The 4 ways how to adapt your alternator (existing or new one) to charge LFP bank

[CaptainRivet]

Warning its a long post but it contains all you need what to do with an alternator if you switch to LFP bank. These are the 4 ways how to do it.

why we need to care about the alternator is that former lead had a resitance in high kilooom figures but new LFP has an very low internal resistance of a few milliohm close to a short and the alternator regulator therefor runs it wide open till it self distructs.
the key to get the alternator under control is temperature control, and the way to do this is current output control, the rest will follow automatically. With lead due to high resistance the alternator is limited in current delivery but with LFP not as described above and how much you need to limit current depends on each individual install and specs of your alternator.
Import spec is current delivery and what stator temps it can withstand, normal one max 130 degrees celcius, then the isolation lacquer of the coil will be destroyed. 110 degrees if max output with reduced lifespan 95 degrees for optimum lifesapn and max output compromise.

You have 4 ways to do that.
1) modify your existing alternator and add an external regulator WITH temp control sensor as if you modify you loose the internal one. The sensor is placed on the case best somewhere in the pulley facing front part but next step measure the temp difference between stator temp (the hottest part that needs limitation with an IR temp tool) and what your sensor measures, substract that delta from 100 degrees celcius (or from 140 degress if you have a seldom alt that has the 170 degrees lacquer) and you have the temp parameter to put in your regulator, it delivers you the max current in your installation dynamically. In case of a sudden disconnect you have to make sure the BMS cuts the field wire first and add a surge protector.
The way to get around modifing your alternator is to use Nordkyn VSR200 regulator that works via the sense wire without any modification to alt. VsR200 works with a lot alternators that have internal temp regulation like Mitsubishi 115A found on all newer Volvo D1/2/4 and partly 6+small Yanmar or the Valeo 125A found on various manufaturer. Be careful it must be originals the aftermarket ones mainly don't have this temp regulation!!! In a well ventilated engine room the 115A Mitzi delivers 85A continuously with the VSR200, in reality most heavy duty small case alternators in that spec range won't do more or maybe max 20A+ for 2000Euro invest...more you only really get with large case alt that most likely won't fit in the original location and be up for 3000Euro+ if you don't DIY everything.
2) if your alternator has internal temp regulation (like original!! 115A Mitsubishi or the 125A Valeo) then you can add a splitting diode like Victron argofet and connect to lithium house and to a lead starter battery. The lead present the dump load in case of a disconnect and also limits current output of alternator and the voltage drop on the diode makes sure that even at 14.7V alternator output only 13.8V or less gets to lithium. The internal temp protection protects your alternator and dials it back when needed. The Mitsubishi 115A internal one is set to very conservative 85 degrees. Like this you can charge a lithium to about 95%, the rest your solar can do from time to time. The alternator get cut off from bank when BMS cut the charge bus due to end of charge parameter reached or you can add a relay just to do that for the alternator, would add a manual switch to control the relay so you can disconnect it from the LFP manually too due to any reason, eg just to charge the starter faster.
3) connect your alt to your starter and use a DC2DC charger. If you have no glue about real temps at the max output capabilities of your alternator i advise max 40% of its rating and add 10A charge for the starter, that together shouldn't exceed 50% of the rating. This limits an 80A alt to 40A and most likely avoid burning it out. I say most likely because you have actually no glue at what temp your alt is really working and if you are in the limits or actually could go to 70% of rating because your installation is well ventilated and the alt has enough self couling capacity. This 50% rule/adivise is based on vast experience of lot installer and the typical alternator specs used and takes bad ventilated engine rooms into account but if you are in the approx 5% where this rule won't work if a) your alt has an internal proper working temp control you are save, if b) no internal temp control like most older alternators that brings me to solution 4.
4) this is for all alternators without or insufficent internal temp regulation: install a temp probe at your alternator and log temps. Use a very hot day, all close up like its in normal operation. Now log in idle, your motorsailnig RPM and typical motor rpm at 33% or 1/3d current load of alternator capacity, so a 90A one on 30A and log temps at startup and all 10min till 2h of operations. Measure at 2h point with an infrared temp tool the stator temp so you get delta of your probe and stator. Add that delta to the temp results. Did your alternator get to 100 degress, if yes thats the current you need to derate it too. If not add gradually 10A load and do the same process then above. If you have derating you can do 2 ways. Way 1 buy a DC2DC charger that fits the derating, thats 100% safe compared to 3). Way 2 is the cheap but complex way: additionally measure field current/voltage at cold startup with motor rpm and at the 2h operation point. Thats the delta you have to derate the field current by a resistor, means you have to inline the resistor (i used 10w one) into the field wire and isolate/ seal it 100% with shrink tube. That has the disadvantage that during the cold startup phase of 15-30min depending of your installation less output of the alternator but its safe in permanent operation. Then use a splitting diode with lead starter like in 2) or connect it directly to LFP with a surge protector device and a diaconnect relay in the dield wire for the BMS. The resistor in the field wire limits the alternator also in max volt put out and limiting it to 30 till 50% should limits voltage to below 14.4V but you need to check that. This needs a BMS that controls the charges sources and just disengage the alternator at 95% SoC like eg a electrodacus, REC, Batrium, TAO BMS.

[Fuss]

I don't know why you keep positing this stuff, its useless information because its not your own personal experience, its regurgitated internet info that you have read.
You should stop this now, its dangerous for the newbies because they actually believe what you're writing.

[CaptainRivet]

Originally Posted by Fuss

I don't know why you keep positing this stuff, its useless information because its not your own personal experience, its regurgitated internet info that you have read.
You should stop this now, its dangerous for the newbies because they actually believe what you're writing.

I request to proof your statements here!
I also never get an answer which experience and qualifications you have to make this statement.

Show me where you find the resistor method in 4) on the internet documented. Not aware of this is documented anywhere.
This we (a very experienced sailor with 3 world circum and myself) figured out on a delivery trip when DC2DC broke down and 90% killed the lead starter and we need to figure out a way to charge the LFP directly with the alternator in the middle of nowhere with no supply.

Every of this methods stated above i installed personally and made my own personal experience with it.

[tanglewood]

Originally Posted by CaptainRivet

Warning its a long post but it contains all you need what to do with an alternator if you switch to LFP bank. These are the 4 ways how to do it.

why we need to care about the alternator is that former lead had a resitance in high kilooom figures but new LFP has an very low internal resistance of a few milliohm close to a short and the alternator regulator therefor runs it wide open till it self distructs.

There's some good stuff in your post, but also laced with some fundamental misunderstanding. I quote only the opening statement as an example.


Lead batteries do not have kilo-ohms of resistance. At moderate SOC there internal resistance is also in the milli-ohm range, and plenty low to accept full output from most any charger. In the absorption stage charger current acceptance tapers off, and this does indeed correspond with an increase in internal resistance, but let's get our orders of magnitude correct.


The real issue for alternators is that when charging lead, full output is inherently time-limited, with survival of the alternator depending on that reduced absorption current to keep it from overheating. Different alternators can last longer at full output, and some alternators additionally include temperature sensing to reduce output even if the loads can take more. External regulators almost always include temperature sensing capability and provide another way to control the alternator and prevent damage from overheating. Last, you can limit max output via a DC/DC converter, or other means like a voltage divider resistor in the field circuit, or the Nordsk which appears to control the alternator by "faking: the sense voltage.

[SailingHarmonie]

Originally Posted by CaptainRivet

Warning its a long post but it contains all you need what to do with an alternator if you switch to LFP bank. These are the 4 ways how to do it.

why we need to care about the alternator is that former lead had a resitance in high kilooom figures but new LFP has an very low internal resistance of a few milliohm close to a short and the alternator regulator therefor runs it wide open till it self distructs.

This is where I stopped reading. This explanation is so completely wrong and reflects a complete misunderstanding of the differences between charging a LA and a LiFePO battery, I trust NOTHING else in the post. Not saying the rest of the stuff is all wrong, but the person who wrote this would never be allowed to work on my boats electrical system.

[CaptainRivet]

Originally Posted by tanglewood

There's some good stuff in your post, but also laced with some fundamental misunderstanding. I quote only the opening statement as an example.


Lead batteries do not have kilo-ohms of resistance. At moderate SOC there internal resistance is also in the milli-ohm range, and plenty low to accept full output from most any charger. In the absorption stage charger current acceptance tapers off, and this does indeed correspond with an increase in internal resistance, but let's get our orders of magnitude correct.

Was a simplified intro for newbees and never ment to be lead versus LFP comparison.
I give a F... about lead as stoneage technology.
Yes large AGM banks are the exception here and quite comparable to LFP in some SOC range, FLA have kiloohms in majority of SOC.
And if you are not in the SOC range then your alternator will burn out...

Simpler statement would have been, "you connect your standard alternator (made for any lead chemistry) to the retrofitted LFP and it runs flat out till it self distructs.
These are the 4 ways to avoid it.
Again here i explained it practical and hands on and simplified some stuff otherwise post would be triple long and i for sure would have missed an exception....
All i posted i tested and install myself, non had an issue with the alternator till now.
And yes its the internal regulator that sees an load close to a short all the time and therefor opens full throttle till it dies from heat.

Issue is temp and not current, current is often the root cause. I saw 200A large case alternator destroyed=burned up that had 2x50A DC2DC connected but engine room was badly ventilated and their motorsailing was just 1400RPM...and the same model in a well ventilated engine room with an external regulator+2 temp sensors that was pulling 170A constantly on an underpowered engine means it was always running high rpm, even motorssiling was 1800... It was the high reving version (majority out there on ebay or wreckyards) and not the low rpm schoolbus version.

[CaptainRivet]

Originally Posted by tanglewood View Post
There's some good stuff in your post, but also laced with some fundamental misunderstanding. I quote only the opening statement as an example.


Lead batteries do not have kilo-ohms of resistance. At moderate SOC there internal resistance is also in the milli-ohm range, and plenty low to accept full output from most any charger. In the absorption stage charger current acceptance tapers off, and this does indeed correspond with an increase in internal resistance, but let's get our orders of magnitude correct [quote]

Was a simplified intro for newbees and never ment to be lead versus LFP comparison.
I give a F... about lead as stoneage technology and may have even something Fundamentally understood wrong with them. I still have 2 FLA as starters but cannot wait to throw them out for 40AH LTOs, they just don't ship them to Canaries...
But i understood all why some standard alternator survived an LFP retrofit without any mods while another fully regulated burn up...simply they forgot that the temp measured is case temp and not stator temp...
Balmar thinks here for the client and to the temp you put into regulator it is actually added automatically the delta from stator to case temp due to tests they done...other don't do that.

Yes large AGM banks are the exception here and quite comparable to LFP in some SOC range, FLA have kiloohms in majority of SOC.
And if you are not in the SOC range then your alternator will burn out...

Simpler statement would have been, "you connect your standard alternator (made for any lead chemistry) to the retrofitted LFP and it runs flat out till it self distructs.
These are the 4 ways to avoid it.
Again here i explained it practical and hands on and simplified some stuff otherwise post would be triple long and i for sure would have missed an exception....
All i posted i tested and install myself, non had an issue with the alternator till now.
And yes its the internal regulator that sees an resistance load close to a short all the time and therefor opens full throttle till it dies from heat.

Issue is temp and not current, current is often the root cause. I saw 200A large case alternator destroyed=burned up that had 2x50A DC2DC connected but engine room was badly ventilated and their motorsailing was just 1400RPM...and the same model in a well ventilated engine room with an external regulator+2 temp sensors that was pulling 170A constantly on an underpowered engine means it was always running high rpm, even motorssiling was 1800... It was the high reving version (majority out there on ebay or wreckyards) and not the low rpm schoolbus version.