Black box

Thank you to our blog readers who left comments and suggestions regarding yesterday’s alternator belt failure.  We ordered two replacement belts for the 175A alternator and a spare for the 45A alternator.  The replacement belts for the 17%A alternator are 6PK1193 whereas the original was 6PK1195.  My understanding of the belt code is the 6PK means the belt has 6 ribs and the 1195 is the length in millimetres.  So the replacement belts are 2mm shorter than the original.  However, as Paul from Waterways Routes pointed out the range of adjustment in the pulleys means belts within a certain range will fit and we should endeavour to identify the minimum and maximum length belts.

Whilst it is possible the problem with the belt was caused by the pulleys not being correctly aligned I’m more inclined to think it was too loose.  Nick, the engineer did remove the alternator to modify it for the Sterling PDAR.  However he is a very competent engineer and I would expect he correctly reinstalled it.  Moreover the edge of the belt showed no sign of fraying or rubbing.  I read somewhere the belt is at the correct tension if it can only be twisted 90°.  The original belt could be twisted slightly more than that so the new belt is tensioned to a 90° twist.   Next time I can lay my hands on a suitable length of straight edge steel I’ll check the pulley alignment.

A good preventative maintenance routine should require the belts to be replaced just before they fail.  George (nb Rock’n’Roll) left a comment advising Beta suggests the belt be replaced every 750 hours.  This ties in with the 250 hour service schedule so I’ll also adopt the routine of replacing the belts every third engine service.  Any future replacement belts will be purchased from an Autoparts suppliers (that’s where the marina obtained them)!

This morning it was a quick trip into Newbury to Wilkinsons and Maplin.  We now own a cheap wire brush.  This will make cleaning any belt residue from the grooves in the pulley easier should we have another failure.  Maplin supplied (at a cost) a cheap soldering iron, solder, a small pack of machine screws along with a small plastic box. 

On my return to Waiouru I took over the galley to do my own bit of baking.  The plan was to cook up a DC to DC converter for the laptop.

The first task was to drill four small holes through the base of the plastic box and fit four long machine screws.  They have a washer and nut on the base which will act as a spacer holding the printed circuit board away from the base allowing air to circulate.

The top part of the box had a hole drilled in each end for the 12v supply cable and the 19.2V output cable to the laptop.

The converter was then wired to the primary and secondary sides.  I used a cable tie as a ‘stop’ to prevent any strain on the converter terminals.  The supply wire was fitted with a 12V cigarette lighter socket and the secondary side had a laptop plug soldered on the end.

The DC to DC converter takes to 12V supply and can convert it to between 12-32V.  There is a small screw to adjust the secondary voltage.  The laptop requires 19.2V and when I initially connected the converter to the boat 12V supply it was producing 19.61V.  The screw was then adjusted to get the voltage down to 19.35V without it being plugged into the laptop.  When connected to the laptop the voltage dropped to the required 19.2V.

The printed circuit board was then fitted onto the four long machine screws in the base, four washers and nuts then went on top to secure the circuit board in place.

It was then a case of screwing the two sections of the base together and doing a final check of the voltage.

The DC-DC converter has a couple of fairly substantial heat sinks so I thought it might be prudent to include some ventilation.  Two rows of small holes were drilled in opposing sides of the plastic box.  This also allows a small amount of light from the red LED on the circuit board to be seen.

So we no longer need to run the 3000W inverter to charge the laptop.  Now the only issue is the lack of 12V sockets in the saloon.  I hadn’t anticipated running the laptop on 12V!  There is a 12v socket in the computer workstation area but it’s being used by the phone.  Fortunately, the layout of the services on Waiouru makes it a relatively easy task to install additional sockets.

Oh….. Jan wanted all our readers to know about the mess I made in her galley during the assembly of the converter.  At least I used a piece of timber to drill on rather than her granite worktop!