Water in the Master switch

[asav8tor]

Vans old 35 amp Honda alt

External Regulator

Split "Cessna" type master switch

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During rainy weather canopy was opened and water got on the master switch. Tried to mop it up but looked like some went down in the switch.

Next day started the aircraft and no amps charging after engine start. Normal bus voltage with engine running is 14.2v now showing 12.2 ( no alt power )

Shut down and blew compressed air into master switch.

Restarted amps charging and normal bus voltage 14.2 noted.

Flew a series of orientation flights. (kids summer camp) After the 6th flight noticed a hum/beat sound in the radio/intercom. Bus voltage was 15.8v

Shut off alt on split master, voltage went down to 12.6v then turned alt switch back on voltage returned to normal 14.2 hum/beat went away.

After engine start the higher voltage was noted several times but could be fixed by turning the alt switch off then back on. It would then stay at the normal 14.2v for the rest of the flight.

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Should I:

(1) Replace the Master switch and recheck.

(2) Replace the Master switch and Voltage Regulator

(3) Replace the alt with a new plane-power 60amp int reg with overvoltage protection

I don't want smoke in the cockpit. If the Voltage regulator was damaged I don't want to start the engine again on the old unit.

Thanks in advance guys,

Mike

[vlittle]

Your problem is that you now have a resistive switch. The Van's 35A alternator and external regulator are very sensitive to voltage drops and resistances in the Alt field circuitry. Evidence of this are the overvoltages you are seeing. Another symptom is pulsating lights.

The short-term fix is to replace the master switch. The long term fix is shown below: Install a relay circuit in the engine compartment, controlled by the ALT position of the master switch. This is vastly more tolerant of voltage drops and resistance in the interconnect/wiring/switch:



Here's a complete schematic:



A write up is at the bottom of this page

[asav8tor]

Ok, I replaced the switch and will test start next.

Took the old switch apart. It had a significant amount of ground up metal inside. Looks like AL shavings from drilling filing when the acft was built. I do not understand how that much junk could have made its way in there. The inside was wet but did not have standing water. There are 2 holes in the bottom of the switch that would allow some air in and water out.

Thanks for the info,

Mike
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UPDATE: Test ran/flew rock steady back at 14.2v

Thank you,

Mike