Going through eBay recently looking for parts for a couple of CRT-based projects, I came across these DC-DC converters.
Apparently rated from 45-390v DC output at 200mA, these should be ideal for driving some of the electrodes (focus, screen, grid) in a CRT.
Above is the top of the board, input voltage header on the left, output voltage adjust in the centre & output voltage header on the right.
This module has a mini-automotive fuse, at 10A for input protection.
On the heatsink is mounted the main switching MOSFET, a RU7088R from Ruichips. This FET is fairly heavily rated at 70v 80A, with 6.5mΩ on-resistance.
PCB Bottom
The bottom of the board has the control components, with a pair of ICs. Unfortunately the numbers have been scrubbed off, so no identification here. The output from the transformer is rectified with a single large SMD diode on the left side of the board.
There’s also plenty of isolation gap between the HV output trace & the low voltage logic side of the circuit, the two being bridged only by a resistive divider for output voltage measurement.
Here’s a quick teardown of an ignition transformer, used on gas fired ovens & hobs. This unit takes mains 240v AC & uses a transformer to step the voltage to several kV, at a low current to ignite the burners.
Bottom
The transformer section is completely potted in Epoxy resin for insulation, but the driver circuitry is exposed, with a pair of leads from the primary winding exposed
Driver PCB
The drive is very simple. The incoming AC flows through a series resistor through a half-wave rectifier to charge up a 2.2µF film capacitor. Once the voltage on the capacitor reaches a certain level, a DIAC in series with the transformer primary fires, discharging the capacitor through the primary.
The current spike induces a very high voltage on the secondary winding, this then arcs across a gap in the gas flow to start ignition.
We’re now on the final leg of the jobs to be done on the boat! Above is the new prop & shaft, supplied to us by Crowther Marine over in Royton. To fit our current stern tube & gland, the shaft is the same diamter at 1-3/8″. Unfortunately no 4-blade props were available, so I had to go for a 17×11 left-hand, but with a much larger blade area than the old one.
Propellers
Here’s the old prop on the right, with the new one on the left, amazing how different 1 inch of diameter actually looks. The opposite hand of the new prop makes no difference in our case, as I can simply switch the hoses to the hydraulic motor on the shaft to make everything reverse direction.
Stripper
Above is the solution to my problem of no weed hatch – a Stripper Rope Cutter from Ambassador Marine. This device has some seriously viciously sharp cutting teeth to help clear any fouling from the prop in operation. Only time will tell if it’s effective at allowing me to stay out of the canal manually removing the crap!
Cutless Bearing
We finally got the bearing mount finished, by S Brown Engineering in Stockport. This is made from Stainless steel to stop the bearing corroding in place & becoming a real arse to replace. Set screws are fitted to make sure the bearing doesn’t move in service.
Attached to the side of the bearing housing is the fixed blade mounting for the Stripper Rope Cutter.
Bearing Test Fit
Above is everything fitted to the shaft for a test before the gear went into it’s home in the stern tube. The Stripper mounts behind the prop, clamped to the shaft. The 3 moving blades move against the fixed blade like a mechanised pair of scissors.
Bearing Strut Welding
10mm steel plate has been used to make the strut for the bearing tube, welded together. In the case of the joint between the stainless tube & the carbon steel strut, special welding rods were needed, at the price of £2 a rod! Using mild steel rods to weld stainless could result in cracking of the welds. Not a good thing on a prop shaft support bearing.
Sand Blasted Hull
Most of the old tube has been cut away to make room for the new bearings, and the bottom of the hull has been sand-blasted ready for welding.
Running Gear Mounted
The bearing mount is welded to the hull, the Stripper & the prop are fitted to the end of the shaft. There’s 1.5″ of clearance from the blade tips to the hull plating. The rudder has about an inch of clearance to the end of the shaft.
Rudder Fence
To help keep the prop wash down, directing more of the force into moving the vessel rather than creating a nice rooster tail, a pair of plates has been welded onto the rudder. These also provide a handy step should someone fall in ;).
Things are coming along nicely with this year’s drydock operations.
Blacking – Second Coat
Shes looking much better, the second coat of bitumen blacking is on, we’re going to continue at a coat a day until we’re due back in the water.
Shaft Tube Damage
I’ve now removed the shaft from the stern tube to gain better access, now the full extent of the damage to the tube can be seen. There’s nothing left at all of the old bearing, which on this boat was simply a nylon bushing pressed into the end of the tube. (I knew it was crap the last time we were out, but ran out of time to get a fix done).
The stainless shaft, having lost it’s support bearing at some point, has been running on the inside of the steel tube, and has neatly chewed straight through it.
Prop Shaft
Here’s the prop shaft removed from the boat – possibly the longest shaft I’ve ever seen on a narrowboat at 6′ 2″. Unfortunately, the fact that it lost the bearing has also damaged the shaft itself, this will have to be replaced.
Prop Taper
Here’s the end of the shaft that would run in the end bearing, it’s badly scored & fitting a new bearing to this shaft would cause failure very quickly. The taper on the end isn’t much better, and a loose fit in the prop has done some damage there also.
Old Prop
Here’s the old prop – a 16×12 that was only fitted a few years ago. This will be replaced with a new 4-blade prop, as this one is far too small for the size of the boat & installed power. Installing a larger diameter prop isn’t possible due to clearance from the swim, so I’ll have to get a more steeply pitched prop, with 4-blades for increased contact area with the water.
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.
Temperature Sensor
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.
ECU PCB
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.
Casing Crimps
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.
ECU PCB Solder Side
Here’s the solder side of the PCB, which has a generous coating of sealant to keep moisture out.
Bad Joint Closeup
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.
Resoldered Joints
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.
It’s that time again, so the boat is out of the water for it’s 3-yearly maintenance. Some things over the past few months have been bugging me, namely a pronounced vibration in the running gear while underway. (Issue was easy to spot here!).
10-Ton Jack
nb Tanya Louise being a very odd vessel, she has quite a significant keel, so once the dock was drained, some manual jacking was required to get her level on the blocks. Without this extra work there is such a pronounced heel that it’s impossible to do anything on board.
Chocks
On the opposite side, wooded blocks are placed for the bottom of the hull to rest against. Jacking up a 58-ft 25-ton boat by hand onto some timbers was nerve-wracking to say the very least!
The bottom of the hull has already been jet-washed to remove 3-year’s worth of slime, weed growth & the old blacking. First job is to get a fresh coat of paint on.
Running Gear
Looking under the hull shows the reason for the high level of vibration – the prop shaft has actually *worn through* the bearing & stern tube, to the extent that there’s not much left of the assembly! The only thing holding the shaft in place at this stage is the stuffing box inside the boat & the shaft coupling to the hydraulic motor.
, stern tube,
A replacement standard-issue Cutless bearing will be fitted, after the remains of the old tube are cut back to make room. To facilitate mounting the bearing, a custom stainless P bracket is being made at a local engineers, for me to weld onto the bottom of the hull.
(Surprised we didn’t lose the shaft, lucky that I kept pestering to get her out of the water!).
Recently my phone decided it was going to die a battery-related death, and having not found much useful information on the Great Google, (all the information I could find, was hinting at many issues from firmware to a faulty motherboard, nobody seems to have actually done any investigation into similar issues), I decided to dig into the phone to try & repair the problem.
Broken Flex
The phone would work correctly for a while, then with the slightest movement or knock, would spontaneously switch off, and not turn back on without being whacked on a hard surface.
This symptom pointed me at a power connection problem. After removing the back of the phone (glass & heavily glued in place, so an awkward process), This was what I was presented with on the cell flex PCB.
In the above photo, the positive connection to the flex is fractured just after the solder joint with the BMS board.
Flex Repair
I managed to scrape some of the insulation off the flex PCB & solder a jumper on to restore power. Unfortunately, this repair generated another fault, where the battery level was always shown at 50%, and plugging into a USB supply wouldn’t charge the phone. The other two pins on the cell are for communication & temperature sensing, clearly one of these traces was also broken in the flex.
The above photo has a pair of very small wire tails as well, for connecting an external charger.
50% Battery
Here’s a screenshot of the phone with the original cell, even though it’s at about 4.15v (virtually fully charged). The battery management is having trouble talking to the phone, so for safety reasons, the charging logic refuses point-blank to charge the thing up.
Flex Cable
The connector on the cell & phone motherboard is absolutely tiny, so I didn’t fancy attempting to solder on any bridge wires to try & bypass the broken flex.
Battery BMS
The cell BMS has some intelligence on board, besides the usual over-current, over-charge & under-charge protection. The very small IC on the right has a Microchip logo, and the marking FT442, but I was unable to dig up any datasheets. The current sense resistor is directly connected to this IC, along with the main power FET to the left.
BMS Reverse
On the other side of the BMS board is another IC, again unidentifiable, and what looks like a bare-die, or CSP IC.
At this stage I figured the only way forward was to buy a new battery, eBay turned one up for less than £5. Above is the new battery fitted to the phone, datestamped 2014, so definitely old stock.
100% Battery
Booting the phone with the new battery quickly lets me know the fix worked, with a 100% reading & the ability to again charge properly!
Since this phone has been in my drawer for some time, I figured it was time for a teardown. (It’s never going to see any more use).
The back cover on these phones is easily removed, as it’s just clipped on.
Motherboard
Once the back cover is removed, the Li-Polymer cell is exposed, along with the logic board. Pretty much all of the PCB is under RF shields.
Motherboard RemovedBattery Management
Under the small RF can on the back of the board is the battery management circuitry & the charger. There’s an extra connection to the cell for temperature monitoring. Just under that circuitry is the eMMC flash storage.
Just to the left of the battery circuit is the NFC transceiver IC, from NXP.
Battery Flex
The cell is connected to the main board with a FFC, with a very small SMT connector, although not as small as the more modern Xperia series phones.
RF Section
The other side of the mainboard holds the large RF transceiver section, with a Qualcomm RTR8600 multiband transceiver IC. In the bottom corner is a Skyworks SKY77351-32 Quad-band power amplifier IC, along with 3 other power amplifier ICs, also from Skyworks.
Gyro & Audio Codec
The top corner of the board holds the various sensors, including an Invensense MPU-3050 3-axis gyro. To the right of that is the Audio Codec, a WCD9310 from Qualcomm.
Logic & CPU Section
Everything is controlled from the last section on the board, with the main CPU & RAM in a PoP (Package-On-Package) configuration. Under the main CPU is the main power management IC, also from Qualcomm. No datasheet for this one unfortunately, but it gives it’s purpose away by being surrounded by large inductors & capacitors.
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.
Tube End Plate
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.
End Caps
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.
Tube Stack
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.
Outer Shell
The outer shell is just a machined alloy casting, with no internal features.
This is something I’ve never seen before. Yesterday, on the Lower Peak Forest Canal, a bunch of kids on off-road bikes came thundering down the towpath – one even pulled a wheelie.
There’s considerable motion blur in the photos, as they were doing some speed, at least 30MPH at that stage.
I did get significant verbal abuse of them for having a camera on them, but thee didn’t bother stopping. This happened at the Romiley side of Woodley Tunnel, just past the portal.
As some will know, I’ve just returned this week from Download Festival, after the yearly pilgrimage to the Mecca of Metal! Click the image below to take a look at the photo albums!
Here’s a useful tool for the kit, a digital angle gauge/protractor. These use a silicon sensor to show the number of degrees the unit is out of level.
Magnets!
Magnets are provided in the base, so the tool can attach to any ferrous surface.
Battery Box
Power is provided by a single AAA cell.
Main PCB
Removing the rear cover reveals the brains of the unit, and there’s not much to it at all. The main microcontroller is a CoB-type device, so no part numbers available from that one.
Sensing Element
The IC to the left of the main microcontroller is the sensing element. There’s no markings on this inclinometer IC so I’m not sure of the specs, but it will be a 3D-MEMS device of some sort.
Power Supply
The other side of the PCB has the power supply for the logic, and a serial EEPROM, probably storing calibration data.
When I ordered the tiny USB soldering iron, I decided a proper iron upgrade would be a good idea. Looking around for something that didn’t require AC mains power turned up the TS100, a Chinese design, that unusually is actually very good! Above is the handle itself, with it’s small OLED display & two operation buttons.
This iron is controlled by a STM32 ARM microcontroller, the firmware & schematics are completely open-source.
DC Input Jack / USB Port
The bottom end of the iron has the main DC input jack, designed with laptop chargers in mind (DC input range from 10v-24v). Above that is the micro USB port for programming.
Heating Element Socket
The iron tips slot into the other end, many different tip types & shapes are available. The one supplied was the simple conical tip.
Standby Screen
Plugging the iron into some power gets a standby screen – it doesn’t just start heating immediately, for safety.
Heating
The left hand button starts the heater, which on a 24v input voltage gets to operating temperature well within 10 seconds.
Temperature Stable
The right hand screen icon changes when the temperature has stabilized. The control PCB has an integrated accelerometer, leaving the iron hot for a few minutes triggers a timeout & it powers down. Once picked up again, the heater instantly restarts.
The operating temperature is adjustable with the pair of buttons, from 100°C to 400°C.
Different Bits
Here’s a selection of bits for the iron. The design is very similar to the Hakko T15 series of irons, but these are a much shorter version. Like the Hakko versions, the actual tips aren’t replaceable, once the bit burns out, the entire assembly is replaced.
TS100 Soldering Iron
Here’s the iron fully assembled. The entire device is about the same length as just the heating element from a Hakko T15!
Here’s a novel little gadget, a USB powered soldering iron. The heating tip on these is very small & might be useful for very small SMD work. Bigger joints not so much, as it’s only rated at 8W. (Still breaks the USB standard of 2.5W from a single port).
These irons aren’t actually too bad to use, as long as the limitations in power are respected. Since nearly everything has a USB power port these days, it could make for a handy emergency soldering iron.
Heater Socket
The heater & soldering bit are a single unit, not designed to be replaced separately. (I’ve not managed to find replacement elements, but at £3 for the entire iron, it would be pretty pointless).
Above is the socket where the heater plugs in, safely isolating the plastic body from any stray heat.
DC Input Jack
The DC input is a 3.5mm audio jack, a non-standard USB to 3.5mm jack cable is supplied. Such non-standard cables have the potential to damage equipment that isn’t expecting to see 5v on an audio input if it’s used incorrectly.
Touch Sensor & LED
There isn’t actually a switch on this unit for power management, but a clever arrangement of a touch button & vibration switch. The vertical spring in the photo above makes contact with a steel ball bearing pressed into the plastic housing, forming the touch contact.
MOSFET
The large MOSFET here is switching the main heater current, the silver cylinder in front is the vibration switch, connected in parallel with the touch button.
PCB
The main controller is very simple. It’s a 555 timer configured in monostable mode. Below is a schematic showing the basic circuit.
555 Monostable
Big Clive also did a teardown & review of this iron. Head over to YouTube to watch.
This website, in various forms, has been around now for about 10 years. Over that time the scope of what I’ve been doing has definitely widened in a big manner.
Considering this, I no longer feel the current website name of “Inside Electronics” is very appropriate, so over the next few weeks, I’ll be re-jigging everything with a new domain name & title:
Experimental Engineering.
The site name is already changed, moving my entire WordPress install over to a new domain will be a bit more labour intensive, with all the internal site links & SEO, so this will be introduced slowly.
(It’s amazing how much this site has evolved over the years, hopefully this evolution will continue!)
Magnetic tape is the medium of choice for my offline backups & archives, as it’s got an amazing level of durability when in storage. (LTO Has a 30 year archival rating).
For the smaller stuff, like backing up the web server this very site runs on, another format seemed to suit better. Above is a HP DDS4 tape drive, which will store up to 40GB on a cassette compressed.
I picked this format since I already had some tapes, so it made sense.
Data Plate
Here’s the info for those who want to know. It’s an older generation drive, mainly since the current generation of tape backup drives are hideously expensive, while the older ones are cheap & plentiful. Unfortunately the older generation of drives are all parallel SCSI, which can be a expensive & awkward to set up. Luckily I already have other parallel SCSI devices, so the support infrastructure for this drive was already in place.
Option Switches
On the bottom of the drive is a bank of DIP switches, according to the manual these are for setting the drive for various flavours of UNIX operating systems. However it doesn’t go into what they actually change.
Controller PCB
The bottom of the drive has the control PCB. The large IC on the left is the SCSI interface, I’ve seen this exact same chip on other SCSI tape drives. Centre is a SoC, like so many of these, not much information available.
Drive Frame
Removing the board doesn’t reveal much else, just the bottom of the frame with the tape spool motors on the right, capstan motor bottom centre. The bottom of the head drum motor is just peeping through the plastic top centre.
Head Drum
Here’s the head drum itself. These drives use a helical-scan flying head system, like old VHS tape decks. The top of the capstan motor is on the bottom right.
Cleaning Brush
Hidden just under the tape transport frame is the head cleaning brush. I’m not sure exactly what this is made of, but it seems to be plastic.
Loading Motor
A single small DC motor with a worm drive handles all tape loading tasks. The PCB to the bottom left of the motor holds several break-beam sensors that tell the drive what position the transport is in.
Tape Transport Mech
Here’s the overall tape transport. The PCB on top of the head drum is a novel idea: it’s sole purpose in life is to act as a substrate for solder blobs, used for balancing. As this drum spins at 11,400RPM when a DDS4 tape is in the drive, any slight imbalance would cause destructive vibration.
Tape Transport
Here’s the drive active & writing a tape. (A daily backup of this web server actually). The green head cleaning brush can be better seen here. The drive constantly reads back what it writes to the tape, and if it detects an error, applies this brush momentarily to the drum to clean any shed oxide off the heads. The tape itself is threaded over all the guides, around the drum, then through the capstan & pinch roller.
In the process of going through the boat mechanically, ready for this year’s cruising season, some damage was discovered on the face of the main hydraulic propulsion pump that drives the propeller.
Face Damage
Here’s the front face of the pump, with it’s drive shaft. The circular ridge isn’t supposed to be there, it’s meant to be completely flat.
The central hub of the Centaflex coupling managed to loosen itself on the shaft (they’re pretty badly designed), and when the steel hub moved backward, it ground a very nice recess into the cast iron pump housing.
This managed to get deep enough where it compromised the circlip groove that holds both the oil seal & the mainshaft thrust bearing in place.
Spacer Ring
To save a considerable amount of cash (replacing the entire base casting of the pump would be hideously expensive), a 6mm ring was machined from steel, to hold the seal in place.
The face of the pump was then drilled & tapped for M5 screws.
Plate Fitted
Above, the repair plate has been fitted, with the spacer ring sandwiched between it & the oil seal, securing everything in place.
Having a replaceable wear plate screwed to the front of the pump also allows for easy future repair if the coupling moves again.
For my latest project, I needed an easier way to paint without messing about with brushes, and the associated marks they leave in a paint job. eBay provided me with a cheap airbrush & compressor.
Airbrush Kit
For less than £30, this kit doens’t look so bad. I’ve never used an airbrush before, but I’ve had no problems with this as yet spraying both water based paints & solvent based paints.
Compressor
Here’s the compressor itself, this runs on 12v & has an output pressure of 1.5 Bar, which is supposed to be adjustable.
Compressor Internals
Removing a couple of screws reveals the internal components. Nothing much unusual here, a DC diaphragm pump, pressure switch & outlet fittings. There’s also a thermal cutout fitted next to the motor for protection.
The pressure switch attached to the manifold trips at 1.5Bar, keeping the pressure to the brush pretty much constant.
Air Block
Next to the air outlet fitting is an adjustment knob, supposedly for varying the pressure. However it’s just a piss-poorly designed adjustable relief valve that vents to atmosphere. There’s not much of a control range.
Messy Wiring
The wiring gets a bit messy where the power LED is concerned, with no heatshrink over the solder joints, but it’s adequate.
Airbrush
The airbrush itself isn’t too bad. It’s solid Brass, with a very nice Chrome finish. I’m not expecting miracles from a very cheap tool, but it certainly seems to be reasonable.
Water Trap
A moisture trap is supplied for the brush, to prevent water drops being sprayed out with the paint. Very handy.
Just a quick note for the regular (and not so regular) readers:
My server infrastructure is currently going through some migration & upgrade processes, so for the next few days the site might be a little on the slow side, but hopefully I can get everything sorted out quickly!
During this time please bear with the slower than normal response times.
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.
LED Capacity Indicator
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.
Label
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.
Interconnect Straps
The casing holds a PCB at the bottom end with the cell straps.
Screw Post
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.
Cell Springs
The top cover holds the cell springs & the electronics.
Button & Cable Seal
Removing the pair of screws allows the top cap to open up. The cable, button & LEDs are robustly sealed off with this silicone moulding.
Top Removed
Here’s the PCB, not much on the top, other than the power button & battery indicator LEDs.
Electronics
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.
A while ago I posted about the glowplug screens in Eberspacher heaters, and making some DIY ones, as the OEM parts are hideously expensive for a piece of stainless mesh (£13).
Old Screen
Above is the old factory screen that I extracted after only 5 gallons of diesel was run through it, it’s heavily clogged up with carbon & tar. The result of this clogging is a rather slow & smoky start of the heater & surging of the burner while at full power.
It wasn’t as badly stuck in the chamber as some I’ve removed, but extracting it still caused the steel ring to deform, this was after using a scalpel blade to scrape the carbon off the rim.
At the time I did some tests with some spare copper mesh I had to hand, but the problem with copper is that it’s very soft & malleable, so didn’t really hold it’s shape well enough. The factory screens are spot welded to keep them in shape, but as I don’t have a spot welder, I am relying on the mesh having a bit of springiness to keep it in place against the walls of the glowplug chamber.
eBay provided a piece of 120 mesh stainless steel mesh, 300mmx300mm for £8. It’s a bit finer than the stock stuff, but appears to work perfectly fine as long as there’s no gunk in the fuel to clog it up.
I cut a strip off the large piece, as wide as the OEM screen, about 32mm. This 300mm long strip is then cut into 4 pieces, each 75mm long. (it’s easily cut with scissors, but mind the stray wires on the edges! They’re very sharp & penetrate skin easily!).
Mesh Screen
These pieces are just the right size to form a complete loop in the glowplug chamber, and the stainless is springy enough so that it doesn’t deform & become loose.
The OEM screen is multiple turns of a more coarse mesh, but the finer mesh size of the screens I’m using means only one turn is required. Multiple turns would probably be too restrictive to fuel flow.
With one of these pieces of mesh in place, the heater starts instantly, without even a wisp of smoke from the exhaust. Burner surging is also eliminated. Even if the service life of my DIY replacement isn’t as long as an OEM screen, the low price for such a large number of replacements certainly offsets that disadvantage!
A piece of mesh from eBay would provide enough material for quite a lot of replacements, and probably more than the service life of the burner itself!
Here’s another Dyson teardown, in my efforts to understand how marketing have got hold of relatively simple technology & managed to charge extortionate amounts of money for it.
This is the DC35, the model after the introduction of the brushless digital motor.
Back Cap Removed
On this version the mouldings have been changed, and the back cover comes off, after removing the battery retaining screw. It’s attached with some fairly vicious clips, so some force is required. Once the cap is removed, all the electronics are visible. On the left is the motor itself, with it’s control & drive PCB. There’s another PCB on the trigger, with even more electronics. The battery connector is on the right.
Trigger PCB
Here’s the trigger PCB, which appears to deal with DC-DC conversion for powering the brush attachments. The QFN IC with yellow paint on it is an Atmel ATTiny461 8-bit microcontroller. This is probably controlling the DC-DC & might also be doing some battery authentication.
“Digital Motor”
Here’s the motor & it’s board. The windings on the stator are extremely heavy, which makes sense considering it’s rated at 200W. The main control IC is a PIC16F690 from Microchip. Instead of using an off the shelf controller, this no doubt contains software for generating the waveforms that drive the brushless motor. It also appears to communicate with the other PCBs for battery authentication.
Stator
Desoldering the board allows it to be removed from the motor itself. The pair of windings are connected in anti-phase, to create alternating North-South poles depending on polarity. Since the existing controller is unusable due to software authentication with the other parts, I might have a go at building my own driver circuit for this with an Arduino or similar.
Blower Assembly
The blower assembly is simple plastic mouldings, pressed together then solvent welded at the seam.
Impeller
The impeller is just a centrifugal compressor wheel, identical to what’s used in engine turbochargers.
Motor Control Board
The inside face of the control PCB holds the 4 very large MOSFETs, IRFH7932PbF from International Rectifier. These are rated at 30v 20A a piece, and are probably wired in a H-Bridge. There’s a bipolar Hall switch to sense rotor position & rotation speed, and an enormous pair of capacitors on the main power bus.
Motor Control Board Reverse
Not much on the other side of the PCB other than the microcontroller and associated gate drive stuff for the FETs.
Battery Pack Opened
The battery pack is similar to the DC16 in it’s construction, a heavily clipped together plastic casing holding 6 lithium cells. In this one though there’s a full battery management system. The IC on the top of the board above is a quad Op-Amp, probably for measuring cell voltages.
Battery BMS Bottom
The other side of the BMS board is packed with components. I wasn’t able to identify the QFN IC here, as it’s got a custom part number, but it’s most definitely communicating with the main motor MCU via I²C over the two small terminals on the battery connector.
Since this is the 300th post on my blog in the 6 years I’ve been at this, I figured I’d do a post with recent site updates & some news.
Site Look
There haven’t been many updates to the general look of the site for quite a while, with some help of a friend I managed to get a new ticker added to the header, which saves on post count for upcoming projects & posts.
The header image is also dynamic, picking randomly from a collection of images, mostly from previous posts, and a few that started as messing about with a camera & turned out looking quite good.
Site Support
Also added to the site’s look is a Tip Jar on the right hand side, so thankful readers can donate something if I’ve managed to post something remotely helpful ;).
People that know me personally know I hate ads with a passion, and as such ads will have no place on my blog for as long as it’s visible on the intertubes. The site does cost quite a significant (to me anyway) amount of cash to keep going, not to mention time, so any donations would be more than welcome!
Radio-Based Posts
I haven’t done any proper Ham Radio based posts in quite a while, mainly due to me not having anything to share on the subject, unfortunately it can be a damn expensive hobby & there are other things taking priority at the moment. (Apparently eating & warmth are essentials, according to the missus at least ;)).
There is going to be a round-about radio based post shortly though, so my Ham readers stay tuned!
Boating Posts
Now that we’re in the new year, when the weather returns to something remotely tolerable to be outdoors in, there’ll be much more boating related stuff on the cards, not only trips but engineering jobs onboard.
Tip Jar
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All collected funds go towards new content & the costs of keeping the server online.
