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#34824 02/24/04 08:47 AM
Joined: Mar 2002
Posts: 37
EVAD7 Offline OP

#34825 02/24/04 07:52 PM
Joined: Oct 2000
Posts: 2,722
Broom Pusher and

Test it as any other Capacitor would be tested.

FYI, here's a method using a standard Analog Ohmmeter to test a non-polarized electrolytic Capacitor from an HID Ballast assembly (value = >10 µF):


[*] Disconnect AC Power feeding the fixture. Test with known working voltmeter to assure circuit is not live at the fixture,

[*] Short out the Capacitor to drain it of any stored charge. Use a screw driver to "short-out" the leads by placing it across both terminals and leaving it shorted for a few seconds,

[*] Remove the Capacitor leads,

[*] Set the Ohmmeter to a high scale - like R × 10,000,

[*] Connect the Meter's leads to the Capacitor's terminals - observe the meter's action.

Prior to attaching the test leads, discharge the Capacitor once again!!!

If the Capacitor is good, the "needle" should swing to the lowest end of the scale, then gradually "build up" until it reads infinity.
Remove the leads, wait a few seconds, then re-connect the leads again. Should be close to infinity, but not back to zero.

If the Capacitor is open, the "needle" will hover around the infinity point - even with the scale settings at their finest - like R × 100,000 or 1M. Be sure to discharge the Capacitor fully before applying the test leads on each successive test (if Capacitor is testing open).

If the Capacitor is shorted, the "needle" will never reach infinity.

These tests use the Ohmmeter to charge the Capacitor. The results of the charge placed upon the Capacitor are seen by the deflection of the scale's pointer ("needle").
At no charge, the Capacitor allows a large level of charge to be drawn from the meter's power supply. This results in a low resistance reading on the scale.
As charge increases (builds up) in the Capacitor, the meter's power supply will have a decrease in current flow. This results in the deflection of the pointer.
Once the Capacitor is stable to the power supply (charged fully + Capacitor's voltage = meter's power supply voltage), the current flow will be extremely-extremely-extremely low. This results in the pointer pegged to the infinity side of the scale.

A Digital readout may be used in lieu of an Analog type, only the visual swing is replaced by increasing numeric values.
Same holds for the test value limits.

I use Analog testers for these tests, mainly for the visual swinging of the pointer.

BTW: Why do you need to test the Capacitor of an HID Ballast kit? Do you just want to know for future, or do you have a suspected fixture?


p.s. came back to edit this message, to add these items:

  • If a draining resistor is connected between the Capacitor's terminals, disconnect it prior to testing, then reconnect it when tests are complete, or replacing the Capacitor's leads,
  • Be sure to use new, fresh Drycells in your meter for this test,
  • Be sure to test the meter's leads for continuity,
  • Be sure to calibrate your meter before testing the Capacitor,
  • If Capacitor is failing, replace with one of equal value - in MFD, Volatge rating, non-polarized type and same package type.


[This message has been edited by Scott35 (edited 02-24-2004).]

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#34826 02/27/04 08:44 AM
Joined: Mar 2002
Posts: 37
EVAD7 Offline OP
We frequently replace caps at a YMCA IN THE POOL AREA. They are with a 400w MH fixture. Why does this happen? At least I can check them now.

#34827 02/27/04 04:37 PM
Joined: Jan 2003
Posts: 73
Is there a mostiure problem?
Is the enclosre where the Cap's are damp?
Is there signs of rusting on the winding's.

Moisture can cause problems.

If your test's as EVAD7 point out shorting is the issues, then you maybe on right track.

Remember "Things happen for a reason" be analytical.

#34828 02/27/04 04:39 PM
Joined: Jan 2003
Posts: 73
sorry I meant Scott35's test procedure.

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