As I've found just scattered pieces of information about this topic over the internet - mainly on discussion forums, I've got an idea to putting them together at on place.

WARNING: If you came across this page by Google search etc., please don't rely on the information below - at least until the statements have been validated by the LG community. If I'm wrong, damages may occur, even explosions, fire or injuries!


Ballast compatibility list

1. Magnetic ballasts for fluorescents and MVs are fully compatible, provided the wattage is the same.
However, the fluorescents need an extra CCT ignition while MVs don't have it.

2. Magnetic ballasts can be connected in series. For example, two 125W magnetic ballasts in series can be used with a 250W MV.

3. MVs or fluorescents should work in series if their parameters are the same. For example, two new 125W MVs of the same type should work with one 250W ballast. But this is not recommended as the parameters can vary when the lamps are getting old.

4. Points 2 and 3 are not true for electronic ballasts. Also mixing magnetic and electronic ballasts won't work.

5. There is a wattage tolerance in case of magnetic ballasts. For example the T12 40W ballasts can operate with T8 36W fluorescents without significant problems. On the other hand, too much lower wattage of the ballast causes the performance loss while too much higher wattage of the ballast shortens the life of the MV or fluorescent.

6. The incandescent or heater with the same wattage can be used as a MV ballast. This is not true for fluorescents as the CCT ignition (starter) in this case won't provide the sufficient voltage to lit the mercury vapours.

7. The MV ballasts are incompatible with HPS/MH ballasts. Moreover, HPSs and MHs need an ignition unit.

8. The HPS and MH ballasts are compatible. However, I once read a technical specification on a MH lamp (cannot remember either the MH type or its brand) and there was written that using the HPS ballast was allowed but with the ~20% performance loss and the colour temperature change.

9. The LED ballasts are something completely different than any kind of discharge lamp ballast. There is no compatibility at all.

10. Don't know if there are ballasts that could make a 120 discharge lamp work with the 240V power supply and vice versa.


Note: Please feel free to tear down anything I've written. You can also add new numbered items to this list if these belong here. Thanks.

You mixed there the rated power of the lamp with ballast electrical parameters. The series choke ballasts are operated in a rather constant current (current does not depend as much on the load voltage) part of their load characteristic, so that mean fro ballast compatibility is imortant the current the ballast feed into the lamp and not as much the lamp wattage (the same ballast deliver 18W into a 55V 60cm T8 lamp, as well as 32W into a 95V T9 circline).
So when you want to combine the ballasts, you have to know what is the rated lamp current you want to reach and what is the arc voltage the lamp will operate.
Now as ballasts are nothing else than impedances, series connection means they sum up. If both are inductive, it means the current become lower. Only when you combine inductance with capacitances, as as they have opposite phases, the sum becomes lower impedance, so higher current. But that would mean you overload the inductor, as it won't be designed for such higher current.
So in order to increase the higher lamp current, you just connect them plain parallel, so the currents sum up (e.g. operate 2.15A 250W MV on two 1.15A 125W MV ballasts mean the lamp will get 2.3A, so will operate at ~270W; that is still acceptable).

And with different lamp types, don't forget thy could be of the same wattage, but in fact need way different current (250W HPS operates at nearly 3A, while the 250W MV is designed for 2.15A; so using a 250W HPS ballast for 250W MV lamp mean 40% overdrive)

But you may use the "150W HPS" ballast to power a 175W US MV or probe MH lamp (the MH with 750V ignitor), as all these are designed for 1.7..1.8A.

Here I didn't count the ignition devices as part of the ballast, however some lamps do need particular type, so it is a matter of course you use the appropriate ignition device for given lamp type (100W MV, 70W HPS and 70W MH use the same choke, but the MH need at least 3.5kV ignitor, while the standard HPS suffice with 1.5kV and the MV uses no ignitor at all)

So in order to increase the higher lamp current, you just connect them plain parallel, so the currents sum up (e.g. operate 2.15A 250W MV on two 1.15A 125W MV ballasts mean the lamp will get 2.3A, so will operate at ~270W; that is still acceptable).

Oops! Sure - parallel. It's only logical. Sorry, I just tried to put everything together and got a bit confused.
But I didn't know about this non-linearity. It means that a circuit with a 125W MV and 250W MV have different cosφ?

And with different lamp types, don't forget thy could be of the same wattage, but in fact need way different current (250W HPS operates at nearly 3A, while the 250W MV is designed for 2.15A; so using a 250W HPS ballast for 250W MV lamp mean 40% overdrive)

I absolutely haven't suggested mixing MVs with HPSs in 3. But again, this so different current (different cosφ again?) is new to me.
I also forgot to mention that HPS tolerance is lower than MV tolerance.

As a conclusion, the situation is a little more complicated than I expected. That's probably why I haven't found a similar list. There aren't general rules and one has to dig into the product sheets and then to calculate.

Thanks anyway.

Quote from: Medved on April 16, 2014, 07:09:55 AM

So in order to increase the higher lamp current, you just connect them plain parallel, so the currents sum up (e.g. operate 2.15A 250W MV on two 1.15A 125W MV ballasts mean the lamp will get 2.3A, so will operate at ~270W; that is still acceptable).

Oops! Sure - parallel. It's only logical. Sorry, I just tried to put everything together and got a bit confused.
But I didn't know about this non-linearity. It means that a circuit with a 125W MV and 250W MV have different cosφ?

The thing is, the ballast losses are quite directly linked to the VA's the ballast has to handle (voltage across the ballast multiplied by the current; for the voltage calculation you have to count with the phase shift). So for lowest losses it is desirable to have as high voltage drop across the lamp as possible, so mainly the current will be the lowest for the desired power. But there is a limit: The arc becomes less stable, when the arc voltage becomes too high. A rule of thumb says the maximum arc voltage should not too much exceed half of the mains voltage. That is the reason, why most European HID lamps (for 230V mains) have arc voltages in the 95..130V range. And generally higher current arcs tend to be more stable than lower current ones, so the 130V apply for the higher power ones and the 95V to the lower power ones.
With low fluorescents there are another limitations: Ballast compatibility among group of lamps (4..13W T5 and PL-S all use the 0.17A ballast), desired lamp shape imposing it's arc voltage (short lamp of 18W would be very difficult to "convince" for a e.g. 95V arc voltage, so it is rather designed with 60V, so two could be operated in series on one common ballast) and so on.
The limit of "mains/2" apply for the complete lamp life, so when a lamp rise it's arc voltage over it's life (e.g. HPS), such lamp should be designed with it's arc voltage being lower when new, so there is room for it to rise before it become too high for a stable arc (so HPS lamps have ~70..90V when new; again 70V is valid for the low power ones, 90V for the high power ones)
The "mains/2" came from the fact, then with that the phase shift is so, the mains voltage is not that far from it's peak when the current crosses zero, so when the arc extinguish and has to reignite for the opposite current polarity. With higher voltages the voltage starts to go down (look at the sinewave shape).

Quote from: Medved on April 16, 2014, 07:09:55 AM

And with different lamp types, don't forget thy could be of the same wattage, but in fact need way different current (250W HPS operates at nearly 3A, while the 250W MV is designed for 2.15A; so using a 250W HPS ballast for 250W MV lamp mean 40% overdrive)

I absolutely haven't suggested mixing MVs with HPSs in 3. But again, this so different current (different cosφ again?) is new to me.
I also forgot to mention that HPS tolerance is lower than MV tolerance.

It is different arc voltage, so that could be, indeed, translated into the different cos-phi. But the difference is there mainly to get the voltage headroom for aging: Even when the voltage rise with age, it shall stay below the 1/2 of the mains, otherwise it will become unstable, so most likely cycle.

As a conclusion, the situation is a little more complicated than I expected. That's probably why I haven't found a similar list. There aren't general rules and one has to dig into the product sheets and then to calculate.

Thanks anyway.

Just fired up a 100W HPS in a 150/175W Metal Halide fixture tonight with no issues.  (temporary until the facilities group gets some more 175W MH bulbs in) 

I had an idea of using an old 220V/40W T12 choke (+ a starter) with a 230V/40W T6 circline that is intended for use with an electronic ballast.
Despite being almost the same voltage and identical power, there's a completely different current specified on those ballasts:

Magnetic ballast: I = 0.42A, electronic ballast: I = 0.18A.

I suppose the T12 magnetic ballast would destroy the T6 circline...? Or, is there something I'm missing? Thanks.

I had an idea of using an old 220V/40W T12 choke (+ a starter) with a 230V/40W T6 circline that is intended for use with an electronic ballast.
Despite being almost the same voltage and identical power, there's a completely different current specified on those ballasts:

Magnetic ballast: I = 0.42A, electronic ballast: I = 0.18A.

I suppose the T12 magnetic ballast would destroy the T6 circline...? Or, is there something I'm missing? Thanks.

General rule: Looking at ballast rated power does not make any sense, when evaluating other than the rated lamp type. What you have to look for is the arc current ratings (that is dictated by the ballast; so e.g. a 0.37A F18T8 ballast will severely overdrive a 0.18A 18W lamp) and then whether the arc voltage of your lamp is in the range the chosen ballast could operate (see below). Only when the arc voltage of the used lamp matches the arc voltage of the rated lamp, the power somehow matches the rated power (so that 18W circline will operate at ~40W on F40T12 ballast - both lamps are of ~100V arc voltage, so the 0.43A would lead to about the same 40W).


It is not matter of electronic vs magnetic, but again the arc voltage vs the ballast open circuit voltage (OCV). In the case of a series choke ballast, the OCV is obviously equal to mains voltage, so in your case 230V.

So you will run into troubles with insufficient OCV: The T6 circline has arc voltage around 240V, so you would need an OCV of around 480V. The 230V mains won't be able to provide that.
And second problem would be the too high current during preheat: The ~0.65A from the F40T12 ballast short circuit (= preheat) current would be way too high for a 0.18A lamp, it will most likely blow it's filaments. The circline woulkd require preheat current of around 0.3A.


With manual start you may reach higher effective OCV by using series LC (operating near the resonance, on the capacitive side; inductor is a standard ballast for the required current, capacitor is calculated so, it has ~1.8x the impedance of the inductor and rated at 450VAC at least) as a ballast. With that you may operate lamps with arc voltages up to ~180V on a 230V mains (voltage available for the arc reignition would be nearly 600V in that case, so an equivalent of ~400Vrms). But standard starter won't work, because in order to form the extra voltage the current has to flow first (hence the manual preheat).

But for your lamp with a 240V arc that would be still by far not sufficient...

Thanks, I hope I got it.
But, as you recently posted in another thread, those values are difficult to get as manufacturers specify "this ballast is compatible with those lamp models" rather than the actual values.
I'm even not sure if these values (such as OCV) can be measured at home with an affordable amateur equipment. You'd probably need a fast recording voltmeter to capture this short period, wouldn't you?

I think that the only exception (that is known to me) are T8 retrofits for T12 fittings (40W -> 36W, 65W -> 58W etc.) but these were made so by design. Here the arc current, arc/OCV voltage values have to be compatible as the T8/T12 relamping has been very common.

Some time ago I was able to download a "Osram lamp catalogue - complete" (in Czech :-) ), where are listed at least the rated arc voltages and currents.
The ignition voltages are more a guess, but generally preheat, as well as electronic ballast tend to have quite a lot of margin, so that is not as much a problem.
A bit trickier is the maximum voltage across the lamp during the preheat (so the lamp won't ignite prematurely), that is required to know for many programmed start ballast concepts (with fixed preheat voltage/frequency/resonator current). The problem is, this is not that much related to the arc voltage, but it strongly depend even on external field (how close are the grounded parts of the fixture,...).
But if you design the ballast with no more than ~1.5..2x the rated arc voltage, usually it works well.

Most problematic is the rapid start concept: There the voltage should be just enough to ignite, but yet insuffucient for cold cathode discharge. That is the reason, why the "true rapid start" (where the filament emission causes the arc to ignite) concept isn't used anymore.

Instead is mostly used the instant start, but with assisted electrode heating (all cheepeese instantly styarting ballasts are actually of this concept): When the lamp operates in cold cathode mode, the electrode filaments  get extra heating power supply boost, usually about 2..5x the rated arc current. This means even when the arc ignites immediately, the time spent in the cold cathode mode is very limited (fraction of a second, compare to about 1second on a "single wire per lamp end" instant start ballast so common in US F32T8 commercial installations).

You can find a lot of interesting data on the Osram website about european fluorescent lamps.

Here for the linear fluorescent lamps:
Part1
Part2

And here for the compact not selfballasted lamps.