To solve some engine oil overheating problems on board nb Tanya Louise, we decided to replace the air-over-oil cooler, with an water-over-oil cooler, with separate cooling drawn straight from the canal, as the skin tanks are already overloaded with having to cope with not only cooling the engine coolant, but also the hydraulic system oil as well.
These units aren’t cheap in the slightest, but the construction quality & engineering is fantastic.
Unbolting the end cover reveals the brass tube end plate, soldered to all the core tubes in the cooler. An O-Ring at each end seals both the end cover & the interface between the tube plate & the outer casing.
The end caps have baffles cast in to direct the cooling water in a serpentine path, so the oil gets the best chance at dissipating it’s heat to the water.
The oil side of the system is on the outside of the tubes, again baffles placed along the stack direct the oil over the highest surface area possible.
The outer shell is just a machined alloy casting, with no internal features.
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.
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.
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.
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.
I’m no fan of power inverters. In my experience they’re horrifically inefficient, have power appetites that make engine starter motors look like electric toothbrushes & reduce the life expectancy of lead-acid batteries to no more than a few days.
However I have decided to do a little analysis on a cheapo “600W” model that Maplin Electronics sells.
After a serious amount of metallic abuse, the bottom cover eventually came off. The sheet of steel used to close the bottom of the aluminium extrusion was wedged into place with what was probably a 10 ton hydraulic press.
As can be seen from the PCB, there’s no massive 50Hz power transformer, but a pair of high frequency switching transformers. Obviously this is to lighten the weight & the cost of the magnetics, but it does nothing for the quality of the AC output waveform.
The 12v DC from the battery comes in on very heavy 8-gauge cables, this device is fused at 75A!
Here’s the fusing arrangement on the DC input stage, just 3 standard blade-type automotive fuses. Interestingly, these are very difficult to get at without a large hammer & some swearing, so I imagine if the user manages to blow these Maplin just expect the device to be thrown out.
On the input side, the DC is switched into the pair of transformers to create a bipolar high voltage DC supply.
The large rectifier diodes on the outputs of the transformers feed into the 400v 100µF smoothing capacitors.
As mains AC is obviously a bipolar waveform, I’m guessing this is generating a ±150v DC supply.
After the high voltage is rectified & smoothed, it’s switched through 4 more MOSFETs on the other side of the PCB to create the main AC output.
The label states this is a modified-sine output, so I’d expect something on the scope that looks like this:
Modified-sine doesn’t look as bad as just a pure square output, but I suspect it’s a little hard on inductive loads & rectifiers.
However, after connecting the scope, here’s the actual waveform:
It’s horrific. It’s not even symmetrical. There isn’t even a true “neutral” either. The same waveform (in antiphase) is on the other mains socket terminal. This gives an RMS output voltage of 284v. Needless to say I didn’t try it under load, as I don’t possess anything I don’t mind destroying. (This is when incandescent lamps are *really* useful. Bloody EU ;)).
About the only thing that it’s accurate at reproducing is the 50Hz output, which it does pretty damn well.
As is usual these days, the whole system is controlled via a microcontroller.