Comparative Safety: 12v v 24v v 48

[ramblinrod]

Originally Posted by brownr377

Faradays law
Gauss law
Ampere's law
Maxwells equations

There is more to it than Ohms law. [edit] Ohms law, yeah, it's good and all, but the other laws are needed to deal with anything other than a pure resistance.

[I'm sure this is already known but why not put it out there for other folks that might be interested in learning things.]

All of the laws stated comply with Ohms Law.

Because in a given circuit current (regardless how it is generated) is derived by it. I = E/R everywhere. There has to be an electro-motive force (voltage), whether caused by a changing magnetic field or other means (e.g. chemical reaction like in a battery), to produce a proportional current, for any given resistance. Has to.

[evm1024]

Originally Posted by ramblinrod

Nope, you just don't understand.

(Watch your sources when you Google something.)

Cutting and pasting something off the WEB is not indicative of understanding.

GFCIs are not only to protect from electric shock drowning.

They are to protect from an electric shock caused by any ground fault.

It is designed to trip if the differential current threshold is reached between the ungrounded and grounded conductor, based on the assumption that some current may be flowing through the grounding conductor, which should not normally be carrying current, if nobody is in the process of being given and electrical shock.

For a better understanding of how GFCIs work and what they do, you should have just asked. I used to manage a large portfolio of them, among other commercial and premise wiring devices. I don't have to Google this stuff and hope the source is knowledgeable and correct. I know it. Have for years.

Sidestepping again I see. Rather than attack perhaps you should backtrack.

Gentle reader the image below tells us much about the why of this discussion.

[brownr377]

Originally Posted by ramblinrod

Unless you can show that a 16 Kv ESD pulse is more dangerous than a 64 kV ESD pulse, or a 2 kV surge pulse is more dangerous than a 8 kV surge pulse, your statement seems to support my claim that EEE and BMF, danger increases with voltage.

No, I won't give you that. Your continued position at least as far as I can understand from your writing, is that a higher potential is more dangerous than a lower potential. Therefore no matter the conditions of the two transients, a 16kV potential has to be more dangerous than a 2kV potential per your argument.

Basically for these tests, you charge the network, flip a switch and a transient gets dumped into the test article. The load impedance in these systems is undefined, it's black box testing, but it's always true that the 2kV surge pulse is quite dangerous and the 16kV ESD pulse is not at all dangerous. Clearly other things must be considered.

Since the potential is not the predictor of safety, analysing voltage alone when assessing safety is foolish and not useful.

[weavis]

Im done with this thread.

It will be put before the mods for evaluation as to continue or close, however I see it is coming down to one electrician being the arbiter of what is correct. This is not a discussion, neither in reality or intent.

Sorry guys..........

[Adelie]

Originally Posted by Dockhead

For this to have even equal cost even in case the fuel efficiency is the same (which it won't be), the amortization and operating costs of the smaller generator would have to 24 times less per hour, than that of the larger generator. I guess there wouldn't be even one single example of that in real life. A case of your favorite beer if you can provide even one real life example, of any marine diesel generator running 24 hours a day, which produces power for less per kW/h than a properly sized diesel generator producing the same amount of power in one hour, considering fuel, maintenance, amortization, and all other costs.




For the record -- "efficiency" means getting the most desired effect for the least effort or cost. Mechanical efficiency or electrical efficiency is only one aspect of this. The end user will care very much about cost, in this equation, and will not care about efficiency considered in a vacuum without regard to cost.

Don’t thinks of operation and amortization costs in terms of per hour run but in terms of per kw produced.

There are non-monetary costs to consider such as weight and space of the respective generators.

[Dockhead]

Originally Posted by Adelie

Don’t thinks of operation and amortization costs in terms of per hour run but in terms of per kw produced.

There are non-monetary costs to consider such as weight and space of the respective generators.

I think you are right to make the bottom line -- cost per kW/h. And that was really my point. The cost of running a smaller generator per kW/h at its optimum load goes up drastically compared to a larger generator per kW/h at its optimum load. So you don't want the generator to be so small that you have to run it more than you could, if only it were bigger. Subject to limitations of weight and space, obviously.


But you also don't want the generator to be so large that you can't keep it loaded much in its optimal range. Keep in mind also that constant speed AC generators are much more vulnerable to wet stacking and bore polishing than variable speed diesels like main engines, because they can't modulate power output with RPM, so they need a bigger percentage of maximum power to run at a healthy cylinder temperature.



All this means that a generator should be sized right, not too big, and not too small, and should be loaded up and run for shorter periods, to the extent practical. Running for shorter periods at a higher load is healthier, is cheaper in terms of fuel, and is much cheaper in terms of maintenance and amortization -- all in terms of kW/h produced.



The best way to achieve that is with good storage -- so either a quite large lead-acid bank, or lithium, which is ideally complementary to generator power (on the other hand, solar and lead-acid batteries go together like cookies and cream).



Leaving a generator running all the time, although it is done on many power boats, is extremely inefficient unless there are constant loads which keep the generator busy 24/7. This gets better and better, with really large vessels because of the diversification of loads. But leaving a generator running all the time is really expensive in any case, unless you are talking about a dock queen that spends limited time off shore power (like many large power boats). I would have put something close to 2000 hours on my generator just last summer, if I had run it like that, a significant percentage of its total useful life. It's expensive not only from the point of view of amortization, but a generator run like that on a boat of my size will spend a significant part of the time running at very inefficient partial loads, costly in terms of fuel, and risky in terms of potential damage from wet stacking or bore polishing. It really makes sense to pair a diesel generator with a battery bank which is capable of absorbing a significant percentage of the generator's maximum output.