# EEVblog Electronics Community Forum

## Electronics => Beginners => Topic started by: Vindhyachal.takniki on February 06, 2017, 05:10:33 am

Title: What is the value & voltage ratings of this capacitor
Post by: Vindhyachal.takniki on February 06, 2017, 05:10:33 am
What is the value & voltage ratings of this capacitor

1. Attached find a pic of a board. This is capacitive supply board & two capacitor in series are used. The boards works upto 440V.

2. What is capacitance & voltage rating of this capacitor.
Is cap = 550uF
& voltage rating=??

3. H684K      C
550MFF4

Not sure if its C in first line end.
Title: Re: What is the value & voltage ratings of this capacitor
Post by: David Hess on February 06, 2017, 05:26:23 am
684K means 68 * 10^4 picofarads or 680,000 picofarads or 680 nanofarads or 0.68 microfarads.  I think 550 is the DC voltage rating.
Title: Re: What is the value & voltage ratings of this capacitor
Post by: tautech on February 06, 2017, 05:36:55 am
684K means 68 * 10^4 picofarads or 680,000 picofarads or 680 nanofarads or 0.68 microfarads.  I think 550 is the DC voltage rating.
The K has nothing to do with the absolute value, it is the value tolerance indicator, in this case +10%

http://www.robotoid.com/appnotes/electronics-capacitor-markings.html (http://www.robotoid.com/appnotes/electronics-capacitor-markings.html)
Title: Re: What is the value & voltage ratings of this capacitor
Post by: Vindhyachal.takniki on February 12, 2017, 05:56:30 am
I have to make a capacitive supply from 440Vac to 9vdc & then regulator 7805.
Will make & see the results. Tested using these capacitors it is working fine.
But I will connect two 2.2uF,400V in series to be used for this since current requirement is bit more, cap as in attaced pic. SO that end capacitance is 1.1uF/800V.
Though They are not safe since they are not X2 type. But I have seen them in so many boards, none of them had any problem due to capacitor or capacitor every busted.

1. Are these two capacitor in series can withstand 440Vac. Since combined voltage value will be 800V.  In ac 440Vac peak will be = 440*(2^0.5) = 622Vac. So I think I am well within limits?
Theoretically for 800V max ac can be = 800V/(2^0.5) = 565Vac.

2. What is voltage variation in these capacitors? is it +-10%?
3. Which fuse value should be used in this? Max ac load comes out to 150mA. So I am placing 1A fuse.
4. What is the MOV selection criteria for this.
Title: Re: What is the value & voltage ratings of this capacitor
Post by: blueskull on February 12, 2017, 06:07:28 am
1. You need a voltage balancing resistor network. 1M Ohm parallel to each cap should be enough.
2. Rated voltage is maximum. You can run it at lower, not higher.
3. If max AC current is 150mA, a 250mA or 400mA fuse will be fine. If it expects high inrush current, then use a slow blow fuse. If it doesn't have a high inrush current, then a fast blow one will give you more safety. Typical high inrush current devices include rectifier+bulk DC capacitor, incandescent light, motor and heater.
4. I'm not an expert on MOVs, maybe someone else can answer? If I were you I would use a MOV that has working voltage (not breakdown voltage) slightly higher than maximum acceptable AC input voltage times 1.414.
Title: Re: What is the value & voltage ratings of this capacitor
Post by: deltalight on February 12, 2017, 06:25:47 am
If I read your objective correctly, you are constructing a transformerless supply where the 2.2uF 400v film cap is in series with the A/C line (220VAC?).
If this is the case, then you may want to use a Panasonic Class X sately film caps:

ECQUA (Class X) Polypropylene
http://datasheet.octopart.com/ECQ-UAAF684K-Panasonic-datasheet-22087606.pdf (http://datasheet.octopart.com/ECQ-UAAF684K-Panasonic-datasheet-22087606.pdf)
ECQUL (Class X2) Metalized Polyester
http://www.farnell.com/datasheets/18742.pdf (http://www.farnell.com/datasheets/18742.pdf)

The film structure in these caps is made in a matrix such that if it fails, it opens and doesn't short for sately reasons. Should be available from DK and Mouser.