Alternator charging dual purpose lithium bank

[jointcustody]

I am in the process of upgrading the batteries on my boat.

Current setup;
The alternator: 137A-116A (two ratings on tag, on initial receipt says 116a, I am thinking 116A is the continuous duty rating?) It is externally regulated with an old next step regulator, but does not have an alternator temperature sensor
(1) 4D starting battery, 9 years old and close to replacement
(4) 6v costco gc, 2 years old, wired series parallel for 420ah (50% DOD = 210AH) (in two battery boxes)
(2) agms in the bow for bow thruster, powered by a small victron dc-dc charger off house bank

The plan;
-keep my 116A duty-rated alternator.
-add balmar mc618 external regulator, alternator temp sensor to boost or buck the alternator as to never overheat
-add sterling alternator protector in case of surge on batteries should they cut out.
-add two ablithium start/deep cycle dual purpose batteries. These are 1400cca each and 150ah each, for a total bank capacity of 300AH. These will start the engine, the genset and serve as my house bank. One of these batteries on its own will start my perkins m135 (spec required is 1400cca)
https://www.ablithium.ca/products#!...-Heated-Battery/p/530327244/category=80052469
- wire the batteries to a simple 1,2 and both switch. While running the engine will have on "both", at anchor switch to 1 or 2, definitely before bed, but shouldnt run out of AH anyhow.
-existing outback 2kw inverter with 80a charger appears to have correct parameters available.

With this change, I would go from having 3 battery boxes in my engine bay to 1. Lose a whole lot of weight and maintenance (watering). Remove a ton of extra battery wiring and complexity, gain a decent amount 30%+? of useable AH, and charge very fast.

If the house/ start bank should go dead I have a hand crank on my genset, a long set of jumpers on board to jump from my agm bow thruster batteries to my engine or genset. I have a sea tow membership lol... and I will be setting up a low voltage alarm. I may even set up a low voltage disconnect.

Does anybody have any suggestions? feel free to poke holes. I've got big shoulders.

Yes these are Chinese batteries but they have great reviews and most of the lithiums are made there or sourced from there.

Thanks, Ty.

 

[DavidM]

I have never heard of a LiFePO4 starting/deep cycle battery with significant CCAs like this one. I know the manufacturer says it can, but I am suspicious. What makes it different?

David

 

[mvweebles]

I have never heard of a LiFePO4 starting/deep cycle battery with significant CCAs like this one. I know the manufacturer says it can, but I am suspicious. What makes it different?

David

Check out Antigravity batteries. Being used as lightweight alternatives in racing motorcycles and the such. This is a drop in auto battery with claimed 1500 "cranking amps"

https://antigravitybatteries.com/products/starter-batteries/automotive/ag-27-rs/

Peter

 

[twistedtree]

Joining (paralleling) and separating LFP batteries shouldn't be done unless they are very close to the same charge level. Your operational procedure will be doing exactly this on a regular basis, so I would rethink that part. When you parallel LFPs at different charge levels, you will get a lot of current flow as the fuller battery discharges into the more empty battery until they equalize. This is much more pronounced that with lead-acid batteries since LA battery voltage will more easily rise or fall to match the two batteries, with much less equalizing current.


I think you would be better off retaining an AGM start battery with a modest DC/DC charger to keep it topped up off the LFP house bank.

 

[jointcustody]

I have never heard of a LiFePO4 starting/deep cycle battery with significant CCAs like this one. I know the manufacturer says it can, but I am suspicious. What makes it different?

David

I noticed Dakota offering batteries such as this, and then a simple google search found more.

https://dakotalithium.com/product/d...t5JJYvJGnv3bCtgKFVeXLgfpkiVeLRMRoCxrcQAvD_BwE

 

[jointcustody]

Joining (paralleling) and separating LFP batteries shouldn't be done unless they are very close to the same charge level. Your operational procedure will be doing exactly this on a regular basis, so I would rethink that part. When you parallel LFPs at different charge levels, you will get a lot of current flow as the fuller battery discharges into the more empty battery until they equalize. This is much more pronounced that with lead-acid batteries since LA battery voltage will more easily rise or fall to match the two batteries, with much less equalizing current.


I think you would be better off retaining an AGM start battery with a modest DC/DC charger to keep it topped up off the LFP house bank.

This is a very good observation. I am assuming then that you are still recommending charging the lithiums first from the alternator and then using a dc-dc charger to charge the agm start? Could I wire it up with an agm to absorb the over-voltage should the bms suddenly disconnect, and avoid having to wire in a sterling alternator protector? I am having a hard time finding a wiring diagram that shows this, if this is acceptable what would that look like... is having the switch on "both" good enough, having that agm there as a "capacitor?" or "dump"

Do people not commonly connect two lithium banks with battery combiners often then? that would be the same thing right?

Thanks a lot.

 

[jointcustody]

nm... having on both wouldnt make sense for charging off alternator.... *sigh*

and i guess i could revamp this, leave the switch on both all the time, and just use a low voltage disconnect or low battery alarm. that way I could recconnect them with enough juice to start the genset or engine...

 

[twistedtree]

This is a very good observation. I am assuming then that you are still recommending charging the lithiums first from the alternator and then using a dc-dc charger to charge the agm start? Could I wire it up with an agm to absorb the over-voltage should the bms suddenly disconnect, and avoid having to wire in a sterling alternator protector? I am having a hard time finding a wiring diagram that shows this, if this is acceptable what would that look like... is having the switch on "both" good enough, having that agm there as a "capacitor?" or "dump"

Do people not commonly connect two lithium banks with battery combiners often then? that would be the same thing right?

Thanks a lot.

My preference is to connect the alternator to the LFP bank, and use DC/DC to top off the start bank. That let's you apply the full output of the alternator to charge the LFP house bank, and allows for a modest DC/DC charger (10-30A is fine). The house bank is the one that's going to need charging and the start bank will need very little, so align the charging capacity accordingly...


If your batteries do not provide a shutdown warning that can be used to turn off the alternator, then adding a Sterling or Balmar protector is a good precaution. Assuming your charging sources are set up correctly, a disconnect will never happen unless something is broken, so it's strictly a precaution. But if something is broken, why also break your alternator....



Leaving the alternator connected to the AGM start battery does let you eliminate the Sterling protector device, but it compromises the system in all other ways. Your alternator output is wasted on the start battery since it will be recharged in short order. And you still need a DC/DC charger, this time for the LFP bank, but it needs to be much larger and more expensive, and even then is likely to be a choke point for charging. You are probably looking at a 100A DC/DC charger instead of 10A, and alternator charging of your LFP will be limited to 100A.


I would advise against just paralleling an AGM with the LFP bank. It's not an uncommon approach because the AGM can absorb the effects of a BMS disconnect. But it creates a dangerous condition if there is an AGM failure because the LFP will dump all it's stored energy into the failed AGM. ABYC recommends against such a configuration, and the draft ISO spec outright prohibits it. So best to steer clear.


BTW, LFP can be paralleled, but there are procedures to do it. You basically have to charge them separately to within a very close voltage difference, then connect them. A lot of people see multiple BMSes as an advantageous redundancy, and it is. If I have 4 batteries and one disconnects, who cares, I can just keep running on three, right? Yes, but be sure to look further at how you will re-introduce a disconnected battery back into the bank. It's much easier said than done.

 

[jointcustody]

wow, thank you for this. very grateful.

what are your thoughts on leaving the start/deep cycle battery order the way it is, continuing to run just this one bank and then running a low voltage disconnect or alarm?
* edit* leaving the batteries combined as effectively one large 300ah bank

I would still have emergency AGM bow thruster batteries i could use to start with jumper cables. a hand crank on genset to fire up my inverter/charger. I also have automatic genset start that i havent set up yet on my inverter. And seatow lol.

 

[Iggy]

I approached the setup the other way. I have the Alt charging my starting bank and using a DC to DC charger 60A to charge the Li bank.

Why? If the BMS on all my house batteries shut down. I can flip two switch's disconnecting the house bank and combining the starting bank to the house loads. In this way I can restore power to get me home with in seconds. Well I may go into the engine compartment first...

I am using remote battery switches. Whats great about them too is. In the winter I don't have to climb down into the engine compartment.

This also protects the ALT, protection device is not needed.

If I need more amps in charging, I can always start the genset and use my charger/inverter with 90 amps of output. After running all season last year with a few long trips. I never started the genset due to this setup. Just for normal things, hot water, microwave, coffee and normal times between charging. My Alt is 120A and the boat uses 25 to 30A when cruising. So the balance if needed can go to charging.

That how I look at it, but thats me.

As a few have mentioned, I would not combine Li and a lead based batteries. The only time thats recommended (and I still would not do it) is that both need to have the same charging profile.

 

[twistedtree]

wow, thank you for this. very grateful.

what are your thoughts on leaving the start/deep cycle battery order the way it is, continuing to run just this one bank and then running a low voltage disconnect or alarm?
* edit* leaving the batteries combined as effectively one large 300ah bank

I'm not following what you are proposing. Can you describe it some more?

 

[jointcustody]

I'm not following what you are proposing. Can you describe it some more?

So a sterling alternator protector, balmar external reg with alternator temp protection, 300ah lithium bank for start and house (and leaving them connected). using a high amp victron battery protector "VICTRON battery protect BP-220" as a low voltage disconnect.
* just to be clear, these are dual purpose batteries, 2-12v wired in parallel.*

then having the other backups as mentioned above. either using jumper cables to bow thruster batts as emergency backup or perhaps wiring in a set of switches to change battery source from engine to bow thruster batteries. Then there is the emergency hand crank on genset and sea tow.

But Iggy's response is definitely interesting, my only concern is not charging the lithiums fast enough but I think two 30amp victron dc-dc chargers for 60A would prob do it or at least be adequate. Our boating style tends to be shorter hops between anchorages so the fast alternator charge setup is appealing.

Thank you all

 

[twistedtree]

So a sterling alternator protector, balmar external reg with alternator temp protection, 300ah lithium bank for start and house (and leaving them connected). using a high amp victron battery protector "VICTRON battery protect BP-220" as a low voltage disconnect.
* just to be clear, these are dual purpose batteries, 2-12v wired in parallel.*

then having the other backups as mentioned above. either using jumper cables to bow thruster batts as emergency backup or perhaps wiring in a set of switches to change battery source from engine to bow thruster batteries. Then there is the emergency hand crank on genset and sea tow.

But Iggy's response is definitely interesting, my only concern is not charging the lithiums fast enough but I think two 30amp victron dc-dc chargers for 60A would prob do it or at least be adequate. Our boating style tends to be shorter hops between anchorages so the fast alternator charge setup is appealing.

Thank you all

Got it. So still using the LFP bank for both house and start power, but adding a voltage sensing disconnect to shut off the batteries and retain a little reserve power for starting. Yes, I think that could work.


Re underway charging capacity, it of course depends on your cruising patterns, but to me one of the big advantages of LFP is being able to charge them back up quickly. After a night at anchor, you will be looking to your alternator for that recharge. Personally I want to take full advantage of it. It's one of the reasons why I have large alternator capacity, and LFP batteries.


That said, if you alternator is around 100A or lower then DC/DC chargers are available around that range, so you aren't giving up much charge capacity if you run everything through a charger. But when you get much over 100A you are talking about two or more chargers, and it just starts getting silly vs a small DC/DC charge tending to the start battery.


Also keep in mind that if you use batteries that have a disconnect warning that can be used to shut off the alternator, the whole issue is moot. And more and more batteries have such a signal. This is how I protect my alternators in the unlikely event of a disconnect. So it's just an external regulator for the alternators and a small DC/DC charger to replenish the start bank. And 400A of charging going straight into the LFP bank, or powering underway loads.


Speaking of underway loads, that's another consideration. If you want to run larger inverter loads underway, then that power will come from the alternator. A DC/DC charger will therefore limit underway loads as well. I realize not all boats do this or want this, but it's something to consider. I commonly run a watermaker, washer/dryer, or electric over while underway, all powered by the alternators. To do that I need all the power available from the alternators.

 

[Iggy]

TT, I am willing to bet you have two ALTs off your main engine. Say one 200A to keep your house up. The other smaller one for starting and a like.

Most of us only have the one Alt. That being said, this situation of loads is no different with a lead battery. Other than Li will charge up quicker.

 

[twistedtree]

TT, I am willing to bet you have two ALTs off your main engine. Say one 200A to keep your house up. The other smaller one for starting and a like.

Most of us only have the one Alt. That being said, this situation of loads is no different with a lead battery. Other than Li will charge up quicker.

Dual alternators, but that’s only to increase capacity. Both connect to the house bank and start batteries are indirectly charged up. I did the same in my last boat with AGMs.

 

[Greg QS]

fyi
abcy recommendation with lithium Not recommended for critical/start applications.

BMS required
I’ve heard anecdotes of lithium batteries being installed on boats without a battery management system (BMS), but I haven’t come across such an installation on the water. As far as I’m concerned, that’s a good thing. Battery management systems ensure the battery is operating within its safe operating envelope (SOE) and disconnect the battery in the event the battery exits its SOE. E-13.7 requires a BMS on all lithium batteries installed on boats.


The end of 13.7 contains several notes. My understanding of notes is that they serve as recommendations but don’t carry the same requirements as items in the main body of the standard. Note 1 in the section recommends alternative power sources for critical systems. It’s worth noting, another lithium battery is acceptable as a redundant power source. The second note suggests that BMS should give an audible or visual signal when a disconnect condition is approaching.

 

[jointcustody]

I contacted alberta lithium (great customer service btw) and asked them about using both batteries on a 1-2-both switch. I discussed my desire to drain one battery completely, and then combine them/ switch to the other to fire the engine back up.

He disagreed with the idea that this would cause a problem. He went to deeper lengths then I can properly explain now- but basically he stated the resting voltage of the full battery would be 13.6 and the fully discharged voltage of the lithium around 12.9. He stated that due to ohms law it cannot discharge at a very high current while balancing the batteries because there is simply not enough of a voltage difference to allow a high transfer of amperage- or something to that extent.

I went to my local marine store the next day where they also sell these batteries, and spoke with their abyc marine electrician. He stated that on top of the ohms law reason, these batteries have an intelligent BMS that knows they are connected in parallel. He claimed that they will reduce the current being transferred to the other battery. He said that is the reason why they only allow 4 batteries to be paralleled together- because the BMS is set up to only recognize 4 batteries.

He stated that he was willing to deeply discharge one of them and parallel it afterwards with another to try it. He would clip the conductor to see the transfer of amps. I gave him my e-mail, I will post the results on here if he gets back to me with the results.

If this is true this could be a game-changer for a lot of battery setups.

*greg_QS* the not recommended for critical/start application may be obsolete now that they offer lithium in a higher cranking battery? these just came out.

Thank you everyone for your input

 

[Iggy]

I contacted alberta lithium (great customer service btw) and asked them about using both batteries on a 1-2-both switch. I discussed my desire to drain one battery completely, and then combine them/ switch to the other to fire the engine back up.

He disagreed with the idea that this would cause a problem. He went to deeper lengths then I can properly explain now- but basically he stated the resting voltage of the full battery would be 13.6 and the fully discharged voltage of the lithium around 12.9. He stated that due to ohms law it cannot discharge at a very high current while balancing the batteries because there is simply not enough of a voltage difference to allow a high transfer of amperage- or something to that extent.

I went to my local marine store the next day where they also sell these batteries, and spoke with their abyc marine electrician. He stated that on top of the ohms law reason, these batteries have an intelligent BMS that knows they are connected in parallel. He claimed that they will reduce the current being transferred to the other battery. He said that is the reason why they only allow 4 batteries to be paralleled together- because the BMS is set up to only recognize 4 batteries.

He stated that he was willing to deeply discharge one of them and parallel it afterwards with another to try it. He would clip the conductor to see the transfer of amps. I gave him my e-mail, I will post the results on here if he gets back to me with the results.

If this is true this could be a game-changer for a lot of battery setups.

*greg_QS* the not recommended for critical/start application may be obsolete now that they offer lithium in a higher cranking battery? these just came out.

Thank you everyone for your input

Anther way to look at this. If you had a problem with ether bank. By combining them, you could bring both banks down. You could depending on the problem.

What I think that makes most of use apprehensive in all this. Is that lead battery technology has been around for years. Between brands they are all for the most part the same. A very forward concept other than! Most battery experts will tell you don't mix wet cell, AGM and gel batteries. So why mix them with lithium which is not lead based and the other are?

When it come to lithium, not all BMSs are the same. Too many variables and its a new technology. Even the cells in them can be of different brands since there made in China.

I my case, I like knowing that one bank can not harm the other. I can "get home" if ether bank went down to run the house. The house bank at 800aH can normal out put 600A constant and 800A surge. It might start my engine?


To each his own and I and no expert in this. I just want to play it safe.

 

[twistedtree]

I contacted alberta lithium (great customer service btw) and asked them about using both batteries on a 1-2-both switch. I discussed my desire to drain one battery completely, and then combine them/ switch to the other to fire the engine back up.

He disagreed with the idea that this would cause a problem. He went to deeper lengths then I can properly explain now- but basically he stated the resting voltage of the full battery would be 13.6 and the fully discharged voltage of the lithium around 12.9. He stated that due to ohms law it cannot discharge at a very high current while balancing the batteries because there is simply not enough of a voltage difference to allow a high transfer of amperage- or something to that extent.

I went to my local marine store the next day where they also sell these batteries, and spoke with their abyc marine electrician. He stated that on top of the ohms law reason, these batteries have an intelligent BMS that knows they are connected in parallel. He claimed that they will reduce the current being transferred to the other battery. He said that is the reason why they only allow 4 batteries to be paralleled together- because the BMS is set up to only recognize 4 batteries.

He stated that he was willing to deeply discharge one of them and parallel it afterwards with another to try it. He would clip the conductor to see the transfer of amps. I gave him my e-mail, I will post the results on here if he gets back to me with the results.

If this is true this could be a game-changer for a lot of battery setups.

*greg_QS* the not recommended for critical/start application may be obsolete now that they offer lithium in a higher cranking battery? these just came out.

Thank you everyone for your input

Just fro clarity, we ARE talking about 1-2 combining of two LFP banks, right? Not combining an LFP bank to a lead-acid bank? I want to be sure I didn't misunderstand because the two situations are quite different.


Combining LA & LFP is much less of an issue because the LA voltage is relatively elastic based on current. We all see this when charging and discharging where there can significant swings in voltage. So if you parallel a LFP battery with LA battery where the two are at significantly different voltages, and bunch of current will start to flow and the LA battery's voltage will rise or fall the match the LFP battery voltage, at which point the current flow will reach a point of equilibrium. The LFP battery voltage will rise or fall a bit too, but MUCH less than the LA battery.


If you parallel two LFP batteries that are at very different states of charge, their voltages will be different, and both will be very resistant to raising or lowering voltage is response to current flow. As a result, it takes a LOT of current flow to equalize the voltage. LFP manufacturers usually require that batteries be within a few tenths of a volt of each other before paralleling them, and there is a caution in ABYC E-13 saying to pay attention to this.


I'm also very skeptical of the dealer's comments. I have never seen or heard of a BMS that regulates or limits current. All I'm aware of are on/off switches. Some are mechanical contactors and some are electronic FETs, but they are all switches. Maybe this product is different. but if so, it's VERY different.

 

[jointcustody]

Just fro clarity, we ARE talking about 1-2 combining of two LFP banks, right? Not combining an LFP bank to a lead-acid bank? I want to be sure I didn't misunderstand because the two situations are quite different.


Combining LA & LFP is much less of an issue because the LA voltage is relatively elastic based on current. We all see this when charging and discharging where there can significant swings in voltage. So if you parallel a LFP battery with LA battery where the two are at significantly different voltages, and bunch of current will start to flow and the LA battery's voltage will rise or fall the match the LFP battery voltage, at which point the current flow will reach a point of equilibrium. The LFP battery voltage will rise or fall a bit too, but MUCH less than the LA battery.


If you parallel two LFP batteries that are at very different states of charge, their voltages will be different, and both will be very resistant to raising or lowering voltage is response to current flow. As a result, it takes a LOT of current flow to equalize the voltage. LFP manufacturers usually require that batteries be within a few tenths of a volt of each other before paralleling them, and there is a caution in ABYC E-13 saying to pay attention to this.


I'm also very skeptical of the dealer's comments. I have never seen or heard of a BMS that regulates or limits current. All I'm aware of are on/off switches. Some are mechanical contactors and some are electronic FETs, but they are all switches. Maybe this product is different. but if so, it's VERY different.

-yes we are talking about 2 LFP batteries on a 1,2,both position switch.
-at this point I am trusting what nobody says lol but I am leaning towards believing what you are saying for sure. I wish he would do the test and email me the results. I am a lineman by trade and what you are saying makes better sense to me.
-Maybe because they are starting batteries they can handle the amps transfer? thats a lot of juice.... and that doesnt happen without heat.

OK lets step back for a minute... I may have found a second solution. So the entire reason I am hoping to split the two batteries apart is so that I have an easy way to start my engine in the morning.
In my bow is 2 -12v agms in series for my 24v bow thruster. Today I found a series/parallel 12/24v switch/relay.
https://www.texasindustrialelectric.com/T_114_12_series_parallel_switch.asp
There are other versions of it, but they were used for decades by truckers to start their large diesels on 24v and then automatically switch back to 12v for their house loads.
What I am thinking about doing (if it turns out I can't equalize these batteries) is leaving the two LFP combined permanently. changing my 2-12v batteries in series in the bow to parallel. Then using this switch here ^ to get 24v whenever my bow thruster is triggered. Then I could simply shut my LFP batteries off and turn a switch or two (not parrallel them) and have a completely separate backup battery bank in case of emergency. They are currently being charged by a small dc-dc charger off my house bank (victron). I could sell that and get a 12-12 verson.

Thoughts?

 

[Iggy]

-yes we are talking about 2 LFP batteries on a 1,2,both position switch.
-at this point I am trusting what nobody says lol but I am leaning towards believing what you are saying for sure.......................

Thoughts?

I thought you were combining different types.

 

[Greg QS]

I have been researching this for about 6 Months and finally have a system plan. I have the bulk of the system already in place. I have to make some changes to install the lithium system. See the cool attachment Only difference is I am using a 6 battery bank


I have 8 -8d I am replacing. I am set up with 2 -4d banks. I have discussed this and started by settig up with 2 -2 bank lithium. I have consulted 2 Victron dealers that both designed a mega system for me. Both did not recommend that layout. for the following reasons.

1 larger bank will last longer under discharge.

2 larger bank minimizes depth of discharge. Thus prolonging battery life. Lower depth of discharge between charges raises cycle life.

3 if the battery banks are connected in parallel and are not balanced , there will be such a high flow of amperage to the lower bank there is a risk (in theory) of fire. Not likely, they say the bms will just kick out on the more charged batteries. Once one bms trips the second will trip and so on. The batteries can absorb more current then they can discharge , this causes the good batteries to trip out.

4 They ( the professionals) both said 1 bank or the other . They do not want to see a manual switch setup like you are discussing. To easy to make a mistake when voltages are un equal. Causing batteries to trip out

When you set up in parallel your new Lithium batteries, It is required to fully charge all batteries in the bank before Paralleling so you don't damage the batteries. The double/parallel switch system is not prudent for Lithium setups. The only way they recommended it is as a either/or switch. Using a bank of 3 to 1 battery , The one battery is isolated so that if my battery primary bank goes down I have "emergency" power. The feel this makes no sense, because in my situation, I would have to switch the bat bank over . If I'm there why not just start the engines or genset. If i have the larger bank, I possibly would have gotten through my scheduled discharge.

In the end they ( the professionals ) said don't do it . They want to see 1 larger battery bank .

If using lithium , They (the professionals) want to see, Isolated engine start batteries, isolated genset batteries. These batteries do not go to the general boat systems. Bilge pumps or anything , Only for starting. Finally isolated from the lead acid batteries, lithium batteries running the whole boat.

If you want to have a back up or parallel switch for starting. Do that only with your lead acid genset and engine batteries. If the genset battery is to small , use a large bat for the genset so you have the parallel ability for starting a weak start battery. But if nothing else is on the start battery it should in theory never need to be paralleled, unless ready for replacement, because there is no house drawing it down.

 

[Iggy]

I have been researching this for about 6 Months and finally have a system plan. I have the bulk of the system already in place. I have to make some changes to install the lithium system. See the cool attachment Only difference is I am using a 6 battery bank


I have 8 -8d I am replacing. I am set up with 2 -4d banks. I have discussed this and started by settig up with 2 -2 bank lithium. I have consulted 2 Victron dealers that both designed a mega system for me. Both did not recommend that layout. for the following reasons.

1 larger bank will last longer under discharge.

2 larger bank minimizes depth of discharge. Thus prolonging battery life. Lower depth of discharge between charges raises cycle life.

3 if the battery banks are connected in parallel and are not balanced , there will be such a high flow of amperage to the lower bank there is a risk (in theory) of fire. Not likely, they say the bms will just kick out on the more charged batteries. Once one bms trips the second will trip and so on. The batteries can absorb more current then they can discharge , this causes the good batteries to trip out.

4 They ( the professionals) both said 1 bank or the other . They do not want to see a manual switch setup like you are discussing. To easy to make a mistake when voltages are un equal. Causing batteries to trip out

When you set up in parallel your new Lithium batteries, It is required to fully charge all batteries in the bank before Paralleling so you don't damage the batteries. The double/parallel switch system is not prudent for Lithium setups. The only way they recommended it is as a either/or switch. Using a bank of 3 to 1 battery , The one battery is isolated so that if my battery primary bank goes down I have "emergency" power. The feel this makes no sense, because in my situation, I would have to switch the bat bank over . If I'm there why not just start the engines or genset. If i have the larger bank, I possibly would have gotten through my scheduled discharge.

In the end they ( the professionals ) said don't do it . They want to see 1 larger battery bank .

If using lithium , They (the professionals) want to see, Isolated engine start batteries, isolated genset batteries. These batteries do not go to the general boat systems. Bilge pumps or anything , Only for starting. Finally isolated from the lead acid batteries, lithium batteries running the whole boat.

If you want to have a back up or parallel switch for starting. Do that only with your lead acid genset and engine batteries. If the genset battery is to small , use a large bat for the genset so you have the parallel ability for starting a weak start battery. But if nothing else is on the start battery it should in theory never need to be paralleled, unless ready for replacement, because there is no house drawing it down.

All very good points. To add to balancing. It is why they suggest in the setup in wiring to balance the bank.

My bow thuster to house batteries are less than 8 feet apart. You can use lithium for that is sized right. I will say that I now have 3 lithium batteries that make up the house bank. Now adding a 4th to keep the thuster running ar full output longer. I don't know if this helps??

By adding the 4th battery I must (per tech support) get the voltage as close as possible between new and old batteries. They did say over time they will balance them selfs out. We did not get into a time period.

 

[Greg QS]

1, Yes

2 . No. The lithium platform is used for back up power and constant draw. It is much more expensive. It is not recommended for use with engine crank or thrusters. Use the lead acid in this application. Sudden high draw bursts of power. The lead acid just has a higher burst discharge rate. If you need more power at the thruster, tie to the start bat or add a second lead acid to it.

3 If you add and additional battery , YES you need to get the voltages as close as possible. They recommend fully charging house and battery the new battery firs. This is the Easiest way to get the voltages as close as possible.

I can here the crowd saying: Lithium is used in cars, bikes , phones and in boats to run them now days. That is not the lithium life pod 4 we are discussing. It is a different chemical make up . The bms systems they install are to prevent all the fires you hear of from those batteries. Purposely shutting the battery down before it can get into a high heat situation. Thermal runaway. This is why ( I think) it is more purposely more sensitive to shock loads in order to make them safe.

Balancing is the natural act of batteries equaling voltage out between each other. Remember inside each battery is a bunch of batteries that also have to balance out. So when you hook the "big " bat together the Small ones inside also have to balance out, so the problem of balancing is magnified. Too much current flow ( ie heat ) and pop goes the bms, to protect the battery.

Did you ever put a single alkaline battery into dead batteries? Like a remote , just to get it to work because you only had 1 left. The remote gets hot. That is the batteries balancing out rapidly . The end result is a dead new battery and heat due to the rapid transfer of voltage to the dead batteries.

 

[mcarthur]

Offgridgarage (YT) just did a paralleling of two LiFePO4 banks that were at 100% and 50% SOC, and their BMS did current limiting I believe...

 

[Iggy]

This guy should have his own show! No fire, no fuse was blown. But the BMS stopped that. Which goes back to how good is your BMS?

With my luck, fuses would have blown! My max charge current is 150A per battery.

If a larger bank dischargers into a smaller bank. There would be a greater chance of damage in some way.