Battery Solenoid

[Andrew Leak]

Just a quick question gents; how hot is the battery solenoid supposed to get? Mine's running bl**dy hot within about 20-30 seconds! You can't really touch it, but then again if it's in the air I suppose it must be getting cooled? I think it may need changing, but I wonder if anyone has had this problem.

Andy

[Phil Burgess]

When energised a 12v battery master soledoid will draw about 1amp to keep the contacts closed. This will result in some heat being generated, but it shouldn't be too hot to touch. Part of the winding may have shorted internally allowing higher current to be drawn and therfore more heat to be generated than normal.

I recently changed mine as the culprit of a starter malfunction. They cost about £15 from LAS.

Alternatively you could have an over voltage situation from your alternator / regulator. Check that the battery voltage foes not exceed 14volts with the engine running and adjust or renew the regulator.

[Steve Brown]

You may well have a starter solenoid instead of a master solenoid.

The latter is designed to be on all the time the a/c is operating and has a high resistance coil giving a light coil load ie 1 amp ish / warm-ish, while the former is designed only to switch high amps starter load during cranking ie hot -ish if left on for more than 10 - 20 secs.

The former has a low resistance high current coil winding that is designed to very quickly snap the solenoid contacts to 'on' against a strong spring when activated, and then snaps it quickly to 'off' when the engine starts.

This reduces the arcing that occurs when switching such high starter currents and the risk of contact erosion/welding/sticking - major problem if the solenoid doesnt release when the engine starts!!!

Check the part no and (since it is not operating right anyway) replace it using the right type.

Regards
Steve

[Andrew Leak]

Thanks for the quick replies. The solenoid is completely part number-less, it's quite old and hasn't got a stamp or anything written on it. It could well be a starter type as it draws about 6.5 amps! I think I'll just get a new one from LAS as suggested - I really don't want to 'torch' the aircraft as it is starting to give off fumes now!

Andrew

[David Hardaker]

SAN weren't daft when they put the cable operated master switch in the battery negative line ! (on small Jodels)
The whole thing must weigh all of 6 ounces, including bowden cable !
Simplest is best.
dh

[Andrew Leak]

Cable operated master switch eh? I've got a box of bits with the aircraft and I think I spotted one of those. I thought it was a pull starter switch that bolted somewhere on the back of the starter motor...how wrong I was. Thanks for that!