Do I need an alternator protection device when switching to Lithium?

[Q Xopa]

Originally Posted by john61ct

I'm not at all saying a full upgrade to a higher output alt, serpentine belt etc isn't worth it when called for by a given use case.

But often **just** a DCDC charger, or

just converting to a good external VR, keeping the same alternator,

is all that's needed, was my point.

Ok, good suggestion I like the B2Bs. But Im sure you know that they cost over $300 and max out at 60A. That will take a little while to get your big LFP bank topped off.

Probably not for those among us that dont want to spend money either.

But I guess as the question was about making your Alternator survive on a LFP bank I suppose that would qualify. Your Alt should last very nicely throttled back at 60A.
Kinda seems a bit of a counter productive way to me of getting the fast charging potential most outta an expensive LFP setup.

[Q Xopa]

Originally Posted by Q Xopa

Ok, good suggestion I like the B2Bs. But Im sure you know that they cost over $300 and max out at 60A. That will take a little while to get your big LFP bank topped off.

Probably not for those among us that dont want to spend money either.

But I guess as the question was about making your Alternator survive on a LFP bank I suppose that would qualify. Your Alt should last very nicely throttled back at 60A.
Kinda seems a bit of a counter productive way to me of getting the fast charging potential most outta an expensive LFP setup.

VR. Voltage Regulator. These arent for free either. And yes I agree that it would help save a stock Alt getting cooked with Temp limiting etc.

Again most people shelling out for an LFP setup arent likely to want to for have their old alternator trickling in a charge to keep it cool. But yes you are completely correct. It is a cost saving option.

Again this is like having a Ferrari but driving it slowly to save on having to put expensive tyres on, and save petrol to go to the corner shop.

[Oceanride007]

I thought about it as well. Decided for me, that will connect Alternator to LA start only. All other charge devices MPPT, invertor/Charger tuned for Lithium connected only to LFP (But could go back to LA if LFP craps out).


Expect there will be more variety of B2B chargers with LFP option, in time to come, (Yes I read the loooong thread as well) but thinking I may be able to run a small charger thru a inverter from LA, if I want more or the other way around.


To the OP, what devise are you referring to ("one of those normal load regulators that switch the alternator charging first to the start battery" )

[john61ct]

60A actually being accepted every minute spent motoring may very well take care of what's needed for average daily energy.

Remember, no need to get the bank to Full, long as the input covers the consumption. Little to do with bank capacity really, might only be DoD 10% most days.

Also for many, alt output is a tiny fraction of total input, solar may be plenty most weeks, or maybe genset's regularly run to make water enough left over from that to refill the bank. . .

So these choices will vary by each use case

[Stu Jackson]

Originally Posted by Oceanride007

>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>



.........but thinking I may be able to run a small charger thru a inverter from LA, if I want more or the other way around.

>>>>>>>>>>>>>>>>>>>>>>>>

What?!?

[Flod]

This was a hot topic! Thanks for the reply’s. When I was writing about the “load regulator” I meant one of those simple relays that separate the battery banks at a certain voltage to protect the start battery from draining. I guess my setup will be ok since the start battery will always be connected to the charging circuit even if the bms cut off the Lithium bank. Then the alternator might need overheating protection etc but I plan on having 200ah lithium and that should go full in a few hours of motoring and then the alternator gets to rest.

Regarding only having the BMS as a last gate as someone wrote above I don’t really get this. Are you suggesting to get some kind of voltage sensitive relay and have it cut off the bank at a certain voltage ?

[john61ct]

Originally Posted by Flod

When I was writing about the “load regulator” I meant one of those simple relays that separate the battery banks at a certain voltage to protect the start battery from draining

That is a VSR, aka ACR, combiner.

> the start battery will always be connected to the charging circuit even if the bms cut off the Lithium bank.

Yes, good, topic of your OP, but that's just one piece.

> Then the alternator might need overheating protection etc but I plan on having 200ah lithium and that should go full in a few hours of motoring and then the alternator gets to rest.

Do some careful V/A monitoring with temp sensing, the alt can overheat quicker than that, basically anything continuous anywhere near rated output is risky.

Raw unfiltered output from a stock setup is rarely OK, really best to use a DCDC or upfit a good VR.

Overtemp often handled by voltage dropping, so no charging.

Voltage may be too high bad for the LFP anyway.

However you design your primary regulatory / safety setup, the whole point of the BMS is the protection of the bank in the event of the primary gear failing.

Protection against cell imbalances, overcurrent, overtemp, undertemp, overvoltage, undervoltage, pack-level vs parallel group vs per-cell levels, all up to you how each decision is handled when DIY designing your own system.

At least IMO, the bank is worth having more than one layer of defense for most of these. But then the close monitoring by a diligent owner can compensate, many run with no BMS at all! Up to you.

[john61ct]

Originally Posted by Stu Jackson

What?!?

Poor man's DCDC, run the shore charger to one bank, off an inverter from the other. Nuts I know wrt energy efficiency, but very common in some circles who don't care about that.

[Q Xopa]

Originally Posted by john61ct

60A actually being accepted every minute spent motoring may very well take care of what's needed for average daily energy.

Remember, no need to get the bank to Full, long as the input covers the consumption. Little to do with bank capacity really, might only be DoD 10% most days.

Also for many, alt output is a tiny fraction of total input, solar may be plenty most weeks, or maybe genset's regularly run to make water enough left over from that to refill the bank. . .

So these choices will vary by each use case

Not how I would do (should I say am doing) it. Spending on a nice LFP setup and bottle necking its capability. But you do you. Your boat if thats the way you want to run it then good for you.

I suspect if you ask one of your favourite Marine electrical vendors their advice to you would be, as they advised me, was to ditch my large case 200A Alts and buy their 350A small case Alternators and all sorts of other goodies, dont ask what sort of deal they were going to do me for that. This seemed too much $ for too little improvement. What do I know eh.
I dont mind spending to get good bang for my buck. I have definately spent 'boat loads' as we all do. Especially when you are trying to do them well.

When you are in Panama next I would be happy to show you my boat in all her imperfections and my mistakes over a beer in exchange for some of your expertese.

From what you say on here Im hard pressed to imagine (my imagination is obviously not so good) how your getting away with your recommendations of-
Fully compliant with all latest industry USCG regulations and AYBC and UL guidelines.
With fully tested and safety proven, best in class technologies.
Without spending any 'uneccessary' money.
My definition of a boat is its all uneccessary.

I still have a lot to learn.

[john61ct]

Originally Posted by Q Xopa

I suspect if you ask one of your favourite Marine electrical vendors their advice to you would be, as they advised me, was to ditch my large case 200A Alts and buy their 350A small case Alternators and all sorts of other goodies, dont ask what sort of deal they were going to do me for that. This seemed too much $ for too little improvement.

Exactly my point.

Sometimes worthwhile, sometimes not.

Too high a C-rate charging is actually bad for the bank, so if getting back to Full in an hour doesn't actually give you any major advantage given **your** usage patterns, it's silly to spend boat bucks on that capability

is all I'm saying.

You appear to be extrapolating over generalizations from case-specific snippets, no need to read in too much.

And yes, I don't drink but a shared meal in Panama would be nice one day

[Q Xopa]

Originally Posted by john61ct

Exactly my point.

Sometimes worthwhile, sometimes not.

Too high a C-rate charging is actually bad for the bank, so if getting back to Full in an hour doesn't actually give you any major advantage given **your** usage patterns, it's silly to spend boat bucks on that capability

is all I'm saying.

You appear to be extrapolating over generalizations from case-specific snippets, no need to read in too much.

And yes, I don't drink but a shared meal in Panama would be nice one day

Im obviously wrong but your point sounded to me more like big alternators were mostly not worth it. Not trying to read too much into things here. Yes agree with your point about charging too fast.

I would say the average punter investing in a LFP bank, 300AH is on the smaller end of the usual installation spectrum. Most people go bigger would make the following example worse.

That would make 60A 0.2C charge rate using a B2B. From 50%DOD would take 2.5 hours. Thats a fairly long motor or Generator run.

Where as if you can get 100A to make a 0.3C charge rate. From 50% DOD to take 1.5 Hrs. Even less time if you dont need to go to 100% SOC.

An hour less fuel and listening to the Honda 220 or the main diesel rattle away sounds like worth a few sheckles to me.

No problems Im sure we can rustle you up a meal and a water or fruit drink.

[Oceanride007]

--Quote (Originally by Oceanride007)---
>>>>>>>>>>>

.........but thinking I may be able to *run a small charger thru a inverter* from LA, if I want more or the other way around.

>>>>>>>>>>>>>>>>>>>>>>>>
---End Quote---

What?!?


Stu, Haven't done it but if I had LA Start batter charged by alternator and I wanted to get some charge in LFP, then either DC2DC charger with a LFP mode or I could connect a inverter to Start Battery, then a small lithium mode charger to charge up the LFP.
Of course there are inefficiencies but I am running the engine, don't care.
And your issue is?

[john61ct]

Originally Posted by Q Xopa

Im obviously wrong but your point sounded to me more like big alternators were mostly not worth it.

Yes that is not what I intended, I was simply refuting the simplification / overgeneralization

Originally Posted by Q Xopa

For Alternator stress relief from LFPs go as big as you can fit and or afford.

with "not always, only sometimes" and "other solutions / aspects are more directly applicable".

To me the biggest advantage with LFP is in modular portability, using the same packs in more than one context, my off-grid home, campers etc. So if you can't pick it up and walk around with it, for my use case that's poor design.

But I try to not let that presumption color general advice about what others should do in **their** use case, obviously if the alternator(s) provide a high proportion of overall energy input, it may be worth spending thousands on them.

Some people may run their propulsion ICE just to charge their batteries and be fine with that, reducing runtimes in that context is a fine goal.

[john61ct]

Originally Posted by Oceanride007

charger with a LFP mode or I could connect a inverter to Start Battery, then a small lithium mode charger to charge up the LFP

As a side note, I have yet to find an LFP mode I would use on a bank I care about.

The key attribute for a LFP charge source IMO is user-custom adjustable setpoints, not just a menu of "canned" predefined choices.

[Q Xopa]

Originally Posted by john61ct

Yes that is not what I intended, I was simply refuting the simplification / overgeneralization



with "not always, only sometimes" and "other solutions / aspects are more directly applicable".

To me the biggest advantage with LFP is in modular portability, using the same packs in more than one context, my off-grid home, campers etc. So if you can't pick it up and walk around with it, for my use case that's poor design.

But I try to not let that presumption color general advice about what others should do in **their** use case, obviously if the alternator(s) provide a high proportion of overall energy input, it may be worth spending thousands on them.

Some people may run their propulsion ICE just to charge their batteries and be fine with that, reducing runtimes in that context is a fine goal.

Yes my 'go as big as you can fit or afford' comment is a generalisation.

Of course as you point out there are always exceptions.

But in this case your exceptions are in the minority for an LFP bank as was being asked.

Its as if you just like to take a contrary view even if it doesnt fit the general concept very well.

Im sure that is not the case.

Carry on.