edit:general questions about electrical safety requirements

[roflchopter]

I am doing my science fair project on electromagnetic induction. I built a capacitor bank, and I am unsure of whether to just list the bank on the materials list, or give details into its construction. also, I mounted all of my transformers and switches to a piece of plywood for ease of use/presentation. Do I need to give details into its construction, and list that I used a circular saw, etc. to cut it? The dimensions of the base have nothing to do with the, and other things like it have nothing to do with the active parts of the system (besides holding them down in an organized way.

thanks in advance,
Chris

[agm]

Hi roflchopter,

Welcome to the forum!

The amount of detail you need to give about the capacitor bank and the mounting board probably depends on the requirements of your teacher and/or the specific science fair you are entering, so it would be best to check with them. However, I think you are on the right track with thinking that aspects of the construction that were largely for your convenience, rather than necessary for the outcome of your experiment, will probably require less detail. In the "real world", a scientific paper should contain enough detail so that another researcher reading it can reproduce the experiment to check its validity. If a procedure has been published before and/or is very well known, it can be referenced rather than repeated in detail. However, K-12 research project reports often require more detailed write-ups in which the student more or less proves that s/he understands all the principles involved. If there are page limitations involved, it's probably most important to fully describe the project at the highest or most advanced level, and leave out 'basic' details as needed to remain within the length restriction. (This is not unrelated to the "real-world" situation: a journal paper will be shorter than a thesis chapter even if written by the same person on the same topic, because the thesis length is less restricted.) In general, summarizing/abbreviating is a better strategy than leaving anything out entirely.

Here's what you could do, if possible: Write a draft of your materials and procedure sections, including the amount of detail that you think makes sense. For the capacitor bank, you will probably want to give a circuit diagram and state whether they were soldered together or if you used a breadboard, etc. For the mounting board, it might be sufficient to state that you mounted all components (after they were constructed and connected as you have described earlier in the section) on a board of a certain size using a certain adhesive, or velcro, or staples, or whatever you used. Now, if it happens to be the case that the mechanical properties of the mounting board are important (e.g. because of large forces produced), or if vibrations could be transmitted between components mounted to it and you had to prevent that somehow, then you should discuss that -- basically use common sense regarding what was important for your experiment. It sounds like someone repeating your experiment could just buy a piece of plywood of the size you used instead of cutting it him/herself, so I think you're correct that you don't need to discuss how you cut it (even if that was a fun part of the work for you).

After you write the draft, show it to your teacher or maybe to your contact at the science fair (depending on your situation) and ask if it's necessary to elaborate on the steps you're concerned about. This necessitates finishing it early, *but* you avoid doing the extra writing if it's not required, and you have more time to polish your discussion, etc.

Sounds like you've put a lot of work into your project -- I hope it's going well, and feel free to post any other questions you have in this thread.

Amanda

[roflchopter]

Thank you for the response. I will take your advice, and only include descriptions of things that could affect the results of the experiments.

EDIT: the project is going well, but I just came up with another question: My system uses 1800 volts as a maximum operation voltage, is having exposed contacts that are at the voltage going to hurt my chances of winning. There is really no alternative, a home-made switch was constructed to handle the immense current, and its design requires that I can close it with an insulated rod. Also, the bank is currently sitting in the box that a case of wine was bought in. The box holds them perfectly, and takes stress off of the screw terminals of the capacitors in transportation. Will the box's reference to alcohol influence the judges' decision?

Thanks

[Craig_Bridge]

is having exposed contacts that are at the voltage going to hurt my chances of winning.

Having any exposed electrical contacts with any potentially dangerous amount of power would exclude you from even displaying the project in working form in most Science Fairs. You need to ask the people running the Science Fair for specific guidance.

My recommendation for being able to display a working project that has potentially dangerous electrical power would be to build an entirely non-conducting enclosure with no exposed metal and one or more sides made out of "plexiglass" (the polycarbonate "window" material used for storm doors) so that the project can be viewed safely.

CSA and UL safety test proceedures utilize some metal "test probes" that resemble fingers and unfolded paper clips. The design requirements would be that no enclosure surface be able to be deformed and make contact with any energized circuit and no opening in the enclosure allow any of the test probes to enter and contact any energized circuit and there be no exposed metal surface. A hole just big enough to allow your rod to enter would be a problem if the rod were not in it. Coming up with a way of preventing your rod from being completely pulled out of the enclosure or falling into the box would be my suggestion for solving that problem. The no exposed metal surface requirements would prevent the use of exposed metal screws or nails

The alternative would be to display a non-functional project without the power source.

What power source are you using? Science Fairs may not allow you to plug anything in. If they do, then what you plug in has to be something that is UL / CSA listed and is used unmodified.

By having an electrical storage device (your capacitor bank), you can't rely on the current limiting nature of any of the UL / CSA listed low voltage transformers and/or battery charger circuits as meeting safety standards.

Will the box's reference to alcohol influence the judges' decision?

Maybe. Mormans, Muslims, and others have religous beliefs that may subconciously affect their judgements. Teachers, Parents, and others may not appreciate any advertising materials in school settings. This is one of those, "If you have to ask" questions, you already know "it is best not to". Come up with something to cover up the potentially offending advertising. Consider making creative use of the space by displaying a project schematic or something project related.

[agm]

My system uses 1800 volts as a maximum operation voltage, is having exposed contacts that are at the voltage going to hurt my chances of winning.

Well, this sounds like a possible safety issue, if people looking at your project (esp when you aren't there to stop them) could touch the contacts and be exposed to the voltage. Would covering them with electrical tape or some other barrier to touching be possible? If that would interfere with the functioning of your experiment, maybe a temporary cover and warning label?

Will the box's reference to alcohol influence the judges' decision?

I would hope not -- I think most science-fair judges realize that the projects are low-budget. In fact, if things (especially the non-essential parts) look *too* polished, it's easy to wonder if the student purchased a kit for the experiment or had excessive help from an adult (where "excessive" means something like an adult performing the work, even when unnecessary from a safety perspective, and the student not really understanding what was going on). My guess is that the worst outcome would be an awkward joke about it, though that could be upsetting if you are already nervous. How about either painting over the box or covering it in plain brown paper? If the box covers the capacitor bank completely, maybe you could even cover the wine label with a diagram showing how the contents are put together.

Edit: See also Craig's excellent advice!

Amanda

[roflchopter]

thank you for your responses. none of the components have been modified in any way, and all were taken from what I assume are UL listed pieces of equipment (variable auto transformer and Microwave transformer, plus diodes and of course the capacitors). If the fact that the system as a whole is not UL listed, and I couldn't demonstrate it at the fair, would I still have to install covers on the exposed switch? If the risk of un-supervised use is the main issue, could have my dad bring a "lockout" home from work that covers the plug and secures it with a keyed lock? I would really rather avoid Plexiglas(I have had extreme difficulty cutting it in the past, and in my experience, it likes to break when drilled.

The whole thing is only at 1800 volts during charging, and immediately before firing( around20 seconds), so uncharged it presents no shock risk at all.

thanks for your time,
Chris

P.s. should I change the title of this topic since it had drifted away from the original question?

edit: just so we are all on the same page, here is a link to some pictures of the setup

EDIT II: well, any chance of live demonstration demonstration went away when my variac caught fire because of over-load(cause of overload is unknown). this also kept me from completing my testing. what is the best way to present this bad news.

also I have an extremely odd outlier that exists even after averaging out data. my disk that was launched with an electrical energy of 2025 joules had less output kinetic energy than the same disk had after being launched at only 1296 joules. again, the energies were averaged from 3 tests, and I am talking about energy, not efficiency.

the graph of kinetic energy vs. electrical energy resembles y=.000015x^2 very nicely without the data for 2025 joules. I was going to re-test at 2025J, but since the variac burned up, there is no current limiting, meaning that my microwave transformer can pull 6,000W (50A), which would trip breakers like no tomorrow.

[Craig_Bridge]

none of the components have been modified in any way, and all were taken from what I assume are UL listed pieces of equipment

Yes but you "manufactured" a new circuit and "assembly" from them so the configuration hasn't been evaluated for safety, so you are outside of what most Science Fair venues would allow to be demonstrated without some safety barrier. Because your project must be connected to the electrical grid and a variac is not a preset unalterable current limiting device it probably would not have been allowed to even be plugged in so coming up with a safety barrier isn't an option.

The fact that your variac caught fire is a strong indication that your device design has some electrical safety issues.

As to your outlying point, I would plot your data with and without the outlying point against your expected y=.000015x^2 curve. If you calculate the deviations and variances of each point from the y=.000015x^2 curve, you can demonstrate that you believe you have an unexplained experimental error with that data point. If I were a judge, my questions to you about that outlying point might be:
1) If the 2025 joules point is at the high end of the points tested, what kind of an unexplained circuit breakdown might explain your result?
2) Back calculating from the measured/calculated kinetic energy, what would you expect the electrical energy to be?
3) What kinds of "leakage" paths might explain this apparent loss of electrical energy in the conversion to kinetic energy?

If I were you, I would do the back calculation and put it in your report. You will have to choose your strategy in terms of attempting to pre-answer questions like 1 and 3. If you pre-answer those, what questions might the judges come up with to probe your understanding of your project? Is it better to not pre-answer those in hopes of being able to field an easier question that you have already had time to pre-think? Just a thought.

In any case, you need to tell the story of the variac being overloaded and if possible figure out what caused it or at least describe what you were attempting that might have caused the overload. In other words, explain why you couldn't go back and retest the point(s) in question within time and budget.

[roflchopter]

thank you very much, although I an not sure I understand what you mean by 1). do you mean the electrical breakdown that caused the variac fire or the breakdown that caused the unexplained data point?

If I progress to the next level of competition would a heating element be a suitable "unalterable current limiting device." If so, I would look into replacing the Variac.

Are you an electrical engineer by any chance? Just curious.

[Craig_Bridge]

1). do you mean the electrical breakdown that caused the variac fire or the breakdown that caused the unexplained data point?

I was refering to some dielectric breakdown or sneak leakage path for current that might have lost or diverted current/charge/power away from the expected kinetic energy result. It is up to you to figure out if this is or isn't related to the variac overheating. The two may or may not be related even if they did not occur at the same time. In other words, some flaw or inadequate dielectric might be responsible for causing the energy loss in your experiment and causing an excessive power draw through the variac and the resulting fire. It is also possible that two totally independent causes exist.

You are going to have to talk to the sponsoring Science Fair organization and find out what their requirements are. My opinion as to what might be allowed doesn't count since you have something that needs to plug into the power grid.

And yes, I have a BSEE / MSEE degree and practiced electrical and other engineering disciplines and have at different points in my career been responsible for designing and testing equipment to meet CSA and UL safety standards.

[roflchopter]

thanks for clearing that up.

next time I do a project, I won't procrastinate (the fair is tomorrow).