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Hybrid LifeP04 - FLA advice

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danphillips

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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.

1602137805982.png

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.
 
Dan that's a good read. He looks at the FLA bank as sacrificial.
 
One issue that you will need to address is inrush when combining the LFP and FLA banks. To get around this connect while both banks are at the same voltage. You will find that the FLA bank will be trickle charged by the LFP until the LFP voltage drops. (As big as your bank is you will not likely see that often) If the load is large enough and the LFP is low enough the FLA will assist the load. Be careful about your fusing on both banks.
 
It has some growing pains. That's what I use. It is adjustable in many ways. When using or charging below one amp the watt and amp hours will be incorrect. With that said except when I have the battery on a bench, may see that condition. Testing found that under my normal use is over one amp and my Bogart TM2030 agrees with the Chargery amp reading. If you like to tinker it is a good choice.
 
not sure what you mean about "Control Charge / discharge.
Charge will be thru either the SCC, Alternator or Inverter Charger
DIscharge is thru the Inverter for AC and DC Panel

My thoughts were to add a second BMS / Battery Saver to shut off charging when cell voltages are full/empty. This second battery saver would be set to disconnect / connect at a safer voltage than what the Battery BMS is set to.
 
I was not clear I see. Are you gonna use relays or DCC,s or direct control. For the on-off controls?
 
This is where I need some help. Not sure DCC's are reliable enough, and relays use a good amount of power. I started reading about latching relays but not sure that would work well. Any suggestions?
 
The Chargery does not support the required signal for latching relays, I'm using Kilovac 500 amp relays. There hold amps are .13 amps. Each ( I run two ) one issue with running two of them is the pull of 3.8 amps each, this would reboot the Chargery due to pulling the 12-volt signal down to two volts causing the reboots. The first fix was a 10-second timer for one relay. The first unit was DOA. After replacing for a working one I decided I could not trust that circuit. I ended up using a micro relay feeding one kilovac. Total amps pull is .34 amps. To put that in prospective, my Inverter pulls 2 amps an hour.
 
What are your thoughts on the new Chargery DCC's. I like how they just plug into the BMS.
Do you like my idea of putting a battery protect cutoff in front of the actual BMS?

I am looking at this unit, it is supposed to boost / reduce charging voltage
Sterling Power Battery to Battery Charger 12V input to 12V output up to 60amps. DC to DC converter
www.sterling-power-usa.com

Sterling Power battery to battery charging system - Smart DC battery to battery charger, marine grade DC powered charger

DC to DC converter. Charge your auxiliary battery bank with the correct multistage, temperature compensated charging curve by using the input power of any vehicles alternator thru the start battery system automatically while the vehicle is running.
www.sterling-power-usa.com
 
I have not tested them. .but I do trust Steve S and Craig's work on improving the Chargery. And I have dealt with Jason, other than language issues, He wants to improve the system and already has. They do reduce the amps load. As far as the sterling goes. I don't think you can go wrong with their products. Oh, and my only issue with a battery protect is another circuit that could fail. But a backup may be wise.
 
Wow this is pretty smart. No need to choose one or the other. FLAs are still cheap and have a small LFP pack to keep them nice and topped off.
 
Blue sea makes a couple battery switches which accept normal DC+ control, but only use 7mA when closed. Gigavac has some dual coil (non latching) relays which only use about 30mA
 
Not clear to me why you want a second BMS.
Why not just do as the first article you quoted and be done with it?
Why make it more complex than it is?

having said all that, I added 200AH LiFePO4 to my SLA battery bank last spring. It has worked exactly as described above.
I did not add any extra chargers or relays.
I did modify my Balmar ARS-5 regulator and added a temp sensor for the alternator.
Nothing else and it works as advertised.
Float voltage stays at 13.34v. SLA are somewhat sacrificial, but they are shot anyway, thus my addition of the Li.
Good luck
 
Thanks for all the comments. This opens up a new world of possibilities. I’m using a Sterling bb1260 but I was thinking about an intelligent way to parallel my FLA. I have done a few videos on this ml-7700 latching relay that can be used for this application I think.
. I also dis covered I could drive the 7700 without a intermediary relay.
 
Last edited:
Luthj said:
Blue sea makes a couple battery switches which accept normal DC+ control, but only use 7mA when closed. Gigavac has some dual coil (non latching) relays which only use about 30mA
Click to expand...
Look at the blue sea latching relay ml-7700 below
 
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