Underdriving Power Compact T5

[George Farmer]

What will happen if one fits a 24w PC T5 tube to an 18w PC T5 ballast? Interpet magentic (non-electronic) ballast.

I'm assuming one of two things can happen.

1) The ballast will supply 18w and the 24w lamp will run with less intensity?

2) The lamp would try to overload the ballast i.e. draw 24w instead of 18w?

Any ideas and possible consequences of the above please?

 

[andywg]

I have no experience of under-driving, but have some of over-driving. As I am sure you are aware, when you overdrive a bulb the higher wattage of the ballast is put into the bulb regardless of the bulbs rated watttage.

I would estimate that if the ballast was udner powered then it would only put in the power it is rated for. this will either light the bulb dimmer than usually (but possibly lead to longer life) or not fire the bulb at all if it cannot get enough power in to the tube.

 

[George Farmer]

Thanks for the reply Andy.

Logically, as you say, it seems that the ballast will supply the 18w if we go by overdriving principles.

Interesting you mention whether 18w ballast will be enough to fire up 24w tube.

 

[andywg]

If you want I can probably have a quick look for you tonight to see. I have some spare 54W T5 bulbs (ballast seems to have had a fit on that one) and a 24W ballast. I can link a larger tube to the smaller ballast and see if it will fire it up. Obviously it is a larger difference between the ballast and bulb but should give an idea of what will happen.

 

[George Farmer]

If you want I can probably have a quick look for you tonight to see. I have some spare 54W T5 bulbs (ballast seems to have had a fit on that one) and a 24W ballast. I can link a larger tube to the smaller ballast and see if it will fire it up. Obviously it is a larger difference between the ballast and bulb but should give an idea of what will happen.

Yes please. That would be very much appreciated. Thank you kind sir!

 

[Lateral Line]

There are a few of issues.

The larger lamp will require a higher striking voltage to start it. The smaller ballast may not have the guts to do that. Second, the lamp, once struck, requires the ballast to reduce the current flowing through it. The smaller ballast may reduce the current sufficiently to extinguish the lamp. I would expect either of these effects to cause the lamp to either not work at all, or flicker. That said, the tolerences used during the construction of the lamp and starter are probably wide enough that they should not come into effect.

What might happen is the increased load might cause the coil to get hotter then it normally would. I doubt it would be enough to break down the insulation though, and as long as reasonable ventilated, that probably won't be a problem when the difference in loading is fairly small as in this case.

All that said, I would always strongly recommend lamps are used with a matching starter, and preferably, a modern, high frequency electronic starter.

 

[George Farmer]

Thanks for that mate. I'll try it out, then get the 24w ballast at the first sign of any "trouble". Unfortunately the UK don't have any electronic PC T5 ballasts (someone please correct me!) We don't even have PC reflectors, we have to DIY T8s (again, please correct me).

I eagerly await Andy's results too.

 

[andywg]

Well, I tried but it wouldn't start. I reckon you will have more success than I as I was trying to fire up a 55W bulb with a 24W ballast.

 

[George Farmer]

Well, I tried but it wouldn't start. I reckon you will have more success than I as I was trying to fire up a 55W bulb with a 24W ballast.

OK, thanks very much.

 

[SkiFletch]

I'm really curious to hear your results

 

[Lead]

It will probably flicker.

 

[George Farmer]

So far so good.

The 24w PC T5 lamp is fitted to the 18w ballast. The 24w lamp starts up fine, a little flicker on start up but no more than the orginal 18w lamp. It seems the ballast is also giving out the 24w too as the tube is noticably brighter.

It's been running 3 days now with no problems. The ballast is no hotter than usual.

 

[SkiFletch]

Interesting, keeping your fingers crossed?

 

[George Farmer]

Still working fine.

My Riccia sp. "Dwarf" is enjoying the new light. Check out the pearling (oxygen bubbles from photosynthesis) -

 

[SkiFletch]

Yeah, plants love PCs . I wish all Corals were so loving