Posted on 11 Comments

Honda GX35 Clone – Are They Any Good?

In a word, no they aren’t any good. As usual, cheap doesn’t equal good, and in this case the cheapo clones are a total waste of money. Read on for the details!

I’ve been looking into using a cheap Chinese clone Honda GX35 engine to drive an automotive alternator as a portable battery charging & power unit. These engines are available very cheaply on eBay, aimed at the mini-bike/go-kart market.
For those not in the know, the Honda GX25/35 4-strokes are strimmer-type engines that traditionally were always of 2-stroke construction. Honda worked out how to have a wet-sump engine without the need to keep the engine always in the “upright” position. They do not require mixing of oil into the fuel for lubrication as 2-strokes do, so should be much cleaner running.

So far I’ve had two of these cheap engines, as the first one died after only 4 hours run time, having entirely lost compression. At the time the engine was idling, no load, having been started from cold only a few minutes before. Having checked the valve clearances to make sure a valve wasn’t being held partially open, I deduced that the cause was broken piston rings. This engine was replaced by the seller, so I didn’t get a chance to pull it to bits to find out, but I decided to do a full teardown on the replacement to see where the cloners have cut corners.

Oil Return Hose
Oil Return Hose

I’ve already stripped off the ancillary components: exhaust, carburettor, fuel tank, cowlings, as these parts are standard to any strimmer engine. The large black hose here is the oil return feed back to the rocker cover from the crankcase. The oiling system in these engines is rather clever. The main engine block is made of light alloy, probably some permutation of Aluminium. There is much flashing left behind between the cylinder fins from the die-casting process, and not a single engine manufacturer’s logo anywhere. (From what I’ve read, the genuine Honda ones have their logo on the side of the crankcase).

Rocker Box
Rocker Box

Here’s the top of the engine with valves, rockers & camshaft. All the valve gear up here, minus the valves themselves & springs, are manufactured from sintered steel, there are no proper “bearings”, the steel shafts just run in the aluminium castings. The cam gear is of plastic, with the sintered steel cam pressed into place. The cam also has the bearing surface for the pin that the whole assembly rotates on. The timing belt runs in the oil & is supposed to last the life of the engine, and while I’d believe that in the original Honda, I certainly wouldn’t in this engine. The black grommet is the opening of the oil return gallery.

Cam
Cam

Here’s the cam on the back of the plastic pulley. A single cam is used for both intake & exhaust valves for space & simplicity.

Intake Valve Stem Seal
Intake Valve Stem Seal

Just visible under the intake valve spring is a simple stem seal, to hopefully prevent oil being sucked down the valve guide into the cylinder by intake vacuum. Running these cheap engines proves this seal to be ineffective, as they blow about as much blue oil smoke as a 2-stroke when they’re started cold. 😉

Starter Side
Starter Side

The starter side is where the oil sump is located on these engines, along with the dipstick.

Flywheel Side
Flywheel Side

The flywheel end of the engine is the usual fare for small engines. Ignition is provided by a magneto, with a magnet in the flywheel. This is no different from the 2-stroke versions. As these ignitions fire on every revolution of the crankshaft, the spark plug fires both on compression, igniting the fuel for normal operation, and again into the exhaust stroke, where the spark is wasted.
One thing I have noticed about these engines is an almost total lack of cooling air coming through the cowling over the cylinder cooling fins. Plenty was flowing over the exhaust silencer side, I believe bad housing design would be what causes this problem. A lack of cooling certainly wouldn’t help engine longevity!

Engine "Sump"
Engine “Sump”

Separating the bottom of the engine was a little difficult, as there is a significant bead of sealant used instead of a gasket. Inside the sump of the engine are a pair of paddles, which stir up the oil into a mist. As the piston moves in the cylinder, it acts as a pump, creating alternating pulses of pressure & vacuum in the crankcase. Oil mist flows through a drilling in the crank from the sump, into the crankcase where it (hopefully) lubricates the bearings & the cylinder wall. Incidentally, the only main bearings are on the crankcase – the far end of the shaft that carries the oil paddles & timing belt is just flapping in the breeze, the only support being the oil seal in the outer housing. The crank itself isn’t hardened – a file easily removes metal from all parts that I could get at. The big end journal pin might be, but these cranks are pressed together so I can’t access that part.

Lubrication Gallery
Lubrication Gallery

The oil mist feeds into the crankcase through this hollow section of shaft, there’s a drilling next to the timing belt pulley to connect the two spaces together.

Lower Crankcase
Lower Crankcase

The lower crankcase is just a simple die casting, there’s a check valve at the bottom under the crankshaft to transfer oil to the rocker cover, through the rubber tube on the outside of the engine. After the oil reaches the rocker box, it condenses & returns to the sump via the timing belt cavity.

Piston Crown
Piston Crown

Removing the crankshaft from the engine block gives me a look at the piston. The factory couldn’t even be arsed to machine the crown, it’s still got the rough finish from the hot-forging press. This bad finish will pick up much carbon from combustion, and would probably cause detonation once enough had accumulated to become incandescent in the heat of combustion. Only the centre is machined, just enough for them to stamp a number on.

Cylinder Bore
Cylinder Bore

A look up the cylinder bore shows the valves in the cylinder head. These engines, like their 2-stroke cousins have a single casting instead of a separate block & head, so getting at the valves is a little more of a pain. The cylinder bore itself is a cast-in iron liner and it’s totally smooth – like a mirror finish. There’s not a single sign of a crosshatch pattern from honing. If the first engine that died on me was the same – I’d be surprised if it wasn’t, this could easily cause ring breakage. The usual crosshatch pattern the cylinder hone produces holds oil, to better help lubricate the piston & rings. Without sufficient lubrication, the rings will overheat & expand far enough to close the end gap. Once this happens they will break.

Engine Valves
Engine Valves

Finally, here’s the valves with their springs removed from the cylinder. These are the smallest poppet valves I’ve ever seen, a British penny is provided for scale.

In all, these engines share many components with the older 2-stroke versions. The basic crankshaft & connecting rod setup is the same as I’ve seen in many old 2-strokes previous, the addition of the rather ingenious oiling system by Honda is what makes these tiny 4-strokes possible. I definitely won’t be trusting these very cheap copies in any of my projects, reliability is questionable at the least. The apparent lack of cooling air flow over the cylinder from the flywheel fan is concerning, along with the corner-cutting on the cylinder finishing process & piston crown, presumably to reduce factory costs.

Posted on Leave a comment

eBay Chinese Chassis Power Supply S-400-12 400W 12v 33A

S-400-12 PSU
S-400-12 PSU

Here’s a cheap PSU from the treasure trove of junk that is eBay, rated at a rather beefy 400W of output at 12v – 33A! These industrial-type PSUs from name brands like TDK-Lambda or Puls are usually rather expensive, so I was interested to find out how much of a punishment these cheap Chinese versions will take before grenading. In my case this PSU is to be pushed into float charging a large lead acid battery bank, which when in a discharged state will try to pull as many amps from the charger as can be provided.

Rating Label
Rating Label

These PSUs are universal input, voltage adjustable by a switch on the other side of the PSU, below. The output voltage is also trimmable from the factory, an important thing for battery charging, as the output voltage needs to be sustained at 13.8v rather than the flat 12v from the factory.

Input Voltage Selector
Input Voltage Selector
Main Terminal Block
Main Terminal Block

Mains connections & the low voltage outputs are on beefy screw terminals. The output voltage adjustment potentiometer & output indicator LED are on the left side.

Cooling Fan
Cooling Fan

The cooling fan for the unit, which pulls air through the casing instead of blowing into the casing is a cheap sleeve bearing 60mm fan. No surprises here. I’ll probably replace this with a high-quality ball-bearing fan, to save the PSU from inevitable fan failure & overheating.

PCB Bottom
PCB Bottom

The PCB tracks are generously laid out on the high current output side, but there are some primary/secondary clearance issues in a couple of places. Lindsay Wilson over at Imajeenyus.com did a pretty thorough work-up on the fineries of these PSUs, so I’ll leave most of the in-depth stuff via a linky. There’s also a modification of this PSU for a wider voltage range, which I haven’t done in this case as the existing adjustment is plenty wide enough for battery charging duty.

Bare PCB
Bare PCB

The PCB is laid out in the usual fashion for these PSUs, with the power path taking a U-route across the board. Mains input is lower left, with some filtering. Main diode bridge in the centre, with the voltage selection switch & then the main filter caps. Power is then switched into the transformer by the pair of large transistors on the right before being rectified & smoothed on the top left.

Main Switching Transistors
Main Switching Transistors

The pair of main switching devices are mounted to the casing with thermal compound & an insulating pad. To bridge the gap there’s a chunk of aluminium which also provides some extra heatsinking.

SMPS Drive IC & Base Drive Transformer
SMPS Drive IC & Base Drive Transformer

The PSU is controlled by a jelly-bean TL494 PWM controller IC. No active PFC in this cheap supply so the power factor is going to be very poor indeed.

Input Protection
Input Protection

Input protection & filtering is rather simple with the usual fuse, MOV filter capacitor & common mode choke.

Main Output Rectifiers
Main Output Rectifiers

Beefy 30A dual diodes on the DC output side, mounted in the same fashion as the main switching transistors.

Output Current Shunt
Output Current Shunt

Current measurement is done by these large wire links in the current path, selectable for different models with different output ratings.

Hot Glue Support
Hot Glue Support

The output capacitors were just floating around in the breeze, with one of them already having broken the solder joints in shipping! After reflowing the pads on all the capacitors some hot glue as flowed around them to stop any further movement.

This supply has now been in service for a couple of weeks at a constant 50% load, with the occasional hammering to recharge the battery bank after a power failure. at 13A the supply barely even gets warm, while at a load high enough to make 40A rated cable get uncomfortably warm (I didn’t manage to get a current reading, as my instruments don’t currently go high enough), the PSU was hot in the power semiconductor areas, but seemed to cope at full load perfectly well.

Posted on 14 Comments

Dyson DC16 Handheld Teardown

DC16
DC16

The Dyson DC16 is one of the older handheld vacuums, before the introduction of the “Digital Motor”. (Marketing obviously didn’t think “Switched Reluctance Motor” sounded quite as good).

These vacuums have a very large DC brush motor driving the suction turbine instead, the same as would be found in a cordless power tool.

Control PCB
Control PCB

Popping the front cap off with the ID label, reveals the brains of the vacuum. The two large terminals at the right are for charging, which is only done at 550mA (0.5C). There are two PIC microcontrollers in here, along with a large choke, DC-DC converter for supplying the logic most likely. The larger of the MCUs, a PIC16HV785, is probably doing the soft-start PWM on the main motor, the smaller of the two, a PIC16F684 I’m sure is doing battery charging & power management. The motor has a PCB on it’s tail end, with a very large MOSFET, a pair of heavy leads connect directly from the battery connector to the motor.
Just out of sight on the bottom left edge of the board is a Hall Effect Sensor, this detects the presence of the filter by means of a small magnet, the vacuum will not start without a filter fitted.

Battery Pack
Battery Pack

The battery pack is a large custom job, obviously. 4 terminals mean there’s slightly more in here than just the cells.

Battery Cracked
Battery Cracked

Luckily, instead of ultrasonic or solvent welding the case, these Dyson batteries are just snapped together. Some mild attack with a pair of screwdrivers allows the end cap to be removed with minimal damage.

Cells
Cells

The cells were lightly hot-glued into the shell, but that can easily be solved with a drop of Isopropanol to dissolve the glue bond. The pack itself is made up of 6 Sony US18650VT High-Drain 18650 Li-Ion cells in series for 21.6v nominal. These are rated at a max of 20A discharge current, 10A charge current, and 1.3Ah capacity nominal.
There’s no intelligence in this battery pack, the extra pair of terminals are for a thermistor, so the PIC in the main body knows what temperature the pack is at – it certainly gets warm while in use due to the high current draw.

Motor
Motor

Hidden in the back side of the main body is the motor. Unfortunately I wasn’t able to get this out without doing some damage, as the wiring isn’t long enough to free the unit without some surgery.

Turbine
Turbine

The suction is generated by a smaller version of the centrifugal high-speed blowers used in full size vacuums. Not much to see here.

Unofficial Charger
Unofficial Charger

Since I got this without a charger, I had to improvise. The factory power supply is just a 28v power brick, all the charging logic is in the vacuum itself, so I didn’t have to worry about such nasties as over-charging. I have since fitted the battery pack with a standard Li-Po balance cable, so it can be used with my ProCell charger, which will charge the pack in 35 minutes, instead of the 3 hours of the original charger.

Posted on Leave a comment

Portable Hearing Induction Loop

Induction Loop
Induction Loop

These units are used to broadcast local audio, such as from a public address system or local microphone. They accomplish this by producing a modulated magnetic field that a hearing aid is capable of picking up.

Back Panel
Back Panel

Not many controls on this bit of equipment. A bi-colour LED for status indications, a microphone, external audio input, charging input & a power switch.

Internals
Internals

Popping the cover off reveals a small lead-acid battery, 2.1Ah at 12v. This is used when the loop is unplugged.

Main PCB
Main PCB

Here’s the main PCB, which takes care of the audio & battery charging. The inductive loop itself is just visible as the tape-covered wire bundle around the edge of the casing.

Audio & Power Input
Audio & Power Input

Here’s the input section of the main PCB. The microphone input is handled by a SSM2166 front-end preamplifier from Analog Devices.

Power Amplifier
Power Amplifier

This audio is then fed into a TDA2003 10W Mono Power Amplifier IC, which directly drives the induction coil as if it were a speaker. Any suitable receiving coil & amplifier can then receive the signal & change it back into audio.

Posted on Leave a comment

Uniden UBC92XLT Teardown

One bit of my equipment that I’ve never looked into is my scanner, a handheld Uniden unit. I got this when Maplin Electronics had them on special offer a few years ago.

Uniden Scanner
Uniden Scanner

Here’s the scanner itself, roughly the same size as a usual HT.

Back Cover Removed
Back Cover Removed

Here the back cover has been removed, and the main RF board is visible at the top of the stack. Unfortunately the shielding cans are soldered on this unit, so no looking under there 🙁
On the right hand side of the board next to the antenna input is the main RF filter network, and it’s associated switching. The RF front end is under the shield closest to the front edge.

Controls & 3.3v Regulator
Controls & 3.3v Regulator

On the other side of the PCB is the Volume & Squelch potentiometers, along with a dedicated 3.3v switching supply. An NJM2360A High Precision DC/DC converter IC controls this one. A 3.3v test point is visible next to the regulator.

RF Board Reverse
RF Board Reverse

Here’s the backside of the RF board, some more interesting parts here. There’s a pair of NJM3404A Single Supply Dual Op-Amp ICs, and a TK10931V Dual AM/FM IF Discriminator IC. This is the one that does all the back-end radio functionality. The audio amplifier for the internal speaker & external headphone jack is also on this PCB, top left. A board-to-board interconnect links this radio board with the main control board underneath.

Control PCB Front
Control PCB Front

Here’s the front of the control PCB, nothing much to see here, just the LCD & membrane keypad contacts.

Control PCB Reverse
Control PCB Reverse

And here’s the reverse side of the control board. All the interesting bits are here. The main microcontroller is on the right, a Renesas M38D59GF, a fairly powerful MCU, with onboard LCD drive, A/D converter, serial interface, 60K of ROM & 2K of RAM. It’s 6.143MHz clock crystal is just below it.
The mating connector for the RF board is in the centre here.

There is also a Microchip 24LC168 16KB I²C EEPROM next to the main microcontroller. This is probably for storing user settings, frequencies, etc.

EEPROM
EEPROM

The rest of this board is dedicated to battery charging and power supply, in the centre is a dual switching controller, I can’t figure out the numbers on the tiny SOT23 components in here, but this is dealing with the DC 6v input & to the left of that is the circuitry for charging the NiMH cells included with the scanner.

PSU
PSU

The last bit of this PCB is a BU2092FV Serial In / Parallel Out 4 channel driver. Not sure what this one is doing, it might be doing some signal multiplexing for the RF board interface. Unfortunately the tracks from this IC are routed on the inner layers of the board so they can’t be traced out.

Posted on Leave a comment

Pringles Speaker Modifications

USB Charging Port
USB Charging Port

These speakers are available free from Pringles, with two packs bought. Normally running on 3x AAA cells, I have made modifications to include a high capacity Li-Ion battery & USB charging.

18650 Battery
18650 Battery

New battery is 3x 18650 Li-Ion cells in parallel, providing ~6600mAh of capacity. These are hot glued inside the top of the tube under the speaker, with the charging & cell protection logic.
The battery charging logic is salvaged from an old USB eCig charger, these are single cell lithium chargers in a small form factor ideal for other uses. Charging current is ~450mA.

Amplifier Board
Amplifier Board

The cells are connected to the same points as the original AAA cells, with the other pair of wires going into the top of the device to connect to the MicroUSB charging port.

The amplifier in this is a LM4871 3W Mono amplifier IC, connected to a 6Ω 1W speaker.
The other IC on the board is unidentifiable, but provides the flashing LED function to the beat of the music.

 

 

Posted on 1 Comment

MicroVision ShowWX+ HDMI Laser Pico Projector

Info
Info

Here’s the teardown of the projector itself! On the right is the info label from the projector, which covers the flex ribbon to the VGA/composite input board below.

This unit is held together with Allen screws, but is easy to get apart.

 

PicoP Display Engine
PicoP Display Engine

Here’s the insides of the projector, with just the top cover removed. The main board can be seen under the shielding can, the Micro HDMI connector is on the left & the MicroUSB connection is on the right. The USB connection is solely for charging the battery & provides no data interface to the unit.

On top of the main board is the shield can covering the PicoP Display Engine driver board, this shield was soldered on so no peek inside unfortunately!

Laser Module
Laser Module

The laser module itself is in the front of the unit, the laser assemblies are closest to the camera, on the left is the Direct Doubled Green module, in the centre is the blue diode, and the red diode on the right. Inside the module itself is an arrangement of mirrors & beamsplitters, used to combine the RGB beams from the lasers into a single beam to create any colour in the spectrum.

Module Innards
Module Innards

 

Here is the module innards revealed, the laser mounts are at the top of the screen, the green module is still mounted on the base casting.
The three dichroic mirrors in the frame do the beam combining, which is then bounced onto the mirror on the far left of the frame, down below the MEMs. From there a final mirror directs the light onto the MEMs scanning mirror before it leaves through the output window.

A trio of photodiodes caters for beam brightness control & colour control, these are located behind the last dichroic turning mirror in the centre of the picture.

Green Module Cavity
Green Module Cavity

This is inside the green laser module, showing the complexity of the device. This laser module is about the size of a UK 5p coin!

Green Module Labeled
Green Module Labeled

 

 

 

 

 

And here on the left is the module components labelled.

 

Main PCB Top
Main PCB Top

Here is the main PCB, with the unit’s main ARM CPU on the right, manufactured by ST.

User buttons are along the sides.

 

Main PCB Bottom
Main PCB Bottom

Other side of the main board, with ICs that handle video input from the HDMI connector, battery charging via the USB port & various other management.