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nbTanya Louise Drive Failure

As I have posted about before, the main propulsion system onboard the boat is all hydraulic. To get the drive from the flywheel of the engine to the hydraulic pump stack, a custom drive plate was machined by Centa Transmissions over in Yorkshire, and a Centaflex A coupling was fitted to this.

Centaflex A Coupling
Centaflex A Coupling

This coupling is a big rubber doughnut, bolted to a centre hub of steel. The steel hub is splined onto the input shaft of the hydraulic pump stack.

Pump Stack
Pump Stack

The problem we’ve had is that to prevent the coupling from riding along the splines in operation, a pair of giant grub screws are provided in the side of the centre steel boss, that compress the splines to lock the device in place. These screws are a nightmare to get tightened down (the engineer from Centa who originally came to survey the system said we’d probably shear some tools off trying).

Because of this, the grub screws have loosened over the last 350-odd hours of running & this has had the effect of totally destroying the splines in the hub.

Spline Remains
Spline Remains

Here’s the backside of the centre boss, with what remains of the splines, the figure-8 shaped gap on the right is where the securing grub screws deform the steel to lock the coupling into place.

No More Splines
No More Splines

Here’s the other side of the coupling, showing the damage. The splines have effectively been totally removed, as if I’d gone in there with a boring bar on the lathe. Luckily this part isn’t too expensive to replace, and no damage was done to the input shaft of the hydraulic pump stack (Mega ££££). Quite luckily, this damage got to the point of failure while running the engine on the mooring, so it didn’t leave us stranded somewhere without motive power.

More to come when the new coupling arrives!

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nb Tanya Louise Deck Welding

The boat being over 50 years old, there are some parts that are suffering from rather bad corrosion. The bow deck plate is about the worst, so this is being replaced in it’s entirety.

However a hole has developed in the stern deck, this has rusted from the inside out due to condensation in the engine bay.

After Grinding
After Grinding

After taking a grinder to the area, this is how it looks. The steel has gone from 1/4″ to paper thin, not surprising after 50 years or so!
It would be a massive job to cut out the entire plate for replacement, so a patch was made from 5mm steel, and welded over the hole:

Patch
Patch

Here’s the patch partially welded. The holes closer to the bottom are another small area of damage, and another patch will have to be cut for this. It’s covering the deck drain channel so it’s frequently under water, so it’s inevitable that this section would corrode.

All that is left to do now is to finish off the welding, grind everything smooth & repaint.

Another small job complete!

73s folks

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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.

Power Brick
Power Brick

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

Cover Removed
Cover Removed

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.

PCB
PCB

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!

Primary Side
Primary Side

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.

Secondary Side
Secondary Side

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.

PCB Bottom
PCB Bottom

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!