Standoffs and Electrolytics

[ildar]

A two-parter here:
1) I bought a package of RS standoffs which are threaded at both ends. How do I attach the one end to the enclosure? I'd rather not have any screw heads on the outside of the box.
2)What is the shelf life of electrolytics? That is, how long can they be stored without being used?

[niftydog]

How do I attach the one end to the enclosure? I'd rather not have any screw heads on the outside of the box.

beats me. I've seen small lengths of "all-thread" effectively spot-welded to the inside of a metal case... but not exactly practical for you to do I would imagine!

I have used counter-sunk screws to do this.

What is the shelf life of electrolytics? That is, how long can they be stored without being used?

There's no hard and fast rules really. It also depends on the conditions they're stored in, and the stress they might be subjected to in a circuit.

Our rule of thumb is that one year of storage and they start to get dubious. Two years of storage and you think long and hard about putting them in a circuit. Particularly the high voltage ones.

For simple audio applications, you'd get away with it. But put them in a power supply or a switch mode and you should be worried.

[Fret Wire]

JB Weld works pretty good for that.

[Paul Perry (Frostwave)]

Since diecast boxes are relatively soft, it should be possible to 'tap' a threaded hole pretty easily, using the corresponding tapping tool. Don't forget the lubricant!!

[R.G.]

1) I bought a package of RS standoffs which are threaded at both ends. How do I attach the one end to the enclosure? I'd rather not have any screw heads on the outside of the box.

Take the RS standoffs, a file, and a hammer. Chuck the RS standoffs into a vise securely, and file them into a fine powder. Then use the hammer to refine the powder into a talcum powder-like dust. Then get some of the nylon adhesive standoffs that just peel and stick to the inside of your box.

2)What is the shelf life of electrolytics? That is, how long can they be stored without being used?

Electros are (were?) designed for a five year shelf life. Of course, that was the industry norm before integrated supply chain management was invented by MBAs so that no one anywhere would ever have any inventory.

[Yuan Han]

I attach the standoffs to the box using epoxy.

[petemoore]

My buddy successfully 'glued his engine block' with the JB Weld... :shock:
...Successfully !!!  Believe it Or Not !!! Ice had blown a 'frown' crack in the block.

[smashinator]

Take the RS standoffs, a file, and a hammer. Chuck the RS standoffs into a vise securely, and file them into a fine powder. Then use the hammer to refine the powder into a talcum powder-like dust. Then get some of the nylon adhesive standoffs that just peel and stick to the inside of your box.

That's hilarious.

[black mariah]

JB Weld. Attach the standoffs to the board lightly, put some JB Weld on the bottom of the standoffs, then place it in the box. Take the board off and clean up any excess. Unless you have a habit of kicking the interior of your pedals, the standoffs aren't going anywhere once the JB Weld is dry.

[erio fraga]

About aluminium ( Al ) electrolytic capacitors, from

http://www.epcos.com/inf/20/30/db/alu_03/00190056.pdf

it's possible to get:
As is the case with all capacitors, an Al electrolytic capacitor comprises two electrically conductive
material layers that are separated by a dielectric layer. One electrode (the anode) is formed by an
aluminum foil with an enlarged surface area. The oxide layer (Al2O3) that is built up on this is used
as the dielectric. In contrast to other capacitors, the counter electrode (the cathode) of Al electrolytic
capacitors is a conductive liquid, the operating electrolyte. A second aluminum foil, the so-called
cathode foil, serves as a large-surfaced contact area for passing current to the operating electrolyte.
The dielectric layer of an Al electrolytic capacitor is created by anodic oxidation (forming) to
generate an aluminum oxide layer on the foil.
The two aluminum foils are separated by paper spacers. The paper serves various purposes, it
serves as a container for the electrolyte â€" the electrolyte is stored in the pores of the absorbent
paper â€" and also as a spacer to prevent electric short-circuits, as well as ensuring the required
dielectric strength between the anode and cathode foils.
Due to the special properties of the aluminum oxide layer that serves as a dielectric, a small current
will continue to flow even after a dc voltage has been applied for longer periods. This current is
called the leakage current. A low leakage current is an indication that the dielectric is well designed.
A high leakage current flows (inrush current) in the first minutes after applying
a voltage to the capacitor, in particular after prolonged storage without any applied voltage. In the
course of continuous operation, the leakage current will decrease and reach an almost constant
“steady-state” value.
The oxide layer may deteriorate when Al electrolytic capacitors are stored without an externally
applied voltage, especially at higher temperatures. Since there is no leakage current to transport
oxygen ions to the anode in this case, the oxide layer is not regenerated. The result is that a higher
than normal leakage current will flow when a voltage is applied after prolonged storage. As the oxide
layer is regenerated in use, however, the leakage current will gradually decrease to its normal level.
Al electrolytic capacitors can be stored voltage-free for at least 2 years. Provided that these storage
periods have not been exceeded, the capacitors can be operated at rated voltage directly after
being taken out of storage. When designing application circuits, attention must be paid to the fact that the leakage current maybe up to 100 times higher than normal during the first minutes following the application of power.
When the capacitors have been stored for more than two years, it is decisive whether the circuit will
tolerate high initial leakage currents. A circuit that has been stored for more than two years with the
capacitors incorporated, should be operated trouble-free for one hour. This will usually regenerate
the capacitors so far that storage can be continued.
It’s possible to perform a reforming process; for this purpose, the rated voltage is applied to the capacitors via a series resistance of approximately 100 ohms for UR < 100 VDC, or 1000 ohms or UR >100 VDC, for a period of one hour.

[Lonestarjohnny]

Here's from the Horse's mouth at Spague, My Buddy is an engineer there, his Poop sheet say's that they recommend keeping them on the shelf for only 2 year's without being reformed, if it's high voltage the cap can be damaged by hitting it with high B+ voltages, I never fire my new cap's up with out reforming them anyway, on low voltage i think you can skimp on the reforming, I've never popped a 9V, cap, But i have seen a few High voltage cap's go and it sure scared crap outa me and was quite the mess to cleanup,
You ever try a Hot Stick Glue Gun, if you get 1 don't cuss me if you ever need to remove whatever you glue down with it, but it stick's to anything just about.
Johnny