kevgermany answered ·

Which model multiplus? Do you have a GX device in the system / multiplus?

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Laurens D avatar image Laurens D commented ·

It's a Multiplus II GX 48/3000, added this to the main thread now.

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fibulainformal avatar image
fibulainformal answered ·

I'm not sure the multiplus model you're referring about. Is a GX device in your system/multiplus?

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kevgermany avatar image kevgermany ♦♦ commented ·
What does it say on the front of the multiplus?
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Laurens D avatar image Laurens D commented ·

It's a Multiplus II GX 48/3000, added this to the main thread now.

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thanar avatar image
thanar answered ·

How do you get the feedback that the battery is indeed being charged all the way to 57.6V? The BMS could trip due to a single cell going above the maximum threshold, if the battery is unbalanced.

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Laurens D avatar image
Laurens D answered ·

@thanar When the SOC is lower it will be +/- 2 a 3 mV difference but at the end it goes rather fast up after 3.4, I think. Though that's the nature of the LifePO4 battery as far I know.

1678866453016.png

55v to 57.6v happens in about 2 minutes.


1678866453016.png (858.0 KiB)
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thanar avatar image thanar commented ·
Indeed, that's thew nature of LFP batteries. According to the screenshot, your battery seems well balanced. So, voltage overshoot should be due to some misconfiguration on the GX. Does the battery show up on the GX device? Maybe you should have a look at Andy's off-grid Garage videos, he's been busy with SEPLOS lately.
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kevgermany avatar image
kevgermany answered ·

If the BMS is compatible and the system correctly wired/configured, the BMS will control the charging through the GX in the multi. Any setting you make in the Multiplus are safety settings in case of BMS comms failure. Have a page through the GX readout, it should be showing external control to confirm the BMS is driving things.


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Laurens D avatar image Laurens D commented ·

Yeah, it seems that might be the thing 'CVL - charge voltage limit' is set depending on the 'Total Voltage Overvoltage Protection' so that's 100% it seems according to seplos.

Makes me wonder If it's better to have this turned off, or limit the charge voltage.

Limiting the charge voltage in dvcc seems to do the trick to allow it to be charged until... after that it stops charging, will change this to 55v to check.

Disabling DVCC might work, but it's not ideal when making a bigger system; hope to get best of both worlds.

- it's funny, I set the charge limit in dvcc to 56v and it keeps overcharging, then decide to throw it back to the grid and it keeps going in/out lol that's probably a too unstable point to keep it at. Seems this is because the keep charged functionality

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