heat – Experimental Engineering

Posted on January 19, 2018 by The Engineer — Leave a comment

Etching PCBs With Dry Film Photoresist

Since I do my own PCBs on a somewhat regular basis, I decided it was time to move to a more professional method to etch my boards. I have been using the cheap toner transfer method, using special yellow coated paper from China. (I think it’s coated in wax, or some plastic film).

The toner transfer paper does usually work quite well, but I’ve had many issues with pinholes in the transfer, which cause the etched tracks to look horrid, (not to mention the potential for breaks & reduced current capacity), and the toner not transferring properly at all, to issues with the paper permanently fusing to the copper instead of just transferring the toner.

BigClive has done a couple of fairly comprehensive videos on the dry film photoresist available from AliExpress & eBay. This stuff is used similarly to the toner transfer method, in that the film is fused to the board with heat, but then things diverge. It’s supplied either in cut sheets, or by the roll. I ordered a full roll to avoid the issues I’ve heard of when the stuff is folded in the post – once it’s creased, it’s totally useless. The dry film itself is a gel sandwiched between two protective plastic film sheets, and bonds to the board with the application of heat from a laminator.

The board is first cleaned with scotchbrite pad & soap to remove any tarnish & oil from the copper.

Once the board has been cleaned, one side of the backing film is removed from the gel with adhesive tape, and the dry film is placed on the board while still wet. This stops the film from sticking immediately to the clean copper, one edge is pressed down, and it’s then fed through a modified laminator:

I’ve cut away most of the plastic covering the hot rollers, as constant jamming was an issue with this cheapo unit. All the mains power is safely tucked away under some remaining plastic cover at the end. The board with it’s covering of dry film is fed into the laminator – the edge that was pressed down first. This allows the laminator to squeeze out any remaining water & air bubbles from between the two so no creases or blisters form.

Once the board has been run through the laminator about 6 times, (enough to get it very hot to the touch), the film is totally bonded to the copper. The top film is left in place to protect the UV sensitive layer during expsure.

The exposure mask is laser printed onto OHP transparencies, in this case I’ve found I need to use two copies overlaid to get enough opacity in the black toner sections to block the UV light. Some touching up with a Sharpie is also easy to do if there are any weak spots in the toner coverage. This film is negative type – All the black areas will be unexposed and washed off in the developer tank. I also found I had to be fairly generous with track spacing, using too small lines just causes issues with the UV curing bits of film it isn’t supposed to.

The PCB is placed on a firm surface, the exposure mask lined up on top, and the whole thing covered with a sheet of standard glass to apply even pressure. The UV exposure lamp in this case is a cheap eBay UV nail curing unit, with 15 high power LEDs. (I’ll do a teardown on this when I get some time, it’s got some very odd LEDs in it). Exposing the board for 60 seconds is all the time needed.

After the board is exposed, the areas that got hit with the UV light have turned purple – the resist has hardened in these areas. It’s bloody tough as well, I’ve scrubbed at it with some vigour and it doesn’t come off. Toner transfer was a bit naff in this respect, most of the time the toner came off so easily that the etchant lifted it off. After this step is done, the remaining protective film on the top can be removed.

The film is developed in a solution of Sodium Carbonate (washing Soda). This is mildly alkaline and it dissolves off the unexposed resist.

Now it’s into the etching tank for a couple of minutes, I’m still using Ferric Chloride to etch my boards, at about 60°C. Etching at room temperature is much too slow. Once this is done, the board is washed, and then dipped in the strip tank for a couple of minutes. This is a Sodium Hydroxide solution, and is very caustic, so gloves are required for this bit. Getting Ferric Chloride on skin is also a fairly bad idea, it stains everything orange, and it attacks pretty much every metal it comes into contact with, including Stainless Steel.

This method does require some more effort than the toner transfer method, but it’s much more reliable. If something goes wrong with the exposure, it’s very easy to strip the board completely & start again before etching. This saves PCB material and etchant. This is definitely more suited to small-scale production as well, since the photomask can be reused, there’s much less waste at the end. The etched lines are sharper, much better defined & even with some more chemicals involved, it’s a pretty clean process. All apart from the Ferric Chloride can be disposed of down the sink after use, since the developer & stripper are just alkaline solutions.

Posted on August 17, 2017August 16, 2017 by The Engineer — 2 Comments

EpEver MT50 Control Panel Teardown

Here’s the MT50 controller from EpEver, that interfaces with it’s Tracer MPPT solar charge controllers, and gives access to more programming options on the charge controllers, without the need for a laptop. The display is a large dot-matrix unit, with built in backlight. Above is the display on the default page, showing power information for the entire system.

The rear plastic cover is held in place by 4 machine screws, which thread into brass inserts in the plastic frame – nice high quality touch on the design here, no cheap self tapping plastic screws. Both power & data arrive via an Ethernet cable, but the communication here is RS-485, and not compatible with Ethernet! The PCB is pretty sparse, with comms & power on the left, LCD connection in the centre, and the microcontroller on the right.

On the left of the board is the RS0485 transceiver, and a small voltage regulator. There’s also a spot for a DC barrel jack, which isn’t included in this model for local power supply.

The other side of the board holds the main microcontroller which communicates with the charge controller. This is a STM32F051K8 from ST Microelectronics. With a 48MHz ARM Cortex M0 core, and up to 64K of flash, this is a pretty powerful MCU that has very little to do in this application.

The front of the PCB has the ENIG contacts of the front panel buttons, and the LCD backlight assembly. There’s nothing else under the plastic backlight spreader either.

The front case holds the LCD module in place with glue, and the rubber buttons are placed underneath, which is heat staked in place.

The LCD is a YC1420840CS6 from eCen in China. Couldn’t find much out about this specific LCD.

Posted on July 2, 2017 by The Engineer — Leave a comment

nb Tanya Louise – Gas Locker Corrosion Part 1 – Removing The Old Locker & Replacing the Deck Plate

This is a part of the boat that hasn’t really had much TLC since we moved aboard, and finally it’s completely succumbed to corrosion, opening a rusty hole into the engine space below. I’ve already used a grinder to remove the rest of the locker – and even this had corroded to the point of failure all around the bottom just above the welds. The bulkhead forming the rear of the locker has also corroded fairly severely, so this will be getting cut out & replaced with a new piece of steel.
This was originally a 1/8″ plate, but now it’s as thin as foil in some places, with just the paint hiding the holes.

I’ve cut out as much of the corroded deck plate as possible – it’s supported underneath by many struts made of angle iron, and got the new 3mm replacement tacked in place with the MIG. I’ve not yet cut out the rotten section on the bulkhead, this will come after we’ve got the steel cut to replace it, as electrical distribution is behind this plate – I’d rather not have weather exposure to the electrical systems for long! Unfortunately more corrosion has showed itself around the edges of the old locker:

Around the corner the steel has pretty much totally failed from corrosion coming from underneath – applying welding heat here has simply blown large holes in the steel as there’s nothing more than foil thickness to support anything.

Some more extensive deck replacement is going to happen to fix this issue, more to come when the steel comes in!

Posted on September 27, 2016 by The Engineer — Leave a comment

Inductive Hour Counter / Tachometer – Petrol Engines

As one of my current projects involves a small petrol engine – a Honda GX35 clone, I figured an hour counter would be very handy to keep an eye on service intervals. (More to come on the engine itself later on). I found a device that would suit my needs on good old eBay.

These engine monitors are pretty cheap, at about £4. The sensing is done by a single heat-resistant silicone wire, that wraps around the HT lead to the spark plug. The unit can be set for different firing intervals via the buttons. In the case of most single-cylinder 4-stroke engines, the spark plug fires on every revolution – wasted-spark ignition. This simplifies the ignition system greatly, by not requiring the timing signal be driven from 1/2 crankshaft speed. The second “wasted” spark fires into the exhaust stroke, so has no effect.

The back cover is lightly glued into place with a drop of cyanoacrylate in opposite corners, but easily pops off. The power is supplied by a soldered-in 3v Lithium cell. The main microcontroller has no number laser etched on to it at all – it appears it skipped the marking machine.

The input from the sensing wire comes in through a coupling capacitor & is amplified by a transistor. It’s then fed into a 74HC00D Quad 2-Input NAND gate, before being fed into the microcontroller.

The pickup wire is simply wound around the spark plug lead. I’ve held it in position here with some heatshrink tubing. Heat in this area shouldn’t be an issue as it’s directly in the airflow from the flywheel fan.

Posted on June 27, 2016 by The Engineer — Leave a comment

Boat Stuff: Bowman Oil Cooler

To solve some engine oil overheating problems on board nb Tanya Louise, we decided to replace the air-over-oil cooler, with an water-over-oil cooler, with separate cooling drawn straight from the canal, as the skin tanks are already overloaded with having to cope with not only cooling the engine coolant, but also the hydraulic system oil as well.
These units aren’t cheap in the slightest, but the construction quality & engineering is fantastic.

Unbolting the end cover reveals the brass tube end plate, soldered to all the core tubes in the cooler. An O-Ring at each end seals both the end cover & the interface between the tube plate & the outer casing.

The end caps have baffles cast in to direct the cooling water in a serpentine path, so the oil gets the best chance at dissipating it’s heat to the water.

The oil side of the system is on the outside of the tubes, again baffles placed along the stack direct the oil over the highest surface area possible.

The outer shell is just a machined alloy casting, with no internal features.

Posted on February 20, 2016December 22, 2018 by The Engineer — Leave a comment

IC Decapping: The Process

As I’ve been posting some photos of decapped ICs lately, I thought I’d share the process I use personally for those that might want to give it a go 😉

The usual method for removing the epoxy package from the silicon is to use hot, concentrated Nitric Acid. Besides the obvious risks of having hot acids around, the decomposition products of the acid, namely NO² (Nitrogen Dioxide) & NO (Nitrogen Oxide), are toxic and corrosive. So until I can get the required fume hood together to make sure I’m not going to corrode the place away, I’ll leave this process to proper labs ;).

The method I use is heat based, using a Propane torch to destroy the epoxy package, without damaging the Silicon die too much.

I start off, obviously, with a desoldered IC, the one above an old audio DSP from TI. I usually desolder en-masse for this with a heat gun, stripping the entire board in one go.

Next is to apply the torch to the IC. A bit of practice is required here to get the heat level & time exactly right, overheating will cause the die to oxidize & blacken or residual epoxy to stick to the surface.
I usually apply the torch until the package just about stops emitting it’s own yellow flames, meaning the epoxy is almost completely burned away. I also keep the torch flame away from the centre of the IC, where the die is located.
Breathing the fumes from this process isn’t recommended, no doubt besides the obvious soot, the burning plastic will be emitting many compounds not brilliant for Human health!
Once the IC is roasted to taste, it’s quenched in cold water for a few seconds. Sometimes this causes such a high thermal shock that the leadframe cracks off the epoxy around the die perfectly.

Now that the epoxy has been destroyed, it breaks apart easily, and is picked away until I uncover the die itself. (It’s the silver bit in the middle of the left half). The heat from the torch usually destroys the Silver epoxy holding the die to the leadframe, and can be removed easily from the remaining package.

BGA packages are usually the easiest to decap, flip-chip packages are a total pain due to the solder balls being on the front side of the die, I haven’t managed to get a good result here yet, I’ll probably need to chemically remove the first layer of the die to get at the interesting bits 😉

Once the die has been rinsed in clean water & inspected, it’s mounted on a glass microscope slide with a small spot of Cyanoacrylate glue to make handling easier.

Some dies require some cleaning after decapping, for this I use 99% Isopropanol & 99% Acetone, on the end of a cotton bud. Any residual epoxy flakes or oxide stuck to the die can be relatively easily removed with a fingernail – turns out fingernails are hard enough to remove the contamination, but not hard enough to damage the die features.

Once cleaning is complete, the slide is marked with the die identification, and the photographing can begin.

Microscope Mods

I had bought a cheap eBay USB microscope to get started, as I can’t currently afford a proper metallurgical microscope, but I found the resolution of 640×480 very poor. Some modification was required!

I’ve removed the original sensor board from the back of the optics assembly & attached a Raspberry Pi camera board. The ring that held the original sensor board has been cut down to a minimum, as the Pi camera PCB is slightly too big to fit inside.
The stock ring of LEDs is run direct from the 3.3v power rail on the camera, through a 4.7Ω resistor, for ~80mA. I also added a 1000µF capacitor across the 3.3v supply to compensate a bit for the long cable – when a frame is captured the power draw of the camera increases & causes a bit of voltage drop.

The stock lens was removed from the Pi camera module by careful use of a razor blade – being too rough here *WILL* damage the sensor die or the gold bond wires, which are very close to the edge of the lens housing, so be gentle!

The existing mount for the microscope is pretty poor, so I’ve used a couple of surplus ceramic ring magnets as a better base, this also gives me the option of raising or lowering the base by adding or removing magnets.
To get more length between the Pi & the camera, I bought a 1-meter cable extension kit from Pi-Cables over at eBay, cables this long *definitely* require shielding in my space, which is a pretty aggressive RF environment, or interference appears on the display. Not surprising considering the high data rates the cable carries.
The FFC interface is hot-glued to the back of the microscope mount for stability, for handheld use the FFC is pretty flexible & doesn’t apply any force to the scope.

Die Photography

Since I modified the scope with a Raspberry Pi camera module, everything is done through the Pi itself, and the raspistill command.

The command I’m currently using to capture the images is:
raspistill -ex auto -awb auto -mm matrix -br 62 -q 100 -vf -hf -f -t 0 -k -v -o CHIPNAME_%03d.jpg

This command waits between each frame for the ENTER key to be pressed, allowing me to position the scope between shots. Pi control & file transfer is done via SSH, while I use the 7″ touch LCD as a viewfinder.

The direct overhead illumination provided by the stock ring of LEDs isn’t ideal for some die shots, so I’m planning on fitting some off-centre LEDs to improve the resulting images.

Image Processing

Obviously I can’t get an ultra-high resolution image with a single shot, due to the focal length, so I have to take many shots (30-180 per die), and stitch them together into a single image.
For this I use Hugin, an open-source panorama photo stitching package.

Here’s Hugin with the photos loaded in from the Raspberry Pi. To start with I use Hugin’s built in CPFind to process the images for control points. The trick with getting good control points is making sure the images have a high level of overlap, between 50-80%, this way the software doesn’t get confused & stick the images together incorrectly.

After the control points are generated, which for a large number of high resolution images can take some time, I run the optimiser with only Yaw & Pitch selected for all images.

If all goes well, the resulting optimisation will get the distance between control points to less than 0.3 pixels.

After the control points & optimisation is done, the resulting image can be previewed before generation.

After all the image processing, the resulting die image should look something like the above, with no noticeable gaps.

Posted on January 31, 2016January 30, 2016 by The Engineer — Leave a comment

Camping Gear – Optimus Nova Multifuel Stove

For as long as I can remember I’ve been using Trangia-type alcohol fuelled stoves when I go camping, even though these have served my needs well they’re very limited & tend to waste fuel. I did some looking around for Paraffin/Kerosene fuelled stoves instead, as I already have this fuel on site.
I found very good reviews on the Optimus Nova above, so I decided to go for this one.

This stove can run on many different fuel types, “white gas” (petrol without any vehicle additives) Diesel, Kerosene & Jet A.

Here’s the “hot end” of the device, the burner itself. This is made in two cast Brass sections, that are brazed together. The fuel jet can be just seen in the centre of the casting.

The fuel bottle is pressurised with a pump very similar to the ones used on Paraffin pressure lamps, so I’m used to this kind of setup. The fuel dip tube has a filter on the end to stop any munge gumming up the valves or the burner jet.

As with all liquid-fuelled vapour burners, it has to be preheated. There’s a fibreglass pad in the bottom of the burner for this, and can be soaked with any fuel of choice. The manual states to preheat with the fuel in the bottle, but as I’m using Paraffin, this would be very smoky indeed, so here it’s being preheated with a bit of Isopropanol.
The fuel bottle can be seen in the background as well, connected to the burner with a flexible hose. The main burner control valve is attached to the green handle bottom centre.

Once the preheating flame has burned down, the fuel valve can be opened, here’s the stove burning Paraffin on very low simmer. (An advantage over the older alcohol burners I’m used to – adjustable heat!)

Opening the control valve a couple of turns gives flamethrower mode. At full power, the burner is a little loud, but no louder than my usual Paraffin pressure lamps.

With a pan of water on the stove, the flame covers the entire base of the pan. Good for heat transfer. This stove was able to boil 1L of water from cold in 5 minutes. A little longer than the manual states, but that’s still much quicker than I’m used to!

The top of the burner opens for cleaning, here’s a look at the jet in the centre of the burner. The preheating pad can be seen below the brass casting.

Posted on November 19, 2015 by The Engineer — Leave a comment

Cree XML-T6 x5 LED Torch

Here’s another torch from eBay, this time with 5 Cree XML-T6 LEDs.

Having 5 Cree LEDs rated at up to 3A a piece, this light has the capacity to draw about 50W from it’s power supply. In this case though, current draw is about 1.5A at 12v input on the full brightness setting.

Here’s the LEDs mounted into the reflector. Fitting this many high power LEDs into a small space requires some serious heatsinking. The casing is made of machined aluminium.

Unscrewing the front bezel allows the internals to come out. The core frame & reflector is all cast alloy as well, for heatsinking the LEDs. The controller PCB is mounted into a recess in the back of the LED mount.

Here’s the controller itself. The usual small microcontroller is present, for the multiple modes, and handling the momentary power switch.

As all the LEDs on this torch are connected in series, their forward voltage is ~12-15v. The battery is an 8.4v Li-Ion pack, so some boost conversion is required. This is handled by the circuitry on the other side of the board, with this large power inductor.

The reflector screws onto the front of the LED array, centered in place with some plastic grommets around the LEDs themselves.

Finally for the torch, the LED array itself. This is attached to the frame with some thermal adhesive, and the LEDs themselves are mounted on an aluminium-core PCB for better heat transfer.
This module unsurprisingly generates quite some heat, so I have improved the thermal transfer to the outer case with some thermal grease around the outer edge.

The supplied charger is the usual Chinese cheapy affair, claiming an output current of 1A at 8.4v. I never use these chargers, so they get butchered instead.

Here’s the main PCB. Overall the construction isn’t that bad, the input mains is full-wave rectified, but there is little in the way of RFI filtering. The supply is fused, but with an absolutely tiny glass affair that I seriously doubt has the ability to clear a large fault current.
Like many cheap supplies, the output wiring is very thin, it’s capacity to carry 1A is questionable.

On the reverse side, there’s a nice large gap between the mains side & the low voltage output. There’s even an anti-tracking slot under the optoisolator.

Posted on August 19, 2015 by The Engineer — Leave a comment

12v CFL Lamp Failure Analysis

On the boat I have installed custom LED lighting almost everywhere, but we still use CFL bulbs in a standing lamp since they have a wide light angle, and brightness for the size.

I bought a couple of 12v CFLs from China, and the first of these has been running for over a year pretty much constantly without issue. However, recently it stopped working altogether.

Here’s the lamp, exactly the same as the 240v mains versions, except for the design of the electronic ballast in the base. As can be seen here, the heat from the ballast has degraded the plastic of the base & it’s cracked. The tube itself is still perfectly fine, there are no dark spots around the ends caused by the electrodes sputtering over time.

Here’s the ballast inside the bottom of the lamp, a simple 2-transistor oscillator & transformer. The board has obviously got a bit warm, it’s very discoloured!

The failure mode in this case was cooked wiring to the screw base. The insulation is completely crispy!

On connection direct to a 12v supply, the lamp pops into life again! Current draw at 13.8v is 1.5A, giving a power consumption of 20.7W. Most of this energy is obviously being dissipated as heat in the ballast & the tube itself.

Here’s the ballast PCB removed from the case. It’s been getting very warm indeed, and the series capacitor on the left has actually cracked! It’s supposed to be 2.2nF, but it reads a bit high at 3nF. It’s a good thing there are no electrolytics in this unit, as they would have exploded long ago. There’s a choke on the DC input, probably to stop RFI, but it doesn’t have much effect.

Here’s the waveform coming from the supply, a pretty crusty sinewave at 71.4kHz. The voltage at the tube is much higher than I expected while running, at 428v.

Holding the scope probe a good 12″ away from the running bulb produces this trace, which is being emitted as RFI. There’s virtually no filtering or shielding in this bulb so this is inevitable.

Posted on July 31, 2015 by The Engineer — Leave a comment

Lethal Chinese Mains Adaptors

With every piece of Chinese electronics I obtain, mainly Baofeng radios, they come with a Europlug-type power adaptor, and a universal plug adaptor for the mains.

The charger units aren’t too bad, there’s a fair amount of isolation between the primary & secondary, and even though they’re very simple & cheap, I can’t see any immediate safety problems with them.

The plug adaptors, however, are a different matter. These things are utterly lethal!

Here’s the inside of the PSU. It’s just a very simple SMPS, giving an output of 10v 500mA. The fuse is actually a fusible resistor.

Here’s the back of the PCB with the SMPS control IC. I can’t find any English datasheets for this part unfortunately.

Here’s the dangerous adaptor. There’s no safety shield, so the live parts are exposed.

Here’s the adaptor split apart. The output contacts are on the left, and rely just on pressure to make contact with the brass screws on the mains input pins to provide power.
This is a very poor way to get a connection, a dirty or worn contact here would create a lot of heat if any significant power is pulled through, and could quite possibly result in a fire.

Not surprisingly, I bin these things as soon as I open the box, and charge all my radios with a 12v charging system.

Posted on October 7, 2014October 7, 2014 by The Engineer — Leave a comment

HPI Savage Petrol Conversion – Fuel & Silicone – Chemical Compatibility

While I was already well aware of the effects of petrol on silicone products – the stuff swells up & dissolves over a very short period of time, which makes it an unsuitable material for seals in a petrol fuel system.

I wasn’t aware the O-Ring on the fuel tank cap of the Savage is silicone, as can be seen in the image above it has swelled up to much larger than it’s original size. It’s supposed to sit in the groove on the cap & fit into the filler neck when closed.
This was only from a couple of hours of petrol exposure, now the seal is such an ill fit that the cap will not close properly.

The solution here is to replace the ring with a Viton O-Ring, 2.5mm cross section, 23mm ID. I assume the fuel tank is made of polypropylene – this should stand up fine to the new fuel.

Another concern was the O-Rings on the carburettor needles, however these seem to be made of a petrol-resistant material already & are showing no signs of deterioration after 24+ hours of fuel immersion.
The O-Rings that seal the engine backplate to the crankcase also seem to be working fine with the new fuel.

Another silicone part on the engine is the exhaust coupling, between the back of the cylinder & the silencer, I’m not aware of a suitable replacement as yet, although as it will mainly be exposed to the combustion products & not raw fuel, it may just survive the task.

The extra heat from burning petrol in one of these engines may also put a lot of stress on this component, if it eventually fails I may attempt a replacement with automotive hose – time will tell on this one.

I’m also not sure of the plastic that standard fuel bottles are made from – their resin identification number is 7, so it could be any special plastic, but I’m guessing it’s Nylon.
However according to the spec sheet for Nylon, it’s chemically compatible with petrol – yet the plastic appears to be getting softer with exposure, so it may be a special blend designed specifically for glow fuel.

Besides these small glitches, the engine is running well on it’s newly assigned diet of petrol, I’m currently running an 18:1 mix of petrol to oil (250ml oil to 4.5L of petrol), this seems to be providing more than adequate lubrication. While it smokes like a chimney, plenty of unburned oil is making it out of the exhaust, so the engine’s internals should have a liberal coating.
I’m yet to actually run the model out in open space so I can start tuning the mixture, but bench tests are promising.

More to come!

Posted on April 6, 2013April 22, 2013 by The Engineer — Leave a comment

Wearable Raspberry Pi SMPS Modifications

A few modifications were required to the SMPS modules to make the power rails stable enough to run the Pi & it’s monitor. Without these the rails were so noisy that instability was being caused.

I have replaced the 100µF output capacitors & replaced them with 35v 4700µF caps. This provides a much lower output ripple.

There are also heatsinks attached to the converter ICs to help spread the heat.

Posted on October 4, 2011 by The Engineer — Leave a comment

LED Lighting Part 1

Here I will document progress in replacing standard halogen MR10 lights with LEDs.

These units are from TruOpto, available through Rapid Electronics in the UK. They are 3W total, from 3x 1W emitters on an aluminium back plate.

Here is the LED attached to a heatsink for testing purposes – these units dissipate nearly 2W in heat at full output.

As the lights are to be run from a 12v battery bank, for simplicity a master regulator is required to provide a stable 11.4v rail for LED supply.

I have used a Texas Instruments part – PTN78020WAH. This is a 6A capable adjustable regulator module.

The LED lights are to be fully dimmable – the low voltage PWM dimmers are in progress of being built.

Posted on February 8, 2011February 4, 2011 by The Engineer — Leave a comment

Hot Laminator

Here is a cheap no brand hot laminator. This pulls the paper, inside a plastic pouch through a pair of heated rollers to seal it.

Top removed, heater assembly visible. PCB attached to the top cover holds LEDs to indicate power & ready status.

Here is the thermostat & thermal fuse, the thermostat switching the indicator on the front panel to tell the user when the unit is up to temperature. This has a self regulating thermostat. Thermal fuse inside the heat resistant tubing is to protect against any failure of the heater.

5 RPM motor that turns the rollers through a simple gear system.

Posted on January 20, 2011January 20, 2011 by The Engineer — Leave a comment

455nm Laser Head

Here’s my prototype 455nm laser head, constructed from the front section of an Aixiz module threaded into a heatsink from an old ATX power supply. This sink has enough thermal mass for short 1W testing.

Connection to the laser diode at the back of the heatsink. Cable is heat shrink covered for strain relief, & hot glued to the sink for extra strain relief.

Looking down the beam, laser is under the camera. Operating around 1.2W here

Camera looking towards the laser. Again operating at ~1.2W output power.

Posted on August 1, 2010 by The Engineer — Leave a comment

Hair Dryer

This is a 1500W hairdryer, death caused by thermal switch failure.

This is the switch unit. Attached are two suppression capacitors & a blocking diode. Cold switch is on right.

Heating element unit removed from housing. Coils of Nichrome wire heat the air passing through the dryer. Fan unit is on right.

Other side of the heating element unit, here can be seen the thermal switch behind the element winding. (Black square object).

The fan motor in this dryer is a low voltage DC unit, powered through a resistor formed by part of the heating element to drop the voltage to around 12-24v. Mounted on the back of the motor here is a rectifier assembly. Guide vanes are visible around the motor, to straighten the airflow from the fan blades.

5-blade fan forces air through the element at high speed. Designed to rotate at around 13,000RPM.