Comparative Safety: 12v v 24v v 48

[evm1024]

Originally Posted by ramblinrod

SNIP

Dockhead is correct that the term "proportionally" implies "directly proportionally" which is a linear relationship.

You were incorrect in stating a proportional relationship is always linear.

FYI, and not really related to this thread, an "inversely proportional" relationship is not linear, it is exponential (with a neat twist that the result cannot be zero).

Some relevant examples of directly proportional (linear) relationships include, "For a fixed resistance, current is directly proportional to voltage", and "Power is directly proportional to voltage and current", that is correct.

A relevant example of a an exponential relationship is, "The energy dissipated in heat, by a fixed resistance, increases exponentially with voltage."

I accidentally used the term "proportionally" rather than "directly", which was actually implied in the original premise "Danger increases with voltage.", so I should have left well enough alone.

The relationship between voltage and danger is not necessarily linear. In fact while I was using the term proportionally, I was describing conditions where danger increases exponentially (not linearly) with voltage which is far worse than a "proportional" relationship.

What I meant was "directly", meaning if one side of the comparison increases, the other increases and if one decreases, the other decreases.

(By the way, a proportional relationship is not always linear, such as in an inversely proportional relationship, where the constant is 1/x and the relationship is negatively exponential but cannot be zero.)

SNIP


So lets play fair, and play safe, after all, this is just for fun.

Inversely Proportional. A relationship between two variables in which the product is a constant. When one variable increases the other decreases in proportion so that the product is unchanged. If b is inversely proportional to a, the equation is of the form b = k/a (where k is a constant). Equation: y = 60/x.



In terms of playing fair please answer the question.

Is a 240 volt toaster more dangerous than a 120 volt toaster [of the same power]?

This question is a test of your premise that higher voltages are more dangerous than lower voltages EEE.

The toasters do the same thing, are the same size and are pretty much identical. In fact they both make toast in about the same time.

A serious question that strikes to the heart of your premise.

[ramblinrod]

Originally Posted by s/v Jedi

Rubber gloves and boots for work on 48V

Please clarify.

I cannot tell if you are agreeing with the point or sarcastically disagreeing.

(If sarcasm was rare in your posts, I could presume the former, alas...I can't be sure without asking.)

[evm1024]

Originally Posted by s/v Jedi

Rubber gloves and boots for work on 48V

Great post, gets right to the point. It really get a laugh and a smile from me.

I almost never use emoticons but I must say

[ramblinrod]

[I]Inversely Proportional....

I suggest you check for your own errors.

Irrelevant and intentionally distracting from the veracity of the main point, and all of the errors in your many contradictions.

A serious question that strikes to the heart of your premise.

If you truly believe so, please repost the question, in a clear and concise manner without all the disrespectful BS innuendo.

(Editted to avoid distraction.)

[evm1024]

Originally Posted by ramblinrod

SNIP



If you truly believe so, please repost the question, in a clear and concise manner without (disrespectful verbage removed).

Sure be happy to.

Rod you have stated that higher voltages are more dangerous than lower voltages. I have a question that you can answer.

Is a 240 volt toaster more dangerous than a 120 volt toaster [of the same power]?

[brownr377]

Holy expletive, this is too much hilarity. I'm calling up UL right now to have them void all my safety certificates cause we forgot to account for the voltage being to high BMF.
.
.
.
That was sarcasm to be clear. What do you mean before mitigating factors??? Are you wanting to run bare copper about the boat and dance around grabbing both poles of the circuit wading in salt water? It's an absurd condition. All electrical systems are chock full of mitigating factors to make them safe.

I promise to no longer engage and go back to lurking mode.

[Q Xopa]

Originally Posted by ramblinrod

No. (Well, I can only speak for myself.)



I suggest you check for your own errors.

Irrelevant and intentionally distracting from the veracity of the main point, and all of the errors in your many contradictions.



If you truly believe so, please repost the question, in a clear and concise manner without all the disrespectful BS innuendo.

(Editted to avoid distraction.)

Strawman alert-
Disrespectful and Cyber bulling. Arent you precious, accusing others of this.
Incorrect-
I get it, that this is what you believe.

[TeddyDiver]

"Is a 240 volt toaster more dangerous than a 120 volt toaster?"

[Jammer]

Originally Posted by GrowleyMonster

Watchband burn. The watchband was destroyed and at the first sparkle I naturally yanked my hand away instantly and still got these cool blisters to show off at cocktail hour that day. A wrench will melt. A quarter lodged across the phase wires of a motor will actually explode when it is energized. Skin contact with 48v is not the demon here. It is contact with metal that contacts the circuit. Eliminate this risk by using proper terminal boots and the battle is half won. The other half is learning not to do stupid stuff. The good thing is that the learning process punishes you just enough to remember your mistakes and not kill or hospitalize you.

Growley


You should be taking the standard safety precautions around that stuff. Take off your ring and your watch and any other jewelry. Be mindful of other conductive materials on or around you, zippers, eyeglasses, belt buckles, remove them if practical. Wear safety glasses or goggles. Tape your tools.


Do those things, and you should never get burned by a short.


The technicians at a telecom company that was run by a former business associate worked on 48v systems every day. Any technician that was seen wearing jewelry or using untaped tools was fired, right there, on the spot. There was one instance I heard about where one of their techs melted a wrench because he hadn't taped it. Boss found out and fired him the next day.


The point being that they take this stuff seriously and you should too.


They had a contract installing current shunts on the breakers in telecom rooms. It was all done hot, nothing was ever shut off. Some of the breaker panels were pretty crowded, and we're talking about hundreds of amps continuous. They did that, hot, every day, very few accidents, very few incidents where equipment was inadvertently powered down.


Be careful

[dfelsent]

Originally Posted by TeddyDiver

"Is a 240 volt toaster more dangerous than a 120 volt toaster?"

That all depends on how hard you throw it.

Seriously folks look up SELV and get over it.

The hairiest thing ( not the highest voltage ) I ever consistently worked with was a 50 amp power supply. Oh yes, 20,000 volts. DC. A megawatt. That demanded respect. So did the 100,000 volt 100,000 amp pulse generator. Yes that’s 8 times more power than Marty McFly had.

The stuff on our boats demands respect and care too. Maintain it. Don’t assume it won’t kill you. It might not shock you but burn the boat down.

A group 31 battery stores 500 more energy than the capacitor bank of that megawatt power supply. And the cap bank had about 1000 times the energy of a lethal bullet.

12 vs 48 is like arguing about whether sea water is wetter than fresh water. They are both wet.

Take care and be safe.

[weavis]

FROM THE MODERATION TEAM.

a tremendous amount of posts have been deleted due to squabbling and name calling.

This is not how CF operates.

Please go read the rules.

Should you choose to ignore the rules, we will have no choice but to close the thread and issue infractions which will impact your ability to post on CF.

Consider this an OFFICIAL WARNING.

[ramblinrod]

OK, so we have gone round and round with lots of good info, and unfortunately, numerous posts that were riddled with errors, or were disrespectful and an attempt to shun consideration of alternate perspectives.

All I can say is, to each their own.

Are we likely to see an increasing number of recreational cruising boats with 48 Vdc systems in the future?

I think so.

Should we all jump on the bandwagon and start converting our boats from 12 Vdc to 48 Vdc, because someone, maybe even a small group of motivated boaters on the internet say it is cool and "The Way of the Future".

Depends. Probably not in most cases.

When considering an original design or modification, one needs to consider the advantages and disadvantages of the options available to them.

So here are some pros and cons between 12 Vdc and 48 Vdc.

12 Vdc Electrical System

Pros:

1. Existing - Many or most boats already have it.
2. Product Base - More to choose from.
3. Cost - Many products are less expensive.
4. Electrocution - No risk (virtually).
5. Electrical Shock - Low risk
6. Fire - Lower risk due to "short circuit".
7. Arcing - Less prone to damage and overheat contact surfaces.
8. Familiarity - Long established standard.
9. Availability - Excellent everywhere.
10. Necessity - Very high (hard to operate with no 12 Vdc system).

Cons:

1. Load Limit: Lower, no "standard" but 3kW for 1 hour, 6 kW for 5 minutes is fine.
2. Heavier Cables: Increased copper cost.
3. Coolness: May be perceived as boring.
4. Generation Efficiency: May be lower.

48 Vdc Electrical System

Pros:

1. Coolness: Maybe perceived as exciting.
2. Load Limit: Higher - I use 12 kW for 1 hour, 24 kW for 5 minutes.
3. Generation Efficiency: May be higher.
4. Lighter Cables: May reduce cost.

Cons:
1. Existing: Rare, may require complete rewire and product replacement
2. Product Base - Less to choose from.
3. Cost - Many products are more expensive.
4. Electrocution - Higher risk (still low).
5. Electrical Shock - Higher risk.
6. Fire: Higher risk due to "short circuit".
7. Arcing: More prone to damage and overheat contrat surfaces.
8. Familiarity: Less.
9. Availability: Limited
10. Necessity: Some/many boats don't "require" > 12 Vdc system.

So to evaluate the real benefits (if any) of modifying an existing system, or designing a new system, around 48 Vdc vs 12 Vdc, one needs to weigh the pros and cons.

Sometimes people get excited focusing on the pros and ignore the cons.

After living with the decision, they may regret the choice.

Some people will "actively promote" their choice, in attempt to gain "support" for, and hence feel better, about their decision.

Some will enjoy the benefits realized which outweigh the cons.

So lets look at the pros vs real benefits of choosing 48 Vdc.

1. Is it really cooler? Some may think so. Others may think, meh, 48 Vdc has been around along as 12 Vdc, just not traditionally on boats (hence lack of product availability and higher cost). Others may be afraid of it. While the higher risk of electrocution, electrical shock, and fire may be low to extremely low, the consequence is so high, that alone kills the idea.

2. Is a higher load limit necessary? If so, it may be warranted on this basis, if the advantage of supporting higher loads weighs out the cons. Do you really want to boil a pot of potatoes in the cabin (heat and humidity) vs BBQ out on the back deck? Do you really need AC, let alone running off batteries, that then you then need the high capacity chargers and batteries to support? Be sure to separate wants vs needs, and determine if they are even worth it.

3. Is generation efficiency really higher or better? In some cases it may be. Be sure to see what this really means to you. In other words, check that every pro "feature" is actually a benefit. If you have ample solar to recharge fully on a partially sunny day, higher charge efficiency may not really mean that much. A more efficient alternator may mean shorter run times, but if you typically only charge by alternator when changing anchorages, this may be no real benefit to you. If you charge by ICE generator EEE, it may only mean the difference of running 1.5 hours instead of 1.3 hours, and burning 75 cents less fuel per ICE generator charge cycle, and 15% less carbon emission, but 15% of almost nothing (in the grand scheme), is even less.

4. Lighter cables. This may save some copper. In a 8 HP thruster installation it may save about $40. In a total boat rewire, it may be $100's, but in comparison to the project cost, this may be infinitesimal. It is very possible for the higher 48 Vdc product costs, to vastly exceed the cable savings, so this may be no real benefit at all.

5. Danger. Just as everyone has different boat models preferences, everyone has different risk tolerance. It is wise to consider likelihood of hazard, vs consequence of hazard. Even if a risk of electrocution is extremely small, the consequence (death) is pretty severe. The higher risk of shock is actually quite possible, and the consequence may range from nuisance to some form of injury. The higher risk of fire is real. By it's very nature, 48 Vdc has a higher potential to start a fire is a short circuit situation. The consequence is very severe.

EVERYONE'S PREFERENCES AND BIASES WILL BE DIFFERENT!

This is why for this, or any significant cost (time and/or money) project, we recommend a thorough vessel design and configuration review, boater needs and wants assessment, with cost/benefit analysis.

Opinions and weighting of pros and cons will differ likely as much as there are numbers of different models of boats.

I believe it is better for boaters to make informed decisions based on their actual boat and personal needs, rather than just jump on the bandwagon of internet "fans" that have nothing to lose if the outcome is high cost with little or no actual benefit realized.

Which is all the more reason why every boater really needs to evaluate "What is best for me", which will naturally be different than for someone else.

Anyway, I hope this summary / review helps.

[evm1024]

For the sake of being on the same page I think it would be useful to use commonly understood meanings for some of the acronyms we are using.

Starting with EEE - Everything Else being Equal

Before I jump off to quoting Wikipedia I do want to say that that it is not Everything Else being Identical

Originally Posted by Wikipedia

Ceteris paribus or caeteris paribus is a Latin phrase meaning "other things equal". English translations of the phrase include "all other things being equal" or "other things held constant" or "all else unchanged". A prediction or a statement about a causal, empirical, or logical relation between two states of affairs is ceteris paribus if it is acknowledged that the prediction, although usually accurate in expected conditions, can fail or the relation can be abolished by intervening factors.[1]

And (underline added)

Originally Posted by wikipedia

The clause is often loosely translated as "holding all else constant." It does not imply that no other things will in fact change; rather, it isolates the effect of one particular change.

To move this over to the comparative safety of 12, 24 and 48 volt systems topic is is obvious to me that EEE means NOT that we take a well engineered 12 volts boat electrical system and slap a 48 volt house bank in it. But rather that we compare a well designed 12 volt boat system to a well designed 48 volt boat system.

Simply stated Equal means equally well designed and implemented systems.

If you do not agree with this then let me offer up an example.

Of course if you were to take a well designed 12 volt system and put 48 volt batteries of equal Wh capacity in place of the 12 volt batteries with all else unchanged the you are going to have problems. All kinds of problems.

By the same token if you took a well designed 48 volt system and replaced the 48 volt batteries with 12 volt batteries of equal Wh capacity with all else unchanged you are gonna have problems.

In the first case the 12 volt system is safer, in the seconds case the 48 volt system is safer. (by reason of cable size if nothing else in regards to the 48 volt system running on 12 volts)

[evm1024]

BMF is the next acronym to address in the hopes of a common understanding. It has been coined in this discussion as Barring Mitigating Factors.

In my opinion BMF is being used in error. The phrase takes its roots from law. Let’s take a look at that and suppose that evm64 and evm32 are fighting. In this fight evm32 kills evm64. We could say that it appears that Barring Mitigating Factors it appears that evm32 is guilty of murder.

As BMF has been used in this discussion BMF means that we do not look at or use any mitigating factors.

But in the example above upon closer look we discover that evm64 was attacking with intent to kill evm32’s mother. And thus evm64 is not guilty of murder due to the mitigating factors.

This goes to show that the mitigating factors are essential to a proper understanding of real world events (and things).

In the case of our boats specifically and life in general mitigation factors are required.

As an example you might make a blanket statement and say that running wire through an engine room is unsafe. And if the wire in question has a 60 degree C temperature rating then the ABYC agrees with you. But the ABYC (and others) mitigate the higher temperature of engine spaces by increasing the required temperature rating of the cable. Thus the minimum temperature in engine spaces is cable rated at 75 degrees C.

ABYC E-11 Table VI has a whole list of parameters that show what the allowable amperage through conductors are for various conditions. This table lists the mitigating factors (e.g. changing the insulating temperature rating to mitigate the elevated temperature expected in an engine room).

Thus in my opinion BMF is acceptable if it means that no extraordinary measures for a well designed system are needed. And we should use it that way.

[Q Xopa]

Originally Posted by ramblinrod

OK, so we have gone round and round with lots of good info, and unfortunately, numerous posts that were disrespectful and an attempt to shun consideration of an alternate perspective.

All I can say is, to each their own.

Are we likely to see an increasing number of recreational cruising boats with 48 Vdc systems in the future?

I think so.

Should we all jump on the bandwagon and start converting our boats from 12 Vdc to 48 Vdc, because someone, maybe even a small group of motivated boaters on the internet say it is cool and "The Way of the Future".

Depends. Probably not in most cases.

When considering an original design or modification, one needs to consider the advantages and disadvantages of the options available to them.

So here are some pros and cons between 12 Vdc and 48 Vdc.

12 Vdc Electrical System

Pros:

1. Existing - Many or most boats already have it.
2. Product Base - More to choose from.
3. Cost - Many products are less expensive.
4. Electrocution - No risk (virtually).
5. Electrical Shock - Low risk
6. Fire - Lower risk due to "short circuit".
7. Arcing - Less prone to damage and overheat contact surfaces.
8. Familiarity - Long established standard.
9. Availability - Excellent everywhere.
10. Necessity - Very high (hard to operate with no 12 Vdc system).

Cons:

1. Load Limit: Lower, no "standard" but 3kW for 1 hour, 6 kW for 5 minutes is fine.
2. Heavier Cables: Increased copper cost.
3. Coolness: May be perceived as boring.
4. Generation Efficiency: May be lower.

48 Vdc Electrical System

Pros:

1. Coolness: Maybe perceived as exciting.
2. Load Limit: Higher - I use 12 kW for 1 hour, 24 kW for 5 minutes.
3. Generation Efficiency: May be higher.
4. Lighter Cables: May reduce cost.

Cons:
1. Existing: Rare, may require complete rewire and product replacement
2. Product Base - Less to choose from.
3. Cost - Many products are more expensive.
4. Electrocution - Higher risk (still low).
5. Electrical Shock - Higher risk.
6. Fire: Higher risk due to "short circuit".
7. Arcing: More prone to damage and overheat contrat surfaces.
8. Familiarity: Less.
9. Availability: Limited
10. Necessity: Some/many boats don't "require" > 12 Vdc system.

So to evaluate the real benefits (if any) of modifying an existing system, or designing a new system, around 48 Vdc vs 12 Vdc, one needs to weigh the pros and cons.

Sometimes people get excited focusing on the pros and ignore the cons.

After living with the decision, they may regret the choice.

Some people will "actively promote" their choice, in attempt to gain "support" for, and hence feel better, about their decision.

Some will enjoy the benefits realized which outweigh the cons.

So lets look at the pros vs real benefits of choosing 48 Vdc.

1. Is it really cooler? Some may think so. Others may think, meh, 48 Vdc has been around along as 12 Vdc, just not traditionally on boats (hence lack of product availability and higher cost). Others may be afraid of it. While the higher risk of electrocution, electrical shock, and fire may be low to extremely low, the consequence is so high, that alone kills the idea.

2. Is a higher load limit necessary? If so, it may be warranted on this basis, if the advantage of supporting higher loads weighs out the cons. Do you really want to boil a pot of potatoes in the cabin (heat and humidity) vs BBQ out on the back deck? Do you really need AC, let alone running off batteries, that then you then need the high capacity chargers and batteries to support? Be sure to separate wants vs needs, and determine if they are even worth it.

3. Is generation efficiency really higher or better? In some cases it may be. Be sure to see what this really means to you. In other words, check that every pro "feature" is actually a benefit. If you have ample solar to recharge fully on a partially sunny day, higher charge efficiency may not really mean that much. A more efficient alternator may mean shorter run times, but if you typically only charge by alternator when changing anchorages, this may be no real benefit to you. If you charge by ICE generator EEE, it may only mean the difference of running 1.5 hours instead of 1.3 hours, and burning 75 cents less fuel per ICE generator charge cycle, and 15% less carbon emission, but 15% of almost nothing (in the grand scheme), is even less.

4. Lighter cables. This may save some copper. In a 8 HP thruster installation it may save about $40. In a total boat rewire, it may be $100's, but in comparison to the project cost, this may be infinitesimal. It is very possible for the higher 48 Vdc product costs, to vastly exceed the cable savings, so this may be no real benefit at all.

5. Danger. Just as everyone has different boat models preferences, everyone has different risk tolerance. It is wise to consider likelihood of hazard, vs consequence of hazard. Even if a risk of electrocution is extremely small, the consequence (death) is pretty severe. The higher risk of shock is actually quite possible, and the consequence may range from nuisance to some form of injury. The higher risk of fire is real. By it's very nature, 48 Vdc has a higher potential to start a fire is a short circuit situation. The consequence is very severe.

EVERYONE'S PREFERENCES AND BIASES WILL BE DIFFERENT!

This is why for this, or any significant cost (time and/or money) project, we recommend a thorough vessel design and configuration review, boater needs and wants assessment, with cost/benefit analysis.

Opinions and weighting of pros and cons will differ likely as much as there are numbers of different models of boats.

I believe it is better for boaters to make informed decisions based on their actual boat and personal needs, rather than just jump on the bandwagon of internet "fan boys" that have nothing to lose if the outcome is high cost with little or no actual benefit realized.

Which is all the more reason why every boater really needs to evaluate "What is best for me", which will naturally be different than for someone else.

Anyway, I hope this summary / review helps.

Terrific Post!

Most of us here know you have a lot to offer.

Informed opinions (even if they are different to others is fine).

I am here to learn, consider new ideas and contribute if I think I can.

This is what I believe is what CF is and should be about.

I think most of us arent really so keen to hear "wrong, correct, strawman etc" in reference posts or to anyone, particularly other repected contributors of which there are many on here.

Thanks.