Electronic Ballast Rating - how flexible?

[dishman]

Hello.

Recently bought a nice little twin T5 tube light fitting with an instant start electronic ballast. I need to replace the tubes as they are far too white.

I noticed that philips have an Eco version of the required tube at 25w rather than the standard 28w (this gives it a lumens per watt of over 100, which is pretty good). Unfortunately, the range, for some reason, does not seem to include the 3500k colour that I want. So I may go for the standard one anyway.

But, if the ballast is rated for a 28w tube (or two), what would the effect of putting a bulb with a lower wattage than specified.

I have read on some sites that the magnetic ballasts would not react well, but the electronic ballast is more flexible. Others say that anything other than the rated bulb is a bad idea. While others suggest you can put a range of tube wattages in. But, I am not convinced.

The box does say the bulb is not compatible with A* and A** bulbs, but I think this is meant to refer to LED tubes (for obvious reasons).

 

[ericmark]

I have a HF ballast with battery back-up in my loft which I seem to remember was rated higher than tube used, tube is 18W, and it was fitted around 1993 and had to renew the tube in 2014 so has lasted 20 years plus at top of stairs so used every day, does need new batteries now, but can't really complain.

But because one works OK, does not mean another unit will do the same, as for magnetic ballast in the kitchen I had old fat tubes 65W and tried to replace with 58W and they worked, but life was around the 6 month mark so not really an option.

Over the years I have found there are some odd systems used with fluorescent, I remember a problem with fly catchers and having to get special starters, the simple universal would not work, also voltage where just a few volts too high could increase current by a huge amount. And folded fluorescent in reading lamp with instructions on tube "not suitable for electronic ballast".

The problem is don't really know why we have odd instructions and how an electronic ballast controls the current, the magnetic is a two function device, one it gives a pulse to help start and two once running it limits current, but not a clue how the electronic ones do the job, likely they are not all the same, and one will work fine and another will fail. If I was stuck in the Falklands with anything ordered taking 6 months then I may give it a try with a fuse and clamp-on ammeter to monitor, but in the UK simply not worth it, just get matching units.

 

[ianniann]

The Philips 25W T5 Eco range is specifically intended as a drop-in replacement for a normal 28W T5 tube, using around 10% less electricity on the same ballast, but producing comparable light output.

 

[dishman]

That is what I assumed, but if it does draw only 25w, and the ballast is rated for a tube of 28w (or 2 x 28), how does the ballast deal with it. I know it is only a 3w (6w with two tubes) difference and probably well within the tolerance of the ballast. Although 6w is a tad more/less that 10% of the total rated load.

Surely a proper drop in replacement would have the same wattage but a much higher lumen output.

Hence I was just curious. How does a higher or lower load affect the ballast?

Oddly the seem to have omitted 3500k colour from the range...so I can't get one anyway.

 

[333rocky333]

Have you read the gunf on the actual ballast, quite often ballasts around that size do various lamps, often 14watt up to 35watt however they usually only state the popular sizes rather than the lower Eco sizes as well.
Though in reality the Eco ones tend to work as well.

I quess the electronics inside tend to adjust the output to the lamp ends to compensate for the difference.
With the older Magnetic ballasts in 2D fittings sometimes the Eco lamps struggle to work, but as yet not had problems with tubes.
A lot of newer electronic ballasts now do an even wider wange of lamps, which I quess aids manufacture and stock levels

PHILIPS QUOTE
"HF-Performer Intelligent for Master and ECO TL5 HE/HO, TL-D and PL-L lampsHF-Performer Intelligent features automatic recognition of the connected lamp and is independently able to adjust its operation parameters exactly to the respective lamp. This results in a substantial benefit, especially for T5 lamps, as it means TL5 HE and HO lamps of the same length can be interchanged.With a choice of seven ballasts, the customer is able to handle efficiently every possible combination of Master TL5 and Eco, TL-D, and PL-L lamps."

 

[dishman]

Have you read the gunf on the actual ballast, quite often ballasts around that size do various lamps

Yes, it just says 2 x 28w. That is the only reference to wattage.

Also, the Philips Eco He tubes come under the A* efficiency band.

On the box, it suggests that it is compatible with A-E but for A* and A** it has a cross next to it. I am tempted to assume this is a poor attempt to say "not led compatible" to prevent people trying to retrofit tubes incorrectly, or just slotting them in without making ballast changes.

 

[aptsys]

That is what I assumed, but if it does draw only 25w, and the ballast is rated for a tube of 28w (or 2 x 28), how does the ballast deal with it. I know it is only a 3w (6w with two tubes) difference and probably well within the tolerance of the ballast. Although 6w is a tad more/less that 10% of the total rated load.

Surely a proper drop in replacement would have the same wattage but a much higher lumen output.

Hence I was just curious. How does a higher or lower load affect the ballast?

Oddly the seem to have omitted 3500k colour from the range...so I can't get one anyway.

The job of the ballast is to drive the tubes with a constant power. Unballasted, that tube will draw 1000's of watts until it destroys itself, so using a 25W lamp in the same fitting will mean that it'll actually run at 28W - probably nothing to worry about, but the tube won't last as long.

There are many multi-wattage ballasts, but you'll notice it is stated what tubes are suitable on the unit and also that they are quite distinct power levels. The ballast attempts to drive the tube and determines what wattage tube is fitted by the voltage drop across it.

 

[ianniann]

The job of the ballast is to drive the tubes with a constant power. Unballasted, that tube will draw 1000's of watts until it destroys itself, so using a 25W lamp in the same fitting will mean that it'll actually run at 28W - probably nothing to worry about, but the tube won't last as long.

There are many multi-wattage ballasts, but you'll notice it is stated what tubes are suitable on the unit and also that they are quite distinct power levels. The ballast attempts to drive the tube and determines what wattage tube is fitted by the voltage drop across it.

Fluorescent ballasts are current regulation devices. Both the 28W and 25W tubes are designed to work on the same current, 0.17A. The 25W tube will drop a smaller voltage and consume less power but still produce the same amount of light. This is not an accident.

The labelling as not compatible with A+ and A++ (yes, they should be pluses, not asterisks) tubes is odd. The ballast has no way of knowing how efficient the tube is, and no reason to care. Perhaps they do aim it at LEDs, but it would have been simpler to say so. T5 fluorescent tubes fall right on the boundary between A and A+ lamps. The 28W falls one side, the 25W producing the same light falls on the other. There is nothing in that difference that would cause the ballast to be damaged or not work correctly.