Question Advice on storing aluminum electrolytic capacitors ?

[cloudff7ps1]

What recommendations on how to prevent deformation of the dielectric layers in aluminum electrolytic capacitors from stored electronic devices that were manufactured in the early 90s and early 2000s and store in my home at a temperature of 33-36C, humidity 57-67% and energized devices at 220v AC 60hz?

 

[Misgar]

Over decades, some degradation in electrolytics is inevitable and storage temperatures over 30C are not ideal. Some people subject old electrolytics to a gradual "reforming" process, instead of simply switching the unit on.
https://www.qsl.net/g3oou/reform.html

This often requires a thorough understanding of power supply operation and the danger of removing covers on mains PSUs, so it is not advisable unless you are a trained electronics engineer, technician or HAM radio enthusiast.

On a 30-year old item of equipment, I regard all power electrolytics as suspect and potential (small) time bombs. I've had electrolytics explode in equipment that has been running in standby mode for many years and then switched on.

When all else fails, I recommend replacing all electrolytics with brand new components. This is best done before powering on the unit containing ancient capacitors. A short circuit capacitor could kill associated semiconductor devices.

 

[BFG-9000]

Well nandobadam, you can't really prevent that but it shouldn't be a problem in itself.

See, electrolytic capacitors built until the 1970s could corrode and fail with a dead short or explosion which could damage circuits if just abruptly powered on again after long storage. So if stored unpowered for many years, they should be gradually preconditioned by gradually raising the voltage to reform the oxide layer slowly. The problem is many circuits are actually damaged if you did this in-circuit, leading to the suggestion to remove them to do so--and if you went to the trouble to remove them anyway, well may as well replace them with more modern equivalents.

Supposedly after that, the components used were high enough purity that this just didn't happen anymore, and the oxide layer will reform properly just by switching it on--it may not operate properly the first time it is switched on after long storage, but shouldn't damage anything. But there's liquid inside which can dry out over many years through the rubber seal on the bottom with two holes in it, and if it did that then the circuit wouldn't work until the capacitors were replaced, but again--very little likelihood of damage from just switching it on with dried capacitors.

In your case the early 90s capacitors should be OK, but 1999-2007 was the capacitor plague when apparently some engineer stole an incomplete copy of the secret electrolyte formula from Rubycon of Japan. All electrolytic capacitors from China or Taiwan during this period are extremely suspect and should be tested before operation, while Made in USA or Japan should be OK if they haven't dried out.