Overview

I was looking to ship small electronic components in anti-static bags, reusing the bags I had on hand, but they were all too big. The obvious solution was to cut them to a reasonable size and seal the edges with a bag sealer. However, I did not want to buy one so I built this simple version using components I had in stock. All I needed to do was to apply a current to a piece of wire to heat it, just enough to melt the plastic without burning it.

Here is the result:

Item	Description
1	Mains power (115v AC)
2	9 volt step down transformer. (rated at 1.3 A)
3	Parallel resistors used in series with the wire for current limiting. (The wire would glow red without this)
4	Momentary switch (Very important for safety. i.e. Not forgetting this thing on!)
5	Nails to keep the wire from touching the wood and to maintain a minimum tension.
6	Heating wire. Made from low conductance material.

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Here are a few more pictures:


The heating wire was obtained by unrolling and stretching a compression spring. It would seem that many springs are made from a metal that does not conduct electricity very well. That's exactly what's needed for this job! (Yes, if it was an utopic perfect conductor, it would not heat at all)

Use

The bag to seal must be maintained on the wire and heated for approximately 5 seconds. The timing of course depends on the plastic thickness, but it's easy to get used to it.

Here's how simple it is to split a bag for packaging small components: (skipping a few steps)

Technical data

• Input voltage: 115v AC (Canada mains voltage)
• Transformer output voltage:
  • Idle: 9.1 volt
  • In use: 8.1 volt
• Heating current: (low voltage side)
  • Cold state: 5.03 A
  • Once hot: 4.85 A (after 1 or 2 seconds)

Yes, the current exceeds the transformer 1.3A rating. The transformer is saturated, the voltage drops, and if this circuit would be left on for too long, the transformer would get very hot. Once again, the switch must be momentary. Also, I highly recommend adding a switch to the mains side or at least disconnecting the whole thing (or switching it off through a power bar) when not in use.

By looking at the picture, people may notice that there is no fuse on the mains side. There should be once for safety. Highly recommended.

Disclaimer

I cannot be held responsible for any damages that could occur to you or your equipment while following the procedures present on this page. Also, I GIVE ABSOLUTELY NO WARRANTY on the correctness and usability of the informations on this page. Please note, however, that the procedures above have worked in my case without any damages or problems.

Now you cannot say that I did not warn you :)