Merged LiFeYPO4 1000Ah Winston prismatic cells and all electric galley...

[john61ct]

A 120 / 180 etc BB, unit could only cover all the lower-current use cases a 60A unit does with LFP, if Charles continues to include the very valuable ability to derate / limit the current actually drawn by the bank.

Say you have a "75A rated" source that in fact can only be allowed to run at 60A continuous draw

not necessarily talking an alternator, any voltage-regulated source without a current limiting feature as is common.

If the 120A or 180A version was not adjustable in its current limiting feature, then those models would be useless for this use case, you'd be forced to buy the 60A unit specifically, and in future when using your bank with a source that can handle larger currents drawn, upgrade then, wasting money.

But since Charles does include the valuable feature of adjusting the current limit, you are now free to spend more on the higher capacity units, and be ready to move your bank to another boat, or use it on your expo truck or as a power bank at home, adjusting the current limited rate to different sources as needed.

Sure if you prefer to spend all that money on refitting that one alternator with a quality VR, nothing wrong with that, but that only fixes the problem for that one source on that one boat.

And since your LFP will last much longer than most people keep any one boat, that money (maybe with new pulley/belts too) will need to be spent every time.

The DCDC becomes a "front end" charge regulator for the bank, used on a large variety of energy inputs, no need to replace the sources everywhere you go.

Again, I am **not** advocating any one solution over another, depends on each use case's factors.

Just trying to show, again, that the ability to limit current, is one of the main **reasons** Charles developed the technology and often why DCDC chargers are purchased. In many cases higher currents will simply do no good, or an alternative VR is unsuitable or impossible to fit.

Also making the point, that the ability to scale that current limiting rate up and down as needed - as ambient temperatures change for example - is one of the main USPs of the Sterling BB series, along with the user-custom adjustable voltage setpoints.

[Q Xopa]

Originally Posted by john61ct

A 120 / 180 etc BB, unit could only cover all the lower-current use cases a 60A unit does with LFP, if Charles continues to include the very valuable ability to derate / limit the current actually drawn by the bank.

Say you have a "75A rated" source that in fact can only be allowed to run at 60A continuous draw

not necessarily talking an alternator, any voltage-regulated source without a current limiting feature as is common.

If the 120A or 180A version was not adjustable in its current limiting feature, then those models would be useless for this use case, you'd be forced to buy the 60A unit specifically, and in future when using your bank with a source that can handle larger currents drawn, upgrade then, wasting money.

But since Charles does include the valuable feature of adjusting the current limit, you are now free to spend more on the higher capacity units, and be ready to move your bank to another boat, or use it on your expo truck or as a power bank at home, adjusting the current limited rate to different sources as needed.

Sure if you prefer to spend all that money on refitting that one alternator with a quality VR, nothing wrong with that, but that only fixes the problem for that one source on that one boat.

And since your LFP will last much longer than most people keep any one boat, that money (maybe with new pulley/belts too) will need to be spent every time.

The DCDC becomes a "front end" charge regulator for the bank, used on a large variety of energy inputs, no need to replace the sources everywhere you go.

Again, I am **not** advocating any one solution over another, depends on each use case's factors.

Just trying to show, again, that the ability to limit current, is one of the main **reasons** Charles developed the technology and often why DCDC chargers are purchased. In many cases higher currents will simply do no good, or an alternative VR is unsuitable or impossible to fit.

Also making the point, that the ability to scale that current limiting rate up and down as needed - as ambient temperatures change for example - is one of the main USPs of the Sterling BB series, along with the user-custom adjustable voltage setpoints.

Yes very imaginative use cases. I cant argue with your possibilities.
Was that really worth your previous bout of hysterics and mud slinging?

[CatNewBee]

It's Nonsens. A current Regulator / b2b charger used to protect the alternator is not good enough to protect all possible sources at the same time. You have to protect each source individually according to their needs.

[Q Xopa]

Originally Posted by john61ct

A 120 / 180 etc BB, unit could only cover all the lower-current use cases a 60A unit does with LFP, if Charles continues to include the very valuable ability to derate / limit the current actually drawn by the bank.

Say you have a "75A rated" source that in fact can only be allowed to run at 60A continuous draw

not necessarily talking an alternator, any voltage-regulated source without a current limiting feature as is common.

If the 120A or 180A version was not adjustable in its current limiting feature, then those models would be useless for this use case, you'd be forced to buy the 60A unit specifically, and in future when using your bank with a source that can handle larger currents drawn, upgrade then, wasting money.

But since Charles does include the valuable feature of adjusting the current limit, you are now free to spend more on the higher capacity units, and be ready to move your bank to another boat, or use it on your expo truck or as a power bank at home, adjusting the current limited rate to different sources as needed.

Sure if you prefer to spend all that money on refitting that one alternator with a quality VR, nothing wrong with that, but that only fixes the problem for that one source on that one boat.

And since your LFP will last much longer than most people keep any one boat, that money (maybe with new pulley/belts too) will need to be spent every time.

The DCDC becomes a "front end" charge regulator for the bank, used on a large variety of energy inputs, no need to replace the sources everywhere you go.

Again, I am **not** advocating any one solution over another, depends on each use case's factors.

Just trying to show, again, that the ability to limit current, is one of the main **reasons** Charles developed the technology and often why DCDC chargers are purchased. In many cases higher currents will simply do no good, or an alternative VR is unsuitable or impossible to fit.

Also making the point, that the ability to scale that current limiting rate up and down as needed - as ambient temperatures change for example - is one of the main USPs of the Sterling BB series, along with the user-custom adjustable voltage setpoints.

Sorry, to be so repetitive but I am still not convinced.

I hear what you are saying but I cant see what practical reason you would use this.

Obviously a B2B, being DC DC, is not applicable to an AC charger charging source. I guess you could put a B2B in between an AC charger and a batt. But I cant see why. Assuming your AC charger is adjustable. I have a Sterling Procharge and it works fine.

Solar panels dont need protecting like Alternator sometimes can.

I assume most of us have Solar charge controllers which do everything needed on the solar side. I personally have 4x 15/75 Bluesea MPPTs and they work fine.

I cant see why you would put a B2B in between an MPPT and a battery.

Are you suggesting not to use Solar controllers?

Hence mostly I see Alternators regulated with VRs like 614 etc.

I really am open to a new possibility and way of doing things but I just cant see why you would practically do what you are suggesting.

I have never seen or heard of this before. You are certainly 'inovative'.

Can you show us an example of where this is actually done?

[john61ct]

Nothing at all innovative here, virtually **every** LFP install that uses a DCDC charger or specialized VR relies on its current limiting feature - it would be a very rare bank that could effectively charge off an alt without that, besides maybe a rate-crippled drop-in whose internal circuitry includes the CL feature, to excess.

Even with a tiny bank that couldn't harm or shut down a stock alt's charging, the rate it pulls would be way too high for the bank's own health.

Parse these first, look for current limiting, alt overheating, "derating"
https://marinehowto.com/lifepo4-batteries-on-boats

https://marinehowto.com/automotive-a...cle-batteries/

Then this from PKSYS https://shop.pkys.com/Alternator-Lithium-Battery.html

Also the data sheets and marketing materials for every external voltage regulator, not just Balmar, but Mark Grasser, the new Wakespeed WS100 and American Power Systems AP500 (I believe both evolved out of @thomasow 's open source project ) etc

e.g. from Nordkyn's VRC-200:
**Active Current Limiting** allows keeping the charge current within the alternator continuous output capability without overheating for reliability and long service life. It also means higher sustained output at low RPM than what is experienced with traditional controllers that blindly reduce the field current.

See Battle Born's website, for customers who think the Sterling B2B is too costly, then the only alternative they recommend (!) is Precision Circuits' "battery isolation manager" that "solves" the overheating problem by duty cycle the alternator 15 minutes on to 20 minutes off, not ideal 8-)

Anywhere alternator overheating and shutting down for safety comes up, Maine Sail makes this point, here's a pretty intact quote from my notes:

______
use "belt manager" to limit the field output and essentially limit the alt output, derate the alternator. It will essentially set a current limit below the alts max output.

"load the alt" to send it into bulk mode and keep it there to heat up the alt and adjust the regulator settings to find your max safe output.

Derate the alternator in belt manager until you find the max continuous output the alt can run at and remain below 225F.... Contrary to popular misconception this is not robbing you of alt output it is actually maximizing the maximum safe limit the alt can physically run at continuously in YOUR engine room. Derating the alt will give you an alternator that can run at the new output all day long and not cook itself.

You NEVER get full output from an alt anyway but pushing them hard, as you are doing, will only lead to an eventual failure... Even high dollar, high output alts benefit from purposely over-sizing them then derating them in belt manager..

As an example the 160A high output alt in our boat is set to a max of 110A-115A. This is simply the most it can run at, in our engine compartment, without exceeding 225F, and I have cooling ducts to help the engine bay stay cooler.

[john61ct]

Originally Posted by Q Xopa

Obviously a B2B, being DC DC, is not applicable to an AC charger charging source. I guess you could put a B2B in between an AC charger and a batt. But I cant see why. Assuming your AC charger is adjustable.

Once you have an appropriately sized DCDC charger to front your LFP bank, you no longer need to worry about the quality of the charge sources up stream from it.

Plug it into the output from any old nominal 12V source, dumb converter or charger, PWMsolar or wind controller as well as DC genset or random alternator.

Yes this ability is not relevant for a bank that stays put where all the infrastructure's already been upgraded at great expense.

But for those who are designing for a planned LFP upfit, this approach can be very cost effective and give great flexibility.

The B2B in effect becomes part of the bank, not tied to any specific location or charge source.

[CatNewBee]

For my setup it would be throwing money out of the window, so I opted against two B2B regulators.

Here's the reason why

We rarely motor, we use to sail, so the contribution of the alternators is neglectable. They are weak, 2 small 40hp Yanmar engines with stock alternators.

There are isolation diodes in place on each side to separate start battery from the house battery, what makes it possible to safely disconnect the house bank without run off of the alternators, the corresponding AGM start battery remains connected.

The alternators yeld a maximum voltage of 14.2V, safe for the LFP any way.

We use to motor, if at all, at 1500..1800rpm, the alternators run on low rpm and yeld about 40A to the house, not much for a 1000Ah battery. To drive a current, there must be a voltage difference between the source and the battery, LFP batteries use to be around 13.2.. 13.4V most of the time, so there is not a big push from the alternator anyway.

I opted to limit the legacy sources to 95% SOC controlled by the Victron BMV.

So no need for B2B chargers at all.

If I would want to charge the house bank from the engines, I would rather spend the money on larger and better alternators than on B2B chargers.

BUT this are the arguments pro b2b chargers:

Running on low rpm they can transform the input to a higher voltage and push / divert energy from the alternator and start battery to the house bank, priori zing their charge.

They can effectively control the charge profile, to make a real IUoU cycle in contrast to dumb alternators W - profile.

They also limit the charge current by their own limitations and also isolate the batteries effectively.

In my opinion, there is no need to protect a alternator from a LFP bank, if an alternator fails, it would have failed with a GEL, AGM or FLA bank too. If one dies eventually, I would replace it with one with an external regulator. But as I said, no use for my sailing habits at all.

[Q Xopa]

Originally Posted by john61ct

Once you have an appropriately sized DCDC charger to front your LFP bank, you no longer need to worry about the quality of the charge sources up stream from it.

Plug it into the output from any old nominal 12V source, dumb converter or charger, PWMsolar or wind controller as well as DC genset or random alternator.

Yes this ability is not relevant for a bank that stays put where all the infrastructure's already been upgraded at great expense.

But for those who are designing for a planned LFP upfit, this approach can be very cost effective and give great flexibility.

The B2B in effect becomes part of the bank, not tied to any specific location or charge source.

Im not arguing with any of the references you posted. They are very good information. Indeed I have read all of those previously, some many times. Obviously my memory and or comprehension is not so good.

But I didnt see any of them saying what you are saying they recommend using a B2B to reduce amperage to save alternators. Maybe I missed it?

And yes I also agree that that if you have a B2B downstream of all your other charge sources then it doesnt matter if those other charge sources are good or not as the B2B will make sure its not too much.

But if you want to charge at more than 60A then unless you double up your B2Bs it wont work. This is the case for the majority of LFP owners.

At the 60A B2B limit that is less than 0.3C for a 200AH LFP bank. This is the smaller end of most LFP banks. This is less than the normally recommended min charge rate. Apart from that is going to be a painfully slow 3ish hour engine run recharge time at max tilt.

This isnt usually what most people have in mind when they think of getting a LFP setup.

If you want to use a B2B to regulate your Alternator, yes it will work, be my guest.

But most use a VR, 614 etc to regulate their Alternator. As indeed all of your references recommend.

Yes I'm aware of, and have a number of the 'open source regulator' you mention. They are great and IMHO better than anything else available.

Yes you are right about many, certainly not most though, LFP installations using a B2B. In fact that's exactly why I have one in preparation for my LFP fit.

But its not there to save the Alternator. That's what my VRs do. I haven't skimped on my Alternators going for large case 24V 110A units, but they were less than the cost of a B2B. The large case 12V 200A units are the same price. But again thats another story.

So to me it doesnt make sense on many levels.

I've got my B2B, as I assume have most others, to charge the Start battery which is a different chemistry FLA.

Mine is also to drop the voltage from 24 to 12V, but that's another story.

[tanglewood]

I can see how a DC/DC charger is an alternative to a programmable alternator regulator. But do keep in mind that some alternators are indeed continuous duty rated, and can be run at full field as long as you want. But I understand many are not, especially smaller frame alternators, and especially in poorly ventilated engine compartments in sail boats. After all, that's why the "belt manager" feature is in the Balmar regulators.


But other charge sources I don't think need to have their output load reduced for LFP, as they are self regulating. Any sort of electronic charger is self limiting, like a solar charger, mains charger, or charger in an inverter/charger. A wind charger is fundamentally an alternator, but I would be surprised if it's not continuous duty rated since it's use is very different from an alternator designed to recharge a start battery.


I also think there is a fundamental issue with using a DC/DC charger as an intervening device between some other charger and a battery. Most expect to be connected to a battery that maintains voltage. But a typical DC/DC charger is not bidirectional, so will not maintain voltage at the input. The solar chargers I've used won't even power up if they are not connected to a steady battery voltage.


So John, have you built any of this? Because I'm pretty sure it won't work in a bunch of cases.


And do you plan to tie together all the outputs of these various chargers, and connect all to the inputs of this DC/DC charger? Or would you use one charger per device?


And all of this is really just a work around for charge sources that can't be programmed or controlled, or where the builder is too lazy to figure it all out.


So I can understand this as an alternative to an alternator regulator, but personally I'd rather fix the root problem that add another intervening device that will only reduce overall reliability, require more spares, etc.

[john61ct]

Yes, each use case and combination of owner preferences is different, what some might think is the "majority" profile, the idea of one size fits all, is not a relevant issue for me.

I certainly have never thought a B2B is needed for most LFP setups for whatever reason, and personally think using one to charge a Starter bank is overkill.

Originally Posted by tanglewood

I'm pretty sure it won't work in a bunch of cases.

You'd need to give a specific scenario, not sure what you mean by "won't work".

No one's claimed DC-DC chargers are bidirectional, and that has nothing to do with any of the functionality required, to allow the target battery to be precisely charged as quickly as possible.

The Sterling B2B specifically are designed to do this by manipulating the V/A "seen" by a dumb VR, mimicking a battery just thirsty enough to get the steady input it needs.

Not sure what you mean by a "typical DC/DC charger", since I would only bother with those allowing precise user customization of the charge profile.

_____
How important the alternator's contribution to overall energy inputs is certainly a major factor here. The 40A that CNB considers unimportant, may make all the difference for another owner, or even act as the primary input.

Investing in an alternator upgrade that includes an external current-limiting VR may very well eliminate the need for a DC-DC unit completely.

My point was simply that that the current **does** need to get limited, and in some cases the DC-DC option can be used to achieve that. As opposed to the claim that its ability to regulate **voltage** is its only raison d'être.

Nor is preventing damage to the alternator the **only** reason current-limiting is required.

Originally Posted by CatNewBee

In my opinion, there is no need to protect a alternator from a LFP bank, if an alternator fails, it would have failed with a GEL, AGM or FLA bank too.

There is no question that it is the **self** limiting nature of lead banks that has allowed industry to historically ignore the need for current limiting in its stock VR's design.

Out of the THREE problems that function solves, "amps too high for the health of the bank" really only arises with the **much higher** CAR of LI chemistry.

Sure, a "relatively high for lead" CAR AGM bank, once they get sized to a very large Ah capacity, can also require limiting current, but usually to solve the second problem of "poor charging output due to inelegant handling of overcurrent / overheating conditions."

The third possible issue, of actual **damage** inflicted on the alt or its diodes by changing over to LFP, obviously only happens when the alt/VR setup's handling of overcurrent / overheating is grossly inadequate, not just "inelegant".

It is true that some alt setups can put out rated amps 24x7, but usually such is not provided stock.

And with higher-CAR chemistries becoming much more common in recent decades, that phenomenon may become increasingly rare for those buying boats with relatively modern engine setups.

_______
For the use case where alternator charging is very important to the overall inputs, **and** existing current output is inadequate, then the owner may - if possible - choose to upgrade the alt setup.

The need to stack B2Bs to get past 60A is only required if you believe precise setpoint regulation for LFP longevity is an important feature. The BBW series goes up to 120A per unit for those who think letting output sit at higher than 13.8V, even 14.4V is OK.

Originally Posted by Q Xopa

At the 60A B2B limit that is less than 0.3C for a 200AH LFP bank. This is the smaller end of most LFP banks. This is less than the normally recommended min charge rate.

Maine Sail slapped me down pretty hard for recommending much higher than that, as rgleason will recall 8-)

The longevity hit of going to up to say .5C may be worth it to some, but that is not something I recommend anymore for normal usage.

0.3C is now my upper limit, but I still try to design to allow as high as 1C when possible, for (hopefully only occasionally) when fast charging is required.

> Yes I'm aware of, and have a number of the 'open source regulator' you mention. They are great and IMHO better than anything else available.

If you could point to relevant projects that are still FOSS I'd appreciate it.

Originally Posted by tanglewood

I can see how a DC/DC charger is an alternative to a programmable alternator regulator. But do keep in mind that some alternators are indeed continuous duty rated, and can be run at full field as long as you want. But I understand many are not, especially smaller frame alternators, and especially in poorly ventilated engine compartments in sail boats. After all, that's why the "belt manager" feature is in the Balmar regulators.

The continuous duty rated issue may be relevant to the health of the upstream power source, but still does not protect the LFP bank from its ability to draw current at too high a rate.

For example, a 12kW supply would damage most LFP banks if there is no current limiting circuitry somewhere in between.

Originally Posted by tanglewood

other charge sources I don't think need to have their output load reduced for LFP, as they are self regulating

What is true, and obvious, is that current-limiting is not required for sources that already include that feature.

And certainly many, but not all modern devices designed to charge batteries do so.

The beauty of a DC-DC charger is that it lets you precisely charge your bank according to (whatever your perception of) its needs from any old DC power source. Or indeed from the combined output of multiple such sources as appropriate.

Whether or not they are designed to charge batteries.

For example even very sophisticated and powerful power supplies and DC-DC converters do not explicitly limit current. They may protect themselves via one of the many industry accepted OCP handling methods, but they don't maintain their voltage setpoint while doing so.

Now, for those already owning say MPPT chargers that are already perfectly suited to your LFP bank, of course there is no point to running their output through a DC-DC charger.

Buying multiple such units is only required if you need to handle greater current output.

> all of this is really just a work around for charge sources that can't be programmed or controlled

My POV is, that it frees you from the need to worry about those issues wrt every possible charge source, in effect delivers on the (often false) promise of drop-in convenience and cost savings

without all the limitations inherent in many drop-in implementations

allowing you to get those benefits, while also buying known-good cells from one of the top-notch makers,

and giving you the flexibility to sacrifice cycle lifetime off the back end in a controlled fashion, when you the owner decide high C-rate charging is important enough.

[Q Xopa]

Originally Posted by john61ct

Yes, each use case and combination of owner preferences is different, what some might think is the "majority" profile, the idea of one size fits all, is not a relevant issue for me.

I certainly have never thought a B2B is needed for most LFP setups for whatever reason, and personally think using one to charge a Starter bank is overkill.

You'd need to give a specific scenario, not sure what you mean by "won't work".

No one's claimed DC-DC chargers are bidirectional, and that has nothing to do with any of the functionality required, to allow the target battery to be precisely charged as quickly as possible.

The Sterling B2B specifically are designed to do this by manipulating the V/A "seen" by a dumb VR, mimicking a battery just thirsty enough to get the steady input it needs.

Not sure what you mean by a "typical DC/DC charger", since I would only bother with those allowing precise user customization of the charge profile.

_____
How important the alternator's contribution to overall energy inputs is certainly a major factor here. The 40A that CNB considers unimportant, may make all the difference for another owner, or even act as the primary input.

Investing in an alternator upgrade that includes an external current-limiting VR may very well eliminate the need for a DC-DC unit completely.

My point was simply that that the current **does** need to get limited, and in some cases the DC-DC option can be used to achieve that. As opposed to the claim that its ability to regulate **voltage** is its only raison d'être.

Nor is preventing damage to the alternator the **only** reason current-limiting is required.

There is no question that it is the **self** limiting nature of lead banks that has allowed industry to historically ignore the need for current limiting in its stock VR's design.

Out of the THREE problems that function solves, "amps too high for the health of the bank" really only arises with the **much higher** CAR of LI chemistry.

Sure, a "relatively high for lead" CAR AGM bank, once they get sized to a very large Ah capacity, can also require limiting current, but usually to solve the second problem of "poor charging output due to inelegant handling of overcurrent / overheating conditions."

The third possible issue, of actual **damage** inflicted on the alt or its diodes by changing over to LFP, obviously only happens when the alt/VR setup's handling of overcurrent / overheating is grossly inadequate, not just "inelegant".

It is true that some alt setups can put out rated amps 24x7, but usually such is not provided stock.

And with higher-CAR chemistries becoming much more common in recent decades, that phenomenon may become increasingly rare for those buying boats with relatively modern engine setups.

_______
For the use case where alternator charging is very important to the overall inputs, **and** existing current output is inadequate, then the owner may - if possible - choose to upgrade the alt setup.

The need to stack B2Bs to get past 60A is only required if you believe precise setpoint regulation for LFP longevity is an important feature. The BBW series goes up to 120A per unit for those who think letting output sit at higher than 13.8V, even 14.4V is OK.

Maine Sail slapped me down pretty hard for recommending much higher than that, as rgleason will recall 8-)

The longevity hit of going to up to say .5C may be worth it to some, but that is not something I recommend anymore for normal usage.

0.3C is now my upper limit, but I still try to design to allow as high as 1C when possible, for (hopefully only occasionally) when fast charging is required.

> Yes I'm aware of, and have a number of the 'open source regulator' you mention. They are great and IMHO better than anything else available.

If you could point to relevant projects that are still FOSS I'd appreciate it.

The continuous duty rated issue may be relevant to the health of the upstream power source, but still does not protect the LFP bank from its ability to draw current at too high a rate.

For example, a 12kW supply would damage most LFP banks if there is no current limiting circuitry somewhere in between.

What is true, and obvious, is that current-limiting is not required for sources that already include that feature.

And certainly many, but not all modern devices designed to charge batteries do so.

The beauty of a DC-DC charger is that it lets you precisely charge your bank according to (whatever your perception of) its needs from any old DC power source. Or indeed from the combined output of multiple such sources as appropriate.

Whether or not they are designed to charge batteries.

For example even very sophisticated and powerful power supplies and DC-DC converters do not explicitly limit current. They may protect themselves via one of the many industry accepted OCP handling methods, but they don't maintain their voltage setpoint while doing so.

Now, for those already owning say MPPT chargers that are already perfectly suited to your LFP bank, of course there is no point to running their output through a DC-DC charger.

Buying multiple such units is only required if you need to handle greater current output.

> all of this is really just a work around for charge sources that can't be programmed or controlled

My POV is, that it frees you from the need to worry about those issues wrt every possible charge source, in effect delivers on the (often false) promise of drop-in convenience and cost savings

without all the limitations inherent in many drop-in implementations

allowing you to get those benefits, while also buying known-good cells from one of the top-notch makers,

and giving you the flexibility to sacrifice cycle lifetime off the back end in a controlled fashion, when you the owner decide high C-rate charging is important enough.

Ok I give up, you win.

I agree the B2B sounds perfect for you.

[Q Xopa]

Originally Posted by john61ct

Yes, each use case and combination of owner preferences is different, what some might think is the "majority" profile, the idea of one size fits all, is not a relevant issue for me.

I certainly have never thought a B2B is needed for most LFP setups for whatever reason, and personally think using one to charge a Starter bank is overkill.

You'd need to give a specific scenario, not sure what you mean by "won't work".

No one's claimed DC-DC chargers are bidirectional, and that has nothing to do with any of the functionality required, to allow the target battery to be precisely charged as quickly as possible.

The Sterling B2B specifically are designed to do this by manipulating the V/A "seen" by a dumb VR, mimicking a battery just thirsty enough to get the steady input it needs.

Not sure what you mean by a "typical DC/DC charger", since I would only bother with those allowing precise user customization of the charge profile.

_____
How important the alternator's contribution to overall energy inputs is certainly a major factor here. The 40A that CNB considers unimportant, may make all the difference for another owner, or even act as the primary input.

Investing in an alternator upgrade that includes an external current-limiting VR may very well eliminate the need for a DC-DC unit completely.

My point was simply that that the current **does** need to get limited, and in some cases the DC-DC option can be used to achieve that. As opposed to the claim that its ability to regulate **voltage** is its only raison d'être.

Nor is preventing damage to the alternator the **only** reason current-limiting is required.

There is no question that it is the **self** limiting nature of lead banks that has allowed industry to historically ignore the need for current limiting in its stock VR's design.

Out of the THREE problems that function solves, "amps too high for the health of the bank" really only arises with the **much higher** CAR of LI chemistry.

Sure, a "relatively high for lead" CAR AGM bank, once they get sized to a very large Ah capacity, can also require limiting current, but usually to solve the second problem of "poor charging output due to inelegant handling of overcurrent / overheating conditions."

The third possible issue, of actual **damage** inflicted on the alt or its diodes by changing over to LFP, obviously only happens when the alt/VR setup's handling of overcurrent / overheating is grossly inadequate, not just "inelegant".

It is true that some alt setups can put out rated amps 24x7, but usually such is not provided stock.

And with higher-CAR chemistries becoming much more common in recent decades, that phenomenon may become increasingly rare for those buying boats with relatively modern engine setups.

_______
For the use case where alternator charging is very important to the overall inputs, **and** existing current output is inadequate, then the owner may - if possible - choose to upgrade the alt setup.

The need to stack B2Bs to get past 60A is only required if you believe precise setpoint regulation for LFP longevity is an important feature. The BBW series goes up to 120A per unit for those who think letting output sit at higher than 13.8V, even 14.4V is OK.

Maine Sail slapped me down pretty hard for recommending much higher than that, as rgleason will recall 8-)

The longevity hit of going to up to say .5C may be worth it to some, but that is not something I recommend anymore for normal usage.

0.3C is now my upper limit, but I still try to design to allow as high as 1C when possible, for (hopefully only occasionally) when fast charging is required.

> Yes I'm aware of, and have a number of the 'open source regulator' you mention. They are great and IMHO better than anything else available.

If you could point to relevant projects that are still FOSS I'd appreciate it.

The continuous duty rated issue may be relevant to the health of the upstream power source, but still does not protect the LFP bank from its ability to draw current at too high a rate.

For example, a 12kW supply would damage most LFP banks if there is no current limiting circuitry somewhere in between.

What is true, and obvious, is that current-limiting is not required for sources that already include that feature.

And certainly many, but not all modern devices designed to charge batteries do so.

The beauty of a DC-DC charger is that it lets you precisely charge your bank according to (whatever your perception of) its needs from any old DC power source. Or indeed from the combined output of multiple such sources as appropriate.

Whether or not they are designed to charge batteries.

For example even very sophisticated and powerful power supplies and DC-DC converters do not explicitly limit current. They may protect themselves via one of the many industry accepted OCP handling methods, but they don't maintain their voltage setpoint while doing so.

Now, for those already owning say MPPT chargers that are already perfectly suited to your LFP bank, of course there is no point to running their output through a DC-DC charger.

Buying multiple such units is only required if you need to handle greater current output.

> all of this is really just a work around for charge sources that can't be programmed or controlled

My POV is, that it frees you from the need to worry about those issues wrt every possible charge source, in effect delivers on the (often false) promise of drop-in convenience and cost savings

without all the limitations inherent in many drop-in implementations

allowing you to get those benefits, while also buying known-good cells from one of the top-notch makers,

and giving you the flexibility to sacrifice cycle lifetime off the back end in a controlled fashion, when you the owner decide high C-rate charging is important enough.

So how would you charge a Start battery if a B2B is a waste?

For me using an Alternator is a waste.

A Start batt is charged in minutes. If you use an Alternator you only get minutes use out of it then it just sits there doing nothing but spinning most of the time. Sounds like a wasted use, or lack of, resource to me. In my case it is a 110A 24V resource.

If you use a B2B, you can use that additional Alternator to feed the main house bank, which is where the majority of the charging is required.

In fact I have got my-
Alternators,
Solor controllers, and my
AC charger
All charging my Main house bank.

The only thing that charges my Start batt is the B2B. 60A is more than adequate for this.

A B2B isnt actually a charge 'source', it simply converts DC current from another source.

[john61ct]

Originally Posted by Q Xopa

Ok I give up, you win.

I have no concern about any "winning", would prefer to be able to not even be aware of the personal aspect in such a medium.

Prefer to focus on the facts, accuracy of communications.

> I agree the B2B sounds perfect for you.

Again, I try to avoid being a fan-boy for any device or technique.

I only felt compelled to defend their use **as an option** from mistaken overly general misconceptions.

Originally Posted by Q Xopa

So how would you charge a Start battery if a B2B is a waste?

Depends on the setup. Many don't even need dedicated Starter batt(s). But they are usually so resilient and cheap, strictly economically speaking spending much more than maybe $50 is IMO overkill.

There are hundreds of solutions on the market in that price range. Including cheaper other-brand DCDC chargers, if you really think that's justified.

Others will feel differently and choose accordingly.

_______
Yes dedicating an alt's output to just Starter is even more overkill than a DC-DC charger.

But then some like CNB have so much input from other sources they can afford to just ignore the alternators.

They really don't cost much being allowed to spin unloaded.

Originally Posted by Q Xopa

A B2B isnt actually a charge 'source', it simply converts DC current from another source.

Well ultimately the sun is the only true source, after that everything, even dino juice, is conversion/inversion/transforming.

[Q Xopa]

Originally Posted by john61ct

I have no concern about any "winning", would prefer to be able to not even be aware of the personal aspect in such a medium.

Prefer to focus on the facts, accuracy of communications.

> I agree the B2B sounds perfect for you.

Again, I try to avoid being a fan-boy for any device or technique.

I only felt compelled to defend their use **as an option** from mistaken overly general misconceptions.

Depends on the setup. Many don't even need dedicated Starter batt(s). But they are usually so resilient and cheap, strictly economically speaking spending much more than maybe $50 is IMO overkill.

There are hundreds of solutions on the market in that price range. Including cheaper other-brand DCDC chargers, if you really think that's justified.

Others will feel differently and choose accordingly.

_______
Yes dedicating an alt's output to just Starter is even more overkill than a DC-DC charger.

But then some like CNB have so much input from other sources they can afford to just ignore the alternators.

They really don't cost much being allowed to spin unloaded.

Well ultimately the sun is the only true source, after that everything is conversion/inversion/transforming.

The cost of a spinning alternator not charging anything to me is lost opportunity cost. I can make 110A at 24V (2.6kW) if I use it nothing if I dont. This is not very little 'cost' to me.

When you say it depends on the setup, I gave you lots of details of mine, which is the example I mentioned.

As for a cheap B2B. Being that I only have one charge source to get my Engine starting capability charged, I'm happy to spring for the name brand. So I dont consider it a waste.

Now I think about this more perhaps I need another cheap back up charger?

If you want to risk the cheaper stuff no arguments from me.

Is this the same person that says you wont consider anything but UL rated wires etc?

[CatNewBee]

True, and my alternators do not spin most of the time.

I would probably not even notice if they fail, because the start batteries are also being charged by solar. Main function of the alternators here is to tighten the v-belt for the water pump... [emoji12]