Large Scale Central

USAT pickups problem

Problem Solving
#21

Greg , Hi ,

Yes , the grease is indeed very much conductive . It was developed (like many things) for military applications ; the stuff I stole (sorry , bought) was developed to ensure good electrical contact between the cover and the cavity containing low power RF circuitry as used in the mixer stage of a radar receiver .

I think it was made by Midland Silicones , but I am sure other companies market similar stuff .

And you are right , of course , about “goo gone” which could be called “body gone” . Best avoided .

Mike Brit

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#22

There’s a caveat worth mentioning about conductive grease, and I know you, Mike, already know this, it’s for people reading the thread:

While conductive grease sounds like the absolute best lubricant where there is metal on metal AND you want to conduct electricity, you should be CAREFUL to only get it where you want it, and not over lubricate, and cause short circuit paths.

I’ve read many times over the years where it has been slathered on and caused short circuits or excessive current consumption.

In a like manner, I know someone who went overboard with graphite and caused a short circuit between an insulated wheel and the uninsulated axle… making a bridge across the plastic insulator between the axle and wheel.

In most cases, as for ordinary lubrication, you only need the amount to coat the surfaces, not pack the cavity like a car wheel bearing.

Regards, Greg

p.s. Mike is it silver or copper that is the conductive “part”?

#23

Greg , I am having a senior moment , it is a metal which is deadly poisonous for which there is no known cure and dammit , the name escapes me . Ah , just thought . Beryllium . Horrid stuff , they find what you are sick from at the post mortem . Can appear looking like sheet copper , which is Beryllium Copper (odd , that) and is widely found in military radars and avionics in general . In a more natural state it looks like a translucent blue plastic . When machined , all turnings and swarf must be carefully collected and disposed of . Abrading it also is dangerous .

I was horrified one day to see someone caressing the body of a high power travelling wave tube with sweaty hands feeling the currugations in the material , notwithstanding the large red sticker on it saying “Danger, Contains Beryllium” .

Weird stuff , best avoided but has desirable properties .

Your comments about sloshing the stuff around are indeed wise , I have seen printed circuits curl up and die due to spillage of the stuff , and as you say , with any grease a thin smear over the mating surfaces is adequate .

Mike Brit

ps The blocking thing doesn’t seem to be working yet .

#24

There are plenty of suppliers here that have copper, nickel, or gold infused conductive greases… most very expensive… I have not found a need for them yet, I have taken action to increase the number of pickups in most cases and found it adequate.

Yes, beryllium is pretty darn dangerous, but I guess if you find someone licking the ends of the axles he’s already in deep trouble!

Greg

#25

Greg , you are right , it can be costly , but the Radio Shack type places stock it in little tubes which will last for ages if used correctly----i.e.sparingly .

Regrettably , the solution of extra pickups is beyond the capabilities of some of the model railway nutters . Nothing wrong in that , we are not all born to having adequate mechanical skills .

The problem is that limited skills can often lead to problems for they who do not recognise their limitations .

As in “Mike , can you sort this out , I put it back together and had a couple of screws left over”.

A short story for you . This dates back as you may realise as you read it .

A chap living just up the road from me came to my house and said “Er , can you spare a minute , I can’t start my car” This was stating the obvious as I had heard the gradually slowing "wang wang wang"of a starter motor .

So I popped up the road to the car and said “Right , what have you been doing?”

“Nuffin’”

"Oh come on , you’ve been on this all afternoon "

“Well , I’ve bin cleanin’ the engine”

“Not taken anything apart then ?”

“Nah , wooden know 'ow to”

“So what’s this then?” sez me picking the rotor arm up off the top of the radiator .

Then he compounded the error by asking , as the battery was flat , could I drive my car up and give him a jump start ? I supposed I could . “Got any jump leads?” he asked .

In a similar vein , the pilot of an aircraft from a country I hesitate to name asked me , as crew chief on the line ,

"Could you give us some ground power , our on board accs are flat and we can’t start the engines "

Jokingly , I said “We can give you a bump start if you like”

“That would be luverly of you” he said .

So the joke was on me because I had to explain what a bump start was , and the tell him I was joking ; he was still bemused . We gave him his ground power of course .

Mike Brit