I have big 100,000uf capacitors from CDE that have been seating on the shelf for 8-10 years. Are they bad? I don't think I can test such a big capacitance, so not sure if I should use them or they are bad and I should get new ones?
They likely will be within normal specs after reforming.
But take precautions against sudden failures during the process.
https://www.6v6.co.uk/vcomp/tech_tips/reform_caps.htm
But take precautions against sudden failures during the process.
https://www.6v6.co.uk/vcomp/tech_tips/reform_caps.htm
Most electrolytic aging is due to elevated temperature drying them out, but unused for long periods will cause some deterioration, both temporary and permanent - reforming is a good plan to get the most from them.
I would recommend replacing electrolytics that have been in service regularly for decades, but 8 years on the shelf isn't so bad especially for good branded caps - unless that shelf is in a hot climate without air-conditioning...
I would recommend replacing electrolytics that have been in service regularly for decades, but 8 years on the shelf isn't so bad especially for good branded caps - unless that shelf is in a hot climate without air-conditioning...
If they were quality e-caps then 10 years on the shelf is unlikely to be an issue. 50 yr old quality e-caps can reform to excellent specs if they haven't been abused.
Perhaps start by checking the leakage current at rated dc voltage. Although I typically reform higher volt large can vintage e-caps, the good lower voltage types still measure well below 100uA (ie. 100mV for 1k ohm series). The older the e-cap the longer it often takes for leakage current to subside - so it may take many hours until it stabilizes - I typically use a variable voltage supply to bring the cap up to rated voltage, and for higher voltage caps I keep max reforming current below say a few mA, but for lower voltage ratings I'd anticipate many 10's of mA would be low risk.
You may find that many capacitance meters could find 100mF too high a value. If possible, use a cap meter that can also measure ESR, and look for similar values for a batch of caps as the aim, as outlier values are not a good outcome.
The link refers to standardised leakage measurement for relatively modern e-caps that haven't been on the shelf for long.
Perhaps start by checking the leakage current at rated dc voltage. Although I typically reform higher volt large can vintage e-caps, the good lower voltage types still measure well below 100uA (ie. 100mV for 1k ohm series). The older the e-cap the longer it often takes for leakage current to subside - so it may take many hours until it stabilizes - I typically use a variable voltage supply to bring the cap up to rated voltage, and for higher voltage caps I keep max reforming current below say a few mA, but for lower voltage ratings I'd anticipate many 10's of mA would be low risk.
You may find that many capacitance meters could find 100mF too high a value. If possible, use a cap meter that can also measure ESR, and look for similar values for a batch of caps as the aim, as outlier values are not a good outcome.
The link refers to standardised leakage measurement for relatively modern e-caps that haven't been on the shelf for long.