question

northcaptain avatar image
northcaptain asked

What is the recommended voltage limit on the BMS

The new BMS 12-200 manual says:

  1. Battery charge limit:

    Set the Battery charge limit (range: 13.0V..15.3V) to a value at which charging should be deactivated. Normally this value should be 14.2V for a Victron Lithium Battery Smart. As soon as this value is reached, the battery charge is stopped by deactivating the alternator/starter battery+ input. The input will turn on again when the battery voltage is 0.5V below the battery charge limit for 10 (consecutive) seconds.


At the same time the Lithium battery manual says:

The charge voltage may vary anywhere from 14V to 15V for a 12.8V lithium battery

We recommend 14.2V (28.4V) as the absorption voltage, but if you want to change it, we advise keeping it between 14.0V (28V) and 14.4V 28.8V)

This is puzzling... Battery want to be charged between 14 V and 15V, but absorption 14.2. BMS will shut off charging at recommended voltage of 14.2.

Something doesn't add up here...


So what is the voltage that we should put in the Smart 12- 200 BMS so that the battery is completely charged using either a 14-15 V or a fixed 14.2 absorption ? Certainly not 14.2 ??

BMS
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2 Answers
Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

@Northcaptain

The answer to your question is 14.2V.

Everything between 14 and 15V corresponds to 100% SoC (If you research LifePO4's charging characteristics, you'll know why). The mentioned range of 14-15V is possible (but not healthy in the long term), therefore Victron recommends 14.2V corresponding to 3.55V per cell for a 12.8V battery.

FWIW: An imbalanced cell in the Victron lithium can reach a maximum of 3.75V when charging. Above this, the BMS automatically stops charging until a healthy value is reached again. Theoretically that would be 15V if it happens to all 4 cells at the same time.


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northcaptain avatar image
northcaptain answered ·

Ok understood... and i've seen the programing of your 614 :

  • AHL High Voltage Limit: 14.2
  • CL Battery Temp Voltage Compensation Limit: 14.2 (therefore no temperature compensation takes place)
  • bu Bulk Voltage Limit: 14.2
  • Au Absorption Voltage Limit: 14.2
  • A1c Minimum Absorption Voltage Duration: 0.3 (corresponds to 18 minutes)
  • Fu Float Voltage Limit: 13.4


So what happen in fact is that your Lithium are never exposed over 14.2. Have you check the programing of the Smart Solar to see if they follow the same logic of not exposing the Lithium to more thant 14.2 ?

And i guess that the deadlock effect that i was anticipating of having the BMS limit to 14.2 and the Balmar programmed to 14.2 doesn't happen because there are losses in the cables and thus even though Balmar push 14.2 it may arrive as 14.1 or 14 to the BMS (other the BMS would cut it)

In my case i have 2 Smart solar 100-50 and one Multiplus that will need to be programmed also not not go over 14.2.


thanks !



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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ commented ·

Yes, of course I checked the MPPTs.

But meanwhile the whole setup has changed. The system is now controlled by a Lynx Smart BMS which provides a voltage target for the MPPTs and the inverter/charger via DVCC (no programming of DVCC compatible chargers necessary). Also the MC-614 is gone and has been replaced by a Wakespeed WS500.

None-DVCC chargers still need to be programmed.

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