Author Topic: 100 watt mercury lamp not running up fully  (Read 5600 times)
Fluorescent05
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100 watt mercury lamp not running up fully « on: March 29, 2020, 11:01:14 PM » Author: Fluorescent05
I got a 100 watt mercury vapor CWA ballast for Christmas. It didn't have a capacitor, so I ordered a fan capacitor of the appropriate value off of Amazon. I also ordered a sunlite 100 watt mercury lamp. However, it only warms up to almost the brightness of a 50 watt mercury vapor lamp (It was the same through side by side comparison). What could be wrong?
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wide-lite 1000
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Re: 100 watt mercury lamp not running up fully « Reply #1 on: March 29, 2020, 11:37:53 PM » Author: wide-lite 1000
Possible suspects : a) Is the capacitor the correct values according to the ballast label ? (voltage and uF rating)  b) Is the capacitor any good ? ( the Wide-Lite started not coming up to full brightness last year, cap was no good !) 
 Only other possibilities are either the lamp or ballast have a problem . I assume everything wired according to the label ?
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Fluorescent05
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Re: 100 watt mercury lamp not running up fully « Reply #2 on: March 29, 2020, 11:45:18 PM » Author: Fluorescent05
Possible suspects : a) Is the capacitor the correct values according to the ballast label ? (voltage and uF rating)  b) Is the capacitor any good ? ( the Wide-Lite started not coming up to full brightness last year, cap was no good !) 
 Only other possibilities are either the lamp or ballast have a problem . I assume everything wired according to the label ?
Everything is wired according to the label. The cap is the correct number of microfarads and the voltage is correct too. How do I check the capacitor?
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Re: 100 watt mercury lamp not running up fully « Reply #3 on: March 30, 2020, 12:02:32 AM » Author: wide-lite 1000
I have a multi meter with a capacitance setting which will tell if the cap is within spec or not . There are supposedly other methods of testing caps. I however , have no idea what they are . Hopefully , others have a bit more info to help you .
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Medved
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Re: 100 watt mercury lamp not running up fully « Reply #4 on: March 30, 2020, 01:36:00 AM » Author: Medved
Disconnect the capacitor from the ballast and wire it in series with an AC A-meter and some higher power incandescent bulb (150..200W or so; acting as a current limit) to tge mains voltage.
Measure the circuit current and voltage across the cap (with 200W lamp it should near the mains).
Then

C = I / V / (2 * pi* 60)

And compare the result with the rating (some small, usually 5% tolerance is normal, lower or higher capacitance reading means it it EOL).
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Fluorescent05
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Re: 100 watt mercury lamp not running up fully « Reply #5 on: March 30, 2020, 11:25:25 AM » Author: Fluorescent05
Disconnect the capacitor from the ballast and wire it in series with an AC A-meter and some higher power incandescent bulb (150..200W or so; acting as a current limit) to tge mains voltage.
Measure the circuit current and voltage across the cap (with 200W lamp it should near the mains).
Then

C = I / V / (2 * pi* 60)

And compare the result with the rating (some small, usually 5% tolerance is normal, lower or higher capacitance reading means it it EOL).
I don't have a meter that can measure AC current.
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Re: 100 watt mercury lamp not running up fully « Reply #6 on: March 30, 2020, 02:21:06 PM » Author: Medved
I don't have a meter that can measure AC current.

How can you then troubleshoot anything with discharge lighting? Better to look for some...

As a MacGyver solution you can use an hot water kettle in series (e.g instead of the incandescent lamp I mentioned) and measure the voltage drop and then calculate the current. Assume your V-meter can measure AC down to V (so minimum AC range is 2V or below; you would need to measure around 2..6VAC with better than 5% accuracy; those cheap meters with 200V as the minimum range have 0.5..1V offset error, so below about 20VAC become useless).
Of course, there needs to be some water in the kettle, as the capacitor may short circuit at any time if it is already bad and in that case the kettle will get full power and without the water cooling overheat and trip the nonresetable fuse within the heater...

Theoretically you may use any resistive thing, but you need to know the exact resistance. So you need something not becoming hot to shift the resistance from cold state at the expected 0.3..0.6A.
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Re: 100 watt mercury lamp not running up fully « Reply #7 on: March 30, 2020, 02:24:18 PM » Author: Medved
Or you may use a DC Ameter with a diode bridge rectifier. Then the reading has to be multiplied by 1.11 = (pi / (2 * sqrt(2))) to get the correct rms value.
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Fluorescent05
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Re: 100 watt mercury lamp not running up fully « Reply #8 on: March 30, 2020, 09:21:47 PM » Author: Fluorescent05
Or you may use a DC Ameter with a diode bridge rectifier. Then the reading has to be multiplied by 1.11 = (pi / (2 * sqrt(2))) to get the correct rms value.
Would that damage the lamp or go over 10 amps? What kind of bridge rectifier should I use? Is 1.1107207345 the number to multiply by?
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Re: 100 watt mercury lamp not running up fully « Reply #9 on: March 30, 2020, 11:16:22 PM » Author: Fluorescent05
Test results:
Using the 10 MFD cap I was originally using:
Warmup time: 30 minutes
Final arc voltage: Hovered around 91-95 volts

I also found out that another cap from my 175 watt MH fixture was also 10 MFD. Its test results were:
Warmup time: 25-30 minutes
Final arc voltage: 98 volts

I also looked it up and the running arc voltage of 100 watt mercury lamps is supposed to be 115 volts.
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Re: 100 watt mercury lamp not running up fully « Reply #10 on: March 31, 2020, 03:44:49 AM » Author: Medved
Would that damage the lamp or go over 10 amps?

In the ballast circuit not. The magnetic part uses to be designed so with shorted cap the current is not higher than normally.
But it causes larger ballast losses - mainly because the primary current is not phase compensated.
But when practically directly across the mains during the testing, there is nothing to limit the current, so then it may go above 10A. Therefore the current limitting (either the incandescent, or the kettle with water in it) in the test setup.



What kind of bridge rectifier should I use?

Any, current rating is to be at least the current imposed by the short circuit current limitting incandescent lamp. It rectifies the current just for the A-meter...


Is 1.1107207345 the number to multiply by?

Yes, but you definitely wont need that many decimals...
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Fluorescent05
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Re: 100 watt mercury lamp not running up fully « Reply #11 on: March 31, 2020, 08:27:16 AM » Author: Fluorescent05
Do I need to use high power diodes?
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Re: 100 watt mercury lamp not running up fully « Reply #12 on: March 31, 2020, 09:39:58 AM » Author: Medved
1N400x should be OK with 200W (2A) current limiter lamp...
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Re: 100 watt mercury lamp not running up fully « Reply #13 on: March 31, 2020, 10:36:40 AM » Author: Fluorescent05
1N400x should be OK with 200W (2A) current limiter lamp...
I don't want to destroy any diodes. I will just get an AC ammeter.
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Re: 100 watt mercury lamp not running up fully « Reply #14 on: March 31, 2020, 12:46:11 PM » Author: Medved
Of course the AC A-metter is the way to go for the future (assume you want to continue with this or similar hobby), but destroying diodes in such experiments by accident is no deal at all - the 1N4007 (1000V 1A) are sold for less than dollar for a strip of 100 diodes. So once you have them, it even does not pay off to dismantle them from one experiment to another one and use new ones instead. The main reason the new experiment/project wont be doomed by a potentially damaged component from the previous one.
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