Thorp Air Command - T18.net

Here's my experience, Lee (and thank you for the very kind words)... a local friend, brand new solenoid mounted horizontally, and it would not make contact after the first few hours. We cut it apart and nothing obvious was found. It looked good, but when energized in the horizontal position it wouldn't work. The armature that slides back & forth in the coil is a fairly loose fit. The possibility of poor/incomplete contact exists in the horizontal position. That & other issues combine to make the unit less reliable in the horizontal position. I've seen this problem personally twice now, and heard of it several other times over the years.

I had this very same conversation with a guy on another forum. He originally didn't think it was a solenoid problem because the unit was brand new. I stated that it probably was the solenoid horizontal mounting position, & I posted the link to the White Rogers site, which I will try again here... it didn't seem to work on my first posting about this. It is an active site:

http://www.emersonclimate.com/Documents ... 003web.pdf

You might find his reply interesting. He explains what he found and his analysis very clearly. He had 3 pictures along with it, but I can't seem to transfer them to this forum:

Today I disassembled the offending relay to see what exactly was going on inside.

Photo 1 shows the internal parts to be in like new condition with regard to wear and tear. It was pretty clear what was not a problem. No dirt, no foreign material, no corrosion, no wear, no galling, no pitting, no burned contacts.

Inspection and measurements of the moving parts turned up the following points: 1) The radial play (side to side) of the core was 0.140" according to my dial gauge 2)There is a certain amount of slop between the copper contactor washer and the core/pin it is mounted on to pull it down. 3)The pull is limited by an anvil at the bottom so the difference between what the pull needs to be and what the limit is, is very little - when it hits the bottom - it doesn't pull down any further - period.

Photo 2 shows what happens if the core is manually pushed down to the limit and to the one side - meter shows no contact. (note the core moves further to the edge in this photo compared to photo 3)

Photo 3 shows what happens if the core is manually pushed down to the limit and to the other side - again - the meter shows no contact. (note the core does not move as close to the edge of the case in this photo but still no contact)

Photo 4 shows what happens when the core is manually pushed straight down to the center - here we have contact as shown by the meter.

So what do I make of this?

1) There is considerable slop in the mechanism.

2) There are very close tolerances on the pull length - I don't know how much this varies from unit to unit. Pull may be adversely affected by cocking due to mounting position, enough to prevent contact.

3) There are certainly manufacturing variations from unit to unit - you cannot make more than one of anything and avoid manufacturing variations from design specifications (tolerances).

4) Given the slop, pull length and manufacturing variations, it is entirely possible for a single unit to mess up even though there is no wear present. Depending on how the alignment of circumstances plays out on a single unit - one or most may work forever in any position you mount it in and another may fail.

5) I am speculating the manufacturer knows all of this and that is why they make the recommendation to mount the unit vertically - to improve the reliability rate.

For my part - hereinafter - all of my relays/solenoids get mounted with the plunger oriented vertically. While some or most units may work forever in other positions - it is evident that I ended up with one that was affected adversely by gravity due to the confluence of circumstances/tolerances particular to that unit.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

Alright folks that solves it! I'm moving my solenids vertical. John Evens, thank you! Like I said I've been known to dispute opinions, but when John speaks ....

Enough said, thanks John!

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

Thanks everyone for the information.

I got everything installed over the weekend. Completed the weight and balance Sunday morning. Looks good. Did a run up after work Sunday evening. Have a few things I need to finish up. Hopefully I can do that Tuesday after work and then test flight Wednesday after work.

I will try and post pictures in the next day or two.

Thanks again,

_________________
Matt Smith
Des Moines, IA
55RC

Well done Matt! Will we see you this weekend?

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

That is still the plan. KY Dam has been my goal to getting this done. It didn't seem like I was going to make it until last night. Now I think I have a chance. Now the wife is mad at me so we will see if I can smooth things out enough so she will come with like was planned.

_________________
Matt Smith
Des Moines, IA
55RC

Whilst on the subject of solonoids, here is a question: should a Master solonoid run on the warm side? I can shut the plane down after a flight,reach back behind the co seat and touch the master solonoid, it is always very warmish,uncomfortable to the touch. My panel draw on the electrical is very minimal. What do ya think John???? Dan

It does have a wire wound coil and might get a little warm, but not to the point that you would not be able to keep your finger on it. I would suspect someone used a momentary "start" solenoid in place of a continious on solenoid. It will eventually burn up. The panel draw should not effect the load, the coil that makes up the contactor when energized will create the heat. Most solenoids you buy from the aviation department at Advanced Auto are start solenoids. When buying a master solenoid make sure it's a "continious on" . First clue is the cost. I used a PIPER master contactor.

There is a "Hints for Homebuilders" that shows the difference.

IIRC
Bob MO

It is a continuos duty solonoid from spruce, the start solonoid is from spruce also it is a momentary solonoid, and there is a big price difference in the two. This master has run warm for 4 years, I have had no trouble with it, it just runs a little warm and wondered if that was the norm. Dan

Dan; The master will run warm . Continous duty . Has any one left the Master switch on over nite ? It will be very warm ! I tend to stay away from the China made units and go with the heavy duty USA made Starter and Master solenoids !

RB

I can't add much of anything to that, Dan. I would do a couple of simple tests - Check the voltage to the coil at the unit to make sure it's correct. I'm assuming it cools off when it's "off". If not, check for voltage then also, of course. Just a quick comment...when a contactor, like these "solenoids", is energized & "pulls-in" properly, everything is good. If the armature (the part that is attracted to, & moves in & out of the magnetic field) cannot move completely to it's designed position in the magnetic field (for whatever reason), the coil will get VERY hot. This can happen, for instance, when the voltage feeding the coil is too low, keeping the armature from being pulled into the proper position because of the weaker magnetic field. It's not uncommon for them to melt or burn up when this happens. You might want to try to compare the temperature of your unit with that of someone elses. BTW, the vast majority of aircraft solenoids, master & start, are made by White Rogers, and are common industrial units.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

Bringing an old topic up. I'm in the process of moving my battery to firewall.

My main solenoid that was mounted with my battery was mounted directly to the metal bracket and no isolation. In all my years building drag cars I've never heard of isolating a solenoid but I've never built an airplane.

Mine was oringally made with with this solenoid mounted to the aluminum bracket and I've never had an issue. I mounted it directly to the firewall now similar to how it was previously mounted. What problems will that cause? Mine always made the click when turned on which means mounting it directly to metal didn't keep it on all the time.

New one on me too and I have been wrenching on production airplanes for over 30 years (not to mention cars, trucks and tractors even longer). They are usually hard mounted to the firewall or battery box on a production aircraft and it is pretty common to have ground wires from other systems routed to the solenoid mount bolts.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Go to the EAA web site and find the homebuilders video section . Look for the video named...Solenoids-Master relay and Starter relay . It will tell you everything you need or want to know about these little buzz bombs . The EAA video section is an EXCELLENT source for reference and "how to" when it comes to maintaining an experimental AC .

RB
CAPTAIN ELECTRON

The usual configuration for a master solenoid has a single coil terminal on the case. The other side of the coil is connected internally to the main switching terminal that the battery connects to. So, the coil is activated by grounding that external coil terminal. Obviously the battery needs to be connected to the proper main terminal so that the coil has a positive connection to the battery at all times. So generally, it doesn't matter if the solenoid is mounted directly to the grounded airframe or not. I have noticed that the common White Rogers solenoids of that type come with plastic on the mounting tabs now, which does isolate the body of the solenoid from ground. That doesn't have any effect on operation & isn't necessary if you have the correct solenoid for that application, as described above. These types of legacy solenoid contactors come in various configurations - like I described for the master application, or with one internally grounded (to the case) coil wire and a single external coil terminal (positive) for starter solenoid applications (the solenoid case must be well grounded for operation). You can also get them with 2 external coil terminals (with no internal power or grounding to the coil).

As a little follow-up comment to my last post on this thread in 2012, It is normal for these contactors to run pretty darn hot. They do draw a good amount of amperage when activated. Also, some are designed for intermittent operation (starter) and others continuous (master).

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE