I'd like some clarification on the effects of lamp & ballast mismatches, since it is commonly done by accident (or sometimes, in the experimenter's case, on purpose).
Generally, what I have observed, that slightly underdriving a fluorescent or HID lamp (as in the case of a "residential"-quality ballast) actually extends lamp life when using the proper lamp.
Do not expect any lamp life extension wen operated on other then rated conditions. The reason is, then lamps components (electrodes, heat management,...) are optimized for the rated power, so the rated power is usually in the minimum of the wear rate.
In the best case scenario (the life does not depend on the change) the life would not change.
But what would deteriorate is the lamp performance (efficacy, color quality,...)
I know that underdriving a discharge lamp to a large degree will cause electrode sputtering (blackening) and shorten life...and overdriving also shortens life by overheating the phosphor (if present) and arc tube (potentially weakening it)...but what is the worst scenario for ballast damage?
Generally what the ballast "see" is the arc voltage (it is dictated by the discharge), so if the "wrong" lamp have the same arc voltage as the "good" lamp, there is no difference for the ballast at all.
If the arc voltage is different, it strongly depend on how the ballast is designed and how it respond to he different arc voltage.
For example, I tried running a 4w T5 fluorescent on a 40w (rated 430mA) electronic ballast. The lamp was overdriven, but only measured to be about 13.5 watts. It didn't seem to massively overheat the lamp nor the ballast.
I am currently running 110w 1500mA PowerGroove lamps on an 800mA electronic ballast, also noting no abnormal effects.
It for sure the F36T8 ballast overheat the F4T5 electrode filaments (by Joule losses, so current), so they will fail soon.
With electronic ballasts you can not judge based on it's external temperatures. The "thermal measurement spot" is there only to check the cooling when mounted inside a fixture, but can not be used as a base to determine, if it does not overheat when mislamped. For the surface emperature it may even happen, then some normally higher dissipation component run cooler, while other, normally cold, is overheating and so fail soon.
To really check, if the ballast does not have tendencies to overheating, you have to open it and compare temperatures of all components with the same ballast running the rated lamp.
As second you have to check critical component electrical loading, if it is not beyond the rating:
- Elecrolytic DC bus tank capacitor (with lower arc voltage lamps get stressed more for the HF ripple, with higher arc voltage lamps for the 120Hz ripple)
- Power semiconductors, as frequently they do not use heatsinks, as they run with very little power dissipation. But changing the ballast loas may cause the inverter to depart from soft switching mode, what could cause their power dissipation to rise even an order of magnitude (cheap, simple selfoscillating 36W ballasts dissipate no more then 0.5W on each power component, what by far does not require heatsink, but with different or faulty lamp this power dissipation may rise to few watts, what then fry them)
- Ballasting inductor
- Peak voltage on the resonant capacitor (parallel to the lamp) vs it's rating. Count with at least factor of 2 margin for lamp aging.
I had been running a 125w mercury lamp on a 100w HX mercury ballast with no noticeable blackening or ballast overheating. What would happen if I ran an 80w lamp? Or a 250w lamp?
If the MV is able to warm up to the level where all mercury is evaporated, all have abut the same voltage (~95..110V).
So for the 100W HX MV ballast:
125W MV: Lamp slightly underdriven (so slightly lower efficacy), ballast OK. Within MV rating for dimming (50%), but without the required 15minutes warmup on full power. As the underdrive is only slight, I think no problem.
80W MV: The lamp 20% overdriven (obviously; so with all consequences), ballast fully OK
250W MV: May get stuck to cold, low power dissipation saturated vapor mode (not all mercury vaporize). That may overheat the ballast, as the arc voltage in such state is lower. MV ballasts are usually not rated for overcurrent, as MV lamps do not expose them to such conditions for longer time. Compare to CWA, HX boost current with lower arc voltage, so hey are more likely to transition the 250W lamp to the correct operating mode (all Hg vaporized), but as CWA does not rise the current, it does not overheat. I would say 250W lamp is too much for 100W ballast.
I frequently see 70w metal halide fixtures running 70w HPS lamps (which are 55v in the US) - they run dimly, but what is this doing to the ballast?
That definitely overheat the ballast.
I tried running a 400w (100v nominal) HPS lamp on my 100w, 55v HPS ballast - it seemed to work fine, only the lamp only ran up about 1/2 way. Ballast didn't seem to be hot. Running a 35w, 55v lamp made the lamp run up too quickly and cycle, but 70w and 150w (55v) lamps seemed to work fine. Would either overheat the ballast over time?
HPS are tricky, as their arc voltage depend on the arctube temperature (saturated vapor lamps).
So 400W/100V lamp on 100W/55V ballast: Check the arc voltage. If it is above ~50V, the ballast is OK.
35W lamp is overloaded, so it's arc voltage rise far above the 55V, so the series choke ballast is not able to maintain the arc. Ballast OK.
70W tube would be overheated, so have shorter life, but the ballast would have easier life (higher arc voltage on series choke => lower power dissiatin => lower temperature)
150W tube would be OK, but the ballast may run hotter (underdriven tube have lower arc voltage => higher ballast temperature)