Whats this cap look like?

[bogart219]

Hello again,
I had a Mallory, type cgs 1400mfd, 400vdc cap laying around that I tested with my ESR meter. I got a 1.0 reading. Going by the chart on the face of the unit, these values were not listed. (thats why I was looking for a more extensive chart in another post). I have to guest what its worse value is. I'm thinking .03 or .04. Does this sound right? If so this cap has very high esr correct? Hope you don't mind all the questions. I came across this site and discovered a bunch of very knowlegable folks on here who don't mind sharing their knowledge. Just trying to learn. Thanks!

[PCBONEZ]

Re: Whats this cap look like?

https://cdn.badcaps-static.com/pdfs/...54a750323f.pdf
1400/400v isn't listed [probably an obsolete size] but it looks like .070 would be about right if it were new.

[bogart219]

Re: Whats this cap look like?

https://cdn.badcaps-static.com/pdfs/...54a750323f.pdf
1400/400v isn't listed [probably an obsolete size] but it looks like .070 would be about right if it were new.

PCbonez, Am I looking at this right. If my esr meter says this cap is 1.0 and if new its around .070 , then 10 times .070 is .7 . So this cap is over 10 times the esr that it should be. Is my math correct? Then this means that this cap is no good right? Thanks!

[PlainBill]

Re: Whats this cap look like?

PCbonez, Am I looking at this right. If my esr meter says this cap is 1.0 and if new its around .070 , then 10 times .070 is .7 . So this cap is over 10 times the esr that it should be. Is my math correct? Then this means that this cap is no good right? Thanks!

It depends on the meter and the application. Note that the ESR of .071 is specified at 120 Hz. Your meter uses a frequency that 100-1000 times higher.
This cap was obviously designed to be used as the filter cap for a line voltage rectifier.

PlainBill

[bogart219]

Re: Whats this cap look like?

It depends on the meter and the application. Note that the ESR of .071 is specified at 120 Hz. Your meter uses a frequency that 100-1000 times higher.
This cap was obviously designed to be used as the filter cap for a line voltage rectifier.

PlainBill

Hi Bill,
So is it correct to say that my dick smith esr meter cannot check all electrilytic caps? Just the ones in the range of the chart on front of the unit?
Also, take that cap in the example above. Whats the best way to test a cap like this? thanks!

[PlainBill]

Re: Whats this cap look like?

Hi Bill,
So is it correct to say that my dick smith esr meter cannot check all electrilytic caps? Just the ones in the range of the chart on front of the unit?
Also, take that cap in the example above. Whats the best way to test a cap like this? thanks!

No, that is not correct. A correct statement would be that the result given by the ESR meter might not be meaningful, depending on the value of the capacitor and it's application.

As an example, I have a defective LCD monitor on the table right now. The problem APPEARS to be on the logic board. There are 11 caps on the board. 10 of them have an ESR reading of .50 or less. One reads 1.10, which is high for that particular cap according to the chart on the meter. Is it the cause of the problem? The answer is - it's hard to tell. This cap (Luxon SM) is not characterized as low ESR. I have no idea how it is used in the circuit.

In your case, the best way to test the cap would be to check it's ESR at 120Hz. I don't have the experience to be willing to predict how the ESR at (100 Khz?) reflects on the ESR at 120 Hz. The second best way would be to observe it's behavior in circuit. Measuring the ripple across it would tell you something.

PlainBill

[bogart219]

Re: Whats this cap look like?

Hey Bill,
I have some of these big old caps that are probably 10-15 years old. Just wanted to see if I could determine if they are any good. More confused than ever about this esr thing and caps. Seems like the older I get the harder it is to grasp something. Thanks for the help

[PlainBill]

Re: Whats this cap look like?

Hey Bill,
I have some of these big old caps that are probably 10-15 years old. Just wanted to see if I could determine if they are any good. More confused than ever about this esr thing and caps. Seems like the older I get the harder it is to grasp something. Thanks for the help

I understand exactly!!! Here is the way I look at it:

ESR is an attempt to express the reactance of a capacitor. The usual formula for calculating reactance assumes an ideal capacitor; we're dealing with real world capacitors. In addition to capacitance, a real capacitor has both resistance and inductance. The inductance will vary with the frequency. If a cap is spec'd with a .07 ohm ESR at 100Khz, measuring the ESR at 120Khz or even 50 Khz should give a reliable good / bad test.

I can come up with a couple of suggestions on how to check the caps. The easiest would be to hook the output of a bridge rectifier to the capacitor and to a smallish (25 watt?) light bulb (or two 40 watt light bulbs in series). Apply power for several minutes, then turn off the power and check the temperature of the cap. This will simulate the cap filtering a 25 watt load. If it gets warm, it's got a high ESR and should not be used.

Of course, if you have a signal generator and a scope you can make the measurement directly.

PlainBill

[PCBONEZ]

Re: Whats this cap look like?

ESR isn't Reactance but like Reactance it's part of Impedance.

Like this:


At low frequencies Xc and ESR behave like parallel resistors in regards to the total Impedance.
Since Xc is HUGE at low frequencies, ESR essentially IS the Impedance at low frequencies.
.

[bogart219]

Re: Whats this cap look like?

I understand exactly!!! Here is the way I look at it:

ESR is an attempt to express the reactance of a capacitor. The usual formula for calculating reactance assumes an ideal capacitor; we're dealing with real world capacitors. In addition to capacitance, a real capacitor has both resistance and inductance. The inductance will vary with the frequency. If a cap is spec'd with a .07 ohm ESR at 100Khz, measuring the ESR at 120Khz or even 50 Khz should give a reliable good / bad test.

I can come up with a couple of suggestions on how to check the caps. The easiest would be to hook the output of a bridge rectifier to the capacitor and to a smallish (25 watt?) light bulb (or two 40 watt light bulbs in series). Apply power for several minutes, then turn off the power and check the temperature of the cap. This will simulate the cap filtering a 25 watt load. If it gets warm, it's got a high ESR and should not be used.

Of course, if you have a signal generator and a scope you can make the measurement directly.

PlainBill

Bill I'm going to try and test them this way. What should the voltage be coiming off that bridge?

[PlainBill]

Re: Whats this cap look like?

Bill I'm going to try and test them this way. What should the voltage be coiming off that bridge?

(Vin x 1.414) - 1.4

PlainBill

[PlainBill]

Re: Whats this cap look like?

Bill I'm going to try and test them this way. What should the voltage be coiming off that bridge?

(Vin x 1.414) - 1.4

But the ripple across the cap would be of greater interest.

PlainBill

[bogart219]

Re: Whats this cap look like?

(Vin x 1.414) - 1.4

But the ripple across the cap would be of greater interest.

PlainBill

Yellow bill, I have no idea what you just said. By using a bridge I assume you meant dc voltage. My question is how much dc voltage, if this is what you were referring to in the first place.

[Wizard]

Re: Whats this cap look like?

bogart219, send a PM to PlainBill a apology for this mistake. This is not yellow name.

Cheers, Wizard

[bogart219]

Re: Whats this cap look like?

bogart219, send a PM to PlainBill a apology for this mistake. This is not yellow name.

Cheers, Wizard

I meant Hello Bill.

[PlainBill]

Re: Whats this cap look like?

OK, enough with the name calling. I'm a PLAIN Bill. Not blue (the grandkids keep me cheerful, not green (gas, electricity, telephone and my wife take all of that), and definitely not yellow (except when criticizing someone who is trying his best).

Elementary electronics. A capacitor stores electricity. If you feed a regulated DC voltage to a capacitor you will learn very little about the characteristics of the cap. Add a load, same thing. The power supply is doing the work. If you feed a varying voltage to a cap you will learn a little more - how well the cap filters out the variations.

The ideal way to test a component is in the actual circuit. By the description, the cap you are trying to test was intended to be used to filter the rectified AC input in a wide input voltage AC power supply. Something like a computer power supply or a heavier version of a monitor power supply.

The nominal AC voltage is the 'RMS' (root mean square) voltage of the sine wave. In simple terms I can understand, both 120VAC and 120VDC will light an incandescent light to the same brightness. The PEAK voltage of 120VDC is 120 Volts. The peak voltage if 120VAC is 120 x 1.414 or 169.68 volts (between friends we can call it 170 volts). The output voltage of a bridge rectifier is two diode drops below the peak input voltage. So depending on load, that will be 168 volts IF the input voltage is exactly 120 VAC.

Now comes the tricky part. If you have no load, a good 1400 Mfd capacitor will read 168 volts. A bad 1400 Mfd capacitor will read the same. If you have a load, the good capacitor will show a slightly lower voltage, the bad cap will show an even lower voltage. The problem is, there are so many variables (the load, the input voltage, the accuracy of the meter, even the characteristics of the bridge) that I can't predict what the voltage will be.

The good news: There are two ways to check the health of the caps. Measure the DC voltage, and the AC ripple across the capacitor, as well as the current through the load (bulbs). Calnculate the effective impedance and compare it to the data sheet. Of do it the easy way - see how warm the cap gets.

PlainBill

[bogart219]

Re: Whats this cap look like?

OK, enough with the name calling. I'm a PLAIN Bill. Not blue (the grandkids keep me cheerful, not green (gas, electricity, telephone and my wife take all of that), and definitely not yellow (except when criticizing someone who is trying his best).

Elementary electronics. A capacitor stores electricity. If you feed a regulated DC voltage to a capacitor you will learn very little about the characteristics of the cap. Add a load, same thing. The power supply is doing the work. If you feed a varying voltage to a cap you will learn a little more - how well the cap filters out the variations.

The ideal way to test a component is in the actual circuit. By the description, the cap you are trying to test was intended to be used to filter the rectified AC input in a wide input voltage AC power supply. Something like a computer power supply or a heavier version of a monitor power supply.

The nominal AC voltage is the 'RMS' (root mean square) voltage of the sine wave. In simple terms I can understand, both 120VAC and 120VDC will light an incandescent light to the same brightness. The PEAK voltage of 120VDC is 120 Volts. The peak voltage if 120VAC is 120 x 1.414 or 169.68 volts (between friends we can call it 170 volts). The output voltage of a bridge rectifier is two diode drops below the peak input voltage. So depending on load, that will be 168 volts IF the input voltage is exactly 120 VAC.

Now comes the tricky part. If you have no load, a good 1400 Mfd capacitor will read 168 volts. A bad 1400 Mfd capacitor will read the same. If you have a load, the good capacitor will show a slightly lower voltage, the bad cap will show an even lower voltage. The problem is, there are so many variables (the load, the input voltage, the accuracy of the meter, even the characteristics of the bridge) that I can't predict what the voltage will be.

The good news: There are two ways to check the health of the caps. Measure the DC voltage, and the AC ripple across the capacitor, as well as the current through the load (bulbs). Calnculate the effective impedance and compare it to the data sheet. Of do it the easy way - see how warm the cap gets.

PlainBill

Biil, thanks for the info!

[PCBONEZ]

Re: Whats this cap look like?

Humphrey needs a spell checker.