Author Topic: Help Identify Capacitors  (Read 491 times)

urover

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Help Identify Capacitors
« on: May 26, 2018, 06:42:09 PM »
I'm trying to source capacitors for our capacitive fan regulators. These regulators keep failing and having to buy new seems wasteful when/if I can DIY solder new components onto it. The regulator has resistors that I can easily buy on eBay. However, it has two capacitors of unkown rating.

Attached is a picture of the regulator with two capacitors of 3.3K and 2.2K 250VAC markings. I've googled this a fair bit but can't seem to find replacements for these caps. I'm thoroughly confused how K convets to uF or pF or nF.

Can someone please explain the rating/capacity of these caps? A link to an eBay listing would be awesome!

As you can tell, I'm not electrically/electronically inclined but I can manage to DIY with instructions.

FireEngineer

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Re: Help Identify Capacitors
« Reply #1 on: May 26, 2018, 06:54:44 PM »
I am going to try to look these up, but I have had luck emailing pictures to digikey or mouser electronics and they track down the parts.

urover

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Re: Help Identify Capacitors
« Reply #2 on: May 26, 2018, 07:12:31 PM »
^ Thank you.

I'm not sure why I didn't find this in my earlier searches, but this seems to be the manufacturer's datasheet for this particular series: http://www.deccapacitors.net/pdf/med_sw.pdf

I've a metallised polyester capacitor with 2.2 and 3.3 uF 250VAC rating.

Question: Are capacitor types interchangeable if I find a different a type of capacitor with the same rating?

FireEngineer

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Re: Help Identify Capacitors
« Reply #3 on: May 26, 2018, 07:33:34 PM »
You're welcome.

My best guess is 3.3k would be 3.3 uF. I'm not familiar with the "k" notation, it might just be a manufacturer short hand.

I just found the same data sheet. Polyester is Pet, so Metalized Polyester is MPET.

https://www.mouser.com/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371?P=1yzshdiZ1z0wquuZ1z0wquy&Keyword=METALLISED+POLYESTER+CAPACITORS&FS=True


but if you send them the data sheet, they can help you find either that brand or a suitable replacement. And they may suggest a higher grade for better reliability.

Yes* if they are the same rating (Capacitance should be matched. A higher voltage rating is okay.) But 250VAC and 250VDC ratings aren't necessarily the same. Also, the style / construction should match.
« Last Edit: May 26, 2018, 07:55:49 PM by FireEngineer »

cerat0n1a

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Re: Help Identify Capacitors
« Reply #4 on: May 27, 2018, 02:36:42 AM »
Seems like you've got all the info you need, but just to add that "k" is a fairly common way to denote uF on capacitor packaging.

I would think you would want a metallised polyester capacitor as a replacement, certainly not a ceramic or electrolytic. Any one of the same capacitance, voltage rating and lead pitch would do.

Do you know why the regulator keeps failing? If you keep having to replace components, it suggests something is wrong somewhere?

urover

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Re: Help Identify Capacitors
« Reply #5 on: May 27, 2018, 08:55:20 AM »
You're welcome.

My best guess is 3.3k would be 3.3 uF...
Thank you.

Do you know why the regulator keeps failing? If you keep having to replace components, it suggests something is wrong somewhere?
Thank you.

That is a good question. I'm guessing poor quality capacitors/components in the regulator itself. Also, these are being operated in India, where power fluctuations, spikes, and failures are way too common. It is possible that the 250VAC upper limit on these caps is being shot, leading to their failure.

------------

Can I trouble you guys with another capacitor identification request? This one is from a refrigerator thermostat timer that powers a quartz to keep time (8hrs08min). However, it works with a mind of its own - it will occasionally keep the timer ticking, and frequently just sits there quietly.

This seems to be a metallized polypropelene axial capacitor, but the 0.085K is once again throwing my searches off (both on eBay and on Mouser.com).

What is this cap's capacity?
« Last Edit: May 27, 2018, 09:41:11 AM by urover »

cerat0n1a

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Re: Help Identify Capacitors
« Reply #6 on: May 27, 2018, 12:25:54 PM »
I think you're correct about the capacitor type and the size would be 0.085uF ie 85nF (the K is just a tolerance figure of 10%)

Do you have a multimeter - if so, does it measure capacitance? Most modern ones do.

I guess if power spikes/surges are a possible cause of failure, there is no harm in over-rating the replacement (i.e. same capacitance, but rated to a higher voltage.)

SpreadsheetMan

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Re: Help Identify Capacitors
« Reply #7 on: May 27, 2018, 01:42:12 PM »
I think you're correct about the capacitor type and the size would be 0.085uF ie 85nF (the K is just a tolerance figure of 10%)

Do you have a multimeter - if so, does it measure capacitance? Most modern ones do.

I guess if power spikes/surges are a possible cause of failure, there is no harm in over-rating the replacement (i.e. same capacitance, but rated to a higher voltage.)

Measuring the values of metalised poly capacitors in mains voltage applications can be deceptive. They  have a long term failure mode where the dialectric fails and self-heals each time by partially evaporating part of the plate metal to clear the short, this results in the capacitance value dropping over time. I fixed an oil level tank monitor recently where a 0.33uF capacitor in the psu had fallen to 0.1uF at which point the circuit wasn't powered properly. Measuring that capacitor wouldn't have helped!

I always try and get a higher voltage replacement if there is room to fit it.


cerat0n1a

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Re: Help Identify Capacitors
« Reply #8 on: May 28, 2018, 12:31:35 AM »
True, doesn't make sense to measure components which are known to be bad.