Starter contactor failure

Hi Adam,

".......starter contactor such that it welds closed.."

Quite a few home builders fit a battery isolating Master Switch. No power no cranking. A KISS solution.

There is a large range of Master Switches available - do aGoogle search.

I have been considering this myself but have yet to work out how to retro fit such a system.

Out of annoying interest - how did you manage to post this question 5 times ?😈

(network error! The other 4 copies have been cleaned up now) 🙂

Musings on the benefits of a Master Electrical (battery) Isolator Switch;

To minimise heavy electrical cable length, I believe some have fitted the Master switch itself, on the firewall, with a rod connection to a knob/large key on the instrument panel.

An electrical Master switch has additional safety potential;

Security, OFF (remove key) no way to start engine without reconnecting battery or turning the Master Switch back on..

Electrical fire, OFF removes the ignition source. Engine keep running on separate circuit.😈

I am thinking of having such a battery master (contactor) in series with the starter alone.  I realise I could have the battery master contactor also disconnecting the main bus (the more traditional use of a master contactor), but I am concerned that if I do so the alternator/regulator - which is connected to the main bus - would not be disconnected from the battery if the battery master were opened.  In the event of a regulator overvoltage, the heavy load that is presented by the battery under these circumstances would not help hold the main bus voltage down.

Re five postings - when I pressed the save/post button I was getting no visible feedback so I thought the web page had frozen or my internet connection had failed.  I banged away a few times before I realised what was going on!

Hi Adam,

I thought your primary concern was the starter relay/contactor welding closed. Starter motor would continue to spin, after engine start and/or continue to turn over engine, after ignition shut down.

The KISS way to do this would be, to use a mechanical isolator (Master Switch) remove the connection from the battery - shutting off all electrical supply. 

Mechanical , as this does not rely on, what may be a malfunctioning, electrical system to be activated.

I assume that you envisage a runaway starter motor, to be an emergency situation, most likly on the ground at engine start. In the unlikly event of other systems being damaged, by isolating the battery/power supply, this would be secondary to the aircraft/your safety.😈