In my last post about running MV lamps on MH ballasts, I learned a lot from @Ash and @RRK. I have messed around in Desmos graphing calculator a lot with some equations and I think I have set up a pretty accurate calculator for ballast impedance for discharge lamps. Here is the link:

https://www.desmos.com/calculator/y8cmvxxsfh

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It requires the following inputs:

"V oc" - The unballasted RMS input voltage
"V lamp" - RMS discharge voltage
"I lamp" - RMS discharge current
"P f" - Discharge power factor which I have calculated:
MV: 0.831
MH: 0.873
HPS: 0.913
LPS: 0.976
FL: 0.915

These power factors may or may not be the actual power factors of the lamp discharges, but they are the numbers that on average make the outputted impedance more or less correct based on existing datasheets. I don't really care what they mean to be honest. MH and FL lamps are a little less accurate than other lamps with this method due to the wider range of wattages and types, but generally still tolerable results in my opinion.

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The calculator simply outputs ballast impedance ("Z bal") in ohms, nothing shows on the graph. This output would be the impedance of a series choke. Obviously more calculation would need to be done to determine the proper inductance based off of that number given out. I am absolutely certain that people will comment on here shouting about how improper this is, and I am definitely ready to learn more. Maybe don't use this to calculate something super critical, but I find it interesting to compare different lamps and see which ones might be able to run off the same ballast.

thats very cool! I stuck a couple known values in there and it aint far off for example F40T12 103V 430mA PF 0.87 220V Mains gives me an impedance of 402 Ohms,

the Reference ballast spec for such a tube according to IEC spec is 220V input, 390 Ohm with a ballast PF of 0.10, ie what is the PF of the ballast itself if you stuck it across the mains with no tube etc, since I dont know what ballast Power Factor your using here, i'd say you have done very well

ditto a I get more or less the correct ballast impedance for a F125T12 tube also (296 Ohms from your calculator vs 300 Ohms for the official IEC spec)

and for a 175W mercury lamp I get 100 ohms which is damn as near it 99.5 Ohms of the official ANSI spec




BTW I think your calculated lamp PF discharge values are a bit off, I know for a fact that HPS lamps have a lower power factor then mercury lamps, usually somewhere in the mid 0.8's


and the SOX one is a bit high


the thing to remember is the nominal wattage of a lamp is often not always its *actual* wattage


for example the British 125W 8ft Tube is actually 123W, many US designs will incorporate cathode heating losses into the wattage ratting which will skew factors as well

this is where study of IEC, ANSI, JIS standards documents is very handy since they will often tell you whats actually what

@LightBulbFun
Thank you! I did have a feeling that my "power factor" may not have actually been the real power factor of the lamp, but at least it works.

I did not know that that US designs incorporated electrode losses is the rated wattage. Good thing my calculator doesn't need wattage, that would be a mess.

Good to know it is working well, even if I don't know for sure how it works.

The lamp PF varies also by the individual lamp spec within the same lamp type. The ballast have some losses that vary by lamp type and power, and by the ballast efficiency class. Those two would further close the gap between the current calculator results and the standard specs

For ballasts here are some examples i recall (all 230V 50Hz chokes)

FL 36W T8/40W T12 :

 - ~1960s 70s ballasts : Seen 10W quoted in a book printed in the early 80s, but i think that "open core" ballasts (which production was ending around that time, but were probably still the most common in installed luminaires) may be less efficient than this

 - Standard from the 80s onwards : Typical 8W

 - Lowloss from the 80s onwards : Typical 6W

MBF 400W (used also for Halides) :
 - Seen 40W in multiple sources. Probably does not vary that much between old and new ballasts

For a fairly big set of measurements of ballasts (power consumption of lanterns or other luminaires) go to Mike Barford's site at https://streetlightonline.co.uk/ , go through the lanterns and other luminaire types in the collection



The website you used for the calculator seems to replicate some of the features of Kmplot - a local (offline) program that has drawing plots with parameters and an expression calculator

@Ash
I did see different power factor numbers for different wattages, but no real trend so I just averaged them. Ideally there would be a special number to plug in for every individual lamp but I am not about to go through all of that effort lol. Ideally if you need a very precise answer for a particular lamp, you wouldn't be relying on something some stranger on the internet made, though I may or may not have done that in the past

I just used Desmos because it is what we were constantly using in middle/high school and it is just what I am familiar with. I am sure there are many more graphing calculator sites out there.

I will definitely click through Street Lights Online later today, that seems like a good source.