Wednesday, 8 August 2012

Vehicle Progress

On sunday Burren finished the remaining plumbing and we leak tested everything to 120PSI. There were a few small leaks but we tightened the leaking fittings which fixed them. I didn't feel comfortable pressurising the tank any higher than 120PSI with us around. On sunday I want to do a complete practise run with water to test out all the systems and also see if there are any leaks at higher pressures. Electronics are now %90 finished, I just need to wire up the fail-safe pressure relief solenoid. This is a normally closed (on) relay wired to the solenoid so the solenoid will be open when the controller is not telling it to stay closed. A mechanical solution would be ideal but I cant find any normally open solenoids that suit our application. We will just have to be careful about checking battery voltage before each test. 

If the systems test on sunday goes well I might also try a quick (unguided) run on the test stand. We assembled the lighting truss last night and although it is not quite as sturdy as I was hopping it should work well. As a friend pointed out might need to weigh down the sides to stop it falling over. 

I managed to burn out the vent solenoid the other day by leaving it on for too long. They are not designed to operate continuously and get extremely hot when operated continuously for more than 30 seconds. As a friend pointed out they take about 9 amps to run so at 12 volts with P=IV they are dissipating more than 100w of power! I took the burnt out solenoid apart and found that one of the wires to the coil had melted. I re-soldered it but because the coil had heated up so much the enamel on the copper enamel wire had flaked off so it was shorting somewhere inside and as such the resistance was negligible and so was like a short circuit and it melted the again. You can buy replacement coils but I didn't want to wait for one so I intend to re-coil it myself. The solenoid would be able to dissipate the heat much better except that the coil is wound on a plastic bobbin which insulates it from the heat sink that is the solenoid body. I intend to re-wind the solenoid directly to the solenoids steel shaft which will allow the heat to be conducted to the solenoid body. I was toying with re-winding with thicker wire to lower the resistance then make up the difference with a power resistor or possibly just running it at a lower voltage. The lathe made it really easy to unwind  the coil. 

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