danphillips
New Member
- Joined
- Oct 29, 2019
- Messages
- 108
I Just purchased a boat that has a 2 year old FLA / Solar / Inverter system nicely configured. Previously I had purchased 12 180ah CALB cells for my previous boat that I would like to add to the new boats existing system.
I read the article below and really like the idea of the Hybrid system – however I would install an additional BMS / battery saver in front of the LifeP04 BMS.
I am not worried about squeezing out every watt on the LifeP04 batteries.
Can this work or am I asking for problems?
The following information is borrowed and condensed from: https://www.zwerfcat.nl/en/lithium-hybrid.html
Please see original link for additional information and charts
Lithium-Hybrid - Lead-acid batteries love to remain fully charged indefinitely but hate to cycle and stay for any time in a discharged state. Lithium batteries however hate to remain charged but love to cycle and to remain forever in a discharged state. It is almost as if they are made to complement each other.
After the lithium battery has only about 20% of charge left the voltage becomes low enough to allow the lead-acid batteries to gradually start taking over the load. Only when the lithium battery becomes fully discharged and is taken offline by the BMS, the lead-acid batteries will fully take over. Most of the time, the lead-acid batteries will remain fully charged, which is exactly what keeps them healthy.
When charging the lithium battery, the chargers "see" a voltage which is similar to the voltage of a lead-acid battery which is in its early bulk phase, so the chargers are providing charge current to the lithium battery while "thinking" they are charging a normal lead-acid battery, patiently waiting for the voltage to increase.
When the lithium battery is fully charged it is taken offline by the BMS, the charging continues with the lead-acid batteries only, following a charge trajectory which the chargers fully recognize, allowing them to do their "end-point-voltage-limiting" thing. If the lead-acid battery has not been used, the voltage will rise quickly to the end-voltage and the charge process will be terminated and revert to a "float" voltage.
As long as there is a charge current available the fully charged lithium battery will remain "parked" aside and the on-board equipment will be fed by the charge sources with the lead-acid battery as a buffer. Only when the lead-acid voltage starts dropping below the float voltage, indicating the absence of a charge source, the BMS will put the lithium battery online again.
Note that OpenHybridBMS implements a "lead-acid priority" feature, where after a (partial) discharge of the lead-acid battery, the lithium battery is held offline to allow the lead-acid battery to first complete its bulk charge phase, then to charge the lithium battery, and then to use the remaining available charge current to finish the lead-acid absorption phase.
I read the article below and really like the idea of the Hybrid system – however I would install an additional BMS / battery saver in front of the LifeP04 BMS.
I am not worried about squeezing out every watt on the LifeP04 batteries.
Can this work or am I asking for problems?
The following information is borrowed and condensed from: https://www.zwerfcat.nl/en/lithium-hybrid.html
Please see original link for additional information and charts
Lithium-Hybrid - Lead-acid batteries love to remain fully charged indefinitely but hate to cycle and stay for any time in a discharged state. Lithium batteries however hate to remain charged but love to cycle and to remain forever in a discharged state. It is almost as if they are made to complement each other.
How can it work?
Operating the lithium batteries and lead-acid batteries in parallel is possible because lithium batteries have a much flatter charge and discharge voltage curve. (See chart in above link)Discharging
While discharging, the lithium batteries stay above 13.0 Volt until they are almost empty. The lithium voltage is higher than the voltage of a lead-acid batttery under load, so the lead-acid battery will hardly deliver any current, if anything at all.After the lithium battery has only about 20% of charge left the voltage becomes low enough to allow the lead-acid batteries to gradually start taking over the load. Only when the lithium battery becomes fully discharged and is taken offline by the BMS, the lead-acid batteries will fully take over. Most of the time, the lead-acid batteries will remain fully charged, which is exactly what keeps them healthy.
Charging
While charging, the voltage quickly rises to about 13.4 Volt, a voltage where the lithium batteries absorb all the available current but a too low voltage for lead-acid batteries to meaningfully charge. So the lithium batteries take up all the current until the BMS takes them offline, and only then the voltage rises enough to charge the lead-acid batteries.When charging the lithium battery, the chargers "see" a voltage which is similar to the voltage of a lead-acid battery which is in its early bulk phase, so the chargers are providing charge current to the lithium battery while "thinking" they are charging a normal lead-acid battery, patiently waiting for the voltage to increase.
When the lithium battery is fully charged it is taken offline by the BMS, the charging continues with the lead-acid batteries only, following a charge trajectory which the chargers fully recognize, allowing them to do their "end-point-voltage-limiting" thing. If the lead-acid battery has not been used, the voltage will rise quickly to the end-voltage and the charge process will be terminated and revert to a "float" voltage.
As long as there is a charge current available the fully charged lithium battery will remain "parked" aside and the on-board equipment will be fed by the charge sources with the lead-acid battery as a buffer. Only when the lead-acid voltage starts dropping below the float voltage, indicating the absence of a charge source, the BMS will put the lithium battery online again.
Note that OpenHybridBMS implements a "lead-acid priority" feature, where after a (partial) discharge of the lead-acid battery, the lithium battery is held offline to allow the lead-acid battery to first complete its bulk charge phase, then to charge the lithium battery, and then to use the remaining available charge current to finish the lead-acid absorption phase.