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 Post subject: Old Capacitors, resistors, question about holding voltage
PostPosted: Jan Thu 17, 2019 11:15 pm 
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Since I'm a layman learning about resistors and capacitors my language will be not of a seasoned technician. At least I am somewhat good at writing to get my point across.

Moving on......

When I look at a old resistor or old capacitor and decipher the voltage rating on the coding, band colors, markings, hieroglyphics, matching them up with the voltage rating numbers in my handy dandy Zenith schematics it fits perfectly.

When I actually test the voltage rating on old capacitors, voltage rating on old resistors with a:

"Transistor Tester, DROK Mosfet Transistor Capacitor Tester, Mega328 NPN/PNP Transistor Diode Resistor Inductor Capacitance MOS SCR ESR Meter Automatic Checker Detector" or what I call my handy dandy chingaderas.

The tester reads the voltage rating on the old resistor, old capacitor differently, so my question is why am I getting different voltage rating numbers compared to the voltage rating on the resistors, capacitors numbers on the body????

Can age change the voltage rating on the resistors, voltage rating on capacitors?????

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Thu 17, 2019 11:57 pm 
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You cannot test the rated voltage of resistors or capacitors with your "Handy Dandy Transistor Tester" You are reading the resistance of the resistors and capacitance, and other parameters of the capacitors, not voltage.

Dave


Last edited by easyrider8 on Jan Thu 17, 2019 11:59 pm, edited 1 time in total.

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Thu 17, 2019 11:58 pm 
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NONE of these testers measure any voltage rating of these devices. All they measure is their Resistance, Capacitance, etc. but NOT their Voltage ratings!


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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 1:05 am 
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This is a fundamental point that is commonly misunderstood---the difference between parameters and ratings.

A parameter is what determines the part's behavior in a circuit. OTOH, a rating only tells you the safe limits for using the part. If you install a part with some rating that is inadequate, you will never know it----until it fails.

In general, you cannot measure ratings---at least directly. You can infer them in some cases, based on comparison with similar parts. You can also run tests to see where parts actually fail. These values will not match the rated values, but you better hope that the actual failure occurs at a point above the rating. Note also that some ratings are tied to lifetime. For one example, run a resistor above its rated power--all that can be said is that it will fail sooner than if it were well under the rating.

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 2:55 am 
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Quote:
A parameter is what determines the part's behavior in a circuit. OTOH, a rating only tells you the safe limits for using the part. If you install a part with some rating that is inadequate, you will never know it----until it fails.


How true!

A 1N4007 is rated at 1000 Volts. I strongly suggest that you not try applying 1000V to see what happens. Be content that it will work well in your 350 V power supply.

My little digital "tester" applies no more than 9 Volts to a part. It helps me sort parts; doesn't tell me anything about ratings or reliability.

Rich


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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 3:33 am 
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Rich, W3HWJ wrote:
A 1N4007 is rated at 1000 Volts. I strongly suggest that you not try applying 1000V to see what happens. Be content that it will work well in your 350 V power supply.
Hi Rich,

Just barely, with no safety margin.

The max unloaded voltage on the filter cap = 350 * 1.414 = 495 volts.
The max reverse voltage on the rectifier = -350 * 1.414 = -495 volts.

So the PIV on the rectifier could reach 2 * 495 = 990 volts.
That's a max value only if the line voltage is nominal, not if it's higher.

For any transformer set I would opt for a 2kv 200ma rectifier.
Mouser has 10 different ones starting at $0.11 each in qty 100.
https://www.mouser.com/Semiconductors/D ... =Pricing|0

- Leigh

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Last edited by Leigh on Jan Fri 18, 2019 3:58 am, edited 1 time in total.

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 3:56 am 
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Ok, now I think I see it now; the resistors, capacitors are not in the chassis so I'm actually testing them all separate, I'm using a 9V testor, so I'm basically seeing if it's:

1. A resistor or capacitor
2. Alive or dead.

Some of the resistors, capacitors are hard to distinguish so the tester will tell me which is which. :shock:

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 4:02 am 
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A leaky capacitor (particularly electrolytic) can appear to be a resistor to a tester.

Learn to identify parts by sight and you won't make an error.

- Leigh

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 4:09 am 
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Using an ordinary DMM:

Resistors:
--will measure some value using the appropriate ohms scale (use the lowest scale that gives a reading)
--the measurement will stabilize in ~ 1 second, and will not change

Capacitors:
--a good one should read close to infinite resistance--at least in one direction
--if the value is at least .01 uF, the reading will change after the leads are applied
--after the reading stabilzes, reverse the leads and observe the resistance increasing again
(the key to the last two statements is the charging of the capacitor)

For testing capacitors get a tester designed for the purpose and/or an impedance bridge

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 4:16 am 
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I'm working on using the schematics, reading the codes on the resister, capacitor, however some are void of anything from age, or they are so small as a pea.

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Another Young Frankenstein!


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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 4:23 am 
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You can always identify them based on where they're connected per the schematic.

- Leigh

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 4:39 am 
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Leigh wrote:
You can always identify them based on where they're connected per the schematic.

- Leigh


I'm still learning things, locations, stuff like that.

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Another Young Frankenstein!


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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 4:42 am 
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walz wrote:
Leigh wrote:
You can always identify them based on where they're connected per the schematic.

- Leigh
I'm still learning things, locations, stuff like that.
Certainly.

We all went through that phase.

But it's an extremely important phase.

What reference books do you have?

I would suggest downloading a copy of the Radio Amateur's Handbook.
These are available free online from various sources.

It's been published annually for over 100 years, except for a couple of years during WWII.
Get one from the 1950s.

The first several chapters have an extremely concise introduction to electronics, including parts identification and function, and how to read schematics. Very well written.

- Leigh

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 5:43 am 
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Leigh, you got me again!

Most radios use a CT rectifier, not a full bridge, so it is indeed 2x pk secondary voltage.

Attachment:
Rectifier table.JPG
Rectifier table.JPG [ 82.34 KiB | Viewed 674 times ]


Most industrial HV circuits use a full bridge and a 1N4007 (single) should be OK. For the CT you want more PRV!

Rich


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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 5:45 am 
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Since you are seeking a working technical vocabulary , always associate
the word capacitor with something that must always be treated as if was charged
with a (lethal) voltage. With that in mind, you will develop rules about how
to see if a capacitor is safely stored.

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 6:10 am 
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Rich, W3HWJ wrote:
Most industrial HV circuits use a full bridge and a 1N4007 (single) should be OK. For the CT you want more PRV!
Hi Rich,

The actual PIV for a 350v FWB (full secondary) is only 0.7v less than for a 350v CT (half secondary).

- Leigh

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 6:22 am 
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Joined: Jan Mon 05, 2015 6:38 pm
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Wow this is a lot to learn.

My father-in-law (who has passed away) was into all of this, he has everything, I never got rid of anything, so I'm trying to read his books from the 1940-1960 era.

One book I'm using is Allied's Electronic Data Handbook from 1956.

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I'm like one of those mad scientist's recreating life in a dead radio.
Another Young Frankenstein!


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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 12:06 pm 
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walz wrote:
One book I'm using is Allied's Electronic Data Handbook from 1956.
That's a good reference book, but it's a reference book.

The first chapters of the Radio Amateur's Handbook are a tutorial intended specifically to teach people with no experience in electronics how a radio works.

- Leigh

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 1:12 pm 
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I think I am siding with Leigh, when I say "you have to start with the basics". For example, read about things like current flow in a circuit. In addition to books like The Radio Amateur's Handbook, the internet is full of tutorials and videos on just about anything. For example, go to Wikipedia and look up Kirchhoff's laws.

Another really good resource is Khan Academy---eg this series of videos:
https://www.khanacademy.org/science/ap- ... its-part-1

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 Post subject: Re: Old Capacitors, resistors, question about holding voltag
PostPosted: Jan Fri 18, 2019 3:58 pm 
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Thanks, this is great, I'm going to start reading them ASAP.

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Another Young Frankenstein!


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