I happened to stumble upon an unbranded E40 700W MV lamp for a price of about a dollar! It seems to have been a part of some public light fixture before it went private, and yes - it seems to have been used somewhat (whitish, grayish, yellowish marks on the quartz tube from the inside, the tube's glass almost opaque).

Now, about testing it, I need a quick answer. Will a 125W simple magnetic MV ballast be OK paired up with this monster? My presumptions are it'll be just fine, as I've successfully tested 125W MVs on a 20W and 40W T12 fluorescent ballasts, but I want to ask just in case... This is a rather powerful lamp, I don't want it to kill my poor ballast.

And second question for further tests - what sort of incandescent ballast combination can you come up with for this lamp? Halogen 1KW? two of them in parallel? Please keep it simple and most of all - cheap, with cheap lamps and sockets as I have none! I'm in a 220V (230V measured) part of the world (Europe) when it comes to electricity.

Thanks, all.

If you have two 400w ballasts you can run them in parallel but the lamp would be overdriven. You could also try two 250w ballasts in series.  hope this helps. 

If you have a 250 W MV ballast and a 400 W MV ballast, running them in parallel (not series) should work quite well.

The 125 W MV ballast alone would likely be unharmed for a short test. Heat is what would damage it, but it takes several minutes to get hot even if the lamp stays at a low arc voltage were the current would be high (if the lamp warms up enough to reach its full arc voltage, even long term would not be a problem for the ballast itself). The problem would much more likely be lamp damage, if the electrodes don't reach a high enough temperature to avoid severe sputtering (but I can't answer this).

What ballasts do you have? Many small ballasts in parallel could work (larger is better, I quickly estimated you would need approximately 14 40 W T12 ballasts to reach the full current..)

Ballasts in series won't work at all. First to connect the outputs in series, the ballast would have to have isolated output, so a CWI or equivalent. And that is not that common.
Second the 700W lamp has practically the same arc voltage as any other mercs, so for the higher power it needs higher currents. And with series operation, the current remains the same, so with two 250W ballast the lamp will get no more than 250W (well and that wioth the assumption it will heat up to the unsaturated vapor state to reach the normal arc voltage).

So the only working way is the parallel connection, but the ballasts have to be of the same phase shift (so both e.g. CWA or both HX; combining HX with CWA woon't work).


To use e.g. fluorescent ballasts you may run into a problem of the open circuit voltage: The OCV shall be at least 220V (twice the arc voltage).
So that method works only in the 230V areas, not on 120V.
Using on 120V mains series choke ballasts won't work - the OCV would be just 120V, that means the arc would not hold, so after warming up the lamp will extinguish. Well, not speaking yet if it will ignite at all...

Lamp has been tested couple of times last weekend. It is working!

Operating on 125W ballast gave it a low light output (I estimate 20-30 % below a 125W MV, but anyway - this is also a used bulb). It seems to have stayed on the edge of saturating the discharge (let me call it that way) - meaning the arc remained relatively wide and low power. That's probably somewhere between a fluorescent and discharge mode of operation. The ballast was fine and got just slightly warm.

To get a higher (full) light output I need your advice on INCANDESCENT ballast for this, as I have only 3 (125/40/20W) magnetic ones, and any new ballasts (especially high power ones) would be too expensive (which is ridiculous to test a warn, 1$ worth bulb). I'm thinking about using a halogen lamp (like R7S) of high power (1 KW?) in series with MV to allow higher current to the arc. I remember starting a 125W MV with a 200W incandescent as a ballast in series - it was fun, but sometimes had trouble starting the arc. What do you suggest for this 700W monster - please use as little and as cheap and common (halogen) bulbs as possible as I have neither them nor sockets and need to buy all. Thanks again.

You need a ballast with more than 210V OCV. With anything as simple as series inductor or resistor (that is the incandescent lamp), the all OCV you may get is the mains input voltage.
So on just 120V there is no way it will work.

The 125W ballast contains some form of a transformer inside, so it's OCV is above the 210V. Plus it is not heating the lamp anywhere close to the rated temperature (I guess there are still liquid mercury droplets inside of the arc tube).
So one option would be to connect 5 pieces of the 125W ballast straight parallel. That could form a ballast capable to tun the lamp in a decent manner (assume the ballast is "magnetic"; either fluorescent, or high pressure mercury vapor).

If you want to use incandescents as the ballast, you need first a 240V outlet. From that assemble incandescent lamps rated for the 240V and drawing about 6..9A (so 1.4 .. 2kW range). Be aware, than when using 120V lamps, you have to connect two exactly the same lamps (same maker, type, age and wear) in series and treat that combination as a single "240V" lamp. Then connecting such "ballast" in series with the lamp on the 240V.

You need a ballast with more than 210V OCV. With anything as simple as series inductor or resistor (that is the incandescent lamp), the all OCV you may get is the mains input voltage.
So on just 120V there is no way it will work.

The 125W ballast contains some form of a transformer inside, so it's OCV is above the 210V. Plus it is not heating the lamp anywhere close to the rated temperature (I guess there are still liquid mercury droplets inside of the arc tube).
So one option would be to connect 5 pieces of the 125W ballast straight parallel. That could form a ballast capable to tun the lamp in a decent manner (assume the ballast is "magnetic"; either fluorescent, or high pressure mercury vapor).

If you want to use incandescents as the ballast, you need first a 240V outlet. From that assemble incandescent lamps rated for the 240V and drawing about 6..9A (so 1.4 .. 2kW range). Be aware, than when using 120V lamps, you have to connect two exactly the same lamps (same maker, type, age and wear) in series and treat that combination as a single "240V" lamp. Then connecting such "ballast" in series with the lamp on the 240V.

Medved: He wrote that he is living in Europe / 220 V area, not 120 V. So the mains OCV is no problem for him.

Medved: He wrote that he is living in Europe / 220 V area, not 120 V. So the mains OCV is no problem for him.

I'm sorry, I completely overlooked that note in the text (I have just checked the profile, but the location is not published there)...

In the 230V the thing is indeed very simple
So indeed, with 230V mains you may either connect multiple chokes in parallel (as all choke ballasts are all inductors, you may freely combine all types to get the desired current, in this case about 5.7A)

With the incandescents you should take into account the voltage across them will be about 140Vrms and that should lead to the rated 5.7A. As the resistance of the incandescents would be nearly the same as on the rated power (just about 10..20% difference), it yields about the 1.8kW of incandescents as the ballast.
A bit lower current won't hurt that much, but better do not go above the rating, so better start from a bit lower.
Check the current by a meter, but wait for the lamp to warm up first.

Could do with a 1.5KW~ space heater. Just not the ones with fan (the fan may not start at the lower voltage and the heater will burn out)

@Ash Hmm, the thought about heaters also crossed my mind, thanks! The small stove we use to prepare coffee is about 500W, and bigger heating elements have 1000-2000W. Stove is convenient to use as it is fairly simple to connect it to the lamp for a short test. I might choose heaters if halogens prove expensive, but R7s halogens also seem fine and simple (I'm just not sure which power ratings there are).

@Medved: Thanks, your electrical knowledge is probably one of the most useful "features" of this site!

I am actually very impressed with incandescent ballasting, although it is completely not practical and useful today.

Stoves do not like the operation without any cooling, they overheat (some contain a thermal switch at leas reducing their power to protect them), so you would have to always use some pot with water on it...
Fr that reason the space heater is way better choice - that device is designed to be cooled just by the surrounding air or the IR radiation, so you do not need to mess up with the water or so.

Two further tests done.

The stove in question had simple 450W 230V heating element, no bimetals, switches, indicators, no anything whatsoever - so it was ideal for the test, as it was (electrically) as simple as a light bulb. It was (I think) 1960s model. I replaced the 125W ballast on a lamp with the mains plug, and used a simple mains splitter on it to get an easy "port" for connecting heating element(s) to the lamp. It started and ran fine, but the light output stayed low (approximately 125W MV output or even lower).

Today's test involved an Pancake maker! It's also a simple 1000W heater, but I used it just for a quick test, as it has a built in thermostat and a "ready" green-neon indicator lighting up when a set temperature threshold is reached. I wasn't sure about the inner connections in a device, so kept the test short to avoid unforseen circumstances. My guess is that the green neon is in parallel to the thermostat, placing it effectively in series with the MV once heating is disconnected - and my logic says that should extinguish the arc, but it's all just a guess. The light output was higher this time, most certainly double than with 450W stove, but I switched it off fairly quickly (after 2 or 3 minutes) as it got very hot (probably because of somewhat higher "starting" currents during MV warmup). I was safe, however - on a temperature scale of 1-5, the heater didn't even reach 1.

Next tests might include 1000W pancake maker in parallel with the 450W stove, perhaps even 550W coffeemaker too. I do however just guess this is a 700W MV, as no marking's visible, but as it's length is about 30cm it should be so.

Halogens proved to be a tough choice. I can buy a holder just for a 300W or 500W model, for about 2eur. The cheapest 500W halogen is about 1.2eur. The 1KW halogen can be obtained, but only Phillips offering, and for a ridiculous rip-off price of about 10eur (fairly usual situation with Phillips' lamps)! I could also set my hands on a (very rusty!) 250W MV ballast for about 2.5eur in the meantime, but it was still a far way off my goal.

Heaters are not really equal to incandescent/halogen lamps. The resistance of the heaters is fairly constant, while the resistance of lamp filaments is not at all. This means higher current at warm up of the Merc lamp, but all it would do is jsut make the lamp run up somewhat faster..... In the end the lamp should just reach the power that it gets on this ballast and stay at that



Heaters are fine for the most part as ballast. Even ones with bimetals - They will just cut out as you said. Be on the lookout for :

 - Some devices are meant to heat to a certain temperature and cut out. This does not at first appear to be a problem if the device heats lessthan intended, but if it stays heated for long without cutting out, the heat may have enough time to transfer to other parts where it does not belong : plastic handles etc. Monitor the temperatures that your ballast heaters reach

 - Some heaters have electromagnetic devices - relay to release something (toaster, coffee maker etc), fan motors and so on. Under lower voltage the magnetics may not work and thats when you are looking at possible damage