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Multiplus II Battery disconnected-- What will happen?

If, while the Multiplus II ("charger only") is connected, charging a LiFePO4-battery and the battery will be disconnected by the BMS, what will happen to the Multiplus?

Will is just go to idle state and continue charging when the BMS has reconnected the battery?

Best Regards

Hartmut

Multiplus-II
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info-6 answered ·

I just would like to bring my question to the fron again, as it is on page 6 already and might be overlooked?

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Alexandra avatar image Alexandra ♦ commented ·
@Info@12V-Power.de

There are several types of disconnects in bms.

Will yours disconnect the entire battery (relay or contactor) or will it just disconnect the charge side of the bms?

In theory if there are no loads and the amps going down into the battery are fairly low then it wont be too much of an issue.

But I imagine in high amp situation may be an issue? The power has to go somewhere. I have not had a battery disconnect in a high amp situation so could not say I know for sure.

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info-6 avatar image info-6 Alexandra ♦ commented ·
Hi Alexandra,

thanks for reply. Yes, BMS will disconnect the entire battery by means of a contactor.

I'm not so much afraid about the high amps, as I have set the multiplus to an absorption volage of 14 V and my BMS will disconnect at 3,5 V/cell. So I believe the charging current will be rather low in that case.

But I am not sure if an operation of the MP, without a battery connected, will damage the MP, if it is set to "charger only".

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Alexandra avatar image Alexandra ♦ info-6 commented ·
The charger will only be actually charging when the target voltages need to be met, so would stop charging before the bms disconnect if set correctly.


The battery disconnecting itself would/should technically only happen if there is a major problem which would be unusual circumstances.

Why dont you set it to disconnect at 3.55v but have the charger still only charge to the 14v? Another thought, you would need to make sure you have no voltage drop over your battery cables as well. 0.2v drop is not uncommon with your sertings so close.

The inverter will remain powered on by the grid side and you will probably get a low battery alarm when the bms disconnects.

As long as there are no loads on the inverter I dont see how there would be an issue.

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info-6 answered ·

Thank's for detailled explanation, Alexandra (and sorry for late reply, I wasn't online for a few days).

To set BMS to 3,55 V is not a real option, as there are other charging sources as well, which are charging with 14,4 V and are not adjustable to 14,0 Volts. So I need to stuck on 3,5 Volts per cell.

Anyhow, I believe there shouldn't be a danger to damage the Multiplus, if it will be disconnected under load of just abt. 20 Amps, should it?

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Alexandra avatar image Alexandra ♦ commented ·

@Info@12V-Power.de

I don't think so. I dont know about repeated occurances. I am assuming you will only be disconnecting during discharge? And by 20A the load on the battery side.

The issue will be on power on instead. There will need to be a decent precharge and no loads to start up immediately if starting from DC only.

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