Capacitor help

[chulios66]

I recently found a old router that was made for businesses or schools and was planning to take it apart for the components. I then saw a capacitor within it rated at 6 amps and am not sure how to discharge it. I have already done some discharging on past capacitors, but the screwdriver terminal method scares me because of the sparks that are right it front of me and the reason for this could be me getting shocked by the electric fence we had when I was younger. I really don't want to discard it so I am wondering if any of you could help me by showing me a safer, spark-free, and reliable method that would aid in my problem. One that was recommended was to use a resistor, but I am not sure what color code would be sufficiant for that size, considering that if it was too low, it could explode. Thank You.

 

[cowboybob]

Welcome, chulios66!

Take about a 1' sheet of aluminim foil and fold it into a smaller square (say 4" on a side). Place it on a non-conductive surface.

Holding carefully, perhaps with working gloves (if you so choose) place the capacitor, terminals down, on the foil, rocking it around while pressing.

The idea is to short the terminals with the foil.

While still pressing down, fold the edges of the foil up and around the body of the cap. Tape in place if you like. An additional piece of tape, side to side directly across the foil at the terminals, is an additional safety feature.

Discard (or save) as appropriate.

Keep in mind that non-electrolytic caps, ordinarily, do not retain a charge, but there's no harm in being careful.

 

[tvtech]

Interesting Bob..

How you doing??

Regards,
tvtech

 

[cowboybob]

tvtech,

Good to see you back.

I'm fine. As usual, in a constant learning cirve (do they ever flatten out??).

ETO seems to have calmed down considerably and (except for this post) is largely on-topic and enjoyable.

Again, welcome back.

CBB

 

[cowboybob]

I recently found a old router that was made for businesses or schools and was planning to take it apart for the components. I then saw a capacitor within it rated at 6 amps and am not sure how to discharge it. I have already done some discharging on past capacitors, but the screwdriver terminal method scares me because of the sparks that are right it front of me and the reason for this could be me getting shocked by the electric fence we had when I was younger. I really don't want to discard it so I am wondering if any of you could help me by showing me a safer, spark-free, and reliable method that would aid in my problem. One that was recommended was to use a resistor, but I am not sure what color code would be sufficiant for that size, considering that if it was too low, it could explode. Thank You.

Having reread the OP;

With the router off and unplugged, short its plug, then turn on the router. Wait, say, 5 minutes. Any possible residual charge will have been discharged back through the windings of the motor. I would still take care in handling the cap and prepare it for storage/discard as above in post #2.

 

[dr pepper]

You could put a 100k resistor across the cap then leave it a day or so, no sparks.

 

[tvtech]

tvtech,

Good to see you back.

I'm fine. As usual, in a constant learning cirve (do they ever flatten out??).

ETO seems to have calmed down considerably and (except for this post) is largely on-topic and enjoyable.

Again, welcome back.

CBB

Thanks CBB.

Bit quite here.

Regards,
tvtech

 

[chulios66]

Having reread the OP;

With the router off and unplugged, short its plug, then turn on the router. Wait, say, 5 minutes. Any possible residual charge will have been discharged back through the windings of the motor. I would still take care in handling the cap and prepare it for storage/discard as above in post #2.

It didn't come with the power cord, which could be why it was thrown away. Thanks for the tip though

 

[chulios66]

You could put a 100k resistor across the cap then leave it a day or so, no sparks.

Do you think that there is a faster method, in relation to using resistors? I haven't been working on anything for a while now, which is why I needed the color code specifically. I was thinking of going that way as well, but wasn't sure.

 

[Pommie]

If you have a multimeter then check the voltage across the capacitor, if it's low (<24V) then no problem with getting a shock (use something like a 100ohm resistor (Black, brown, brown)). If it's high then report back.

Mike.

 

[dr pepper]

I suggested a 100k, brown black yellow, as I didnt know the voltage across the cap and was deliberatly picking a high value.
What is the voltage rating of the cap, should say on the side.

 

[chulios66]

I suggested a 100k, brown black yellow, as I didnt know the voltage across the cap and was deliberatly picking a high value.
What is the voltage rating of the cap, should say on the side.

I can only see that it is 6 amps, not sure how to convert that into voltage though.

 

[chulios66]

If you have a multimeter then check the voltage across the capacitor, if it's low (<24V) then no problem with getting a shock (use something like a 100ohm resistor (Black, brown, brown)). If it's high then report back.

Mike.

Can you verify that capacitors don't spark unless the terminals touch together. Doing so would be very helpful and thanks for the feedback.

 

[MrAl]

Hi,

The thing to do is measure the DC voltage across the cap, then choose a resistor based on that measurement. If you can find the farad spec of the cap that would help determine how long it takes to discharge with a given resistor value.

The resistor is chosen based on the DC voltage and the power of the resistor:
P=V^2/R

or:
R=V^2/P

For a 1/2 watt resistor type and voltage of 10 volts we get:
R=10^2/0.5=10^2*2=200 ohms.

For a 10 watt resistor type and voltage of 100 volts we get:
R=100^2/10=10000/10=1000 ohms.

Depending on the value of the capacitance (Farads) the cap discharges either fast or slower.

Measure the voltage after 10 seconds and see what it went down to.

A useful formula to determine the approximate capacitance is:
C=10/(R*ln(Vcx/Vc+1))

where
C is the capacitance in Farads,
R is the resistance of the resistor in Ohms,
Vc is the initial value of the voltage at t=0 seconds,
Vcx is the capacitor voltage 10 seconds after connecting the resistor,
ln is the natural log function.
This assumes that Vcx and Vc are not zero or very close to zero.

If a timing interval of 10 seconds is not convenient or not enough, then use:
C=t/(R*ln(Vcx/Vc+1))

making 't' whatever is convenient to measure.

 

[dr pepper]

If there is not a direct short or near short across the terminals then a capacitor will not spark, however to answer your question if you want to pull a cap from a board esp a larger one the only way to be sure not to get a spark is to discharge it first.
Electrolytics have a reasonably high leakage and the circuit may well put a load on it, so if you know the device hasnt been plugged in for 24 hours or more its unlikely you'd get a big flash off one pulling it out.

 

[ChrisP58]

I don't think that I have ever seen a capacitor with a current rating printed on it. Many capacitors do have ripple current ratings, but those are in the data sheet, and usually have frequency dependent modifiers.

Are you certain that it is indeed a capacitor? Could you please post a picture of the part? Or the manufacturers name and part number?

 

[chulios66]

Going to test voltage, I will check back in with this.

 

[KeepItSimpleStupid]

Take a pic. I'll bet it's an LC line filter. Could look like this https://www.newark.com/te-connectiv...r-line-filter-10a-700/dp/52K4492?CMP=KNC-GPLA or other variations.

6 amps would not normally be on a capacitor.

FWIW. The product of R and C is what's called the time constant. And, FWIW, it takes about 5 time constants for a capacitor to discharge to 98% of it's value. That gives you a mechanism of selecting a resistor and time.

Measuring the voltage is OK as long as the rating is < 600 V. High voltage caps require more precautions.

The color code can be found anywhere, but you have to be aware that not all resistors follow the exact same code. Some use 2 significant figures and a multiplier and some use 3 sig figs and a multiplier.

It boils down to the following mnemonic "0-Bad (Black) 1-Boys (Brown) 2-Rape(Red) 3-Our (orange) 4-Young (yellow) 5-girls (green) 6-But (blue) 7-Violet (Violet) 8-Gives (Grey) W-Willingly (white).

To avoid the black brown discrepancy, you can substitute Black for Bad and get the raciest version. Then you have Grey and Green to deal with.

So, for a 4 band resistor having black brown red gold, you get 10 as significant figures and red is 2, so you add 2 zeros and get 1000 ohms, The Gold is 5%, Silver is 10% and no band is 20%, Brn black blk brn is also 1K and likely 1%. That brn can get confused with gold. So, even if you think you know the value, measure with an ohmmeter to be sure.

Power has lots of formulas: P=V^2/R would work for you discharge problem. You can use the voltage rating of the cap as V and R as the resistor, Use 5*RC = 10-20 sec and you can figure out what wattage resistor you need If P is 0.375, go to 1/2 Watt.

So, you can now select a resistor and the power rating and determine how long you should hold the resistor across the terminals.

It won't cover brown black gold gold, but they aren't too common.

Resistor wattage is based on physical size: 1/8, 1/4, 1, 2 , 3. and 5 Watts are common,

Special precautions exist for high capacitance like in Farads and high voltage. Very high capacitance is used for a back up battery. Very high voltage caps like for 10 kV do not discharge completely and will "come back to life" after being discharged.

 

[chulios66]

Thanks guy, tested it and had no current. I appreciate all of the helpful feedback that was given.

 

[ChrisP58]

A more politically correct version of the color code mnemonic is:

0-Black (Black) 1-Bears (Brown) 2-Race (Red) 3-On (orange) 4-Yellow (yellow) 5-Grass (green) 6-But (blue) 7-Violet (Violet) 8-Generally (Grey) 9-Wins (white)

At least that's the one the teacher taught us in high school.