Film caps can be checked with an ohmmeter, but that doesn't apply high voltage to the cap. Some people don't have a cap tester that applies high voltage.

Here's another idea. Connect a DMM in series with the cap under test. Using a suitable source of high-voltage DC within the cap's rating, possibly a radio's B+ supply, apply voltage across the series circuit. Read the DC voltage across the voltmeter.

What we have is a simple voltage divider. The DC resistance of the cap can be calculated by knowing the voltages and the input impedance of the DMM. If the cap is in good shape, I would expect most of the total voltage to be across the cap, not the DMM.

My DMM's specs show input impedance >10M, which adds some uncertainty to the test, but not enough to worry about. Ideally, the cap's resistance should be many megohms, right?

This procedure could be used for either film caps or or electrolytic caps, but with e-caps, watch the polarity.
Doug

:Film caps can be checked with an ohmmeter, but that doesn't apply high voltage to the cap. Some people don't have a cap tester that applies high voltage.
:
:Here's another idea. Connect a DMM in series with the cap under test. Using a suitable source of high-voltage DC within the cap's rating, possibly a radio's B+ supply, apply voltage across the series circuit. Read the DC voltage across the voltmeter.

Doug:
When checking aircraft strobe light capacitors, we used a digital milliAmpere meter, in series with the cap, connected to the rated Voltage of the cap (fused, of course) If I remember, the limit was 12 mA at 459 Volts, but there was no doubt in my mind, a good cap would be 4=5 mA, and a bad one (or soon to be) was 30-40 mA, and would increase as the tempurature went up. Most bad ones were easy to spot, as the guts were all over the inside of the housing. But, I think that is an excellent way to check the condition of a capacitor, rather than at the 2-3 Volts a DMM uses.
Lewis
:
:What we have is a simple voltage divider. The DC resistance of the cap can be calculated by knowing the voltages and the input impedance of the DMM. If the cap is in good shape, I would expect most of the total voltage to be across the cap, not the DMM.
:
:My DMM's specs show input impedance >10M, which adds some uncertainty to the test, but not enough to worry about. Ideally, the cap's resistance should be many megohms, right?
:
:This procedure could be used for either film caps or or electrolytic caps, but with e-caps, watch the polarity.
:Doug
:
:

OOPs, didn't mean to bust into the middle of your post. It's getting close to my bedtime. Sorry.
Lewis

::Film caps can be checked with an ohmmeter, but that doesn't apply high voltage to the cap. Some people don't have a cap tester that applies high voltage.
::
::Here's another idea. Connect a DMM in series with the cap under test. Using a suitable source of high-voltage DC within the cap's rating, possibly a radio's B+ supply, apply voltage across the series circuit. Read the DC voltage across the voltmeter.
:
:
:
:
:Doug:
:When checking aircraft strobe light capacitors, we used a digital milliAmpere meter, in series with the cap, connected to the rated Voltage of the cap (fused, of course) If I remember, the limit was 12 mA at 459 Volts, but there was no doubt in my mind, a good cap would be 4=5 mA, and a bad one (or soon to be) was 30-40 mA, and would increase as the tempurature went up. Most bad ones were easy to spot, as the guts were all over the inside of the housing. But, I think that is an excellent way to check the condition of a capacitor, rather than at the 2-3 Volts a DMM uses.
:Lewis
::
::What we have is a simple voltage divider. The DC resistance of the cap can be calculated by knowing the voltages and the input impedance of the DMM. If the cap is in good shape, I would expect most of the total voltage to be across the cap, not the DMM.
::
::My DMM's specs show input impedance >10M, which adds some uncertainty to the test, but not enough to worry about. Ideally, the cap's resistance should be many megohms, right?
::
::This procedure could be used for either film caps or or electrolytic caps, but with e-caps, watch the polarity.
::Doug
::
::

I usually place a 1 meg ohm resistor in series with the cap being tested and place my VOLT meter across the resistor. This gives me a close enough micro amp leakage rating of the capacitor. The voltage reading can be translated directly as micro amps since it is measured across a 1 meg resistor. I said close enough barring the 10 meg internal resistance of the meter paralled across the resistor. If you want to be more accurate you could calculate the parallel resistances and adjust as needed.

MRO

:OOPs, didn't mean to bust into the middle of your post. It's getting close to my bedtime. Sorry.
:Lewis
:
:
:
:
:
:::Film caps can be checked with an ohmmeter, but that doesn't apply high voltage to the cap. Some people don't have a cap tester that applies high voltage.
:::
:::Here's another idea. Connect a DMM in series with the cap under test. Using a suitable source of high-voltage DC within the cap's rating, possibly a radio's B+ supply, apply voltage across the series circuit. Read the DC voltage across the voltmeter.
::
::
::
::
::Doug:
::When checking aircraft strobe light capacitors, we used a digital milliAmpere meter, in series with the cap, connected to the rated Voltage of the cap (fused, of course) If I remember, the limit was 12 mA at 459 Volts, but there was no doubt in my mind, a good cap would be 4=5 mA, and a bad one (or soon to be) was 30-40 mA, and would increase as the tempurature went up. Most bad ones were easy to spot, as the guts were all over the inside of the housing. But, I think that is an excellent way to check the condition of a capacitor, rather than at the 2-3 Volts a DMM uses.
::Lewis
:::
:::What we have is a simple voltage divider. The DC resistance of the cap can be calculated by knowing the voltages and the input impedance of the DMM. If the cap is in good shape, I would expect most of the total voltage to be across the cap, not the DMM.
:::
:::My DMM's specs show input impedance >10M, which adds some uncertainty to the test, but not enough to worry about. Ideally, the cap's resistance should be many megohms, right?
:::
:::This procedure could be used for either film caps or or electrolytic caps, but with e-caps, watch the polarity.
:::Doug
:::
:::

Mark, I like your approach better.
Doug

:I usually place a 1 meg ohm resistor in series with the cap being tested and place my VOLT meter across the resistor. This gives me a close enough micro amp leakage rating of the capacitor. The voltage reading can be translated directly as micro amps since it is measured across a 1 meg resistor. I said close enough barring the 10 meg internal resistance of the meter paralled across the resistor. If you want to be more accurate you could calculate the parallel resistances and adjust as needed.
:
:MRO
:

All:
I didn't really like the way we did those strobe caps, but since it was aircraft, they wanted them to be tested as closely as possible to actual in-flight conditions, which meant 450 Volts right out of the power supply. Of course, they were Ohmmeter tested and low Voltage charged before we gave them the full Voltage current test. Almost everything bad was caught on the first tests, hardly anything failed the final test.
Lewis

:Mark, I like your approach better.
:Doug
:
:
::I usually place a 1 meg ohm resistor in series with the cap being tested and place my VOLT meter across the resistor. This gives me a close enough micro amp leakage rating of the capacitor. The voltage reading can be translated directly as micro amps since it is measured across a 1 meg resistor. I said close enough barring the 10 meg internal resistance of the meter paralled across the resistor. If you want to be more accurate you could calculate the parallel resistances and adjust as needed.
::
::MRO
::
:

Lewis, how big, farad-wise, were those aircraft strobe caps? Maybe their charge would be enough to kill a horse?
Doug

:All:
:I didn't really like the way we did those strobe caps, but since it was aircraft, they wanted them to be tested as closely as possible to actual in-flight conditions, which meant 450 Volts right out of the power supply. Of course, they were Ohmmeter tested and low Voltage charged before we gave them the full Voltage current test. Almost everything bad was caught on the first tests, hardly anything failed the final test.
:Lewis
:
: