Master Solenoid failures

[tamarack]

Does anyone have a suggestion for a master solenoid that will work reliably when it gets 20 below? Sure am having problems with solenoids that won't activate during cold weather.

Thanks, Vickie

[slowmover]

I used to have that problem. A tap on the solenoid with a Leatherman was all it took to get it to connect. Of course I found this out the hard way after handpropping and returning to a Class D field NORDO.

[tamarack]

Thank you Slowmover for the quick reply, however, taps do not work on these inop solenoids. Nor do blows, bams or slams. You've heard the saying, "Words are mightier than swords?" Words don't work either.

Vickie

[Webfoot]

For a temporary fix for a frozen solenoid I put some hot water in a ziplock bag and wrapped it around the solenoid to warm it up for a few minutes. Got it working, but didn't cure anything. Sometimes tapping works, sometimes not.
Webfoot

[Steve Pierce]

Almost 80 degrees here today. Luckily we didn't have any melted solenoids.

[WIflier]

Are these solenoids failing on aircraft or new ones or used ones you are replacing? If they are ones you are replacing make sure they are Master (continuous) or Starter (intermitent) they can be positive or negative activated.

Si

[koldham]

I have had this same problem on my Cub off and on since 1985.

I can't offer a real fix, but what I have done is turn on a load item (nav lights for example) then cycle the master on and off until the lights stay on. this seems to "stick" the solenoid on. I'm sure this makes no sense from a theoretical/electrical perspective, but I this has quickly gotten me power to get home.
I used to change solenoids (part number from parts book) to no real effect.

Is your battery under the seat?

[Crash]

My suggestion is to order new one from Stoddards and when you install it, connect the positive cable coming from the battery to the starter solenoid post first then run a short #6 or #8 wire (depending on your load) over to feed the master. This takes the starter hit off the master solenoid (makes them last longer) and worse case you can get it started without the master working. Some Cessna models are set up this way I am told. Take care! Crash

[Steve Pierce]

I just wired a Stearman how Crash describes. It was wired where the power went through the master relay and then the starter relay. The small single engine Cessna wiring diagram I looked at was wired this way and I think that is why I have replaced so many master relays on them over the years. I agree with Crash, the starter current going through the master relay is going to limit the life of the relay and I also would like to start the engine master relay or not. Tony Bengelis's book shows current go through the master relay and then the starter relay. I wish he was here so I could debate this issue with him.

[tamarack]

Crash and Steve you are brilliant!

As I think on it, the airplanes that seem to be eating master relays do have the starter circuit going through the master relay.

So, why is the current going through the master relay? What is the advantage?

Also, an "emergency starter circuit" would be a good idea, although probably not legal. But definitely a really good idea at 20 below with an injected engine...

Thanks!

Vickie

[fireball111]

Don't forget to put a mega fuse from batterie to starter solenoid if you wire it like that . Just in case of a shorted starter or wire .The master was your protection before. should be a mega fuse close to batterie in any case (breaker still).Just an idea

[Steve Pierce]

I hadn't thought of that. Did have the starter relay stick on a Cessna 210 one time and was able to kill the master to stop it.

[KelvinG]

Here is Bob Nuckolls, (Aero Electric) response when ask this question:

Q Most, if not all, aircraft electrical systems put the starter (and its solenoid) in series with the master solenoid. The master solenoid is required to carry a huge load that is otherwise far beyond its need and, in addition, becomes just another voltage drop on the way to the starter. Why is it done this way? Thanks, Glenn Giere

A The contactor most likely to stick is the starter contactor. Running the starter current through a battery master contactor or switch gives you a way to shut things down if the starter contactor DOES stick. Further, the idea of a battery master is to disconnect ALL major current carrying pathways in an airplane. Items we wire to an always hot battery bus are generally loads of 5A or less (which I like to protect with VERY fast fuses). Bob . . .

While I understand and like the idea of not running the starter current load through the master contactor, replacing a master contactor may be a small price to pay compared to what could happen if starting contactor gets stuck and there is not an alternative way, (fuse, master contactor, etc.) of killing the current draw.

KelvinG

[bobnall]

Interesting thread for me as I'm now in the throes of getting the electrical system installed in my rebuild. I'm working with a guy (EE type) that's drawn out an electrical schematic, and included in there is a 35 amp pullable type curcuit breaker that will between the battery and one of the solenoids (master or starter). This is to replace the double fuse system that was previously installed.

We haven't worked out the physical details yet, but when that gets done, I'll post here about how we did it.

-Bob

[T.J.]

delete

[KelvinG]

On PA-18 S/N 18-7409140 thru 18-7709198 the "HOT" lead from the main buss went to both the Master and Starter solenoids, and not thru the Master first. There is no disconnect in the starter circuit.

T.J,
No fuse, CB, or anything huh?

I really like the idea of not running the starter current load through the Master contactor and plan on wiring my experimental that way. Right now I am leaning toward a good hefty fuse as providing adequate safety but maybe that's overkill.

KelvinG

[Greg Smith]

I believe you are talking about a Current Limiter. It is like a slow blow fuse on steroids.
Flat copper with ceramic or phenolic looking insulation, and a little window to see if it is
blown. It allows a momentary excessive draw as the starter motor gets rolling.

http://images.google.com/imgres?imgu...3Doff%26sa%3DN

But fuses and current limiters protect circuits, not appliances. If the motor or circuit is
shorted, it will blow. But if the contactor (Relay or solenoid) is stuck, there wouldn't likely
be enough of an increase in draw, at least for awhile. The current limiter won't know the
contactor is stuck, it will just know that an acceptable amount of power is going through
it. Eventually the starter gets damaged (then the current limiter blows) or the battery dies.

I would think you would want a positive way to disconnect power from inside the aircraft.

[fireball111]

If the starter would stay on you could shut off breaker witch is a switch and a fuse

[Ted Richey]

Have had the same problem over the years with contactors. My electrical guy explained that in the battery contactor there is a fibre washer which is under no pressure when the contactor is engaged and the vibration of the Cub engine running could cause the washer to vibrate and shed dust which coated the contacts and it would not switch on. This only applied to the ones brought from automotive shops which appeared identical to the aircraft ones. Apparently the genuine Cessna item has this washer coated with something that stops the dust coming of it when vibrating. Changed to a Cessna part number and the trouble went away. For what its worth.

[Steve Pierce]

Makes my old push botton starter contactor
in my Clipper and some of the early
Pacers more attractive.

[hankster]

Contactors and relays fail by two main mechanisms. (1) Every time they
open or close, they arc a little bit at the contacts. Over time, they become
badly pitted and prone to stick. They may even spot weld themselves
closed. (2) They wear out mechanically because of number of cycles.

Putting the starter circuit on the master contactor contributes to neither of
these. The master contactor is already engaged when the starter is
engaged, so no arcing at the contacts, and engaging the starter does
nothing to add to the cycles of the master.

Cold weather may exaggerate the mechanical problems of a worn
contactor. Things that are worn to the marginal point may not fit well
enough to work reliably when cold. Also, the presence of a little frost in
the works might contribute to the problem.

My 2c. . .

Hank

[mikeo]

Try using one of the HD 75 amp Bosch solinoids good for one million cycles and won't run battery down overnight plus weigh ounces

[Crash]

There are over 60 million cars running around without a master switch or master solenoid. A #2 cable runs from the positive post of the battery to the starter solenoid. A number 8 wire runs to the power distribution box (fuse panel). I have never had a starter solenoid stick on my car or plane. If it did I would shut the engine off and disconnect the battery cable. No big deal. Take care. Crash

[wacodriver]

What master solenoid ? Did a search on my one ('62 military model PA 18-150) and couldn't find it. The #2 wire connects the battery to the starter relay. a #8 wire connects the hot side of the starter relay to the main bus via the twin fuses to the main switch. Looks like it is the original setup.

[Steve Pierce]

Early ones only had one relay.

[nanook]

I've noticed on my cub that the master solenoid suffers frequent failures due to moisture/condensation problems.
The solenoid is located behind the Atlee Dodge extended baggage on the stock battery box. The problem seems to be that the area back behind the baggage never warms up enough to get rid of the moisture. It gets just warm enough to melt the frost to liquid then it freezes again.
I'm recovering this cub this winter and removing the Dodge baggage and moving the battery/solenoid up under the pilot seat where, I hope, the heater will keep them warm and dry.