Question On Battery Charging

[GeneraiT001]

Still trying to get my thought methodology straight on this. Assuming the following:

Scenario #1
I have a high output alternator + external regulator (set to 50% of its charging ability). This is connected to the Lead Acid Battery for charging. The Lead Acid Battery connects to a DC-DC charger that also connects to a Lithium bank (house battery). So, in this scenario, the DC-DC charger will charge the Lithium once the Lead Acid Battery is "full" and there is no chance that the alternator can "explode" due to a sudden energy spike.

Will the DC-DC charger provide enough amperage to charge the Lithium battery effectively "quickly"? Is this the standard setup for this scenario?

Scenario #2
Instead of charging the Lead Acid Battery the alternator (through the external regulator) charges the Lithium battery and then a DC-DC charger connects to the Lead Acid Battery for charging. The danger (I think) is that there is no protection for the alternator once the Lithium battery is full and the BMS stops accepting more charge resulting in an alternator catastrophe. Is this correct?

Is there a way to protect the alternator is this scenario? Is there a device (the Wakefield 500?) that can sense that the Lithium has stopped accepting a charge and can prevent the resulting energy spike from destroying the alternator.

I'm guessing the more prudent scenario is scenario #1...but it seems like you cannot take full advantage of that high output alternator via a DC-DC charger in that setup? Hopefully I'm wrong (again)

 

[Cap'n Deke]

The two scenarios aren’t created equal, and one of them has a way of turning a fine alternator into an expensive paperweight.

On your first setup:
That’s the traditional “be kind to the alternator” arrangement. The lead-acid sits as the shock absorber, and the DC-DC charger minds the lithium bank. It’s not elegant, but it’s steady.

The catch, as you already smelled, is that the DC-DC charger becomes the choke point. A 60- or 80-amp alternator can’t shove its full enthusiasm through a 30- or 40-amp DC-DC. The lithium will charge, but never as quickly as the alternator could deliver. If you’re running big loads underway, you’ll feel the shortfall.

Still—it’s safe, predictable, and the alternator sleeps well at night.

On your second setup:
This is where many alternators go to Valhalla.

An alternator shoving straight into lithium will try to give everything it has, for as long as the battery will take it. When the BMS slams the door - which it will (or should), and usually without warning - the alternator loses its load instantly. That’s the part that cooks diodes for breakfast.

You’re correct: without protection, that's a failure mode waiting to happen.

There are ways to protect the alternator in this arrangement, but they’re not magic charms.

A WakeSpeed WS500 (not Wakefield) can handle this - if it has a reliable current shunt and a charge-acceptance signal from the BMS. The WS500 can back the alternator down gracefully instead of letting it run blind. But the system has to be wired and configured correctly. Miss a setting, lose a communication line, or rely on Bluetooth, and the alternator is back to living dangerously.

So which is the prudent path?
Scenario #1 is the safe, conservative, old-salt approach.
Scenario #2 is the high-performance, high-risk approach that only works if you build a proper communication loop between the alternator regulator and the lithium BMS. If you half-do it, you’re rolling dice with hot metal.

Your instinct is sound: #1 will always keep the alternator alive, but you’ll never see the full output you paid for. #2 can give you everything the alternator has, but only if you treat it like a whole system rather than a collection of parts.

If it helps, I’ve run both kinds over the years. I'd stick with #1 when reliability matters, and #2 only if I’ve built the system myself and can hear it in my sleep.

 

[dLj]

The two scenarios aren’t created equal, and one of them has a way of turning a fine alternator into an expensive paperweight.

On your first setup:
That’s the traditional “be kind to the alternator” arrangement. The lead-acid sits as the shock absorber, and the DC-DC charger minds the lithium bank. It’s not elegant, but it’s steady.

The catch, as you already smelled, is that the DC-DC charger becomes the choke point. A 60- or 80-amp alternator can’t shove its full enthusiasm through a 30- or 40-amp DC-DC. The lithium will charge, but never as quickly as the alternator could deliver. If you’re running big loads underway, you’ll feel the shortfall.

Still—it’s safe, predictable, and the alternator sleeps well at night.

On your second setup:
This is where many alternators go to Valhalla.

An alternator shoving straight into lithium will try to give everything it has, for as long as the battery will take it. When the BMS slams the door - which it will (or should), and usually without warning - the alternator loses its load instantly. That’s the part that cooks diodes for breakfast.

You’re correct: without protection, that's a failure mode waiting to happen.

There are ways to protect the alternator in this arrangement, but they’re not magic charms.

A WakeSpeed WS500 (not Wakefield) can handle this - if it has a reliable current shunt and a charge-acceptance signal from the BMS. The WS500 can back the alternator down gracefully instead of letting it run blind. But the system has to be wired and configured correctly. Miss a setting, lose a communication line, or rely on Bluetooth, and the alternator is back to living dangerously.

So which is the prudent path?
Scenario #1 is the safe, conservative, old-salt approach.
Scenario #2 is the high-performance, high-risk approach that only works if you build a proper communication loop between the alternator regulator and the lithium BMS. If you half-do it, you’re rolling dice with hot metal.

Your instinct is sound: #1 will always keep the alternator alive, but you’ll never see the full output you paid for. #2 can give you everything the alternator has, but only if you treat it like a whole system rather than a collection of parts.

If it helps, I’ve run both kinds over the years. I'd stick with #1 when reliability matters, and #2 only if I’ve built the system myself and can hear it in my sleep.

With all due respect, I strongly disagree. I'll say more below.

Still trying to get my thought methodology straight on this. Assuming the following:

Scenario #1
I have a high output alternator + external regulator (set to 50% of its charging ability). This is connected to the Lead Acid Battery for charging. The Lead Acid Battery connects to a DC-DC charger that also connects to a Lithium bank (house battery). So, in this scenario, the DC-DC charger will charge the Lithium once the Lead Acid Battery is "full" and there is no chance that the alternator can "explode" due to a sudden energy spike.

Will the DC-DC charger provide enough amperage to charge the Lithium battery effectively "quickly"? Is this the standard setup for this scenario?

You pretty much don't need a high output externally regulated alternator for this scenario. This method is commonly done where folks are trying to not spend the money on that equipment. You can't charge you LFP batteries at anywhere near the rate you could if not using this set-up.

Scenario #2

Instead of charging the Lead Acid Battery the alternator (through the external regulator) charges the Lithium battery and then a DC-DC charger connects to the Lead Acid Battery for charging. The danger (I think) is that there is no protection for the alternator once the Lithium battery is full and the BMS stops accepting more charge resulting in an alternator catastrophe. Is this correct?

The external regulation devices sense the fully charged battery before the internal LFP BMS shuts the system down and bring the charging amps down so that this doesn't happen. I personally prefer using the Wakespeed 500 (or the Wakespeed 500 pro) but I understand the Zeus is also similar - see the conversation in your other thread - Dave mentioned the differences between the Balmar devices and these two.

Is there a way to protect the alternator is this scenario? Is there a device (the Wakefield 500?) that can sense that the Lithium has stopped accepting a charge and can prevent the resulting energy spike from destroying the alternator.

As an additional failsafe in my system, I have a Sterling Power Alternator Protection Device connected to each of my alternators.

I run my alternators at 75% of full power (not the 50% you mentioned above).

I'm guessing the more prudent scenario is scenario #1...but it seems like you cannot take full advantage of that high output alternator via a DC-DC charger in that setup? Hopefully I'm wrong (again)

In my opinion, scenario 2 is absolutely the best way to do it. There is a long list of reasons why...

dj

 

[Cap'n Deke]

In my opinion, scenario 2 is absolutely the best way to do it. There is a long list of reasons why...

If the alternator regulator and the lithium BMS are in proper conversation, then yes - running the alternator straight into the lithium bank can be a beautiful, efficient system. (That's what I currently have.) But that whole arrangement hangs on good communication, good wiring, and good failsafes. Miss any one of those and you’re depending on luck to save your diodes.

So, I’m genuinely curious what your list of reasons looks like. If there’s a safer or more elegant way to tame that setup than I’ve seen, I’d be glad to hear it. I've learned to stay suspicious of "best" solutions and more so of "absolutely the best". There are pros and cons of both strategies.

What are the advantages you’re leaning on besides efficiency? Efficiency is only a concern if it is required and it isn't always. If you run your engine two hours a day and you only need an hour of inefficient charging, it doesn't matter. If you only fire up your engine as-needed to charge batteries, it's worth paying more attention to efficiency.

The word "best" should be treated with some suspicion on boats - "absolutely the best" even more so. Maybe you could share some of those reasons? There are pros and cons with both approaches. You would be hard-pressed to make the case that one is absolutely the best, but I'm happy to be proven wrong. I was wrong once before and I got over it.

 

[dlochner]

Scenario #1
I have a high output alternator + external regulator (set to 50% of its charging ability). This is connected to the Lead Acid Battery for charging. The Lead Acid Battery connects to a DC-DC charger that also connects to a Lithium bank (house battery). So, in this scenario, the DC-DC charger will charge the Lithium once the Lead Acid Battery is "full" and there is no chance that the alternator can "explode" due to a sudden energy spike.

Most of this is correct. The charging isn't sequential, i.e., the battery charges first and then the DC-DC gets the current. Electricity is lazy, it always takes the path of least resistance. The start battery, once fully charged pretty much stays that way in either scenario. Starting an engine takes a lot of amps for a very short time. The net effect is that very little of the battery's charge is actually used, sometime less than 1 ah. Do the math, 300 a for 5 seconds is 60 amp seconds, which is 1 amp minute, or 1/60 of an amp hour. (no guarantees on perfect math, but the concept is right). Since the battery is near 100% SOC, the battery's resistance is very high. More electrons, being lazy, will prefer to go through the DC-DC charger with less resistance than to the battery. The result is both batteries are charged simultaneously.

DC-DC charging has improved over the past couple of years. Victron now makes a 50a charger which is better than the 30a charger because it is more efficient and charges the LFP batteries at a higher rate.

Scenario #2
Instead of charging the Lead Acid Battery the alternator (through the external regulator) charges the Lithium battery and then a DC-DC charger connects to the Lead Acid Battery for charging. The danger (I think) is that there is no protection for the alternator once the Lithium battery is full and the BMS stops accepting more charge resulting in an alternator catastrophe. Is this correct?

Yes, however there are ways to mitigate the negative effects of a rare BMS shutdown. See below.

Is there a way to protect the alternator is this scenario? Is there a device (the Wakefield 500?) that can sense that the Lithium has stopped accepting a charge and can prevent the resulting energy spike from destroying the alternator.

I'm guessing the more prudent scenario is scenario #1...but it seems like you cannot take full advantage of that high output alternator via a DC-DC charger in that setup? Hopefully I'm wrong (again)

There are a couple of solutions for this. The simplest and cheapest solution is an Alternator Protection Device which attaches to the alternator. The danger in this scenario is the alternator churning out power and suddenly there is no where for it to go because the BMS shut down charging. This causes a huge spike in voltage which the internal workings of the alternator can't handle, the diodes blow. An APD provides a path to ground and reduces the voltage spike. Sterling Power and Balmar make them. The cost is low about $100 USD. Cheap insurance.

The other method, which you allude to relies on a good communication link between the BMS and the regulator. A few seconds before the BMS will shut down (and isolating the battery from the charge source) it sends a signal to the regulator to cut the field current. The regulator cuts the field current, the alternator stops producing electricity, and everybody is safe and happy. Both the Wakespeed and the Zeus regulators have this ability. At this point the default standard in communication is the Victron system, this works with batteries that can communicate with the Victron system.

For your intended purposes, long cruises offshore Scenario 2 is most appropriate because you will be using a lot of electricity and the ability to recharge with the alternator quickly is important. The APD is a more economical choice than going with a more expensive Victron based system.

I chose Scenario 2 for my cruising using an APD with the Balmar 618 Regulator and a 165a Balmar regulator. This was the state of the art in 2020 when I upgraded my batteries. If I was doing the upgrade today, I would get a Zeus Regulator and Alternator and with Victron Cerbo monitoring and communication system. And that is something we haven't talked about yet, the monitoring system. It is as or more important than any other part of the electrical system.

A question for @GeneraiT001, what are your cruising plans now? Still crossing the Atlantic to the Med? Or Down the coast to Panama and up to BC?

 

[dLj]

If the alternator regulator and the lithium BMS are in proper conversation, then yes - running the alternator straight into the lithium bank can be a beautiful, efficient system. (That's what I currently have.) But that whole arrangement hangs on good communication, good wiring, and good failsafes. Miss any one of those and you’re depending on luck to save your diodes.

Did you read what I wrote on putting an Alternator Protection Device on the alternator?

Every point you state above should be adhered to no matter what system you put in.

Why would you put in crap wiring in either system?

So, I’m genuinely curious what your list of reasons looks like. If there’s a safer or more elegant way to tame that setup than I’ve seen, I’d be glad to hear it. I've learned to stay suspicious of "best" solutions and more so of "absolutely the best". There are pros and cons of both strategies.

The only "pro" in the first system that I can think of is initial cost.

What are the advantages you’re leaning on besides efficiency? Efficiency is only a concern if it is required and it isn't always. If you run your engine two hours a day and you only need an hour of inefficient charging, it doesn't matter. If you only fire up your engine as-needed to charge batteries, it's worth paying more attention to efficiency.

Why would you run your engine 2 hours every day? I wouldn't even put that into my planning... Why do that?

Maybe you could share some of those reasons? There are pros and cons with both approaches.

I've already talked at some length to this question. But I'll begin by explaining some of the fundamentals of LFP vs LA batteries.

LFP batteries provide a completely new level of energy storage on a sailboat. LFP batteries don't care about being in a PSC (partial state of charge). They can accept almost as much current as you can throw at them (with an upper limit depending upon the specific LFP). Their acceptance rate does not decrease with state of charge. Yeah sure, they shut down at full charge - easy to handle.

LA batteries increase their resistance significantly as they approach full charge so you can't charge them quickly - not to 100% full charge. LA batteries most commonly die through sulfation. Sulfation occurs whenever a LA battery is not a full charge. It takes hours to bring a LA battery from 90% to 100%. I posted a graph of this in Generals other thread on this. In order to break down sulfation in a LA battery, you perform equalization. What's required for a good equalization is as close to impossible on a sailboat to simply say it's impossible. I've also talked about this in that other thread. LA batteries also undergo self-discharge at rates that depend upon the specific batteries and especially temperature. I've also talked about this in the other thread.

Given the above, you should run all charging straight into you LFP batteries - charging from all sources, engine, solar, whatever. You then take the LFP batteries and charge them off the LFP's via a DC to DC charger. In this way you can allow the LA battery to take as long as it needs to go back to a 100% state of charge. The amount of energy needed for that last X% for the LA to achieve 100% is done automatically from the LFP and is insignificant to it's state of charge. Doing this creates a substantially better system, allowing to take advantage of the two different battery types with their pro's and con's.

Setting the system up this way also allows easier upgrading, changing or adding in charging sources.

Over say a 10 year period, it's actually less expensive to run this system including taking into consideration the different upfront costs.

It's an easier system to have on-board with a whole lot less fuss and concerns about.

And I haven't even mentioned charging efficiency...

dj

 

[dLj]

And that is something we haven't talked about yet, the monitoring system. It is as or more important than any other part of the electrical system.

I'm really glad you brought this up - absolutely this will need to be addressed...

A question for @GeneraiT001, what are your cruising plans now? Still crossing the Atlantic to the Med? Or Down the coast to Panama and up to BC?

I look forward to the answer this question.

dj

 

[dlochner]

You then take the LFP batteries and charge them off the LFP's via a DC to DC charger.

I think you meant, "take the LA batteries..."

 

[GeneraiT001]

The two scenarios aren’t created equal, and one of them has a way of turning a fine alternator into an expensive paperweight.

On your first setup:
That’s the traditional “be kind to the alternator” arrangement. The lead-acid sits as the shock absorber, and the DC-DC charger minds the lithium bank. It’s not elegant, but it’s steady.

The catch, as you already smelled, is that the DC-DC charger becomes the choke point. A 60- or 80-amp alternator can’t shove its full enthusiasm through a 30- or 40-amp DC-DC. The lithium will charge, but never as quickly as the alternator could deliver. If you’re running big loads underway, you’ll feel the shortfall.

Still—it’s safe, predictable, and the alternator sleeps well at night.

On your second setup:
This is where many alternators go to Valhalla.

An alternator shoving straight into lithium will try to give everything it has, for as long as the battery will take it. When the BMS slams the door - which it will (or should), and usually without warning - the alternator loses its load instantly. That’s the part that cooks diodes for breakfast.

You’re correct: without protection, that's a failure mode waiting to happen.

There are ways to protect the alternator in this arrangement, but they’re not magic charms.

A WakeSpeed WS500 (not Wakefield) can handle this - if it has a reliable current shunt and a charge-acceptance signal from the BMS. The WS500 can back the alternator down gracefully instead of letting it run blind. But the system has to be wired and configured correctly. Miss a setting, lose a communication line, or rely on Bluetooth, and the alternator is back to living dangerously.

So which is the prudent path?
Scenario #1 is the safe, conservative, old-salt approach.
Scenario #2 is the high-performance, high-risk approach that only works if you build a proper communication loop between the alternator regulator and the lithium BMS. If you half-do it, you’re rolling dice with hot metal.

Your instinct is sound: #1 will always keep the alternator alive, but you’ll never see the full output you paid for. #2 can give you everything the alternator has, but only if you treat it like a whole system rather than a collection of parts.

If it helps, I’ve run both kinds over the years. I'd stick with #1 when reliability matters, and #2 only if I’ve built the system myself and can hear it in my sleep.

Thanks. Great write up

 

[dLj]

I think you meant, "take the LA batteries..."

Hahaha - Thanks - yes that is correct (I can't even blame that one on autocorrect)

dj

 

[GeneraiT001]

With all due respect, I strongly disagree. I'll say more below.



You pretty much don't need a high output externally regulated alternator for this scenario. This method is commonly done where folks are trying to not spend the money on that equipment. You can't charge you LFP batteries at anywhere near the rate you could if not using this set-up.



The external regulation devices sense the fully charged battery before the internal LFP BMS shuts the system down and bring the charging amps down so that this doesn't happen. I personally prefer using the Wakespeed 500 (or the Wakespeed 500 pro) but I understand the Zeus is also similar - see the conversation in your other thread - Dave mentioned the differences between the Balmar devices and these two.



As an additional failsafe in my system, I have a Sterling Power Alternator Protection Device connected to each of my alternators.

I run my alternators at 75% of full power (not the 50% you mentioned above).


In my opinion, scenario 2 is absolutely the best way to do it. There is a long list of reasons why...

dj

Thanks. #2 is the way I'd like to go and you have alleviated some of my concerns

 

[GeneraiT001]

Most of this is correct. The charging isn't sequential, i.e., the battery charges first and then the DC-DC gets the current. Electricity is lazy, it always takes the path of least resistance. The start battery, once fully charged pretty much stays that way in either scenario. Starting an engine takes a lot of amps for a very short time. The net effect is that very little of the battery's charge is actually used, sometime less than 1 ah. Do the math, 300 a for 5 seconds is 60 amp seconds, which is 1 amp minute, or 1/60 of an amp hour. (no guarantees on perfect math, but the concept is right). Since the battery is near 100% SOC, the battery's resistance is very high. More electrons, being lazy, will prefer to go through the DC-DC charger with less resistance than to the battery. The result is both batteries are charged simultaneously.

DC-DC charging has improved over the past couple of years. Victron now makes a 50a charger which is better than the 30a charger because it is more efficient and charges the LFP batteries at a higher rate.



Yes, however there are ways to mitigate the negative effects of a rare BMS shutdown. See below.



There are a couple of solutions for this. The simplest and cheapest solution is an Alternator Protection Device which attaches to the alternator. The danger in this scenario is the alternator churning out power and suddenly there is no where for it to go because the BMS shut down charging. This causes a huge spike in voltage which the internal workings of the alternator can't handle, the diodes blow. An APD provides a path to ground and reduces the voltage spike. Sterling Power and Balmar make them. The cost is low about $100 USD. Cheap insurance.

The other method, which you allude to relies on a good communication link between the BMS and the regulator. A few seconds before the BMS will shut down (and isolating the battery from the charge source) it sends a signal to the regulator to cut the field current. The regulator cuts the field current, the alternator stops producing electricity, and everybody is safe and happy. Both the Wakespeed and the Zeus regulators have this ability. At this point the default standard in communication is the Victron system, this works with batteries that can communicate with the Victron system.

For your intended purposes, long cruises offshore Scenario 2 is most appropriate because you will be using a lot of electricity and the ability to recharge with the alternator quickly is important. The APD is a more economical choice than going with a more expensive Victron based system.

I chose Scenario 2 for my cruising using an APD with the Balmar 618 Regulator and a 165a Balmar regulator. This was the state of the art in 2020 when I upgraded my batteries. If I was doing the upgrade today, I would get a Zeus Regulator and Alternator and with Victron Cerbo monitoring and communication system. And that is something we haven't talked about yet, the monitoring system. It is as or more important than any other part of the electrical system.

A question for @GeneraiT001, what are your cruising plans now? Still crossing the Atlantic to the Med? Or Down the coast to Panama and up to BC?

Hi, Thanks for that informative write - up. This is in line with my thoughts.

Yes, still planning across the Atlantic (Azores Pit Stop) then thru the Med into Israel. Spend maybe 4 mnths in Israel and then back thru the Med down towards the Canaries and onto the Caribbean for a bit. Then down to Panama and thru the Canal and up the west coast to Nanaimo, BC. Planning on about a year to a year and a half.

 

[dlochner]

Hi, Thanks for that informative write - up. This is in line with my thoughts.

Yes, still planning across the Atlantic (Azores Pit Stop) then thru the Med into Israel. Spend maybe 4 mnths in Israel and then back thru the Med down towards the Canaries and onto the Caribbean for a bit. Then down to Panama and thru the Canal and up the west coast to Nanaimo, BC. Planning on about a year to a year and a half.

That's ambitious. Be sure to get Jimmy Cornell's World Cruising Routes (US Amazon Link).

 

[mermike]

I didn't see any mention of managing alternator temperature. As voltage control is to the batteries, temperature control is to the alternator. If you're charging LFP from an alternator, you must have a way of controlling the output of the alternator based on its temperature. The regulators I commmonly see (Wakespeed, Arco Zeus and Balmar) all have this capability. They use a thermistor which gets bolted to the alternator. My advice is to use a stainless steel clamp around the circumference to hold the thermistor against the body of the alternator where it is hottest. My 106A Ample Power alternator has been happily charging my 400AH LFP bank for over 3 years.

Note: the thermograph below was taken before I reduced the temperature limit on my Balmar 614 from 100°C to 80°C.

 

[mermike]

Hi, Thanks for that informative write - up. This is in line with my thoughts.

Yes, still planning across the Atlantic (Azores Pit Stop) then thru the Med into Israel. Spend maybe 4 mnths in Israel and then back thru the Med down towards the Canaries and onto the Caribbean for a bit. Then down to Panama and thru the Canal and up the west coast to Nanaimo, BC. Planning on about a year to a year and a half.

That's nowhere near enough time

 

[CrispyCringle]

I didn't see any mention of managing alternator temperature. As voltage control is to the batteries, temperature control is to the alternator. If you're charging LFP from an alternator, you must have a way of controlling the output of the alternator based on its temperature. The regulators I commmonly see (Wakespeed, Arco Zeus and Balmar) all have this capability. They have a thermistor which is bolted to the alternator. My advice is to use a stainless steel clamp around the circumference to hold the thermistor against the body of the alternator where it is hottest. My 106A Ample Power alternator has been happily charging my 400AH LFP bank for over 3 years.

This is a good point. I properly temp regulated alternator will not produce anywhere near 100% output for very long. And if you dont regulate the temperature its not going to last. Thats why many recommend limiting the regulator output to around 50%.

 

[dLj]

This is a good point. I properly temp regulated alternator will not produce anywhere near 100% output for very long. And if you dont regulate the temperature its not going to last. Thats why many recommend limiting the regulator output to around 50%.

There are a lot of details that haven't been mentioned - controlling alternator temperature is one of them. I control output with a maximum of 75% and I control alternator temperature. I have a max temperature my alternators can see and if that temperature is approached then the output is reduced.

dj