Hello everyone.
In some videos where I saw guys tearing down things like microwave ovens, they say that the big caps inside can kill and therefore should be shorted carefully before you touch anything around them.
So for example, If I have a capacitor rated at 3300uF 16V and I charge it with 5V@1A until it is fully charged, could the short actually kill or cause any harm? I'd like to understand more about capacitors through this question.
Thanks in advance,
128ITSH

 

Under 50v is considered a non-dangerous level.
Microwave capacitors charge to very high voltage levels, and could possibly be a cause of concern if handling them without care or while in the process of trouble shooting the circuit.
Max.

 

5V is not a potential that can make your skin conduct. Your example is safe.

 

5V is not a potential that can make your skin conduct. Your example is safe.

Does it meant that when I charge a cap with a specific voltage, it's potential in the end of the charge will be the same voltage, or it's maximum rated volage? will it be fully charged (even though the charging voltage was lower than the maximum rated voltage)?
Does it also mean that even if the capacitor is 100000uF but the voltage is low, it will not harm?

 

It is no different than handling a battery that has a charge of equivalent value.
Max.

 

The capacitor's rating states what voltage it is designed to handle. You can take a capacitor that is rated for 480 volts and charge it to 5 volts and all you'll get out of it is 5 volts. Your 16 volt cap doesn't MAKE voltage it stores it at what ever level you put into it. So if you put in 5 volts and let it charge at 5 volts for 10 years, in 10 years all it will have stored is 5 volts. (assuming it doesn't dry out in that time - in that case it won't hold the voltage).

Microwave capacitors (the ones that are connected to the magnetron) boost the voltage from the transformer by reverse phase charging. The output of the high voltage winding is 1000 volts RMS. When the current swings (lets assume) positive the capacitor takes that charge (1000 volts). When the phase of the transformer reverses then the capacitor acts in series with the output creating the 2000 volts the magnetron needs.

MO caps (Microwave Oven) have a bleeder resistor on them to slowly drain them to where they're safe to handle. I'd make sure the MO was unplugged for a day if possible before messing with it. 1000 volts CAN kill you quick. The size of the cap also comes into play. a 470 microfarad cap stores far less energy than a 3300 microfarad cap when both are charged to the same voltage (in your example ~ 5 volts). The discharge time for the 470 is far shorter than for the 3300, meaning with the longer discharge time you're exposing yourself to a longer duration of energy. Remember, voltage moves (current) depending on the resistance it encounters. So if you discharge a 470 µF cap through a 100KΩ resistor versus the 3300, the current will be the same but the duration will be much longer. I'd give you specific times regarding the 470 and the 100K but I've never been good at figuring out the RC time thing. I suppose I can do it if I need to. In fact, somewhere on my computer I have a spread sheet where I input the capacitance and the resistance and it outputs the time period for discharge at 1 tau (the standard considered charge / discharge rate when building a timing circuit) (It's considered to be 5 tau to fully charge or fully discharge a cap). And by fully I mean nearly fully.

I may LOOK smart but I got many people fooled into thinking that's so.

 

The capacitor's rating states what voltage it is designed to handle. You can take a capacitor that is rated for 480 volts and charge it to 5 volts and all you'll get out of it is 5 volts. Your 16 volt cap doesn't MAKE voltage it stores it at what ever level you put into it. So if you put in 5 volts and let it charge at 5 volts for 10 years, in 10 years all it will have stored is 5 volts. (assuming it doesn't dry out in that time - in that case it won't hold the voltage).

Microwave capacitors (the ones that are connected to the magnetron) boost the voltage from the transformer by reverse phase charging. The output of the high voltage winding is 1000 volts RMS. When the current swings (lets assume) positive the capacitor takes that charge (1000 volts). When the phase of the transformer reverses then the capacitor acts in series with the output creating the 2000 volts the magnetron needs.

MO caps (Microwave Oven) have a bleeder resistor on them to slowly drain them to where they're safe to handle. I'd make sure the MO was unplugged for a day if possible before messing with it. 1000 volts CAN kill you quick. The size of the cap also comes into play. a 470 microfarad cap stores far less energy than a 3300 microfarad cap when both are charged to the same voltage (in your example ~ 5 volts). The discharge time for the 470 is far shorter than for the 3300, meaning with the longer discharge time you're exposing yourself to a longer duration of energy. Remember, voltage moves (current) depending on the resistance it encounters. So if you discharge a 470 µF cap through a 100KΩ resistor versus the 3300, the current will be the same but the duration will be much longer. I'd give you specific times regarding the 470 and the 100K but I've never been good at figuring out the RC time thing. I suppose I can do it if I need to. In fact, somewhere on my computer I have a spread sheet where I input the capacitance and the resistance and it outputs the time period for discharge at 1 tau (the standard considered charge / discharge rate when building a timing circuit) (It's considered to be 5 tau to fully charge or fully discharge a cap). And by fully I mean nearly fully.

I may LOOK smart but I got many people fooled into thinking that's so.

Thank you for the clarification. I learned a lot from your answer.

 

While a capacitor charged to 5 V (or likely even 50 V) isn't a direct electrocution threat, they can still cause other things to happen. If you short a cap you can get an arc and that arc can burn you or can ignite a fire. It's also possible to damage your circuit and then the damaged circuit might become a threat.