silicone – Experimental Engineering

Posted on July 1, 2018October 16, 2019 by The Engineer — 2 Comments

Goodmans Quadro 902 Composite Video Mod

Here’s the CRT & it’s drive board removed from the main chassis. Nicely modular this unit, all the individual modules (radio, tape, TV), are separate. This is effectively a TV itself, all the tuner & IF section are onboard, unlike in other vintage units I’ve modified, where the tuner & IF has been on a separate board. There’s a 3-pin header bottom centre for the tuning potentiometer, and external antenna input jack. The internal coax for the built in antenna has been desoldered from the board here. here a the usual controls on the back for adjusting brightness, contrast & V Hold, all the other adjustments are trimmers on the PCB.
Unfortunately after 30+ years of storage, this didn’t work on first power up, neither of the oscillators for vertical or horizontal deflection would lock onto the incoming signal, but a couple of hours running seemed to improve things greatly. The numerous electrolytic capacitors in this unit were probably in need of some reforming after all this time, although out of all of them, only 21 are anything to do with the CRT itself.

Here’s the anode side of the unit, with the small flyback transformer. The rubber anode cap has become very hard with age, so I’ll replace this with a decent silicone one from another dead TV. The Horizontal Output Transistor (a 2SC2233 NPN type) & linearity coil are visible at the bottom right corner of the board. Unfortunately, the disgusting yellow glue has been used to secure some of the wiring & large electrolytics, this stuff tends to turn brown with age & become conductive, so it has to be removed. Doing this is a bit of a pain though. It’s still a little bit flexible in places, and rock hard in others. Soaking in acetone softens it up a little & makes it easier to detach from the components.

There’s little on the neck board apart from a few resistors, forming the limiting components for the video signal, and the focus divider of 1MΩ & 470KΩ feeding G3. No adjustable focus on this unit. There’s also a spark gap between the cathode line & ground, to limit the filament to cathode voltage. The flyback transformer is nestled into the heatsink used by the horizontal output transistor & a voltage regulator transistor.

The CRT is a Samsung Electron Devices 4ADC4, with a really wide deflection angle. It’s a fair bit shorter than the Chinese CRT I have which is just a little larger, with a neck tube very thin indeed for the overall tube size.
Unusually, while the filament voltage is derived from the flyback transformer as usual, it’s rectified into DC in this unit, passing through a 1Ω resistor before the filament connection. I measured 5.3v here. The glow from the filament is barely visible even in the dark.

The electron gun is the usual for a monochrome tube, with 7 pins on the seal end.

The electrodes here from left are Final Anode, G3 (Focus Grid), Accelerating Anode, G2 (Screen Grid), G1 (Control Grid). The cathode & filament are hidden inside G1. In operation there’s about 250v on G2, and about 80v on G3.

The chipset used here is all NEC, starting with a µPC1366C Video IF Processor, which receives the IF signal from the tuner module to the left. This IC outputs the standard composite signal, and a modulated sound signal.
This then splits off to a µPC1382C Sound IF Processor & Attenuator IC, which feeds the resulting sound through the two pin header at the right bottom edge of the board to the audio amplifier in the chassis.
The composite video signal is fed through a discrete video amplifier with a single 2SC2229 transistor before going to the CRT cathode.
The remaining IC is a µPC1379C Sync Signal Processor, containing the sync separator, this is generating the required waveforms to drive the CRT deflection systems from another tap off the composite video line.
From this chip I can assume the unit was built around 1986, since this is the only date code on any of the semiconductors. Besides these 3 ICs, the rest of the circuit is all discrete components, which are well-crammed into the small board space.
There are 5 trimmer potentiometers on the board here, I’ve managed to work out the functions of nearly all of them:

SVR1: IF Gain Adjust
SVR2: H. Hold
SVR3: V. Size
SVR4: B+ Voltage Adjust
SVR5: Tuner Frequency Alignment? It’s in series with the tuning potentiometer in the chassis.

The PCB bottom shows the curved track layout typical of a hand taped out board. The soldermask is starting to flake off in places due to age, and there a couple of bodge wires completing a few ground traces. Respinning a board in those days was an expensive deal! Surprisingly, after all this time I’ve found no significant drift in the fixed resistors, but the carbon track potentiometers are drifiting significantly – 10KΩ pots are measuring as low as 8KΩ out of circuit. These will have to be replaced with modern versions, since there are a couple in timing-sensitive places, like the vertical & horizontal oscillator circuits.

Here the anode cap has been replaced with a better silicone one from another TV. This should help keep the 6kV on the CRT from making an escape. This was an easy fix – pulling the contact fork out of the cap with it’s HT lead, desoldering the fork & refitting with the new cap in place.

Here I’ve replaced the important trimmers with new ones. Should help stabilize things a little.

Injecting a video signal is as easy as the other units. Pin 3 of the µPC1366C Video IF Processor is it’s output, so the track to Pin 3 is cut and a coax is soldered into place to feed in an external signal.

After hooking up a Raspberry Pi, we have display! Not bad after having stood idle for 30+ years.

Datasheets for the important ICs are available below:
[download id=”5690″]
[download id=”5693″]
[download id=”5696″]

Posted on March 22, 2017April 24, 2017 by The Engineer — Leave a comment

Philips LED PAR38 Lamp Teardown

These large LED Philips PAR38 lamps were recently on clearance sale in my local T.N. Robinsons electrical contractors for about £3, so I decided to grab one in the hopes I might be able to hack it into a low-voltage LED lamp. These are full-size PAR38 format, with most of the bulk being the large aluminium heatsink on the front. The back section with the power supply module is secured with silicone, so some unreasonable force was required to liberate the two pieces.

These lamps are rated at 18W in operation, and are surprisingly bright for this power level.

The front has the moulded multi-lens over the LEDs, to spread the light a bit further than the bare dies.

The LED array is two series strings of 4 LEDs, for ~24v forward voltage. Unusual for a high power LED array, this PCB isn’t aluminium cored, but 0.8mm FR4. Heat is transferred to the copper plane on the backside by the dozens of vias around the Luxeon Rebel LEDs. There is a thermal pad under the PCB for improved heat transfer to the machined surface of the heatsink.

The power supply & control PCB is pretty well made, it’s an isolated converter, so no nasty mains on the LED connections.

Posted on February 9, 2017February 9, 2017 by The Engineer — 3 Comments

Anker PowerPort Speed 5 USB Rapid Charger Teardown

Here’s a piece of tech that is growing all the more important in recent times, with devices with huge battery capacities, a quick charger. This unit supports Qualcomm’s Quick Charge 3 standard, where the device being charged can negotiate with the charger for a higher-power link, by increasing the bus voltage past the usual 5v.

The casing feels rather nice on this unit, sturdy & well designed. All the legends on the case are laser marked, apart from the front side logo which is part of the injection moulding.

The power capacity of this charger is pretty impressive, with outputs for QC3 from 3.6-6.5v at 3A, up to 12v 1.5A. Standard USB charging is limited at 4.8A for the other 3 ports.

The two of the 5 USB ports are colour coded blue on the QC3 ports. The other 3 are standard 5v ports, the only thing that doesn’t make sense in the ratings is the overall current rating of the 5v supply (4.8A), and the rated current of each of the ports (2.4A) – this is 7.2A total rather than 4.8A.

The casing is glued together at the seam, but it gave in to some percussive attack with a screwdriver handle. The inside of this supply is mostly hidden by the large heatspreader on the top.

This is a nicely designed board, the creepage distances are at least 8mm between the primary & secondary sides, the bottom also has a conformal coating, with extra silicone around the primary-side switching transistor pins, presumably to decrease the chances of the board flashing over between the close pins.
On the lower 3 USB ports can be seen the 3 SOT-23 USB charge control ICs. These are probably similar to the Texas Instruments TPS2514 controllers, which I’ve experimented with before, however I can’t read the numbers due to the conformal coating. The other semiconductors on this side of the board are part of the voltage feedback circuits for the SMPS. The 5v supply optocoupler is in the centre bottom of the board.

Desoldering the pair of primary side transistors allowed me to easily remove the heatspreader from the supply. There’s thermal pads & grease over everything to get rid of the heat. Here can be seen there are two transformers, forming completely separate supplies for the standard USB side of things & the QC3 side. Measuring the voltages on the main filter capacitors showed me the difference – the QC3 supply is held at 14.2v, and is managed through other circuits further on in the power chain. There’s plenty of mains filtering on the input, as well as common-mode chokes on the DC outputs before they reach the USB ports.

Here’s where the QC3 magic happens, a small DC-DC buck converter for each of the two ports. The data lines are also connected to these modules, so all the control logic is located on these too. The TO-220 device to the left is the main rectifier.

Posted on September 6, 2016August 16, 2016 by The Engineer — 2 Comments

CRT Flyback / Line Output Transformer Destructive Teardown

Here’s a small flyback / Line Output Transformer from a portable colour TV set. Usually these transformers are vacuum potted in hard epoxy resin & are impossible to disassemble without anything short of explosives. (There are chemical means of digesting cured epoxies, but none of them are pleasant). This one however, was potted in silicone, so with some digging, the structure of the transformer can be revealed.

The cap was glued on to the casing, but this popped off easily. The top of the core is visible in the silicone potting material.

A small screwdriver was used to remove the potting material, while trying not to damage the winding bobbin & core too badly. The bulge in the casing that I originally thought might house a voltage multiplier turns out to be totally empty. The white plastic bobbin is becoming visible around the core.

After some more digging & a lot of mess later, the entire transformer is revealed. The primary & auxiliary secondaries are visible at the bottom of the transformer, next to the pins. These transformers have multiple windings, as they’re used not only for supplying the final anode voltage of several Kilovolts to the CRT, but many of the other associated voltages, for the heater, grids, focus electrodes, etc. These lower voltage windings are on the same part of the core as the primary.
Above those is the main high voltage secondary winding, which looks to be wound with #38-#40AWG wire (about the thinnest available, at 0.07mm diameter. This is wound in many sections of of a few hundred turns each to increase the insulation resistance to the high voltage. The main anode wire emerges from the top of the bobbin.

Hidden in a recess at the top is the main HV rectifier, which on this small transformer is a single device (it’s probably not internally, most likely a series stack of diodes to get the PIV rating required).

Posted on August 12, 2016August 4, 2016 by The Engineer — Leave a comment

Aspen Universal Condensate Pump

Here’s another piece of commercial gear, from an industrial air conditioning unit. These pumps are used to drain the condensate from the evaporator unit, so water doesn’t end up raining down from the ceiling.

This is a peristaltic pump, with a silicone hose forming the pumping element.

The test switch & electrical connections are on the back, along with the data label.

The electrical connections are all on a single 5-pin socket. Along with 240v AC mains, there are a pair of thermistors connected to the unit, which switch the pump on when a 5°C temperature difference across the evaporator coil is detected. When air is cooled, it’s capacity for moisture drops, so the water condenses out on the coil.

Here the front cover has been removed from the pump, showing the silicone tube & roller wheel. The wheel was originally Cadmium-plated, but exposure to the elements has oxidized this into highly toxic Cadmium Oxide.

Here you can see the rollers. These pinch the tube at the inlet, and the rotation carries a slug of liquid through the tube to the outlet side.

Here’s the tube itself, the main wearing part of the pump. This is replaceable as a spare part.

Inside the casing is a shaded-pole motor, connected to a large gearbox, to give the slow rotation for the pump head. The rated speed is 51RPM.

There’s not much to the control PCB. The large resistor forms a voltage dropper, to reduce the mains 240v to a more suitable level for the logic. There’s a TL062C Low-Power JFET Op-Amp & a CD4060BCM 14-stage binary ripple counter forming the logic. The set point is adjustable via the potentiometer.

The pump motor is switched via this Z7M SMD triac, not much switching power is needed here as the motor is only a very small shaded-pole type.

Posted on July 2, 2016 by The Engineer — 2 Comments

Eberspacher D5W ECU Constant Overheat Error

Here’s another Eberspacher control unit, this time from an ancient D5W 5kW water heater. The system in this case is just flaky – sometimes the heater will start without fault & run perfectly, then suddenly will stop working entirely.
The error codes are read on these very old units via an indicator lamp connected to a test terminal. In this case the code was the one for Overheat Shutdown.

Considering this fault occurs when the heater is stone cold, I figured it was either a fault with the sensor itself or the ECU.

The temperature sensor is located on the heat exchanger, right next to the hot water outlet fitting. I’m not sure what the spec is, but it reads exactly 1KΩ at room temperature.

The PCB is held into the aluminium can by means of crimps around the edge that lock into the plastic terminal cover. Inserting a screwdriver & expanding the crimps allows the PCB to be slid out.

The factory date stamp on the microcontroller dates this unit to March 1989 – considerably older than I expected!
Unlike the newer versions that use transistors, this ECU has a bunch of PCB relays to do the high current switching of the water pump motor, fan motor & glowplug.
Overall the board looks to be solidly constructed, with silicone around all the larger components.

Here’s the solder side of the PCB, which has a generous coating of sealant to keep moisture out.

Looking at the solder joints for the row of relays on the top side of the PCB, it looks like that there’s some dry joints here.
I suspect that years of vibration has taken it’s toll, as the relays are otherwise unsupported. It wouldn’t be possible to use silicone to secure these devices as they are completely open – any sealant would likely stop them from operating.

Using a very hot soldering iron I managed to get the joints to reflow properly, using lots of flux to make sure the conformal coating didn’t interfere with the reflow.

Posted on March 23, 2016 by The Engineer — Leave a comment

“SolarStorm” eBay 4x 18650 Battery Pack

Since the 4×18650 battery pack supplied with my Cree head torch is pretty shit, even by China’s standards, I figured something I could put my own cells into would be a better option. An eBay search turned up these battery boxes, not only with a direct battery output for my torch, but also a USB port for charging other devices when I’m low on charge.

The output to the lamp connector is directly connected to the battery, through the usual Lithium Ion protection, but the USB output is controlled from a single power button. Battery charge condition is displayed on 3 LEDs. Not sure why they used blue silicone for the seal & then used green LEDs… But it does work, even if a little dim.

Essential information. Does claim to be protected, and from the already existing electronics for the USB this would be expected in all but the cheapest crap.
An IP rating of IPX4 is claimed, yet just above that rating is a notice not to be used in water. Eh?
This is sealed with an O-Ring around the edge of the top cap & silicone seals around the cable & retaining screw. I did test by immersion in about 6″ of water, and it survived this test perfectly fine, no water ingress at all.

The casing holds a PCB at the bottom end with the cell straps.

Someone wasn’t that careful at getting the brass screw insert properly centred in the injection mould when they did this one. It’s mushed off centre, but i’s solidly embedded & doesn’t present any problems to usability.

The top cover holds the cell springs & the electronics.

Removing the pair of screws allows the top cap to open up. The cable, button & LEDs are robustly sealed off with this silicone moulding.

Here’s the PCB, not much on the top, other than the power button & battery indicator LEDs.

Desoldering the cell springs allows the PCB to pop out of the plastic moulding. There’s more than I expected here!

Bottom left is a DC-DC converter, generating the +5v rail for the USB port, this is driven with an XL1583 3A buck converter IC.

Bottom right is the protection IC & MOSFETs for the Lithium Ion cells. I wasn’t able to find a datasheet for the tiny VA7022 IC, but I did manage to make certain it was a 7.4v Li-Ion protection IC.

Top right is a completely unmarked IC, and a 3.3v SOT-23 voltage regulator. I’m assuming that the unmarked IC is a microcontroller of some sort, as it’s handling more than just the battery level LEDs.

A pretty decent 4-core cable finishes the job off. For once there’s actually some copper in this cable, not the usual Chineseuim thin-as-hair crap.

Posted on February 8, 2016 by The Engineer — Leave a comment

De La Rue Coin Counting Machine Followup – PSU Oddness

I did a little more digging into the PSU circuitry of the small coin counting machine, and it’s even more strange than I thought!
The part I originally thought was a transformer on the PSU board is in fact a DC-DC converter module!

Here’s the device after desoldering it from the PCB. It turns out that instead of a transformer, it’s an inductor.

Underneath is the controller electronics, with an COB controller & the switching transistors are under a protective covering of silicone.

Driving this whole lot of PSU randomness is the mains transformer, with a secondary voltage of 35v.

The only reason I can think of that the manufacturer went to this much expense with the power supply is stability – a coin counting machine that miscounts due to power supply surges, sags & spikes wouldn’t be very much use. It’s not likely I’ll see anything similar again, unless I manage to get hold of something like medical grade equipment.

Posted on August 12, 2015 by The Engineer — Leave a comment

Chinese 12v 10A Power Brick Analysis

I recently ordered a PSU to run one of the TVs I converted to 12v operation, and being an older TV, it’s a fairly heavy load at 6.5A. eBay to the rescue again, with a cheap 10A rated supply.

Like all similar supplies these days, it’s a SMPS unit, and feels suspiciously light for it’s power rating.

Luckily this one is easy to get into, no ultrasonic welding on the case, just clips. Here’s the top cover removed, big alloy plate between the heatsinks.

The top heatsink plate was glued to the top of the transformer with silicone, some gentle prying released it. From the top, things don’t look too bad. There’s some filtering on the mains input & it’s even fused!

Here’s a closeup of the primary side of the PSU, the main DC bus capacitor is a Nichicon one, but it’s clearly been recovered from another device, look at the different glue on the end!
it’s also flapping about in the breeze, the squirt of silicone they’ve put on does nothing to stop movement.
Also here is the mains input fuse, filter capacitor & common mode choke. At least there is some filtering!

The main control IC is a UC3843B High Performance Current Mode PWM Controller, operating at a switching frequency of 250kHz.
The main switching transistor is visible at the bottom left corner, attached to the heatsink.

Here’s the secondary side of the supply. The transformer itself is OK, nice heavy windings on the output to suit the high current.
It’s using proper opto-isolated feedback for voltage regulation, with a TL431 reference IC.
The output diodes are attached to the heatsink at the top of the photo, I couldn’t read any numbers on those parts.

The output filter capacitors are low quality, only time will tell if they survive. I’ll put the supply under full load & see what the temperature rise is inside the casing.

On the bottom of the PCB things get a little more dire. There isn’t really much of an isolation gap between the primary & secondary sides, and there’s a track joining the output negative with mains earth, which gets to within 2mm of the live mains input!

As with all these cheapo supplies, there’s good points & bad points, I will update when I’ve had a chance to put the supply under full load for a while & see if it explodes!

Posted on July 7, 2015 by The Engineer — Leave a comment

Mobile Radio Shack Bag

There are times when I am frequently away from home base, usually either on the canal system or at a festival. During these times it’s very handy to be able to just grab a bag, without having to be concerned about sorting everything out.

This post will only detail the portable shack bag. The power supply kit that goes along with it with be detailed in another post.

The bag I use is an VHS Camcorder bag from the early 80’s. It’s very well built, & copes easily with the weight of all the radio gear.

Total weight for this system is 13.4lbs (6kg).

Above is the bag packed. Obligatory International Ameteur Radio Symbol patch front & centre. Being an old camera bag, this easily slings over the shoulder, with it’s padded strap.

Here is all the current equipment laid out. All the equipment to enable me to set up a station anywhere.
In the following photos I will go into the details.

First off, my main radio. This is the same Wouxun KG-UV950P mobile rig I have posted about previously. I have heatshrunk the power cable to keep it together & attached my standard power connector to the end. More on these later on.

In the bag I also carry three Baofeng UV-5R handhelds. Extremely useful for short range site communications, along with their charger bases. The charging base on the right has been slightly modified to support charging of my main LED torch as well, which uses similar Li-Ion based packs as the Baofengs.

As the charger bases for the Baofeng HTs take a supply of 10v DC, I have constructed a 12v adaptor system for them. (Which utter prat of an engineer at Baofeng picked 10v?)

Also included is a small Alinco ELH-2320 35W 2m linear amplifier. This was given to me from the local HackSpace in Manchester. (They don’t have any ham members, besides myself). Also here is my small SWR & Power meter, SDR kit & a pair of syringes. These are filled respectively with Copaslip copper loaded grease, (very good for stopping fasteners exposed to the weather from seizing up), and dielectric silicone grease. (I use this stuff for filling connectors that are exposed to the weather – keeps the water out).

I always keep essential tools in the bag, here is the small selection of screwdrivers which fit pretty much any screw fastener around, my heavy-duty cable shears (these buggers can cut through starter cable in one go!) and my trusty Gerber Diesel multitool.

Main antenna magmount & a spare Raspberry Pi.

Finally, the antennas for the HTs, main dual-band antenna (Nagoya SP-45) for the magmount, a small selection of spare plugs, sockets & adaptors. Also here is a roll of self-amalgamating tape, very handy for waterproofing wiring connections (especially when used in conjunction with the silicone grease), & a roll of solder wick.

Now, the main power connectors of choice for my equipment are Neutrik SpeakOn type connectors:

These connectors have many advantages:

They are positive locking connectors. No more loose connections.
They have a high continuous current rating of 30A RMS.
Relatively weather resistant.

Also, they have two pairs of pins – and as some of my bigger non-radio related equipment is 24v, this allows me to use a single set of plugs for everything. Without having to worry about plugging a 12v device into a 24v socket, and letting out the magic blue genie.

Once everything is packed up, here’s the bag:

Everything has a neat little pocket for easy access. Some closeups below.

I will post more about my portable power system later on, as this bit of my kit is being revamped at the moment.

Stay tuned!

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 October 6, 2014October 6, 2014 by The Engineer — Leave a comment

HPI Savage X 4.6 Ignition Conversion – Initial Carburettor Settings & Module Mountings

The engine now with it’s required ignition sensor, it is now mounted back on the chassis of the model. I have replaced the stock side exhaust with a rear silencer, so I could fit the ignition module in place next to the engine.
For the mounting, I fabricated a pair of brackets from 0.5mm aluminium, bent around the module & secured with the screws that attach the engine bed plate to the TVPs. The ignition HT lead can be routed up in front of the rear shock tower to clear all moving suspension parts, with the LT wiring tucked into the frame under the engine.
In this location the module is within the profile of the model chassis so it shouldn’t get hit by anything in service.

New exhaust silencer fitted to the back of the model. This saves much space on the side of the model & allows the oily exhaust to be discharged away from the back wheel – no more mess to wipe up.

The ignition switch fitted into the receiver box. This is wired into channel 3 of the TF-40 radio, allowing me to remotely kill the engine in case of emergency. I have fitted a 25v 1000µF capacitor to smooth out any power fluctuations from the ignition module.
The radio is running from a 11.1v 1Ah 3S LiPo pack connected to a voltage regulator to give a constant 6.5v for the electronics. I found this is much more reliable than the standard 5-cell Ni-MH hump packs.

The stock silicone fuel tubing has been replaced with Tygon tubing to withstand the conversion to petrol.

High speed needle tweaked to provide a basic running setting on petrol. This is set to ~1.5mm below flush with the needle housing.

Low speed needle tweaked to provide a basic running setting on petrol. This is set to ~1.73mm from flush with the needle housing.

As petrol is a much higher energy density fuel, it requires much more air than the methanol glow fuel – ergo much leaner settings.
The settings listed should allow an engine to run – if nowhere near perfectly as they are still rather rich. It’s a good starting point for eventual tuning.

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

Solar Cable Upgrade & Pseudo-MPPT

As the cable supplied with the panel is far too short, inflexible & does not even allow the cable gland on the terminal box to form a seal, I have replaced it with some high quality twin core guitar cable, with silicone insulation.

The cable is removable from the panel tail by means of a screwlock two pin connector.

On another note, I have noticed a side effect of fitting a switchmode regulator to the panel: it seems to have formed an MPPT-type regulator setup, as even in low light conditions, when the bare panel is outputting 18.5v at 50mA short circuit, with the switching regulator I can get a useable 13.25v at ~170mA.
This effect is increased in full light, where I can obtain 4.5A short circuit current & ~1.8A at 13.25v output.

Posted on February 2, 2013 by The Engineer — Leave a comment

He-Ne Laser

Having had a He-Ne laser tube for a while & the required power supply, it was time to mount the tube in a more sturdy manner. Above the tube is mounted with a pair of 32mm Terry Clips, with the power leads passing through the plastic top. The ballast resistor is built into the silicone rubber on the anode end of the tube. (Right).
Output power is about 1mW for this tube, which came from a supermarket barcode scanner from the 90’s. The tube is dated August 1993 & is manufactured by Aerotech.

Inside the box is the usual 2.2Ah 12v Li-Po battery pack & the brick type He-Ne laser supply. The small circuit in the centre is a switchmode converter that drops the 12v from the battery pack to the 5v required for the laser supply.

Posted on July 14, 2012 by The Engineer — Leave a comment

AutoFace HID Ballast & Bulb

I bought one of these cheap HID kits from eBay to build a high-brightness work light that I could run from my central 12v supply.

At £14.99 I certainly wasn’t expecting anything more than the usual cheap Chinese construction. And that’s definitely what I got 😀

The casing is screwed together with the cheapest of screws, with heads that are deformed enough to present a problem with removal.

As can be seen here, the inside of the unit is potted in rubber compound, mostly to provide moisture resistance, as these are for automotive use.
The ballast generates a 23kV pulse to strike the arc in the bulb, then supplies a steady 85v AC at 3A, 400Hz to maintain the discharge.
This module could quite easily be depotted as the silicone material used is fairly soft & can be removed with a pointed tool.

Here is the bulb removed from it’s mount. Under the bulb itself is a solenoid, which tilts the bulb by a few degrees, presumably to provide dim/dip operation for a headlight. This functionality is superfluous to my requirements.

Closeup of the arc chamber of the bulb.