Computing stuff tied to the physical world

Can’t be done

In Hardware on Jan 27, 2012 at 00:01

As you may know from posts a short while ago, I’ve been working on creating an ultra-low power supply, providing just enough energy to a JeeNode or JeeNode Micro to let it do a little work, report some data over wireless, and then go to sleep most of the time.

I even designed a PCB for this thing and had a bunch of them produced:

Screen Shot 2012 01 25 at 01 57 45

The good news is that it works as intended and that I’ll be using this circuit for some projects.

The bad news is that they won’t be available as kits in the shop. Ironically, this was the first time where I actually had a batch of kits all wrapped up and ready to go, ahead of time.

But the reality is that I can’t pull it off. For two different reasons:

  • The circuit is connected to live AC mains @ 230 VAC and that means there is a serious risk if you build this stuff, try it out, and then hurt yourself because of some mistake. And even after that, there is the risk that the whole circuit is not properly protected, exposing these voltages (even just humidity and condensation).

  • The other risk is that once everything works, it gets built-in for permanent use and becomes part of your house. What if it gets wet or malfunctions for some other reason, and your house burns down?

As supplier, I’d be liable (rightly so, BTW – there is no excuse for selling stuff which might be dangerous).

The hardest part of all is that even if an accident has nothing to do with this Low-power Supply, I still have to prove that this stuff is safe under any circumstance and that it complies with all regulations!

I’m not willing to go there. Life’s too short and I don’t have the pushing power to go through it all.

Having said this, I do intend to use this supply myself and create all sorts of nodes for use here at JeeLabs. Because I know the risks, I know which failsafe features have been built into the supply, and I’m ok with it:

DSC 2894

The design is available in the CafĂ©, to document what I’ve done and for others to do whatever they like with it.

I’m not happy about this decision, in fact I hate it. I’m really proud of finding out that it is possible to create sensor nodes which run off just 12 mW of AC mains power. But the right thing to do is to stop here.

  1. That’s disappointing as I wanted a couple myself. What if you ask for some sort of waiver. I will be willing to take the risk and if I don’t buy it from you I’ll have to make something else myself.

  2. Although you might hate your own decision, I think it’s the only wise thing to do in this case. In fact, for me, it’s comforting to see that our safety is in good hands here.

  3. We all understand your decision and you already gave so many good things :)

  4. Why not offer pcb only plus hard to find parts? You are not selling a product…

    Anyway, I respect your decision

    • If he sells the PCB’s he’s still liable, because he sold an intermediate good that might be dangerous.

      The only method of this working out correctly is having everyone sign an agreement which makes them aware that this is untested and dangerous stuff and that they are aware of all the risks, which is nearly impossible, because those risks stretch further than most hobbyists might initially imagine.

      Then there are the insurance companies. (Yes, they are just one of those risks). In fact it remains to be seen if JCW’s insurance still covers him if he uses these things inside his own house. In fact you are not even insured anymore if you do not have the proper training and certificates to mess with the mains wiring in your own home! Good thing that this wiring is usually trivial, so they can’t find something to complain about and thus you can (nearly always) get away with it. But if we start talking about gas-lines, there are a few very subtle details that you may not know about, but will immediately give away that you didn’t call a certified person to do the job properly. JCW sure made the right choice if it comes to keeping everyone in here safe and in covering his own ass at the same time.

      Meanwhile to ease the disappointment a bit: DX has some pretty cheap solar mobile phone chargers with LiPo batteries inside. If your project can run off this little power supply of JCW, then it will also run of a <12$ DX Solar Phone charger. In my experiments, the ambient light provided enough energy to keep a powered down JeeNode running all day and charges enough to keep it powered through the night! These are a much safer choice to play around with and they enable you to get an energy source nearly everywhere in, or outside your home.

    • There are two different things to consider:

      If you are a manufacturer of a product or sell a product, you might be held liable in case this product hurts someone (or puts a house on fire, …). This is (one reason) why JC decided not to put it on the market. ( To save HIS ass, plainly said)

      If YOU decide to build something like this AC supply from a pcb offered by JC (or completely on your own), YOU will be liable if something bad happens. So maybe your health or life insurance does not pay if you are hurt or killed or your building insurance will not pay in case of fire. So YOU should decide, if you want to take this risk. (To save YOUR ass …)

  5. JCW I am always learning much from your diary type writing. On this issue I have learnt that it is possible to run a Jeenode off 230V mains using incredibly low power and have gone down the learning path with you, and now know how it can be done probably in the best manner. I found this this very useful and if I had tried to do it myself may have been electrocuted. The knowledge is invaluable.

  6. jcw, I understand and agree with the position you have taken. You great work has done all the research and you have made your designs available to anyone to make there own assessment as to the risk. Great work and right decision given the moral and legal challenges with mains connected equipment.

  7. It is an unfortunate commentary on life that while one can be very conscientious with regard to the safety of others, the Western “Liability Mentality” has an unquenchable need to allocate blame somewhere – even if the issue is a direct result of misuse or ignorance. Hence the schools of legal sharks waiting to sue (for a fat slice of the potential damages awarded).

    Contrast this with the flood of “cheap” electronics products arriving from China – clones, optimistic specs, shoddy construction, safety marked without testing …..

    Different rules for imports? No, but who do you sue? Ebay? The importer? Often a “shell” company with limited capital or closed down within a year – good luck.

    Difficult to see restoring a more equitable balance.

    • That’s exactly why I pointed to the Solar chargers. They can catch on fire if used improperly but the risk of serious injuries is much lower than with JCW’s low-power supply. Most of them have proper charging circuitry inside which makes them just as (or even less) dangerous as using a JeeNode USB connected to a LiPo battery. (See JCW’s radioblip nodes)

      A good rule of thumb: Never buy anything cheap that connects to mains power from cheap stores in China! It could be really dangerous!

  8. Consumption will be even less If you put diod before zenner, I suppose.

    • buslik – not the case here. To get the series capacitor store/release cycle, the discharge through the forward biased zener diode is required. Your method works when C is replaced by R – but then much more power is wasted in the R than you gain.

      You can get more efficiency by using a bridge rectifier input, but this particular design was aimed at an application that needed the DC output referenced directly to one of the AC inputs – this is lost when using a bridge input.

  9. Got it – indeed, like this is more interesting.

  10. buslik – if you are interested, there is further explanation of the design here.

  11. I read your posts every day, and enjoy and learn from them. That said, it is TRUELY a shame, that we believe we can make EVERYTHING safe, for EVERYBODY, ALL of the time. You can put as many labels on a ladder as you want, but someone is still going to place it on top of the wheel borrow (to get that little extra height) and then fall and break their foolish neck! I agree that you must do what you have, but how many years back in time would we all be if folks did not experiment on the edge and take acceptable risks, because they “might” have gotten hurt? We can only hope that folks like JCW keep exploring the edge, and drag all of us along!

  12. Could you sell them as trendy, high-tech key fobs?

    • Only way to sell ‘em, is if there’s a serious low-power use for this thing. But that’d just be playing games to get around a valid requirement.

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