Hey everyone, had a quick question.

So I recently obtained two 125W HPMVs (Philips/Signify and Crompton) for rather cheap, ie. under $2 (190 INR) each. However the ballast is, as per some searching, rather pricey. I was wondering, is there any wattage of tungsten lamp that I can use to power it up with in series instead, and if so, what is the wattage? Would it be okay to use two different wattage lamps in parallel to achieve the rating, example 40W + 60W = 100W?

I tried looking it up online but all I got was an AI overview about how the lamp would explode, and most results were unrelated or about regular copper-wound ballasts. So just hoping someone more knowledgeable about this could help me out.

Thanks in advance!

Yes you can. An 125w MV lamp runs at 1,15a and 125v.

This means for a 250v mains voltage, you need a lamp that draws 1,15a at 125v. So in other words, an american 100w + 15w and/or 25w would be appropriate.

The incandescent lamp will be overloaded on startup, but when the MV lamp is at full brightness the current should be correct. Of course you have to measure this.

Yes you can. An 125w MV lamp runs at 1,15a and 125v.

This means for a 250v mains voltage, you need a lamp that draws 1,15a at 125v. So in other words, an american 100w + 15w and/or 25w would be appropriate.

The incandescent lamp will be overloaded on startup, but when the MV lamp is at full brightness the current should be correct. Of course you have to measure this.

I would not use 120V lamps at all, they will not survive the massive overload that they would get upon startup when the voltage drop of the mercury lamp is still low (and trust me I speak from painful experience in that regard)

if your aiming to try and get a more efficient/brighter light from the incandescent lamp then what would normally be got with a 240V lamp, then a Photoflood lamp would be a good compromise in this regard. the only way you could use 120V lamps is to use 2 identical ones in series and only once the lamp has run up enough, to then switch them in parallel (which is something I want do want to try in itself at some point along with the photo flood lamp ballast)

Hey everyone, had a quick question.

So I recently obtained two 125W HPMVs (Philips/Signify and Crompton) for rather cheap, ie. under $2 (190 INR) each. However the ballast is, as per some searching, rather pricey. I was wondering, is there any wattage of tungsten lamp that I can use to power it up with in series instead, and if so, what is the wattage? Would it be okay to use two different wattage lamps in parallel to achieve the rating, example 40W + 60W = 100W?

I tried looking it up online but all I got was an AI overview about how the lamp would explode, and most results were unrelated or about regular copper-wound ballasts. So just hoping someone more knowledgeable about this could help me out.

Thanks in advance!

you can indeed quite comftably ballast a HPMV lamp with an incandescent lamp in series with the mercury lamp


for a 125W Mercury lamp a 500W incandescent lamp should provide about the right current, if you dont have one of those, you can use a combination of smaller GLS lamps in parallel with each other, just make sure the whole gaggle of them is then wired in series with the mercury lamp



you could also ballast the 125W mercury lamp by putting some fluorescent tube chokes in parallel if that is something you might also have to hand, for example 2 4ft 40W choke and a 2ft 20W choke in parallel would likely work pretty well for a 125W mercury lamp

Hey @Laurens , thanks for the response!

You mention using an approx equal value resistor for the lamp which runs at 125W@125V → ~125W lamp in series. However I don't have access to any 120V/American lamps so I came up with this, please feel free to correct me.
By applying P = V^2 / R, I figured that by using a 500W@240V halogen instead, it would still effectively scale down to around a 125W dispersal. You said to use a 100W American lamp in parallel with a 15W or 25W to reduce the combined resistance, so:

120V / (125W / 120V) ≈ 115 Ohms
240V / (500W / 240V) ≈ 115 Ohms
Hence, if ~125W@120V can deliver the 1.15A required to run the lamp, so should 500W@240V.
Is that right?

Edit: Turns out @LightBulbFun responded too, I was stupid and didn't refresh the page . But again thank you very much for your inputs, really appreciate it. Have a g'day!

Thanks for reaching out, @LightBulbFun .

Let me guess, you've blown up a merc cause of a faulty incandescent ()?
Yep I landed on the same conclusion by following Laurens's solution, and I'll be going with a 500W halogen as you suggested. While using fluorescent chokes would be the most accurate and fun, I don't have any lying around so unfortunately this'll have to suffice.

Many thanks for the advice, have a great evening!

Keep in mind that the resistance of a tungsten filament varies with it's temperature. The resistance is lower when cold and higher when hot. This means that while it may be 115 ohms while dropping 240V, it's resistance will be lower while dropping only 105V (230V-125V=105V, excluding power factor). At 220V, a 125W MV lamp demands 134 ohms of impedance according to it's reference specs, and of course it will want even more than that at 230V. So 500W is almost certainly too high of a wattage but it's not that big of a deal especially for MV.

I have deliberately run 120V incandescents on 240V, and it took several minutes to blow, but I do agree that a 120V incandescent approach would be non-ideal. A 500W incandescent may slightly overdrive a 120W mercury vapor lamp, but just a quick test to prove me wrong won't really be a problem. It's not gonna blow up. I am thinking 400W incandescent might be a better fit but there's only one way to find out. Definitely let us know the results if you have means of measuring the lamp current.

But be ready to finetunr the incandescents, the voltage distribution effects are rather far from the ideal "mains is the sum of ballast and MV" unless you take into account the real exact waveform shapes of voltages and currents.
As a first guess 140Vrms across the ballast lamp (to look for their characteristics) is close enough as a starting point, but you need to measure the resulting current and adjust...

For ballast lamp the halogens seems to be the ideal option: Not that inefficient at the 140V as the standard, yet designed to handle the full 230V for startup.
Definitely would not use ane lower voltage rated lamp, you are risking flashover.
You may get away with ballasting two 120V incandescents in series for start and switching to one as the thing warms up and builds up the voltage drop, but still the 140V across a 120V lamp would mean rather short life.

Photofloods will have very short lifetime: Usually in the 25h ballpark at full power, while it is exposed to that full mains for about 5..10 minutes per start (the 140V run means the lifetime from filament evaporation in just the run phase is beyond the MV, so practically no wear), so about 150 starts...

Yeah @Multisubject your approach seems right, I completely forgot to account for hot v. cold resistance. I found both some generic 400W and 500W linear halogens listed on Amazon, so I'll try it with both, what's the worst that could happen?

I don't care for running the lamp for 24000 hours or whatever it's rated for, a few thousand is plenty for me. I'll buy both, give it 5 minutes to warm up and then measure the current on each (400W@240V and 500W@240V). I'm actually pretty surprised your incandescents lasted a few minutes. I'll absolutely let you know the results for both lamp voltage and current with either halogen, let's see how it ends. Thanks!

@Medved Honestly, 150 starts is pretty pathetic so I'll go with halogen for two reasons:

• Halogens are dirt-cheap
• Instead of spending $50 on one imported 100W@120V lamp → $100 for two lamps ≈ 10K INR, I might as well buy the actual ballast for a fifth of the price

Although I'll end up either underdriving or overdriving a lamp, since my usage is minimal I think I might get away with it. But thanks, and have a good day !

Keep in mind that the resistance of a tungsten filament varies with it's temperature. The resistance is lower when cold and higher when hot. This means that while it may be 115 ohms while dropping 240V, it's resistance will be lower while dropping only 105V (230V-125V=105V, excluding power factor). At 220V, a 125W MV lamp demands 134 ohms of impedance according to it's reference specs, and of course it will want even more than that at 230V. So 500W is almost certainly too high of a wattage but it's not that big of a deal especially for MV.

I have deliberately run 120V incandescents on 240V, and it took several minutes to blow, but I do agree that a 120V incandescent approach would be non-ideal. A 500W incandescent may slightly overdrive a 120W mercury vapor lamp, but just a quick test to prove me wrong won't really be a problem. It's not gonna blow up. I am thinking 400W incandescent might be a better fit but there's only one way to find out. Definitely let us know the results if you have means of measuring the lamp current.

thats for a magnetic ballast, remember a magnetic ballast is out of phase with the lamp its running while an incandescent lamp is not


take say a regular choke ballast F14-F20 setup, and messure the voltage at the mains, across the lamp, and then the voltage drop across the choke and you will see they dont sum up (and the voltage drop across the choke will probably be higher then your expecting)



so you cant use magnetic ballast impedence specfications for resistive/incandescent ballasting situation

@Medved @LightBulbFun

Yeah yeah I know, the voltage across the incandescent won't be the same as the sum of both lamps but it's gonna be a lot closer with incandescent than it would be with a choke since incandescent PF is ~1. Of course the MV lamp is gonna throw that way off but probably not as bad as a choke would. I should have explained my thinking. We'll just have to see which one performs better.

Yeah even though the magnetic ballast may be out of phase, the incandescent (halogen) will give a much higher PF than the EM ballast without a PF correction capacitor. Even though the lamp will mess up the PF by a bit, shouldn't be too significant even though an actual ballast would be a bit out of phase.
400W seems a bit harder to obtain but I'll try and let y'all know the results with 500W. Will definitely tag everyone with an update, hopefully by this month.

Just grab three surplus 36/40W fluorescent chokes and connect them in parallel. You will get about right ballast impedance for 125W MW lamp.

 

I don't wanna come off as dismissive but I won't be going with this right now for two reasons:

• I only have one and they're seemingly rarer than HID ballasts as per the three shops I've been to
• For the price of them I might as well buy the regular 125W ballast

Again apologies, but maybe I'll do it sometime in the future. Thanks for the suggestion though!

As an effect of 'ledization', old fluorescent luminaires are often thrown away. So you sure can find a lot of such chokes for free just by looking hard enough.

Alternatively, try three regular 100W 230V incandescents in parallel as a makeshift ballast. Should work. I'd check the current after the lamp run-up. If below lamp's prescribed 1.15A, add another 40-60W lightbulb in parallel.