Many years ago, in a Grade 7 or 8 Social Studies class, Paul Kardash spoke some words which have stuck with me ever since. Their longevity has more to do with their incongruity than their insight. “One day Buddha was sittin’ under a tree when enlightenment come to ‘im” Words that only a barely literate Ukrainian history teacher could ever formulate but a memorable quote nonetheless. Well, yesterday Bob was sittin’ on his boat when enlightenment come to him too. Twice.
We left the boat unplugged this summer so the first thing we did when we got back onboard was to plug it in and then turn on the breakers. We have a kind of flaky “system” for our air horn which involves a pancake air compressor running off AC. It works reasonably well and gives us a very loud horn but its a kludge. When I turned the breakers on of course the compressor started up. It sits on the flybridge under the forehead so its pretty loud in the cabin because it runs directly over our heads. It used to really bother the damncat. When we arrived on Sunday it ran and ran and ran and ran so eventually I went up top and unplugged it. Yesterday I resolved that problem which turned out to be simply that I had left a garden hose attached to the compressor. We used the garden hose to blow the lines before we left the boat. No big deal – smallish enlightenment.
The other problem was more serious. We have a 48 volt bow thruster. Its a pretty good thruster – hydraulic would be better but high voltage is good. The 12 volt thrusters are pretty well crap – they simply can’t draw enough amps for long enough to do anything useful. I’ve seen lots of 24 volt units and they have a decent reputation. Ours is the only 48 volt system I have ever encountered. The advantage of a hydraulic system would be that you could lean on the control and leave it on all afternoon without it ever letting up. We can thrust for maybe a minute at a time before it starts to run the batteries down.
I’m getting close to ready to fire the engines so I was trying the rest of the systems yesterday. When I tried the thruster I got nothing. No little light, no thruster noise and when I checked the batteries, no voltage. Seriously not good in other words. The way the system works is that we have 4 x 12 volt batteries wired in series to run the thruster. They are charged by a great big heavy 48 volt transformer that runs off 110 service. Underway the transformer gets its power from the inverter. The transformer is only 2 years old but when I tested its output I got nothing. That kind of pissed me off because I just replaced the damn thing 2 years ago. As it turns out I likely didn’t need to do that but its too late now.
When I was about 8 years old I tore apart a windup clock to see how it worked. I couldn’t put it back together and went to bed in tears but by the next morning father had put it back together. As a result of father’s kindness (and no doubt some serious late night frustration) I never really learned anything from the experience. I’ve never been shy about tearing things apart since – lacking father’s assistance to restore them to working order overnight I sometimes regret my enthusiasm for disassembly but I continue undeterred.
I don’t really know jack shit about electronics but I figured the transformer wasn’t working anyway so what did I have to lose? When I got the covers off it was a lot more complicated than I was expecting but I was able to recognize the output windings and when I measured the voltage across them it was around 93 or 94 volts AC. That seemed to me to be about what it should be. I recall reading somewhere that AC output will be slightly less than twice what the resulting DC voltage will be after it is rectified. 48 times 2 would be 96 so 93/94 volts seemed reasonable.
The rectifier circuit board looked OK too – no burn marks, no exploded capacitors or corroded connections. It has 2 medium sized transistors with big heat sinks that clearly do the rectifying but it also has a bunch of other smaller wires coming off the board and leading back to the input circuit board. That’s when enlightenment come to me. For some reason it occurred to me that perhaps the output circuitry was watching for voltage on whatever it was supposed to be charging in order to turn itself on. Clearly the transformer was putting out power – I could measure it, I could hear it humming and it was slightly warm to the touch. That power just wasn’t making it through rectification to the output wires.
So I ended up kludging everything back together in the engine room with a couple of leads hanging out connected to the output side of the transformer. Then I jump started those leads to the 12 volt engine system. There was a great big spark when I did that, likely because the depleted batteries would look like a dead short. However when I tested the voltage on the dead batteries after the spark, sure enough they were reading just over 5 volts. More usefully that 5 volts slowly climbed to over 6 volts and then declined to under 3 volts. I left it alone for a few hours and the next time I checked it had climbed to 54 volts. I haven’t checked it again this morning but I expect it has stabilized somewhere over 50 volts. The little green LED on the transformer also came on and stayed on. The lesson learned is that likely the transformer I threw out 2 years ago had nothing at all wrong with it.