Relay Failure

[jrevens]

Thank you, Mr. Pitkin. It seems as though the group can always rely on a thorough analysis of a question or problem from you. I must agree with your opinion that the master solenoid orientation has probably been over-analyzed and is not really critical. I believe that these guidelines have been passed on and accepted by many of us for generations. I know that I first learned of this orientation issue with regard to these Series 70 White Rodgers solenoids (may have been built by Allen-Bradley back then?) almost 40 years ago when I first started building & flying "real" airplanes. Here is a link to a White Rodgers site that specifies the recommended mounting position as vertical, with the dome or cap down. http://www.emersonclimate.com/Docume.../R-4003web.pdf

There are other solenoid/relays that are designed for horizontal mounting.

While it may appear that the possibility of the plunger sticking while in the horizontal position is slim, I have heard of it happening - again, maybe an old-wives tale? There is definitely less chance of excessive wear or binding with vertical positioning. Maybe there was softer, less wear resistant material used on older units?

I guess I've probably beaten the subject to death. It would be interesting to see what Dave's unit looks like when taken apart. Let us know, Dave.

[Dave S]

John E & John P,

I want to thank both of you for your input. This is valueable and I have learned from both of you.

I don't have the solenoid disassembled yet, but will do that as soon as I have time.

The failed unit is a series 70 R-W.

I will heed the manufacturer's recommendation on mounting position - Generally, a manufacturer has a reason for a recommendation based on their knowledge of the product - this one I was not aware of when the unit was originally installed.

Thanks again and I'll get back once I get the can opened/inspected and have a little better knowledge of what happened inside this one. Hoping I find something definitive I can take a photo of.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp Drive

[Dave S]

Good Morning,

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.

Sincerely,

Dave S
KF7 Trigear
912ULS, Warp Drive