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  #1  
Old 11-11-2010, 02:21 PM
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spinnaker spinnaker is offline
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Default Rent or borrow ESR Meter in Pittsburgh area?

Does anyone know where I can rent (at a reasonable cost) or borrow an ESR meter in the Pittsburgh area?


A suggestion in this thread said I might have a bunch of bad filter caps in my non working Tek scope. It would probably be just as easy to just replace them since they probably need to be replaced anyway but it would be nice to know if the caps are my problem. Where can I get one of these things aside from shelling out the $$$ to buy one.

I know I can build one with another scope, a function generator or a 555 timer (and I guess even a PIC which I have on hand). But I do not have a another scope.
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Old 11-11-2010, 02:57 PM
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Hello,

Why not make one yourself?
Here is a schematic with a PCB:
http://kakopa.com/ESR_meter/index.html

Bertus
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  #3  
Old 11-11-2010, 03:07 PM
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Hello,

Why not make one yourself?
Here is a schematic with a PCB:
http://kakopa.com/ESR_meter/index.html

Bertus
The problem with that is I do not have most of those parts on hand. And I would need to have confidence that I had it working right.
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  #4  
Old 11-11-2010, 03:20 PM
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Hello,

If you would buy one, what would be the budget?
Here is a kit for $79 or completerly assembled for $109:
http://www.anatekcorp.com/blueesr.htm

Bertus
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  #5  
Old 11-11-2010, 04:01 PM
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Hello,

If you would buy one, what would be the budget?
Here is a kit for $79 or completerly assembled for $109:
http://www.anatekcorp.com/blueesr.htm

Bertus

Yeah I have seen them for around $80 built.

http://cgi.ebay.com/In-Circuit-Capac...item3f04b2d609
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  #6  
Old 11-11-2010, 04:39 PM
someonesdad someonesdad is offline
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For us hobbyists, measuring ESR usually involves observing the change of a voltage Vo in the attached circuit when the capacitor under test (modeled by the pure capacitance and the ESR (equivalent series resistance) in the dashed box) is inserted in the voltage divider circuit. Two test leads are often run from the capacitor connection points to allow in-circuit testing. The method is:

Set V to the voltage and frequency you want to test at. Measure Vo with no capacitor attached; call the measured value V1. Then attach the capacitor to be tested and measure Vo again; call this value V2. Then an estimate of the ESR of the capacitor is made from the ratio V2/V1.

The lower the ratio V2/V1, the lower the ESR is -- and the capacitor's impedance is better at shorting out the voltage across R2. An ideal capacitor would short out the voltage completely, making the voltage V2 zero.

You calibrate your ESR checker with some resistors -- say, 0.1, 1, and 10 ohms. You substitute these for the capacitor and measure their voltage ratios just like you would for a capacitor. You can plot R versus the voltage ratio to let you estimate a capacitor's ESR from the graph.

So, if you wanted to make a practical checker, what should you use for V? A function generator is the usual choice or you can make your own oscillator. Another choice could be a 6.3 VAC filament transformer. This will test at line frequency; the usual test for filter caps is at twice the line frequency because they're filtering a full-wave rectified signal. But this is an order-of-magnitude test, so line frequency should be fine. Commercial ESR testers often test at 1, 10, and 100 kHz besides line and twice-line frequencies.

You'll want to choose the resistors R1 and R2 to ensure you put appropriate voltages across the capacitor. If you're doing in-circuit testing, the voltages should be kept low enough to avoid making any semiconductor junctions conduct. Possible starting values are R1 = 1 kΩ and R2 = 5 Ω. Use what you have on hand. You can use a DMM to measure the voltages if you don't have a scope as long as you keep the frequency of V in the DMM's bandwidth. This is a comparative and screening measurement, so accuracy of measurement tools isn't all that important.

I haven't tried this with a filament transformer, but it should work OK for big filter caps. I have used the method with a function generator and a scope and it works well for frequencies in the 10 kHz - 100 kHz range.

Added in edit: Make sure the capacitor is discharged before you measure it. Also, a shorted capacitor will appear to be a good capacitor with this test, so you might want to check a vanishing-ESR capacitor with a DC resistance measurement.
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Last edited by someonesdad; 11-11-2010 at 05:00 PM.
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  #7  
Old 11-11-2010, 05:06 PM
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For us hobbyists, measuring ESR usually involves observing the change of a voltage Vo in the attached circuit when the capacitor under test (modeled by the pure capacitance and the ESR (equivalent series resistance) in the dashed box) is inserted in the voltage divider circuit. Two test leads are often run from the capacitor connection points to allow in-circuit testing. The method is:

Set V to the voltage and frequency you want to test at. Measure Vo with no capacitor attached; call the measured value V1. Then attach the capacitor to be tested and measure Vo again; call this value V2. Then an estimate of the ESR of the capacitor is made from the ratio V2/V1.

The lower the ratio V2/V1, the lower the ESR is -- and the capacitor's impedance is better at shorting out the voltage across R2. An ideal capacitor would short out the voltage completely, making the voltage V2 zero.

You calibrate your ESR checker with some resistors -- say, 0.1, 1, and 10 ohms. You substitute these for the capacitor and measure their voltage ratios just like you would for a capacitor. You can plot R versus the voltage ratio to let you estimate a capacitor's ESR from the graph.

So, if you wanted to make a practical checker, what should you use for V? A function generator is the usual choice or you can make your own oscillator. Another choice could be a 6.3 VAC filament transformer. This will test at line frequency; the usual test for filter caps is at twice the line frequency because they're filtering a full-wave rectified signal. But this is an order-of-magnitude test, so line frequency should be fine. Commercial ESR testers often test at 1, 10, and 100 kHz besides line and twice-line frequencies.

You'll want to choose the resistors R1 and R2 to ensure you put appropriate voltages across the capacitor. If you're doing in-circuit testing, the voltages should be kept low enough to avoid making any semiconductor junctions conduct. Possible starting values are R1 = 1 kΩ and R2 = 5 Ω. Use what you have on hand. You can use a DMM to measure the voltages if you don't have a scope as long as you keep the frequency of V in the DMM's bandwidth. This is a comparative and screening measurement, so accuracy of measurement tools isn't all that important.

I haven't tried this with a filament transformer, but it should work OK for big filter caps. I have used the method with a function generator and a scope and it works well for frequencies in the 10 kHz - 100 kHz range.

Added in edit: Make sure the capacitor is discharged before you measure it. Also, a shorted capacitor will appear to be a good capacitor with this test, so you might want to check a vanishing-ESR capacitor with a DC resistance measurement.
Any reason it has to be 6.3 VAC?

The shack has a 12V CT .


They have a 12.6 but does not say if it is CT.


I also have a PIC on hand. Could I just use it? What frequency should I use for a pulse?


What is the safest way to discharge those big caps?
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  #8  
Old 11-11-2010, 05:51 PM
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Yeah I have seen them for around $80 built.

http://cgi.ebay.com/In-Circuit-Capac...item3f04b2d609

The BlueESR is awesome. I would suggest getting the kit, it is really hard to do "wrong". I use mine nearly daily, and have nothing bad to say about it!
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Old 11-11-2010, 08:08 PM
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The BlueESR is awesome. I would suggest getting the kit, it is really hard to do "wrong". I use mine nearly daily, and have nothing bad to say about it!
Other than getting the caps on this scope tested. I can't imagine what I would use it for. I will mainly be working with digital, mcus and such. It is hard to justify spending $80 on something I will probably not use.
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Old 11-11-2010, 08:23 PM
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Other than getting the caps on this scope tested. I can't imagine what I would use it for. I will mainly be working with digital, mcus and such. It is hard to justify spending $80 on something I will probably not use.
I use it a lot of the time as a battery tester/matcher. It is very accurate and can tell you the state of charge on the battery.

It also lets you know the ESR of a cap (obviously), and can alert you to some problems in an etched PCB track from the ability to measure very low resistance.

With digital stuff, you'll be working with power supplies, and being able to go through the whole supply in a few seconds to rule out a lot of cap related issues speeds things up.

If you don't use it that often, no need to get one, but I was amazed at the uses I found for an AC Ohmmeter.
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