Charging LFP and FLA batteries at the same time

[mikereed100]

The current setup on my cat has externally regulated 100a alternators charging The 400ah AGM house bank. The sealed FLA automotive start batteries are in turn charged from the house bank via Echo Chargers.

I will be switching to a 400ah LFP house bank soon and plan on connecting the start batteries directly to the alternators via Victron ArgoFETs to protect the alternators in case the BMS detects a fault and isolates the house bank.

I worry that, on the starboard side, it is a 66' round trip from the alternator to the house bank. Even using 4/0 cabling, the voltage drop is .45 volts, and that is not accounting for connections and fuses, which will increase the voltage drop further. The regulator, which senses voltage at the house bank, will increase the charge voltage so that the house bank sees 14.4 volt as required. This will send 14.9 volts, or higher, to the start battery as well until the house bank is charged, possibly for hours. My concern is that this will cook my start batteries. On the bright side, by some miracle of chance and smaller cable size the voltage drop between the alternator and the start battery is almost exactly the same (calculated, not measured) as the voltage drop to the house bank so I suspect they will be OK. After all, automotive batteries are used to being charged at 14.4 volts for hours at a time in cars.

Just wondering if anyone else had had similar concerns or am I keeping myself up at night for no reason?

[markcouz]

If it was my boat (and I wish it was, I am one of those on a mono that gazes longingly at the cats in my vicinity!) I would go the DC2DC route which seems to be as contentious as the "which anchor is best" debate.

Connect each alternator directly to the local start FLA,
Connect each start FLA to a separate DC2DC located close to LFP bank,
*you can use 6mm2 (AWG#9) for this run and save a fortune on 4/0 cable discussed - I guess more than enough to cover the cost of the DC2DC chargers,
Connect both DC2DC to LFP in parallel.

Your FLA will act as a dump load so no more concerns regarding BMS disconnect,
No concerns regarding overcharging of FLA as alternator is charging as designed,
No concerns regarding volt drop to LFP as charge profile is set at programmable DC2DC,
No concerns regarding cooking of alternator as charge current is limited by DC2DC,
*you will probably be limited to around 30A per DC2DC, if you want higher charge rate and feel that your alternator can support it then you could double up on the DC2DC.

No more lost sleep!

[CaptainRivet]

Originally Posted by mikereed100

The current setup on my cat has externally regulated 100a alternators charging The 400ah AGM house bank. The sealed FLA automotive start batteries are in turn charged from the house bank via Echo Chargers.

I will be switching to a 400ah LFP house bank soon and plan on connecting the start batteries directly to the alternators via Victron ArgoFETs to protect the alternators in case the BMS detects a fault and isolates the house bank.

I worry that, on the starboard side, it is a 66' round trip from the alternator to the house bank. Even using 4/0 cabling, the voltage drop is .45 volts, and that is not accounting for connections and fuses, which will increase the voltage drop further. The regulator, which senses voltage at the house bank, will increase the charge voltage so that the house bank sees 14.4 volt as required. This will send 14.9 volts, or higher, to the start battery as well until the house bank is charged, possibly for hours. My concern is that this will cook my start batteries. On the bright side, by some miracle of chance and smaller cable size the voltage drop between the alternator and the start battery is almost exactly the same (calculated, not measured) as the voltage drop to the house bank so I suspect they will be OK. After all, automotive batteries are used to being charged at 14.4 volts for hours at a time in cars.

Just wondering if anyone else had had similar concerns or am I keeping myself up at night for no reason?

Hi Mike,
Your alternator has a voltage sensing wire and that won‘t have such big voltage drop. In your current installation you are charging AGM from both and have no such problem. with LFP there is no change here.
I would skip a starter in the STB hull and have one starter/house LFP (assume house bank is in STB as it typically is). Add what you saved to the house and get extra battery/set of cells to the house for bigger capacity. Especially your anchor windlass will like that a lot, as the the starter of your STB engine too.
Both alternators charge the STB LFP starter/house as they do it now with AGMs.
The BMS can shut of the field of your externally regulated alternator by eg putting a relay into the ignition field wire, you don‘t need an argofet and lead. If your BMS cannot do that Jedi described in that post how to do this with a Victron BMV712.
In the BB hull I would keep a lead starter that is charged from the starter/house via DC2DC as backup and starter for BB engine.
Alternatively the STB alternator charges directly LFP starter house and BB you use an argofet and charge BB lead starter and STB LFP starter/house.
You can always start your STB engine from BB starter lead in Case house is totally down.

[wholybee]

You have a 100A externally regulated alternator. I assume it has an alternator temperature probe.(If not, add one) That is the ideal setup for LFP. I would keep your setup exactly the same, charging to LFP, with the echo to the start.

The BMS should NEVER disconnect while charging. Something is very wrong with your regulator or charger programming if that happens. Be very sure to set them up correctly. So it is a slim(but non-zero) chance that will happen. Sterling and Balmar both make relativity inexpensive protection devices to cover that non-zero case.

Some will argue that a 100A alternator should only be run at 30A continuously anyway, so they prefer charging the start battery first. That may be true if you are motoring for 24 hours, in which case the regulator will back off the alternator based on temperature. But if you ever need to top off your battery with the engine because it is low, getting 50Ah in in 30 minutes might be all you need to make it until solar can take over. Instead of ~90 minutes for the same with a 30A echo charger.

[CaptainRivet]

Originally Posted by wholybee

You have a 100A externally regulated alternator. I assume it has an alternator temperature probe.(If not, add one) That is the ideal setup for LFP. I would keep your setup exactly the same, charging to LFP, with the echo to the start.

The BMS should NEVER disconnect while charging. Something is very wrong with your regulator or charger programming if that happens. Be very sure to set them up correctly. So it is a slim(but non-zero) chance that will happen. Sterling and Balmar both make relativity inexpensive protection devices to cover that non-zero case.

Some will argue that a 100A alternator should only be run at 30A continuously anyway, so they prefer charging the start battery first. That may be true if you are motoring for 24 hours, in which case the regulator will back off the alternator based on temperature. But if you ever need to top off your battery with the engine because it is low, getting 50Ah in in 30 minutes might be all you need to make it until solar can take over. Instead of ~90 minutes for the same with a 30A echo charger.

Wrong the BMS can and will shutdown the LFP in a Desaster or Low voltage disconnect event and in this case before this happens the BMS need to interrupt the field wire of the alternator (and give an audible warning due to the AYBC rules). And this case shouldn’t be covered by Sterling protection device as these are also single use protection means need to be replaced after event happened.
There are also different types of BMS out there eg my Electrodacus that controls all charges as the spider in the web and not the charge sources themselves to optimize the LFPs banks charge.

[wholybee]

Originally Posted by CaptainRivet

Wrong the BMS can and will shutdown the LFP in a Desaster or Low voltage disconnect event and in this case before this happens the BMS need to interrupt the field wire of the alternator (and give an audible warning due to the AYBC rules). And this case shouldn’t be covered by Sterling protection device as these are also single use protection means need to be replaced after event happened.
There are also different types of BMS out there eg my Electrodacus that controls all charges as the spider in the web and not the charge sources themselves to optimize the LFPs banks charge.

What do you mean I am wrong? Of course the BMS will shut down charging or discharging if something goes very wrong. But that should *never* happen. I did have an LVE when I wasn't on the boat and it rained for 2 weeks(solar didn't keep up), but that isn't going to damage the alternator or anything else. Otherwise, I am 3+ years in, without a single HVE. I don't expect I ever will. HVE events are what could damage the alternator and will only happen if something is terribly wrong. Consider, how likely are you to have a LVE when the alternator is charging at a high amperage? That doesn't even make sense. And, if overcharged, the LFP isn't accepting a high current, so an HVE then isn't likely to damage the alternator, unless the alternator is charging at 16V or something wrong like that.(bad programming, failed regulator) And in those *really* rare cases, the Sterling product is perfectly fine, and not single use, only when the HVE is exceptionably bad is it damaged. And it has an LED/relay, so you know if something goes wrong and your system needs to be checked.

Things that will cause an event that could damage the alternator:
Alt Regulator or charger is programmed wrong and over charges the battery.

Alt Regulator or charger fails, and over charges the battery.

Poor system design, which allows charging at too high current. Maybe running a shore charger and alternator at the same time if the BMS won't allow it. Or installing a very large alternator with a battery that won't support it.

Cell imbalance, which itself is the result of a bigger problem, and shouldn't happen in a properly set up system. If you have a BMS that allows you to see cell voltages, you should catch this long before it becomes and issue.

If the system is designed properly, none of those things should ever happen. The regulator or charger failure is the one that is can rarely randomly happen, and if that does happen, I'm not opposed to spending $80 for a new protection device when I buy my new charger to save the $1000 for a more complex battery system. The OP didn't even state if he was building a system or using drop-ins. If drop ins, everything you are talking about, the interrupt for the alternator, the alarm etc, isn't even possible, and is certainly not required.

I favor simplicity and fewer points of failure. I am not a fan of drop-ins, but don't really have anything against them(as long as the right brands are used). But I feel the over complex systems with total integration of the BMS into everything else is a waste of money. KISS principle applies here. Put effort into programming and testing the setup, but don't buy more stuff. The effort put into programming will work better.

Also, ABYC does NOT require an audible warning, it recommends it. And it is a stupid recommendation, as that means that if you have an HVE or overcurrent situation, you are *not* supposed to protect your battery immediately, but give a warning for some time first? How dumb is that? I'll rather protect my battery, thank you. *IF* that every happens, because as I said, it should NEVER happen.

[mikereed100]

Originally Posted by wholybee

You have a 100A externally regulated alternator. I assume it has an alternator temperature probe.(If not, add one) That is the ideal setup for LFP. I would keep your setup exactly the same, charging to LFP, with the echo to the start.

This is likely what I will end up doing. The chances of a HVE or battery/alternator overheating event are slim with my setup as all charging sources are programmable and all have battery temp sensing. The batteries are drop in Kilovaults with a fairly robust BMS in each battery. In the unlikely event of a battery shut off, the other battery would still be accepting charge, hopefully until I could shut down the engine or disconnect the field wire. In addition I have a Balmar voltage spike protectors on each alternator.

Balmar recommends decreasing their alternator's output by 35- 40% with LFP batteries. This still gives me much faster charging than with a 12v/12v converter.

In practice, we are rarely more than 100ah down when charging begins, so cooking the alternators should not be an issue. Especially if the sun is out and our 800w solar bank is contributing.

[CaptainRivet]

Originally Posted by wholybee

What do you mean I am wrong? Of course the BMS will shut down charging or discharging if something goes very wrong. But that should *never* happen. I did have an LVE when I wasn't on the boat and it rained for 2 weeks(solar didn't keep up), but that isn't going to damage the alternator or anything else. Otherwise, I am 3+ years in, without a single HVE. I don't expect I ever will. HVE events are what could damage the alternator and will only happen if something is terribly wrong. Consider, how likely are you to have a LVE when the alternator is charging at a high amperage? That doesn't even make sense. And, if overcharged, the LFP isn't accepting a high current, so an HVE then isn't likely to damage the alternator, unless the alternator is charging at 16V or something wrong like that.(bad programming, failed regulator) And in those *really* rare cases, the Sterling product is perfectly fine, and not single use, only when the HVE is exceptionably bad is it damaged. And it has an LED/relay, so you know if something goes wrong and your system needs to be checked.

Things that will cause an event that could damage the alternator:
Alt Regulator or charger is programmed wrong and over charges the battery.

Alt Regulator or charger fails, and over charges the battery.

Poor system design, which allows charging at too high current. Maybe running a shore charger and alternator at the same time if the BMS won't allow it. Or installing a very large alternator with a battery that won't support it.

Cell imbalance, which itself is the result of a bigger problem, and shouldn't happen in a properly set up system. If you have a BMS that allows you to see cell voltages, you should catch this long before it becomes and issue.

If the system is designed properly, none of those things should ever happen. The regulator or charger failure is the one that is can rarely randomly happen, and if that does happen, I'm not opposed to spending $80 for a new protection device when I buy my new charger to save the $1000 for a more complex battery system. The OP didn't even state if he was building a system or using drop-ins. If drop ins, everything you are talking about, the interrupt for the alternator, the alarm etc, isn't even possible, and is certainly not required.

I favor simplicity and fewer points of failure. I am not a fan of drop-ins, but don't really have anything against them(as long as the right brands are used). But I feel the over complex systems with total integration of the BMS into everything else is a waste of money. KISS principle applies here. Put effort into programming and testing the setup, but don't buy more stuff. The effort put into programming will work better.

Also, ABYC does NOT require an audible warning, it recommends it. And it is a stupid recommendation, as that means that if you have an HVE or overcurrent situation, you are *not* supposed to protect your battery immediately, but give a warning for some time first? How dumb is that? I'll rather protect my battery, thank you. *IF* that every happens, because as I said, it should NEVER happen.

what never should will happen, Murphy is waiting around the corner
And that must be part of your stress test points: what happens if a desaster event takes place, is everything shut off like it should?


And then comes the first 1 month in operation: you will have some kind of hickups... a crimp is not good, a remote wire disconnects, a breaker was faulty, a Victron battery protect did suddenly strange things like switching on different voltages then setting because it was a monday version...all caused a desaster switch off during motoring on the last boat i helped installing, good design so no damage...and we heavly stress tested the system for 2 weeks before. Well i was on board in this first month of normal too and we could quickly fix all, happens. After that nothing in last 4 month.


cell imbalance is not always a bigger problem, if you just have a 100mA passive balancer but a 900AH battery bank with eg 3p4S 304 AH cells and you draw frequent 0.5C loads they will differ appart slowly and the 100mA passive balancer has no chance of getting that sorted, its simply too small. you will just see that in operation, no problem just add an active balancer and all is fine. Happened eg to CatNewBee after a year with his 1000AH Winstons and his install is highly sophisticated and heavly monitored, still happened.


i don't find an audible warning dumb if it comes before(!) the event in a resonable timing eg LVC at 20% SOC and at the same time switch off all big loads like inverter to prevent it actually happens. I am not watching the BMS all the time and notice it immediatly if the big inverters get shut off when eg lounging on the trampoline.

Makes you aware and gives you time to look for the root cause and take measures and at the same time the BMS creates more time for you by shutting of the big loads so bank drains less. Same for HVC eg a solar controller is faulty and doesn't stop charging...


sterling writes in the product description that it can be damaged and has no protection for that, so one use product only if your lucky not...


regarding dropins and not possible: sure it is possible and needed, read Jedi's post in another thread about using BMV 712 to make this possible and even indicate the shut off. i actually have exactly this as last borderline too if my BMS fails (yes double backup BMS does it on cell voltage level, the BMV on total voltage=> the bank was expensive) and also installed this in my friends boat mentioned above. The BMS did all the desaster shut offs in his case, so good system design :-)

[CarlF]

The problem is that 30 amps from a typical DC2DC charger is a drop in the bucket when charging a large lithium house bank. Doesn’t do enough to be worth the effort.

I’ve been charging a large Kilovault bank for over a year with no problems. I charge the house bank from the Balmar XT 170amp alternator and use a DC2DC charger to keep the start battery charged. A 30 amp charge to the start battery is plenty. The XT is designed to handle the draw of a lithium bank - and of course has a temperature sensor should it get too hot.

I do the following four things to protect the alternator. It is more than enough.

1) The alternator regulator goes to float when voltage reaches 14.0v - at about 92% charge - well short of the BMS disconnect. The solar controller has a higher absorption voltage setting to get the batteries to 100%. This was recommended as also being better for the batteries to reduce the charge rate as you approach 100%

2):The Victron DC2DC charger is always active. It will absorb the surge from a BMS dump by directing the amps to the LA start batteries.

3) The Balmar alternator (and most modern alternators) has avalanche diodes that are usually not destroyed by a disconnect

4) There is a Balmar Alternator Protector on the alternator. These are not “one time use” like the old zap stoppers.

[HeywoodJ]

The cheap solution is to wire to the house bank and install a beefy diode between the charging circuit and your start battery to give a constant ~0.7V drop going into the start battery.

This is a really common solution with the Volvo Dx-yy series engines that whine about higher charging voltages for the house bank. The diode drop runs the starting battery in float mode while the house bank charges at bulk levels. Since starting the engine only takes a couple of Ah there isn’t a lot of reason to run it through the absorption phase, especially for a long time.

[CaptainRivet]

DC2DC chargers in 12V are avaliable till 50A from Renogy, till 70A from Sterling and till 100A from Victron. And thats just the well known one.
You are not stuck with 30A ones but they are so most common.

A tip for cats with 2 engines but you run mostly one for a longer periode of time.
Eg your engine has the 115A Mitsubishi, capable of 70-80A longthermed. So to max it out 2x30A DC2DC=60A +15A for Nav+lights+fridge=75A.
Install an FLA per engine and combine them with a Victron battery combiner when engine are running.
Then connect the two DC2DC to the starter where also the house is located,mostly STB.
So if one engine is running, doesn't matter if BB or STB both lead starter are connected together and the two DC2DC start charging (if starter is not low) and max out the one alternator running. Only if both engines are running you give away 60A that these 2 could produce more but running both engines longer is very very seldom.
One 30A DC2DC are normally carring other continious loads like freezer while the other 30A permantly charges the LFP bank so 10h motorsailing puts 300AH netto into the bank. And beeing overpowered with 18x13 instead 11x12 props i can motorsail with +2kn for 1l/1h on 1300rpm, a no brainer to do, especially below 50degrees AWA as i have no daggerboards.
Aim is here bank gets not further depleted and a bit a top up, alternators run save for 500Euro (when using Victron Orion smart) or 200Euro when using renogy and you cannot get more out of 1 alternator when modifing with external regulator and directly charge LFP and that will coat you muchnmore then 500Euro.
Main charge source is 2500W solar, 2nd 3500W mobile gas gen via 180A@24V shore power charger of my new Studer inverter/charger.

[lmxr]

Originally Posted by mikereed100

I worry that, on the starboard side, it is a 66' round trip from the alternator to the house bank. Even using 4/0 cabling, the voltage drop is .45 volts, and that is not accounting for connections and fuses, which will increase the voltage drop further. The regulator, which senses voltage at the house bank, will increase the charge voltage so that the house bank sees 14.4 volt as required. This will send 14.9 volts, or higher, to the start battery as well until the house bank is charged, possibly for hours. My concern is that this will cook my start batteries.

LFP batteries charge most of the time at 13.6 V (3.4 V/cell) or less and it is only in the last few to ten minutes of the charging process that the voltage goes up to 14.6 V (3.65 V/cell). In addition, some people only charge to 14.0 V (3.5 V/cell). So, the duration for which 14.9 V will be pumped into the start battery will be rather brief.

If you're using two independent alternators regulators, an option could be to program the one furthest from the battery with a lower maximum voltage (e.g. 14.0 V instead of 14.6) to avoid the elevated voltage on the start battery but still let the alternator contribute just as much during almost the full charging process (as the battery only climbs above 14.0 V in the last few percent SoC).

[donradcliffe]

My advice would be to hook the regulator voltage sensors to the start batteries and set the regulator for 14 volts. Use a relay to tie in the LFP bank, and size the wiring size and length to the LFP bank to limit the alternator current. Instead of thinking about 4/0 wires and DC-DC charging, think about just using wires that will limit the alternators to 80 amps each for the worst case when the LFP bank is under 12 volt

Simpler and much cheaper.

[Pete7]

Originally Posted by CaptainRivet

(and give an audible warning due to the AYBC rules). And this case shouldn’t be covered by Sterling protection device as these are also single use protection means need to be replaced after event happened.

When did ABYC introduce rules? I thought they just an advisory body.

What makes you think the Sterling alternator protect is a one shot pony?

https://sterling-power.com/collectio...tection-device

[CaptainRivet]

Originally Posted by Pete7

When did ABYC introduce rules? I thought they just an advisory body.

What makes you think the Sterling alternator protect is a one shot pony?

https://sterling-power.com/collectio...tection-device

Since insurances and authorities use the ABYC standards they are kinda rules...some is good like the warning, some is ridicilous eg that 2 parallel cables cannot be used instead a bigger one. Even eg Victron states in their inverter manuals 2x70A or 1x120mm and tested that. The AbYC argrument is if one breaks the 2nd is not able to pull that current. What happens is if one 120qmm breaks? BS a 70mm can carry 400A, just has a huge voltage drop while 200A is fine, 2 in parallel is 400 and slightly superior to one 120qmm, easier to route and i eg have equipment till 70qmm, above you need a different and much more expensive set of tool plus bigger then 70qmm is often not avaliable.


Regarding sterling you are right, they have changed that. its not standing anymore in the installation guide "device is not protected and can be destroyed during an event. In this case it need to be replaced."