Comparative Safety: 12v v 24v v 48

[transmitterdan]

Originally Posted by AKA-None

I admit I scrolled through the long recent posts but I don’t see any mention of the charge voltage for a 48 volt bank.

It would be 4 times the 12V bank charge voltage.

[Dockhead]

Originally Posted by ramblinrod

We seem to be confusing 48 Vdc with Lithium here too. Unrelated.

What made you think I'm confusing anything?


It's thread drift, but the question of battery chemistry was raised, and it is related to the original topic.


Lithium power and higher system voltage are both possible elements of advanced DC power systems as implemented on some boats with a high demand for autonomy.


Although higher system voltage also may be really useful, and add to the safety, of boats with large power demand and which are using lead -- for two reasons: (a) to avoid paralleling of batteries, which can be very dangerous with lead batteries (and I have first hand knowledge of this danger); and (b) to reduce voltage sag problems for high power consumers.

[Dockhead]

Originally Posted by ramblinrod

. . . However, I really question the idea of the validity of electric propulsion in a typical cruising boat or passagemaker wishing to cover around 150 nm / day, wind or not (especially to get out of the path of a whirly girl) and how they will recharge this bank for the motor (and all the other stuff they claim to need or want) without an ICE generator running almost constantly but that's another discussion.

That is another discussion indeed, and there are dozens of threads on it, but I think most people would agree with that, including most people who are actually using electric propulsion.

Originally Posted by Jdege

They are called sailboats for a reason.

There are a number of liveaboards who seem happy motoring only into and out of harbor, and if there is no wind, simply waiting.

Where they are typical, or not...

I guess everyone agrees.

[CatNewBee]

Regarding system voltage / charge voltage / chemistry.

As always, it depends.

You mentioned LFP.

LFP batteries have a cell voltage between 2.9V and 3.45V, charging voltage is up to 3.65V for a full cell, normal operation 3.3V per cell.

The trick is to get as close as possible to your system voltage.

for a 12V system you need 4S cells, what allows a range from 11.6V .. 13.8V, most of the time the bank will be above 13.2V, fully charged the bank will be at 14.6V.

4x4S or 16S
If you scale this to 48V, that means a voltage range from 46.4V ... 55.2V, fully charged at 58.4V, normal operation voltage would be around 52.8V.

This could be way too high for your gear, but you can chose instead of a 16S cell configuration a 15S cell configuration (what most 48V batteries made of single cells and external BMS do).

So then you end up at a voltage range between 43.5V ... 51.75V, Charge voltage 54.74V, Operation voltage most of the time at 49.5V, what would be perfect. But you cannot built this from 12V batteries, you must use single cells or use 48V packs with internal 15S config.

It is different with lead acid batteries, the range is around 11.2V ... 12.6V, (FLA are built of 2.1V cells, 3 cells in series for a 6V battery, 6 cells in series for a 12V battery) usually a battery is around 12.2V under load, so a 4S configuration of 12V batteries leads to 45V...50.4V, Operation usually at 48.8V, Charge between 56.8V (wet lead acid), 57.6V (GEL) and 59.2V (AGM). This pack is then a 24S configuration if you want to built it from FLA cells.

As you can see, a 15S LFP config is even better than a FLA configuration regarding voltage stability and voltage range at 48V, your devices will be operated near they specs regardless of charging or discharging.

[AKA-None]

That makes sense

[ramblinrod]

Originally Posted by Dockhead

But advanced DC systems on sailboats are intended to reduce IC engine running and efficiently harvest and store power produced by solar or as a by-product to propulsion.

Well, the intent may be to reduce ICE running, but all good intentions...

If the energy demand vastly exceeds the renewable energy charge source (solar, wind, hydro), and as soon as we talk about electric propulsion with any useable range on a cruising sailboat we know it will, there WILL BE significant ICE generated power required to make up the shortfall.

So yes, it would be possible to install a huge bank of heavy batteries to store up a whole lot of energy and install a huge heavy generator and charging systems so the generator run time is reasonably short (say 3 hours / day), which will produce those high currents that everyone was so scared of when discussing 12 Vdc systems) or we could install a smaller bank of batteries to support the light load systems, and a much smaller generator and charging system to run constantly while the heavy loads are required.

For those worried about weight (performance boats and racers) the latter will reduce the freakish sized solar array and windmill farm, the size of the battery bank (and despite which battery technology used, the more batteries the more weight) and the weight of the generator.

There's definitely a choice to be made.

Generally (and yes we can make blanket statements knowing full well there can be exceptions to every rule) for vessels with high energy demands, it is usually far more economical (money) and practical (space) to design the system around ICE generation being on, whenever the heavy loads are in use, so that these loads are not so dependant on energy storage, that will be so difficult to have adequate renewable energy charging sources to replace.

Lithium-ion battery technology does not produce energy; it only stores it.

Using L-ion, helps reduce the amount of weight (around half) and space (well maybe not), which will be countered by the size and weight of the charging systems required to replenish the energy consumed.

Net improvement?

Not so much.

This requires a large battery bank, and in particular a large lithium bank.

I fully agree with the first part of this sentence, but we should add the adjective "freakishly" (large battery bank).

As to the last part, "Say what?" this is going to require a large battery bank no matter what technology, but it can be done with any technology, it does not "require" lithium, though their may be some space and weight savings, at significantly higher project cost.

This is where a 48v backbone" makes sense.

I disagree with this statement. The term "backbone" implies running high load 48 Vdc cable the length of the boat to various high demand loads and dropping DC-DC converters where lower voltage is required.

For all of the reasons stated earlier, I believe this to be more dangerous than it is worth.

A far safer system, would be to have the high energy demand loads running off the (higher voltage, lower current yet) AC system (that will already be present anyway, unless someone intends to power all AC loads by inverter, which can get even more ridiculous yet) powered by the generator, when away from shore power.

The idea, of developing a large 48 Vdc bank and large solar, wind, and generator systems to recharge it, so that huge loads (large capacity water maker, washer, dryer, windlass, thruster, A/C, water heating, refrigeration, etc., can be powered by it, rather than keeping the battery bank and charging system reasonable, and powering the energy hogs with a generator, is not likely to be the best solution, in my opinion.

I'm sorry to burst bubbles, but the higher the energy demand, the more likely running a generator is going to be the only real practical and safe solution.

[ramblinrod]

Originally Posted by CatNewBee

Regarding system voltage / charge voltage / chemistry.

As always, it depends.

You mentioned LFP.

LFP batteries have a cell voltage between 2.9V and 3.45V, charging voltage is up to 3.65V for a full cell, normal operation 3.3V per cell.

The trick is to get as close as possible to your system voltage.

for a 12V system you need 4S cells, what allows a range from 11.6V .. 13.8V, most of the time the bank will be above 13.2V, fully charged the bank will be at 14.6V.

4x4S or 16S
If you scale this to 48V, that means a voltage range from 46.4V ... 55.2V, fully charged at 58.4V, normal operation voltage would be around 52.8V.

This could be way too high for your gear, but you can chose instead of a 16S cell configuration a 15S cell configuration (what most 48V batteries made of single cells and external BMS do).

So then you end up at a voltage range between 43.5V ... 51.75V, Charge voltage 54.74V, Operation voltage most of the time at 49.5V, what would be perfect. But you cannot built this from 12V batteries, you must use single cells or use 48V packs with internal 15S config.

It is different with lead acid batteries, the range is around 11.2V ... 12.6V, (FLA are built of 2.1V cells, 3 cells in series for a 6V battery, 6 cells in series for a 12V battery) usually a battery is around 12.2V under load, so a 4S configuration of 12V batteries leads to 45V...50.4V, Operation usually at 48.8V, Charge between 56.8V (wet lead acid), 57.6V (GEL) and 59.2V (AGM). This pack is then a 24S configuration if you want to built it from FLA cells.

As you can see, a 15S LFP config is even better than a FLA configuration regarding voltage stability and voltage range at 48V, your devices will be operated near they specs regardless of charging or discharging.

Well, there have been lots of discussions about this before; I suggest anyone considering this to review the threads regarding series vs parallel battery banks. (Beware that this topic results in a lot of misinformation IMHO.)

As I have stated many times, and likely will in my dying breath, when it comes to boat design or modification, there are pros and cons to every solution.

I personally, would not have a vessel with a single series string of batteries, to power any critical load. I prefer to have a degree of redundancy, where if there is a malfunction in the bank, the offending series string can be immediately and instantly isolated (manually or automatic), and the vessel continue on its merry where, with all system functional until the problem is detected, repaired, and that string can be brought back on line. If in heavy conditions (when things tend to break) it could be days before it is even plausible to stick ones head in the battery compartment.

[ramblinrod]

Originally Posted by Dockhead

Many people on here have similar use cases, and even if you already have the heavy duty generator, you don't necessarily want to run it for weeks on end, if you can arrange your system somehow so that you can "coast" on battery power for a day at a time or so.

Yeah, but this is my point.

The battery banks of these vessels with high electrical demands, do not recharge themselves.

To replenish the energy consumed over 24 hours in a short ICE run time, will take a prohibitively large battery bank (even Lithium) and generator.

The statement, "If you can arrange your system somehow, then..." makes this a mythical statement.

Exactly how, is one going to arrange their system, so that (lets say) one hour of ICE generator run time, is going to replenish all of the energy consumed over the last 24 hours?

I am asking you, for the purpose of challenging you to evaluate your statement, as my opinion is and has been, "In most cases, absolutely impractical, regardless of what available technology is employed.

Lithium offers...

Lithium is not the end all and be all. There are pros and cons to every design decision. The (relatively) recent availability of Lithium batteries, does not suddenly make 48 Vdc systems any more plausible, it just stores energy in a somewhat smaller and lighter package.

Downside is that you can't just drop them into a system designed for lead -- lithium is so different from lead, that it needs a rather different system architecture with different control systems and infrastructure.

Agreed!

But this is not a Lithium vs anything thread. Many posters have caused threads on that subject to be closed, so lets leave it out of this one.

My next boat...

But his thread is not about your next boat, it is about the comparative safety of various system voltages.

It's not impossible...

So avoiding the double negative we have, "It is possible..." Thank you for acknowledging this.

I will take it one step further, "It is possible that this true for this entire discussion and subject matter." (I believe this to be true, for anything remotely relevant.)

I have posted well prepared information to support my positions, when contradicted by others, that when they realized were irrefutable, have gone on to challenge other aspects, which I have also successfully contradicted with facts, logic, and reasoning, until exhausting opportunity to find error, which simply wasn't there, they started launching rather vicious personal attacks.

Exactly how much of this nonsense should one be required to tolerate, regardless of their qualifications, to state their opinions, they believe to be of value to forum members?

[evm1024]

A backbone dies not have to be a single physical bus.

For example the backbone of the internet are highspeed transmission lines that are organized in a number of topologys that form the principal data routes.

Basically, the backbone is for 'mass' transmission.

One of the very nice things about using a backbone with a higher voltage for power transmission is the point of presence conversion to the voltage needed by the load.

Once one frees their mind of the this is good enough mindset one can see possibilities.

Take the nav station for example.

In the old guys way of thinking you take power from your house bank, run it through a main panel to the nav station and then to the various devices there. Perhaps you run individual circuits from the main panel or run a single circuit to a sub panel at the nav station.

Lose your house bank and you use critical, life saving devices. So you split your house bank to be redundant. Or some variation on that theme.

Enter a distributed scheme with a distribution backbone and point of presence conversion and you could have a local battery at the nav station. That battery is the redundancy.

So lets work it back....

We start with all of the instruments at the nav station and decide how much power they need and a runtime on local battery. This sizes the local battery.

Knowing the maximum draw of the navstation we install an intellegent DC to DC converter that is sized to run the navstation even without a battery there. Remember that the Dc to DC converter is intelligent and is in fact a BMS/Battery-charger with a bypass should there be a fault.

The DC to DC converter connects to the backbone be it at 12,24,36,48, 144 volts etc. The backbone uses cable and connectors that are of a design that limits risks of accidental contact, shorts or other faults.

Far fetched? Hardly, it is is use in a number of places.

Too expensive? LiFePO4 batteries are more expensive than they should be. They or other advanced (over LA) batteries will come down in price. Generators are expensive, Solar is expensive etc.

There are no such DC to DC converters. Oh wait, all of those solar controllers are exactly that the POS DC to DC converter is. Change the firmware and we are golden.

Pie in the Sky? Perhaps you remember Rocky and Bullwinkle in their Metal Munching Mice story line. There were satellite dished on top of every house and for 1960 that was considered Pie in the Sky.

[Dockhead]

Originally Posted by ramblinrod

Well, the intent may be to reduce ICE running, but all good intentions...

If the energy demand vastly exceeds the renewable energy charge source (solar, wind, hydro), and as soon as we talk about electric propulsion with any useable range on a cruising sailboat we know it will, there WILL BE significant ICE generated power required to make up the shortfall.

So yes, it would be possible to install a huge bank of heavy batteries to store up a whole lot of energy and install a huge heavy generator and charging systems so the generator run time is reasonably short (say 3 hours / day), which will produce those high currents that everyone was so scared of when discussing 12 Vdc systems) or we could install a smaller bank of batteries to support the light load systems, and a much smaller generator and charging system to run constantly while the heavy loads are required.

For those worried about weight (performance boats and racers) the latter will reduce the freakish sized solar array and windmill farm, the size of the battery bank (and despite which battery technology used, the more batteries the more weight) and the weight of the generator.

There's definitely a choice to be made.

Generally (and yes we can make blanket statements knowing full well there can be exceptions to every rule) for vessels with high energy demands, it is usually far more economical (money) and practical (space) to design the system around ICE generation being on, whenever the heavy loads are in use, so that these loads are not so dependant on energy storage, that will be so difficult to have adequate renewable energy charging sources to replace.

Lithium-ion battery technology does not produce energy; it only stores it.

Using L-ion, helps reduce the amount of weight (around half) and space (well maybe not), which will be countered by the size and weight of the charging systems required to replenish the energy consumed.

Net improvement?

Not so much.



I fully agree with the first part of this sentence, but we should add the adjective "freakishly" (large battery bank).

As to the last part, "Say what?" this is going to require a large battery bank no matter what technology, but it can be done with any technology, it does not "require" lithium, though their may be some space and weight savings, at significantly higher project cost.



I disagree with this statement. The term "backbone" implies running high load 48 Vdc cable the length of the boat to various high demand loads and dropping DC-DC converters where lower voltage is required.

For all of the reasons stated earlier, I believe this to be more dangerous than it is worth.

A far safer system, would be to have the high energy demand loads running off the (higher voltage, lower current yet) AC system (that will already be present anyway, unless someone intends to power all AC loads by inverter, which can get even more ridiculous yet) powered by the generator, when away from shore power.

The idea, of developing a large 48 Vdc bank and large solar, wind, and generator systems to recharge it, so that huge loads (large capacity water maker, washer, dryer, windlass, thruster, A/C, water heating, refrigeration, etc., can be powered by it, rather than keeping the battery bank and charging system reasonable, and powering the energy hogs with a generator, is not likely to be the best solution, in my opinion.

I'm sorry to burst bubbles, but the higher the energy demand, the more likely running a generator is going to be the only real practical and safe solution.

Well, you're missing the point completely. No bubbles burst here at all.



If you are getting most of your power from running one diesel or another, then it will be that much more efficient and pleasant, if you can cover your power needs with less engine running time.


If you have little storage, and particularly little lead-acid storage, which is further limited by low charge acceptance rates, then you can't cover much of your power needs with power produced as a by-product of propulsion, and you have to run the generator a long time to get the batteries charged, and then run it again when the small capacity bank runs out. That adds up to a lot of generator run time.


A larger lead-acid bank is better, and some people might prefer at this point to go to AGM for the greater charge acceptance rate. But a bigger bank automatically means a higher charge acceptance rate. So now if you have a correspondingly large charger, you can pack in more power in a shorter period of generator run, and you end up running the generator fewer hours.


Now shift up another gear and use not only a large bank, but a lithium one. Here you have an even higher charge acceptance rate, and by this time you might think about installing a very large second alternator on the main engine. These are readily available in 5kW or 6kW or even larger capacity (of course you have to take care with the drive system, but that's also solvable. Now if motor a bit during the day, you might have stored up quite a lot of power, and you might not need to run your generator at all.


And with lithium -- you never need to run a generator just to put a "finishing charge" on. You run the generator (or main engine) as long as you like or as long as it's convenient, and stop whenever you want. This can further reduce generator run time and remove one big headache from the life of an off-grid, remote areas cruiser.




For those of us dependent on running diesel engines to make our power budgets -- it is enormously valuable, to be able to capture as much power as possible, from the main engine, when the main is being used for propulsion. That is really efficient, not just in terms of fuel, but especially in terms of the maintenance and amortization cost of an hour of engine running, and also from the point of view of listening to a diesel engine running -- it's running anyway. I already do this on a smaller scale -- I have a 2.5kW school bus alternator which I do use to charge my lead-acid bank when the main engine is running, and it is great to arrive at an anchorage with the batteries already replenished, or anyway with power put back into them.



And what all of us do, who use generators -- of course, we choose the time for running the generator, to coincide with the heaviest power demands. Usually the evening cooking, but also if washing and/or drying a load of clothes, running a watermaker, etc. But that's also a use case, which benefits from efficient and capacious storage -- it means you can collect and store more energy during those times.


Yet another reason for having good energy storage: Under sail in boisterous weather, especially bashing upwind on a heel, you worry about oil starvation in the generator (or main engine). If you sometimes do days of this on end, as I do, this can be a real problem. More storage means you don't face this problem as often. I have even been forced to heave to, to run the generator and recharge depleted batteries -- something I hated to have to do. More storage would have helped to avoid that, and batteries with a higher acceptance rate -- like lithium -- would have reduced the time lost being hove to while the batts were being charged.


How much is "more"? Different boats and crews will have different ideas about this. I have 420 amp/hours @24v nominal, equivalent to 840 amp/hours at 12v nominal. These are lead batts, so usable capacity maybe 40% of nominal. If I wear out these batteries before my next boat is built, I will replace them with lithium -- about 500 amp/hours worth at 24v (or 250 @ 48v). That will give me a bit more than double my existing usable capacity, and I'll be able to go from 70 amps (@24v) of charging capacity to a good triple that or maybe 5kW, just doable on my 6.5kW heavy duty generator. That means I can get the equivalent stored power of what my present bank is able to store from 100%, in about an hour of generator running (or two hours of motoring if I don't upgrade my alternator). That will radically reduce the necessity to run the generator.





As to system voltage -- on this boat, I will most likely stick with 24v, but the next one might very well have a 48v "backbone". Just because it's more efficient, and I believe, on the basis of all of the information shared in this useful thread, that using 48v for high power consumers like the inverter bank, and a large bow thruster, will be safer also, since the otherwise very large currents, will be halved, compared to 24v.

[ramblinrod]

Originally Posted by transmitterdan

Rod,

The arc that happens when interrupting a DC motor is not caused by a change in magnetic field. It’s the exact opposite. The arc happens because the magnetic field does not change rapidly.

I disagree.

In all of your posts on this subject, you keep disregarding or ignoring, that P = E*I (without exception).

P represent energy in Watts.
E represents voltage.
I represents current.

Energy is not proportional to current (without consideration of voltage).

The proof is that we can have lots of current (at very low voltage) through an extremely low resistance, that dissipates very little energy (won't even get slightly warm).

Energy is not proportional to voltage (without consideration of current).

The proof is that we can have a high voltage (with little current) through a very high impedance, that dissipates very little energy (won't even get slightly warm).

So there was a phenomenon I presented earlier in the thread, where some people, very knowledgeable in the electrical field, who are working with fixed voltages all the time, may consider power or energy to be directly proportional to current.

This is true and only true, if the alternate variable (voltage) remains constant. As soon as we consider a voltage change, energy is not directly related to current, because in fact, it is ALWAYS equal to voltage times current.

When we start talking about a change in both, we have to consider the impact of both on the energy dissipated.

If we increase the voltage by 400% and decrease current by 400%, the power or energy dissipated is exactly the same.

When considering a specific fault resistance, if the power sources are capable of exceeding the max current demand, (such as is often the case with batteries) the higher the voltage the greater the current, the more energy dissipated and the greater the risk of damage or fire (aka DANGER).

Now lets look at the subject or arcing.

The voltage required to cause an arc can be expressed as Voltage/Gap Distance.

This is a proportional relationship, the larger the gap the higher the voltage required to cause the arc.

Obviously, all switch and breaker contacts are designed to be capable of preventing arcing in the open state.

Obviously, when the switch contact is being made or broken, in it's travel, it will approach the separation where the arc can be initiated or extinguished.

If the power source has sufficient current available to initiate and sustain an arc, the arc will occur over a greater distance (and time) during this travel, the higher the voltage. This is a directly proportional relationship.

Now, due to the nature of arcing, once an arc is started, it is much easier to sustain over a greater gap distance.

So the more significant issue, is when the contact is opening.

Incidentally, there is likely a contact arc, when it is opened at any voltage we are discussing here, the question we are dealing with, is how damaging it is likely to be.

When the contact is opening, the arc is initiated the instant the contacts initially open, and is sustained until the contacts have travelled far enough apart, that the arc cannot be supported.

The distance that the arc can be supported is directly proportional to voltage.

Note that designs for lower voltage (12 Vdc) may not be suitable for higher voltage (48 Vdc) for this very reason.

The damage caused to the contacts is directly proportional to the energy dissipated in the arc.

The energy dissipated in the arc is calculated by P=E*I.

So it takes a higher voltage to initiate an arc and sustain it over a wider gap, and damaging energy dissipated, is also increased by the higher voltage assuming the maximum current for the circuit resistance is available, (as it will usually be, when switching high power loads.)

This is true for resistive loads, (e.g. water heater, electric range, lighting, etc.)

When we have an inductive load (e.g. motor), we have an additional consideration.

The transient voltage spike that can be generated when the circuit is suddenly opened.

In this case, the magnet field, produced by the energized coil (inductor) collapses and induces an EMF (call it "back", or "kickback", or whatever you wish) within that same coil.

Depending on the circuit, this EMF (voltage) can be much higher than the supply voltage.

There are a lot of things that come into play to determine just how high this voltage will be, but make absolutely no mistake, the higher this voltage, the more likely an arc between contacts will be initiated and the longer it will be sustained, as long as there is sufficient current available.

When we consider the energy stored in a inductor, we may determine it by considering the current through it and its impedance (resistance and inductance),but make no mistake whatsoever, the amount of current through it, everything else being equal is proportional to voltage.

Therefore the energy stored within an inductor is proportional to circuit voltage.

As we can clearly see, the relatively simple and general statement "Danger Increases with Voltage", holds true, regardless what complex situations we wish to consider, assuming there are no mitigating factors (such as something capable of limiting current, so that the energy available is reduced), and this is true and always true, regardless who claims it and what their qualifications are.

In other words, you guys with the parchments (supposedly) should know better, and the guy without, should not have to be teaching or reminding you of these principles, you have not been properly considering.

[brownr377]

Rod,

If you truly believe this:

"Therefore the energy stored within an inductor is proportional to circuit voltage."

I'm out.

The magnetic field stored in an inductor is related to current and has nothing to do with voltage. This is a fundamental fact in our understanding of electromagnetism if you can disprove Maxwell's equations more power to you, but I don't feel the need to play along.

[evm1024]

Originally Posted by ramblinrod

Yeah, but...

SNIP %<

I have posted well prepared information to support my positions, when contradicted by others, that when they realized were irrefutable, have gone on to challenge other aspects, which I have also successfully contradicted with facts, logic, and reasoning, until exhausting opportunity to find error, which simply wasn't there, they started launching rather vicious personal attacks.

Exactly how much of this nonsense should one be required to tolerate, regardless of their qualifications, to state their opinions, they believe to be of value to forum members?

I read your posts as I'm sure that others do. Some are more factual than others but none were irrefutable. Other posters make valid points that directly contradict your assertions frequently and this does not appear to cause any change in your opinion. (e.g. transmitterdan's posts)

Case in point - you misunderstood my statement regarding energy per charge and disagreed with me in post #339. I showed you where you had misunderstood in post #341. There has not been any acknowledgement of your error as of yet. Simply sidestepped - you went on to challenge other aspects....

Simply put your (and my) opinion amounts to nothing in terms of the laws of physics. Our understanding of how things work is an abstraction of what is actually going on. (the earth turns)

Further

IMHO your statements quoted above are distracting from the topic of discussion, It adds nothing to this thread and appears to be a "playing the victim" ploy.

Transactional analysis distinguishes real victims from those who adopt the role in bad faith, ignoring their own capacities to improve their situation.[9] Among the predictable interpersonal "games" psychiatrist Eric Berne identified as common among by victim-players are "Look How Hard I've Tried" and "Wooden Leg"

Regarding how much of this one should one be required to tolerate - I was advised (and I am only speaking of my personal experience) that if I found myself in a thread that I found intolerable the best course of action would be to just not post in that thread. I was advised to walk away.

[ramblinrod]

Originally Posted by Dockhead

Well, you're missing the point completely. No bubbles burst here at all.

I am missing no point; I am just politely disagreeing with the "Incorrect" ones posted based on other opinions, that are in disagreement with my own.

If you are getting most of your power from running one diesel or another, then it will be that much more efficient and pleasant, if you can cover your power needs with less engine running time.

This is your opinion. My opinion is that your opinion is "Incorrect!".

It is far more efficient to run a properly sized generator for longer duty cycles (even constant), than a properly sized generator of shorter duty cycles.

If you have little storage, and particularly little lead-acid storage...

Again this is not a battery technology comparison thread. Whether on voltage is safer than another has nothing to do with battery chemistry.

Therefore, I will not engage in lengthy explanation why your assertions on this matter are flawed in this thread. If you wish my detailed input on the matter, please start your own thread on that subject.

As to system voltage -- on this boat, I will most likely stick with 24v, but the next one might very well have a 48v "backbone". Just because it's more efficient, and I believe, on the basis of all of the information shared in this useful thread, that using 48v for high power consumers like the inverter bank, and a large bow thruster, will be safer also, since the otherwise very large currents, will be halved, compared to 24v.

Yes, without performing the necessary design and configuration review and boater needs and wants review, there is a high likelihood, that the best solution (in my opinion) is to stay with the current system voltage of your current vessel.

However, I disagree with your statement that a 48 Vdc system will be more efficient for a new design. This does require a complete design, configuration, and user needs/ wants review. They higher voltage may not be superior in any way and in fact may be detrimental.

If high loads are powered by generator, there is no need for a large inverter bank.

Actually, for the argument of choosing a higher system voltage (to achieve lower current) the same argument would favour choosing to power high demand loads with the AC electrical system which is at much higher power yet, and has more safety mitigating factors (e.g. GFCIs and ELCIs) incorporated.

[ramblinrod]

Originally Posted by brownr377

Rod,

If you truly believe this:

"Therefore the energy stored within an inductor is proportional to circuit voltage."

I'm out.

The magnetic field stored in an inductor is related to current and has nothing to do with voltage. This is a fundamental fact in our understanding of electromagnetism if you can disprove Maxwell's equations more power to you, but I don't feel the need to play along.

I'm not disputing Maxwell's equations.

Any equation that indicates something is impacted by the level of current, is necessarily impacted by voltage, due to first principles, Ohm's Law, which clearly indicates that "I" (current in Amps) = "E" (voltage in Volts / R (resistance in ohms).

...ALWAYS AND FOREVER (no exceptions).

As soon as we talk about current, we have to consider what is driving that current. For any fixed resistance, it is always voltage. ALWAYS.

I agree with Dockhead, this is very basic.

We are talking about first principles.

First principles do not go away, just because we wish to consider other related issues.