Another HV Propeller Application - Hot Wire Foam Cutter Power Supply And Controller
idbruce
Posts: 6,197
Hello Everyone
I just finished up one HV application this morning, now it is time to finish another. Approximately a year ago, I developed an inexpensive yet sturdy hot wire foam cutter for making lost foam casting molds. And once again, it was one of those items that turned out so nice that I intend to add it to my product line. I am thinking of preparing all the parts and selling them as a kit on eBay. Anyhow this project is incomplete, and I still have to create the power supply and controller. However, before I get into the interesting specifics pertaining to the creation of a power supply and controller, I would like to discuss a few other things.
Although I believe this unit will become a profitable venture for me, I do have some liability concerns, and therefore I have some questions.
Before the "forum police" start attacking my thread by asking questions like, "How does this apply to the Propeller chip?", don't worry, this thread will evolve.
Bruce
I just finished up one HV application this morning, now it is time to finish another. Approximately a year ago, I developed an inexpensive yet sturdy hot wire foam cutter for making lost foam casting molds. And once again, it was one of those items that turned out so nice that I intend to add it to my product line. I am thinking of preparing all the parts and selling them as a kit on eBay. Anyhow this project is incomplete, and I still have to create the power supply and controller. However, before I get into the interesting specifics pertaining to the creation of a power supply and controller, I would like to discuss a few other things.
Although I believe this unit will become a profitable venture for me, I do have some liability concerns, and therefore I have some questions.
- A hot wire foam cutter can definitely become a fire hazard. How would a business limit their liability in such a product to the bare minimum? I personally believe that by selling it in kit form I should be able to limit some of the liability, but I could be wrong.
- Can I also limit my liability by selling the resistance wire seperately?
- How does one go about protecting themselves when selling a 24VDC @ 2A power supply and controller?
Before the "forum police" start attacking my thread by asking questions like, "How does this apply to the Propeller chip?", don't worry, this thread will evolve.
Bruce
Comments
Bruce,
I don't think there i any liability for a hot wire foam cutter. Sure, you need to indicate that that there is a POTENTIAL of fire, but I have not seen it in normal use. I use any thing from a hand held gun type, to a bow slicer, to a full blown 13' x 13' CNC foam cutter.
Here a a link to a company I buy my supplies from. I don't see anything on the site indicating thier products are a potential hazard.
There is always liability when offering any kind of product or any type of service.
Bruce
EDIT: If a person manufactures and sells red rubber balls, there are still liability issues.
EDIT: If a person rakes leaves for a living, there are still liability issues.
I see your concerns, but wouldn't that be a question for a lawyer, not a electronics forum?
But, perhaps, others in here have been through this before.
I have a product that I have almost completely developed for controlling Christmas lights using the Propeller. The liability and product certification issues have just about killed my will to move forward. I might simply sell it as a kit through a LLC or some other form of corporation, if I do anything at all with it.
Yes a lawyer or insurance agent, but a little knowledge goes a long way. As you said:
@ke4pjw
I believe if you sell something in kit form, I believe the consumer assumes most of the risk.
The problem with the disclaimers is that a person or business may disclaim anything, however a court in a civil or criminal litigation may see things quite differently.
Bruce
Bruce
Get insurance.
Get all safety testing/approvals done.
Plaster the product and it's packaging in acres of warning notices.
Set up a limited liability company to sell the thing.
... and when it's all said and done if someone cuts his own nose off with the hot wire you'd probably still get sued. Unfortunately, we live in a very litigious society.
Just like investment, it's a matter of risk/reward. You have to pick the spot in the scale where you find the risk acceptable. If you want near-zero risk, then it'd probably cost more to achieve that than you'd ever make from selling the product. If you're willing to accept zero reward, then you can probably achieve low risk by publishing the design in the public domain without selling anything.
And then get ready for the lawsuits, anyway. Sadly, too many poeople in our society make their "living" by taking from others -- guilty or not -- via lawsuits. While driving through Beverly Hills a few months ago I saw a vanity plate: ISUEYOU. I really wanted to smash into that Ferrari, but my love of exotic cars and not dealing with a vampire lawyer stopped me
Enough of the boring legal details, I will now start progressing into discussing the power supply and then ultimately the controller itself, however both the power supply and the controller will reside within the same housing.
Over the next couple days, I will start designing a linear power supply. During this time, I will document my selection of components, the math behind the selections, and a schematic.
I hope that you will find this thread interesting and of use. Please stay tuned for future updates.
Bruce
That'll be quite interesting. I've had a few projects where I've needed a 24V power supply myself, but have ended up buying an aftermarket switching supply rather than building a linear supply. Generally for me the issue was finding a decent price on the transformer. They often cost as much as a whole switching supply. I look forward to seeing your design.
http://www.walmart.com/ip/Schumacher-SpeedCharge-Battery-Maintainer-and-Charger/13005742
FYI It is not really HV as there are definitions for LV, ELV, etc. IIRC ~60V and above come into a new classification, at least for Europe which we tend to follow in Oz.
OT They use wire cutters to make foam wings for model airplanes. I have a flying wing which I bought from a local guy who cuts these. But, then I found QuadCopters and they are far more interesting because I can use a prop! Alas, time has prevented me completing this project yet (and my 3D ABS printer for which my prop pcb is just about complete)... Just too many prop projects and not enough time
Bruce
Rule #1 - Through out old rules and definitions, and create new ones
For a listing of their available transformers, you can go to the following link.
http://www.mpja.com/products.asp?dept=45
and here is a link to the transformer that I will be using for this current project.
http://www.mpja.com/prodinfo.asp?number=7843+TR
Please note that this transformer is a 18V center tap (9V-0-9V) 2A transformer
In an earlier post, I stated that I would be shooting for a 24VDC @ 2A power supply, when in reality, considering that I will be using a full wave bridge for rectification, the output will be much closer to 25.2V after rectification from the output of the transformer. When using a full wave bridge for rectification, multiply the secondary output from the transformer by 1.4 to obtain the rectified voltage. Please refer to the attached documentation for rectification and other pertinent information.
Bruce
*NOTE - This is a design in progress. These parts are subject to change!
18V center tap (9V-0-9V) 2A transformer $5.95
http://www.mpja.com/prodinfo.asp?number=7843+TR
200PIV 4A In-Line Bridge $0.88
http://www.mpja.com/prodinfo.asp?number=5238+BR
I will probably be changing the following capacitor value to somewhere around 7000uF
50V 20,000 uF Aluminum Electrolytic Filtering Capacitor $8.01
http://www.mouser.com/ProductDetail/Panasonic-Electronic-Components/ECO-S1HP223EA/?qs=sGAEpiMZZMtZ1n0r9vR22RSFeKT%2fCuZ6nFFOdk7sEfs%3d
2A 250V 3AG FUSE (Qty. 10) $0.99
http://www.mpja.com/prodinfo.asp?number=15779+FU
AC Power Line Filter (Optional, but recommended) $4.80
http://www.mouser.com/Search/ProductDetail.aspx?qs=HFfMDpzxxd2bsSUsfWbMdA%3d%3d
Don't get wrapped up in the liability concerns - just provide the best safety features and properly describe use of the product.
Ken Gracey
Thanks for your input Ken.
Never heard of that before
Bruce
That transformers are more efective.
http://www.tabtronics.com/TECHNOLOGY/ElectromagneticBasics/ToroidalTransformerBasics/tabid/112/Default.aspx
Okay, but for the initial investment, please provide the link for an 18V toroidal tranformer for less than
18V center tap (9V-0-9V) 2A transformer $5.95
http://www.mpja.com/prodinfo.asp?number=7843+TR
Bruce
EDIT: For those of you who would like to put more dough out front and save on the backend, here is a link to well priced toroidal transformers
http://www.antekinc.com/index.php
I just did a search on Errors and Omissions insurance, and it sounds pretty cool to me. Thanks Ken.
Bruce
EDIT: For those of you who are interested, here is a nice article that describes Errors and Omissions insurance.
The Ins and Outs of Errors and Omissions Insurance - Source: Insurance Journal
http://www.insurancejournal.com/magazines/west/features/2004/07/19/44745.htm
"product is defective because of improper design, improper manufacturing, or negligent marketing. Improper design is when a product, even when used correctly and for its intended use, is dangerous to property, the user, or to others. Improper manufacturing is just as its name implies: the product is incorrectly made and consumers are at risk because of the mistake. Finally, negligent marketing is when a product has insufficient warnings, labels, diagrams, or instructions, or is marketed for a use other than its intended purpose."
Educate your consumer, post appropriate warnings on your product as required by law (such as OSHA requirements) and even common sense notes. (ever notice that a tube of toothpaste even says if you swallow more than intended for brushing, that you should call a poison control center immediately?)
As for HV vs LV, it depends on which standard you are using. For residential wiring, 48v is the crossing point. So, CAT5, telephone, alarm signals, etc are LV, but 110/220 AC are high voltage. According to definitions by the IEEE, high voltage is AC above 1000v and DC above 1500v. These levels are used to determine when a product requires high voltage warning labeling as well. Inverters in laptops are marked with high voltage warnings, but they are never above 1000v AC.
As for a Propeller powered foam cutter, what will be the purpose of the Propeller in the device? All of the foam cutters I have seen or used were simply a resistive element and a power supply. Are you planning on utilizing features from your CNC?
No I am not, don't get me started
Bruce
EDIT: I almost forgot that I still need to design a small rip fence for it.
*NOTE - This is a design in progress. These parts are subject to change!
*Sorry for the bump, just setting aside space that I should have allocated earlier.
Bruce
There's also some modules with integrated filter, fuse, and switch that can be handy if you don't mind having a switch right next to the power plug. I've used something similar (but not identical) to this in a few projects: http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2114124_-1?CID=PDF
Thanks very much for posting the PDF on rectifier/transformer math. I'm saving that in particular in my useful stuff folder, it's convenient to have all that math in one place and so easily diagrammed and explained. In my last power-supply project (part of the packetron-9000), I spent a few hours with an oscilloscope, a voltmeter, and a handful of rectifiers and capacitors trying to figure out how much voltage would come out of the transformer in various configurations.
You could always add an ENC28J60 to the prop and add ethernet/IP control... One can never have too many devices with built in web servers.