Project – Page 5 – Tog Hackerspace

01/02/201712/05/2018

Fixing the Variac……..Part 2

A few months ago we did a blog post about our variac. It was tripping the circuit breakers on our distribution board and we made some mods to the variac to reduce the inrush current. Our story generated a lot of interest and was picked up by Hackaday. We used a 2 terminal NTC inrush current limiter from Ametherm.

Following our story, the good folks at Ametherm and Rhopoint Components (our local distributor) were in touch with us. They gave us some great technical advice and did some calculations for us. They have a whole range of limiters and it turns out that we had actually chosen quite a good model for our application. They kindly sent us some samples.

There are many ways to soft start a load. We originally thought about adding a series power resistor and a shorting relay. We also had some suggestions around Triac and IGBT solutions. Each of these methods have their merits and can allow fine grained control of switch-on. Unfortunately there was very little room inside the variac case and we didn’t want some kind of external box. So we looked at these relatively simple 2 terminal limiters.

Carefully chosen, these components are an elegant solution. They can probably last the life of the application with no maintenance. Placed in series with the load, they have a relatively high resistance at room temperature which limits the initial inrush current. When current flows through them they self-heat and the resistance falls very quickly, so they have little effect on the normal operating current.

We have now done a rev 2 of our mod. This time selecting the model MS32 5R020 limiter. It has a lower cold resistance of 5 ohms which should keep the operating temperature down a bit. Originally, we connected the limiter using PVC insulated wire, solder and heatshrink. Given the relatively high temperatures, we have replaced this with tubular glass fibre insulation and ceramic connectors. We should have no temperature worries now.

One other gotcha we found, is that our distribution board circuit breakers are actually B-curve and not C-curve as we earlier thought. That makes them even more sensitive to surges. When we did our original mod, we didn’t do a full load test. We did a quick run with our heatgun (about 9 amps). This time we did a full load test. At 12A of output current and an ambient temp of 20 deg c. The body of the limiter measured 200 deg C, which is hot, but below the 225 deg C max rating of the device. This was quite an extreme test, but we’ll continue to monitor and do some tweaks if possible.

If you’d like to take a look at our variac, or do something else with electronics, our regular Electronics, Microcontroller and IOT evening takes place every 2nd Monday. Check out the events section of our website for details.

15/01/201712/05/2018

Ultra Reliable Electronics?

sanyo tv Once upon a time, TV repair shops were everywhere. Now there are hardly any left. There are reasons for that, probably based on a mix of cost, reliability of electronics, and a throw-away culture. Even in the few TV repair shops that are left, would anyone actually take a scope, schematic and a soldering iron to a TV these days? Maybe they would just replace the circuit board or display.

This is a tale of a Sanyo TV, made in the UK in ~1992, based on the date codes of the components inside. It has worked continuously since then. Lately the picture has gone a bit red-ish. The TV was recently replaced by a new flat screen TV, so we’ve had a chance to take a look inside. This is the first time that the back has been off since manufacture….. ~25 years ago. Depending on your point of view, you might think that 25 years isn’t that long, but it’s not too bad either for a CRT-type TV, considering also that it has never needed a repair. If you have some other electronics that has been working without repair for a very long time, we’d be interested to hear.

Inside it is remarkably clean. Apart from the one on the tube, everything else is on a single circuit board. If the tube is not the cause of the reddish picture, then this TV is probably repairable. Some further investigation is pending. If you’d like to take a look, drop into our regular Electronics, Microcontroller and IOT evening which takes place every 2nd Monday.

04/12/201612/05/2018

A Sign for Radiona

Last October, our own Jeffrey Roe visited Radiona, a makerspace in Zagreb,Croatia. While their he gave Skull Radio workshop and hung out in their space. As a thank you, we decided to make them a new sign for their door. Taking a raster image from the Radiona website, we turned their logo into an SVG and made a sign. We went for a raised lettering effect with 3mm Plywood and using CF glue to stick the letters.

For photos of the build, check out our gallery.

A video of the sign being cut.

Check out some photos of Radiona in our gallery.

03/12/201603/12/2016

DIY Vacuum Former

Last month Tog hosted Science Hack Day Dublin. A weekend where 80 makers took over the space to build all sorts of projects. A group of Tog members got together to make a home made vacuum former.

The idea came about while chatting on our IRC channel about what tools we should add next to our workshop. As just recently a got new CNC , we where looking for something we could build in a weekend and we landed on a vacuum former.

Starting off on the Saturday of the Hack Day, we formed a team to bring our idea to reality. After checking out some YouTube videos we formed a basic design.

Once we had the design, we slit the team up into three. One worked with the laser cutter to make the box. One worked with the CNC machine to make a frame to hold the plastic. Final the person worked with our electric oven to figure out the settings to melt the plastic.

Someone had the idea of drilling the holes by hand on the top of the box. Such a waste of time. So many holes we should just have laser cut them.

After a few hours all the parts where ready for our first test. It did not take us long to think of what our first object should be. A video of the inaugural us of the vacuum former is below.

Check out our gallery for photos of some of the things we have vac’ed.

Parts We Used

Cookworks Mini Oven
Shopvac
Lasercut Box (Download our design here)
CNC Frame (Download our design here rename to .dxf)
HIPS Plastic

01/11/201612/05/2018

First cuts with TOG’s DIY CNC router

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A few months ago we’ve mentioned a DIY build of a CNC router. The project turned out to be more complicated than we anticipated. The steel-based construction is not very forgiving, and the large size of the machine doesn’t help. Still, due to all the help from many members we managed to overcome a number of difficulties and do a few test engravings in MDF.

MDF is not a difficult material to mill – the most noticeable problems are the awful dust and the fluff around the edges of the cut. The furry edge is easily fixed using sand paper, but the dust will probably require some more drastic measures in order to protect our lungs. Eventually we’re planning to cut and engrave a variety of materials, many of which have interesting properties but are incompatible with our laser cutter.

Visit us during one of our Monday CAD nights to see the new machine in action or in the video below.

Continue reading “First cuts with TOG’s DIY CNC router”

28/10/201612/05/2018

Rebuilding an Ebike Battery

ebike-battery A few of our members and visitors use Ebikes. We were presented with an Ebike battery which had a dead cell. The plan was to replace the cell with a new one. This is not ideal, since you end up with a mix of old and new cells, but the balance circuit should make it usable. On further investigation we found that there were a number of dead cells. So we set about rebuilding the whole battery with new 10Ah cells.

The cells are 10Ah LiFePO4 type…. 12 of them in all. The new ones are a little bigger than the old ones, so we will have to modify the case a bit, but that won’t be a show stopper. Drop in during our fortnightly electronics night to see the build in action.