Function of Cemented Ceramic Caps Connected in Series.

[ToddB74]

Greetings Everyone!

I will use AA dry cell non-rechargeable batteries and cemented ceramic resistors for an analogy to pose a question, as follows:

As most of us know, the AA's can be connected series fashion in a DC circuit with the result that their output Volts (and Amps) accumulate when a load is applied, i.e. two 1.5v batteries produce 3v or slightly more when new and for some time afterward as they begin to degrade.

OK, so my question is "what is the effect on the output/input functionality of two new cemented ceramic resistors of some value when connected series fashion in a DC circuit and then a load is applied.?".

I'm really not looking for a string of physics formulas; just please answer briefly in general fashion if you can, and the following Link that might be of some help in your endeavor.
Thanks,
ToddB74

https://phys.libretexts.org/Bookshelves/College_Physics/College_Physics_1e_(OpenStax)/21:_Circuits_Bioelectricity_and_DC_Instruments/21.06:_DC_Circuits_Containing_Resistors_and_Capacitors

 

[Tony Stewart]

They can handle twice the voltage if equal C but the effective C is like 2 same resistors in parallel or 50% of C.
Sometimes a large C is added in series to a small C just to trim it lower.

When a small C is added in parallel to a larger C , that trims it a bit higher.

In this respect, Resistors are just the opposite.

Was there a specific example?

 

[ToddB74]

They can handle twice the voltage if equal C but the effective C is like 2 same resistors in parallel or 50% of C.
Sometimes a large C is added in series to a small C just to trim it lower.

When a small C is added in parallel to a larger C , that trims it a bit higher.

In this respect, Resistors are just the opposite.

Was there a specific example?

Please NOTE! This post was Edited (by Toddb74 on 3-11-2024) to make corrections from Capacitor to Resistor, or "resistor" where appropriate, and thanks to Niggel Goodwin, Super Moderator and Most Helpful Member for catching these errors.). While editing, a few other minor changes were also made, just to improve clarity. Also, the words "Cemented Ceramic Caps" in the title should have been simply "Resistor" (Sorry folks..... Apologies). In addition, the following two videos below are added help clarify where the author got his idea for his project and what he is trying to make.

Crawling out with bowed head and tail between legs..........ToddB74
______________________________________________________________________________________

Thanks Tony !

Yes, my project is making a Capacitor Discharger, based on a ubiquitous and simple device you're probably aware of, that I saw on the internet in U-Tube Videos recently. For my project, the parts list will consist of the following:

(1) piece of 1/8" dia. x 10 or 11 " Length of brass rod (Front tip ground to blunt point and smoothed, the other end slightly rounded and smoothed).
(1) White Cemented Ceramic Resistor 5W 470 Ohm (With single bare wire at opposite ends for connections; one end soldered to brass rod and the other end soldered to test lead.).
(1) Test Lead of multi-strand copper wire, either 16,14, or maybe 12 AWG with flexible rubber or silicone covering (One end soldered to one of the resistor wires and the other end soldered, or screwed, to an Alligator clip with a soft silicone insulation cover.).

A decision is made for the most comfortable position to place the resistor on the brass rod, for grasping the device. Then after all soldering/connections are completed, except for the front tip of the brass rod (To be ~3/4" bare) the resistor is anchored on the rod with hot glue or Gorilla glue, etc., etc. and the entire device, except for that front tip, is covered with appropriate-size/layers of shrink-wrap tubing insulation which is of course shrunk with a heat gun, or alternately a hair dryer on High setting.

My choice of shrink-wrap tubing has water-tight glue inside. This prevents any moisture from sweaty hands (Or rain in the case of working on a car outside sometime in the future.) from getting under a loose end of the tubing and conducting an electrical shock from the brass rod to the hand holding the device. Perhaps this seems far-fetched, but stranger things have happened!

ToddB74

 

[Nigel Goodwin]

Thanks Tony !

Yes, my project is making a Capacitor Discharger, based on a ubiquitous and simple device you're probably aware of, that I saw on the internet in U-Tube Videos recently. For my project, the parts list will consist of the following:

(1) piece of 1/8" dia. x 10 or 11 " Length of brass rod (Front tip ground to blunt point and smoothed, the other end slightly rounded and smoothed).
(1) White Cemented Ceramic Capacitor 5W 470 Ohm (With single bare wire at opposite ends for connections; one end soldered to brass rod and the other end soldered to test lead.).

That's a resistor, NOT a capacitor.

What are you trying to discharge?, the mention of a car seems to suggest you perhaps don't really know?.

 

[AnalogKid]

I'm lost. Please post a photo, webpage link, or video link to what you are trying to do.

ak

 

[ToddB74]

That's a resistor, NOT a capacitor.

What are you trying to discharge?, the mention of a car seems to suggest you perhaps don't really know?.

Nigel and AnalogKid......My apologies for the confusion caused by errors in my posts. I've made corrections to post #3 and also added two videos that I hope will clear up what my project is all about.

Thanks for your interest and help.

Toddb74

 

[sagor1]

Depending on the voltage being discharged, using a full length brass rod is NOT recommended. Heat shrink or other insulation around it is not enough to protect you.
A proper discharge stick would be made from an insulated material (rod), with a shorter piece of brass rod attached at the tip, and the grounding wire attached to that. That way, there is no danger of any high voltage reaching the user's hand. By keeping everything away from your hand, you isolate any high voltage to remain at the tip of the brass rod to the grounding strap only.
You could use a Bakelite rod, or perhaps a Plexiglass rod as the handle. Keep the brass tip and wire at least 6" away from where your hand will be holding the "stick".
Now for lower voltages (50V or less), the method shown with the brass rod may be safe enough with proper insulation of the rod where you hold it. But, I would never build that design because "someday" someone will try to discharge a 3000V capacitor with that stick and possibly electrocute themselves. Do not built "unsafe" tools.

 

[ToddB74]

Depending on the voltage being discharged, using a full length brass rod is NOT recommended. Heat shrink or other insulation around it is not enough to protect you.
A proper discharge stick would be made from an insulated material (rod), with a shorter piece of brass rod attached at the tip, and the grounding wire attached to that. That way, there is no danger of any high voltage reaching the user's hand. By keeping everything away from your hand, you isolate any high voltage to remain at the tip of the brass rod to the grounding strap only.
You could use a Bakelite rod, or perhaps a Plexiglass rod as the handle. Keep the brass tip and wire at least 6" away from where your hand will be holding the "stick".
Now for lower voltages (50V or less), the method shown with the brass rod may be safe enough with proper insulation of the rod where you hold it. But, I would never build that design because "someday" someone will try to discharge a 3000V capacitor with that stick and possibly electrocute themselves. Do not built "unsafe" tools.

Thanks much Sagor1. I will be sure to add a Cautionary label to my Cap discharger stick, something like "WARNING !! This discharger is only safe to use for Capacitors of 50 Volts or less. Test all Capacitors with a VOM before discharging to be certain of the voltage."

Since I've already purchased a pack of (4) brass rods, (10) resistors and a plastic box containing a selection of (200) shrink-wrap tubing, I'll go ahead and build that full-length brass rod model and attach a warning label. Then if my electronics work shows a need for discharging Caps "higher than 50 volts", I'll build another discharger in accordance with your suggestions for higher voltage situations.

Being retired and having leg problems from diabetes at age 83, I need something to do inside to keep me occupied. I like to design and make small projects, so electronics is the ideal hobby at this stage of my life.

One last question Sagor1, is it safe to test Capacitors marked, or the circuit diagram indicates, 50 Volts or less, using a good brand VOM while the caps are still connected in the circuit, the circuit switch is OFF and the circuit is unplugged?

ToddB74

 

[Nigel Goodwin]

Thanks much Sagor1. I will be sure to add a Cautionary label to my Cap discharger stick, something like "WARNING !! This discharger is only safe to use for Capacitors of 50 Volts or less. Test all Capacitors with a VOM before discharging to be certain of the voltage."

Why do you feel the need for a discharge device?, I worked as a TV/Audio service engineer for 46 years, and have repaired thousands of valve devices. I never had a discharge device, and have never heard of an engineer who has - everyone uses a screwdriver, on the odd occasion they might need to discharge a capacitor.

One last question Sagor1, is it safe to test Capacitors marked, or the circuit diagram indicates, 50 Volts or less using a good brand VOM while the caps are still connected in the circuit and the circuit switch is OFF and the circuit is unplugged?

ToddB74

Nothing is 'carved in stone', but generally you don't test capacitors in-circuit, as the connected components will mostly prevent any worthwhile test. The main exception would be electrolytic capacitors in switch-mode PSU's, where you can 'mostly' check them in-circuit using an ESR meter - a multimeter, or capacitance meter, is useless for this, an ESR meter is essential.

However, randomly testing components isn't how you repair things - you do so by fault finding, and mostly by voltage measurements or signal injection/tracing. Randomly trying to test components rarely works well, if at all, and can easily cause more problems than you started with.

Exactly what are you trying to do?, perhaps we can make better suggestions than a discharge device?.

 

[ToddB74]

Why do you feel the need for a discharge device?, I worked as a TV/Audio service engineer for 46 years, and have repaired thousands of valve devices. I never had a discharge device, and have never heard of an engineer who has - everyone uses a screwdriver, on the odd occasion they might need to discharge a capacitor.



Nothing is 'carved in stone', but generally you don't test capacitors in-circuit, as the connected components will mostly prevent any worthwhile test. The main exception would be electrolytic capacitors in switch-mode PSU's, where you can 'mostly' check them in-circuit using an ESR meter - a multimeter, or capacitance meter, is useless for this, an ESR meter is essential.

However, randomly testing components isn't how you repair things - you do so by fault finding, and mostly by voltage measurements or signal injection/tracing. Randomly trying to test components rarely works well, if at all, and can easily cause more problems than you started with.

Exactly what are you trying to do?, perhaps we can make better suggestions than a discharge device?.

 

[ToddB74]

Nigel......I really appreciate your help trying to steer me in the right direction. Other than building small electronic projects from kits, my long-term objective is to recycle electronic components from various devices that are no longer working, like CFL's, radios, old telephones, or any other small devices my family or neighbors are getting rid of.

This "hands-on" recycling process of identifying & labeling "still good" components and learning how they work, will help me in designing & building projects in the future. Of course, I have limited space in my apartment, so not looking for a deluge of stuff. With this objective in mind, I believe I need one or two Cap discharge tools.

At age 83, retired, and legs not too good anymore due to diabetes, I need something to keep myself occupied inside and I like designing and putting together small electronics projects.

ToddB74