WOW!
Perhaps this thread should have been more aptly titled:
Truth vs Perception vs Mindset vs Pride. ;-)
I hope any psychiatrists or sociologists on the forum can comment...
...or do I actually know that is what I wish? ;-)
Despite all of the light saber rattling, name calling, intelligence questioning, (which is really a shame that some have to resort to this, but that too is human nature unfortunately, I guess, but think I know), I hope everyone has found this thread as interesting and entertaining as I have.
It didn't really strike me until the sun rising issue was discussed.
I declared how I "knew" the sun would rise in the east.
I do know for sure that an event has happened every dawn and sunset, and throughout the day, and technically I knew that the earth revolves around the sun, and spins on it's axis (or do I) ;-), and yet knowing full well that the sun is not actually rising and falling, I was fully prepared to defend my statement that it does.
Then it dawned on me. (har).
How can I possibly be correct and all of these knowledgeable gentlemen be so wrong.
And it struck me, I was trying to present a truth, that contradicted perception, that was firmly entrenched in a mindset, that pride was preventing acknowledement.
Instead, many were prepared to argue ad infinitum their misperceived mindset was correct, as a matter of pride; pride in being correct.
So lets look at the pride issue. From early childhood we are taught that we should strive to succeed. We go to
school and are taught that we need to learn things. If we learn well, we score an A+++, and the teacher is proud they did a good job, our parents are proud that they raised a bright child, and we develop a sense of pride in what we know, especially what we know that others don't.
Well that is a generalization that is not always true.
Some people could care less to let others do the thinking and be correct. "Meh", may be a term they use a fair bit.
I admit my own academic pride diminished somewhat about the time I learned about girls, cars, and parties.
Others could spend all of their time with noses in
books and worry about their A+++, whereas I would be perfectly satisfied to party hardy and receive a solid B.
The A+++ earners developed a perception that they had greater intelligence.
Though I learned later on in my life that this was not necessarily so.
In fact in many cases, I could learn knew things, and change gears much faster when presented with new information that contradicted my prior thinking.
This came up time and time again when we would have a product development team meeting that I was leading, and when a problem was encountered, all of the table pounding and chest beating took place between all of the "technical" people from Phd's in electrical science, through all the different disciplines and levels of engineers and technologists, down to well, me, a lowly electronic technician.
Yet I led the group.
I was perfectly happy to let the thinkers "know" what they knew, so they could get on with their job, making calculations, researching various technologies and methodologies, and whatever else they did to fill up their day.
But every once in a while, maybe 3 times per
project, we would run into a problem that the team really struggled with.
After one such meeting a young, recently hired
engineer walked up to me and asked, "How do you do that?"
"Do what?", I asked.
He replied, "We've all been going around in circles and in-fighting for days, you call a meeting, ask 5 questions, and we have an answer and direction forward, yet you didn't come up with it, we did?"
I smiled and replied, "Experience".
I had enough experience in situations where "technical" people tend to stumble, that I could walk in cold, see the fallacy(s) in play, draw them out into the open, so the team could think straight.
I could say that "I know" that is what happened here, but in fact, "I think (with a high degree of confidence"), that is what happened here. ;-)
Truth.
I think everyone here, probably knows that with greater amounts of stored energy, comes greater
danger should it be accidentally unleashed.
Take for instance, a jerry can of gasoline and lets say this has X units of stored energy.
While filling the lawnmower, if a drop of gasoline is spilled on the floor, it is no great concern.
But if we knock over that jerry can and empty it's contents onto the floor, we get very concerned.
We "know" that we just unleashed a significant amount of potential energy onto the floor, and a
single fault (flame or spark) could turn that from potential energy to active energy, and very bad things could happen, very quickly.
Now ask yourself this question, (forgetting about evapouration for a second) what real difference does it make how quickly the gasoline poured out of the jerry can?
I think most will agree, that it doesn't really make any difference how quickly the gasoline got there, the real issue is the amount.
Well, it isn't the amount. The same amount of
water would not be nearly as dangerous with respect to a fire.
It is the amount of potential energy that is now not under control (on the floor instead of in the jerry can) that has us concerned.
So lets go back to our 12 Vdc vs 48 Vdc discussion.
If the total potential energy available, and which could be released uncontrolled in a dangerous manner is, 480 Watts, it doesn't matter whether that energy is unleashed by 12 Vdc @ 40 A, or 48 Vdc at 10 A, the potential energy available to be unleashed in a dangerous way is exactly the same, 480 W.
Just like the speed of the gasoline spill, the speed of the current flow, has no real bearing, once it is all unleashed.
Now, this is where a whole bunch of intelligent folks stumbled.
Because we normally work with a fixed voltage supply, it doesn't matter what it is, but lets say 12 Vdc, some associated the potential energy (and potential danger) with the amount of current.
Obviously the more current, the more energy and the greater the risk.
200A oh my, 400 A, geesus, 800 A, yikes!!!!
Agreed! 1000%
Why?
Well at 12 Vdc, 200 A = 2400 W of energy, 400 A = 4800W and 800 A = a whopping 9600 W of energy.
So RamblinRod, higher current is more dangerous, so you are incorrect that higher voltage is more dangerous! (A lot of people jumped on this.)
Incorrect.
As I correctly stated, if we have a 12 Vdc circuit of very low resistance, designed to handle 800 A, it isn't dangerous at all.
It sits there happily running day in and day out, doesn't even break a sweat.
If a fault occurs, and the potential energy of that circuit is unleashed in an uncontrolled and dangerous way, the total potential energy is 9600 W.
So if instead we had a circuit capable of delivering only 200 A at 48 Vdc, that would be much safer, because it is only 200 A, right?
Wrong.
Interestingly, every person with any electrical background "knows" this.
Do they?
Yup. They have just established a mindset, from constantly thinking about a higher current with a fixed voltage, that they have incorrectly associated the danger with the current, when the potential danger is really associated with the total energy, which is the product of the voltage and current.
While they were working in their fixed voltage realm, this worked perfectly fine for them.
BUT, as soon as we increase the voltage by the same amount we reduce current, their established mindset causes them to make a mistake, even though they know that P = E*I; total energy = voltage * current, and if we increase one by the same amount we decrease the other, nothing changes as far as risk of danger.
Lowering current only makes the circuit less potentially dangerous if we do not increase voltage "DIRECTLY PROPORTIONALLY". (Dockhead may be pleased to know that I used this term correctly this time.)
If we lower current by 400% and increase voltage by 400% we have the same total potential energy - 9600W.
If that amount of energy can be converted into heat, to start a fire, it makes absolutely no difference whatsoever that one circuit had a 12 Vdc supply and the other 48 Vdc.
OK so we were wrong that risk of danger is proportional with current, but thankfully Ramblin' Rod was also wrong, because he said risk of danger is proportional with voltage and he just proved that voltage doesn't matter it is the total potential energy that is proportional to danger.
Well one might think so, if the amount of current was always reduced by the same amount that the voltage was increased. But it isn't.
As shown in one of the prior examples, when we increase voltage, across a fixed resistance, the current also increases. So if we have a short circuit of X ohms in a 48 Vdc circuit, the potential energy released is exponentially greater than that in the 12 Vdc circuit.
Of course there is no guarantee that a release of potential energy is going to do something bad, just like the gasoline on the garage floor that gets mopped up and safely put away, electrical energy can certainly be released without starting a fire.
It happens every time we use an electrical appliance.
However, there is always the potential that electrical energy can be released in an uncontrolled way, that will be dangerous, and the degree of that potential is proportional to the electrical potential (voltage).
Now, we do have certain measures in most electrical systems to prevent unleashing unlimited electrical potential. Power supplies usually have a current limiter, so that only so much energy can be released in Watts.
Batteries often have
fuses so that only so much energy can be released before the circuit is opened and current flow stopped. Note that the potential, based on the circuit voltage, is still there. If someone puts a jumper across that fuse. Look Out!!!.
We interrupt this program for the following public service announcement...Many boats have been built or modified with no fuse on the house bank.
For ABYC standards compliance , a fuse is not required on the starter battery (if there is no way it can be combined with the house bank, or anything else, and current distributed out of the starter circuit).
If your boat does not have a fuse (or breaker) very near the house bank positive terminal, please put one there, of the proper size and ratings.
If your boat does not have a fuse (or breaker) very near the starter battery positive terminal, please put one there, of the proper size and ratings. (While this is not required for ABYC standards compliance, these standards represent the minimum safety level. The starter battery fuse, greatly improves safety for very little money. (Just ensure the fuse or breaker is rated high enough, that it will not interrupt starter motor current under normal and even extreme (cold weather, fully loaded engine) conditions.
Now back to our regularly scheduled program.
In the example illustrated in post # 169....
Quote:
Lets consider the example that a short circuit of 1 ohm develops somewhere across the 30' power cables.
P (Watts) = E (Volts) ^ 2 / R (ohms)
Heat (BTU/h) = P (Watts) X 3.4
For 12 Vdc, P = E^2/R = 144V/1 ohm = 144 W * 3.4 = 490 BTU/h
For 24 Vdc, P = E^2/R = 576V /1 ohm = 576W * 3.4 = 1958 BTU/h
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This illustrates that the risk of danger (unleashing energy in an uncontrolled way that could be bad) increase significantly, proportional with voltage.
The risk of danger, is as simple as using Ohm's and Watt's laws.
Whether the danger is unleashed, (potential energy in the electrical circuit converted to active energy that can be harmful) depends on all of the circumstances, which is most definitely more complicated, but pretty much completely unnecessary to consider for these purposes.
More unleashed potentially dangerous energy is bad as compared to less unleashed potentially dangerous energy.
Every thing else equal, as shown in the short circuit example above, (which is quite plausible) in a condition where current is not otherwise limited (which can be many cases) the risk of danger increases proportionally with voltage.
The really surprising thing is; everyone responding in this thread with an electrical background knows this, and likely has for a long, long time; it was just their continued experience always worrying about higher current with a fixed voltage, that was preventing them from realizing the truth.
Then pride and inherent desire to be correct crept in, and prevented them from seeing the truth, that they actually knew, even when I spelled it out directly in front of them.
No offense meant to anyone in this thread by this post whatsoever.
I just hope others find this phenomenon as fascinating as I do, and can use this example to help them understand it, should they encounter it again in the future.
Let this be proof, that the "opinion" of the majority, even when it is filled with subject matter experts, that are basing their arguments on "facts", is not necessarily always the "truth" and in fact, they may even "know" differently but due to apparently conflicting information, can't access that knowledge.
FWIW, when considering adding a high power load to a vessel, it is always safer to choose the lowest voltage supply practical.
If the vessel has a 12 Vdc supply, and that can be safely used (there reasonably affordable
cables and components necessary to supply the recommend current and voltage to the terminal) it is usually best to go with that.
When designing a new
electrical system form scratch, it is still safest, to choose the lowest voltage supply possible and practical, to supply the electrical
appliances in the vessel.
For this reason, I generally recommend, for all rec boats less than about 50', that a primary 12 Vdc electrical system be used. If there is a very high load, like a thruster, it may be wise to mount a 12 Vdc battery very close to it. To reduce the cabling in a high load circuit that could potentially short circuit anywhere along it's length, and unleash a significant amount of potentially dangerous energy, because due to the nature of the load, the over-current protection devices in the circuit MUST allow a high degree of energy to be released, WHICH IS PROPORTIONAL TO CIRCUIT VOLTAGE (up to the limit of the over-current protection device).
So if there are any psychologists or sociologists in the house, that can help me understand / define the phenomenon described herein, please either post (if your OK with declaring in public), or PM me (for complete confidentiality).
Absolutely fascinating.
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