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lps ballast

lps ballast

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eBay find. Now I need to get a 135 or 180 LPS lamp.

IMAG1125.jpg Circline_ballast.jpg IMAG1060.jpg IMAG1061.jpg

Light Information

Light Information

Manufacturer:advance transformer co.
Model Reference:71A0750
Lamp
Lamp Type:low pressure sodium
Fixture
Ballast Type:magnetic
Electrical
Wattage:135 or 180
Voltage:120 or 240
Physical/Production
Factory Location:usa

File information

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Filename:IMAG1060.jpg
Album name:paintballer22 / Ballasts
Keywords:Gear
File Size:371 KB
Date added:Oct 17, 2013
Dimensions:2050 x 1155 pixels
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rjluna2
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Robert


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Oct 17, 2013 at 12:24 PM Author: rjluna2
It is interesting that the capacitor is hooked up before the autotransformer here

Pretty, please no more Chinese failure.

arcblue
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Oct 18, 2013 at 12:27 PM Author: arcblue
Nice! These are getting hard to find.

I'm lampin...

Medved
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Oct 18, 2013 at 01:05 PM Author: Medved
It is a NPF HX (auto)transformer, the capacitor is then added only to correct the power factor, it does not influence the lamp operation.

No more selfballasted c***

don93s
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Oct 16, 2015 at 08:16 AM Author: don93s
Unlike HPF mercury, I don't think I've seen LPS ballasts with the cap in series with the lamp. Does it have something to do with crest factor on these lamps?
Medved
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Oct 16, 2015 at 11:28 AM Author: Medved
The series capacitor allows very stable current and stable arc operation with not that high OCV, so for lamps starting with significantly lower arc voltage than the operating (so sufficing with the limited OCV for the start as well) it means keeping the secondary OCV, so ballast losses and weight low.
The drawback is, the capacitor rating should be at least twice the ballast OCV.

And that is the main problem for the LPS: LPS do need rather high OCV for ignition and start (only the lowest wattages suffice with about 220..250V, higher need even 400V or so). And that would require voltage ratikngs so high, it would be practically not possible to justify them (life vs cost).
Plus the high OCV with still rather low arc voltage means there would be no efficiency/mass benefit from the series capacitor as it is the case for the CWA, so there is not much reason for that complicated high voltage capacitor (180W SOX requiring 500V OCV would requires capacitor rated above 1kVAC).

The lamp starting is not only about the first breakdown (that could be easily provided by an ignitor), problem is with cold electrode glow discharge, where the arc voltage gets elevated by extra (order of) 150V cathode drop, yet the ballast still should deliver significant current into such load. With high pressure lamps, which have anode column drop just some 20..30V that means cold electrode voltage of about 120..170V, so pretty close to normal operation, so the ballast feeds there at least half of the rated current. The anode drop then rises as the lamp warms up, but at that time the cathodes are already hot, so have drop of less than 15V.
But with a low pressure discharge the anode column drop is all the time the same, so with a normally 100V arc lamp you need a ballast able to feed the total discharge voltage of more than 250V. And that needs a ballast with at least 400..500V OCV.
A bit different situation would be, if the lamp design allows preheating the cathodes, then just the normal arc drop with optionally some ignition pulse are sufficient (viola, we have a RS or preheat or similar fluorescent ballasts).

There are HF oscillator based ignitors in use (mainly in Europe, where otherwise just a series choke suffices for many lamps), but these are getting more complex, so become usable just when that mean the possibility to use more efficient series choke for the given lamp (and that is for LPS only in 230V areas). When an autotransformer would be necessary, it gets easier and cheaper to just wind the transformer to deliver enough OCV to not need any ignitor at all.

Quite popular method is emplying a resonance to boost the voltage for the start (the L-C-L T-cell), but that needs again the 230V mains, so for the 120V world it would require again an extra transformer step. So again too complex to be viable, compare to just a simple HX transfoprmer with high enough secondary.

Of course, way other story are the HF electronic ballast, these rely solely on the resonance (for the start) and eventual DCDC conversion to boost the input voltage (on the PFC stage), there the property of the HF supply making the arc way more stable is, what makes it possible without the need for impractical components. Plus because the high frequency means the energy stored in the LC elements is low, way more complex circuit may be constructed without a consequence of too high losses or cost. So making a ballast able to feed a 300V arc (lamp just ignited a fraction of a second ago, so in cold cathode mode) with nearly the same current as when the cathodes warm up and the voltage drop fall to the normal level.

No more selfballasted c***

don93s
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Oct 18, 2015 at 01:48 PM Author: don93s
Thanks for that info, Medved. I was wondering about the idea of converting a MH ballast into 18w LPS. For example, a 70w ballast with ignitor, would an appropriate choke added in series with lamp to reduce current work? With 250ocv, the three wire ignitor poses the question of where the series choke would fit in there, if possible. But, in an open circuit or failed lamp, would the 2-3kV ruin the choke?
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Oct 31, 2015 at 04:47 AM Author: Medved
So do I understand it correctly as a HX 70W MH ballast, with an additional series choke on the output?
That may work, provided the additional choke sets the output current to the required 0.37A.
However the ignitor within the MH ballast should not be used. There are two reasons for it:
- The additional coil will attenuate the pulse (but that should not be that much a problem)
- Due to the impedance of the additional coil, the output of the MH ballast will see about 180V or so, so "think" the lamp hadn't ignited yet, so continue pulsing all the time. And that would mean eating it's lifetime pretty fast (it is designed to strike few times for each power ON and some hot restarts, but definitely not to pulse all the time).

The 18W LPS should selfignite already on 240V, so just disabling the MH ignitor should be fine. Or if you would like to use some higher power lamp as well (25W or so), you may use an European SOX ignitor designed for a series choke ballast.

No more selfballasted c***

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