Fluorescent tubes use more power than they should.

[Malcolmkeith]

I have been conducting an electricity audit in my house as my bills are too high. I replaced two halogen bars (4 x 50 W each) of lighting in the kitchen for 4 x 36W fluorescent tubes and 6 x 60W candle bulbs with 6 x 11W cfls in the lounge.
I have a portable energy meter so I can walk round switching things on and off and seeing what everything is consuming.
Well interestingly my meter shows that on switch on the 6 x 11W cfls are only consuming 38W total (not 66W). This may increase as they warm up, but its difficult to tell without switching off everything as fridges and freezers can switch on over a period and confuse the readings.
Now here's the interesting bit. One of the 36 W tubes in the kitchen has failed so there are only 3 x 36W tubes working. My energy meter shows these tubes are consuming 261W! i.e. nearly 90W each! I though that maybe one was faulty and using most of the power so I took them out one by one and behold each one is consuming about 90W acccording to my meter.
Can any one explain this?

 

[Bill Stickers]

Sounds like your meter isn't very good

 

[AdrianUK]

The problem is two fold.

Firstly, the 36W shown is the power consumption of the TUBE alone. It doesnt include the losses of the control gear/ballast (remember that the ballast gets warm, hence it is consuming energy and disapating it as heat)

Secondly, your "energy meter" isnt! Its only really a guide. It isnt an 'instrument', it isnt calibrated & it isnt accurate! One of its main problems is it makes an assumption about the system voltgae & power factor in order to calculate power - its answer can easily be 25% out!

Adrian

 

[Gavin77]

Can any one explain this?

Yes, I assume your 'Meter' is a clamp around the one of your meter tails. And therefore it is only accurate if it is measuring resistive loads.

 

[AndyPRK]

order two new bulbs and replace the broken and suspect one.

I assume its no brighter than the others.

 

[ericmark]

I had a problem with florescent tubes many years ago when on the building of Sizewell Power station. I needed to light some tunnels and had decided to use 60W 110V lamps and since the transformers were fitted with 16A MCB's I want each run to use less than 16A. Quick calculation said I should be able to use just under 32 units if 1/2A each so decided to use 25 units per run to give some leeway. However the 16A MCB tripped so it was then measured with a clamp on ammeter and they were drawing around 22A no wonder it was tripping.

So at this point I took a unit and opened it up on the bench and tried different things to see why. As it was each unit was drawing 0.8A so in case some of the power factor correction capacitors were faulty I tried removing it an re-measuring it. Now 1.2A wow didn't expect that. Next was since 110v they used a auto transformer which had an option of 110v or a 127v tapping. I swapped them to the 127v tapping and bingo down to 0.6A.

However when I came to fit them I found the volt drop would stop last few firing up so last few were corrected to 110v tapping.

So this experiment shows the florescent fitting using an inductive ballast for starting and run control is very voltage dependent and fitting 220v units where the supply is 240v can cause them to use well over the rated wattage. Also using 240v units where the supply is 220v may mean they will not strike. And any capacitors blowing can really lift the power used.

There is however another way to control and fire florescent tubes. It is called a HF unit and it will compensate for minor under or over voltage and also the tubes will last up to 5 times longer and the light output from the tubes does not fall off as quick so all around a better method. However the price sores from around £12 to around £60 so it's a balance between unit price and economic power use. They are also not so robust as the old inductive ballast so if you continue to use after a tube goes they tend to fail. An added benefit is less stroboscopic effect with HF units.

So you have to decide if you want to pay the price. The 2D lamps I note are not so marked with price difference and they also look better but the maximum size is around 55W but not so common so 28W seems more the norm.

 

[Adam_151]

. However the price sores from around £12 to around £60 so it's a balance between unit price and economic power use. They are also not so robust as the old inductive ballast so if you continue to use after a tube goes they tend to fail. An added benefit is less stroboscopic effect with HF units.

Eric, think you are a little out ith your HF ballast prices, last time I checked a HF ballast for a 5 foot pop pack was around the £25 mark.

Most of the 28w 2D fittings (unless you buy the cheapest) come with HF controlgear these days.

Last HF ballast I did cost £45, but it was a 0-10v dimming part. It didn't even require the wound filters fitted with the fitting that the previous ballast needed as technology had moved on

 

[Stoday]

There is however another way to control and fire florescent tubes. It is called a HF unit and it will compensate for minor under or over voltage and also the tubes will last up to 5 times longer and the light output from the tubes does not fall off as quick so all around a better method. However the price sores from around £12 to around £60 so it's a balance between unit price and economic power use. They are also not so robust as the old inductive ballast so if you continue to use after a tube goes they tend to fail. An added benefit is less stroboscopic effect with HF units.

When I built my house 5 years ago, I installed 16 1200mm 70W fluorescents. I found the extra for HF ballasts was only 10% or so on the cost of batten plus diffuser, so they're all HF.

I think you should look for another wholesaler.

 

[ericmark]

At the time I was fixed to one whole sale outlet by contract. It was RS components so that was very likely why the high prices were on these units.
My boss considered the fact that using RS he didn't need a store keeper as part of there contract was to do the stock checks compensated for extra cost. I had no option.

I have bought one 2D unit of late and the main requirement was it had to be class II. I paid what seemed well over the odds for the Class II marked lamp and was surprised to find it was not a HF unit. But it did the job and replaced the 40W florescent fitting which required an earth when there were no earth connections to the lights.

Which reminds me I must check the firm attached the sticker on the CU to inform on earth on lights.

But we used 12v, 24v and 230v 2D lamps in the Falklands and I was impressed they did seem to give a reasonable amount of light from a neat relatively small unit.

The problem with all florescent units is as they get old they can draw far more power than their rating and this was something which came up as a regular discussion how to monitor lights to high light when this is the case? One guy wanted us to provide a handy loop from each MCB controlling lights so a clamp on ammeter could be used regularly to check the current used. He had done a thesis for Uni where he reckoned he could show keeping records of power used by lighting was a cost effective way to work out when to re-lamp. The boss however went for using a light meter and after a re-lamp he would record the light and when it dropped around 15% would order a re-lamp as he considered with switch mode HF units it was unlikely that they would draw extra power without there being a drop also in light output. But where power factor correction capacitors are used in the fittings may be the Uni guy had a point!

But how would the normal home owner monitor the power used? We when monitoring tower cranes used some recording boxes but these were not cheap and when I consider the information given likely one of the plug in power monitoring devices would give same information. But I am not completely sold on the idea of disconnecting the lights from the consumer unit and fitting a plug so you could use on of these units. My clamp on ammeter does to my mind a good enough job.

But likely this poster does not have a clamp on and even if he did I would not want to suggest a normal person removes the front off his consumer unit in order to use it.

So open to suggestions? How would a normal person monitor his lights to identify when for example a power factor correction capacitor has blow? Not how we would do it but how a normal person would do it?

 

[Stoday]

The problem with all florescent units is as they get old they can draw far more power than their rating and this was something which came up as a regular discussion how to monitor lights to high light when this is the case?

I have not heard of ageing fluorescents using more power. Neither have I been able to google up anything about a power increase as they age. Indeed, I can't think of a reason why the components of a "fluorescent unit" should increase power consumption.

Current consumption will increase as power factor capacitors fail, which will not be noticed by most consumers. Only a very few of the largest consumers are charged for bad power factor. The power increase due to increased losses from bad power factor is insignificant.

Lumens will fall, both due to lamp emission as phosphors wear out and as dirt accumulates.

None of the above significantly increases power consumption.

So, I don't believe there is a problem.

 

[big-all]

remote energy meters often have a final 60w or so that can affect the meter
in other words induces current will add around 60w to the reading so a light bulb to tv will show consumption plus 60w so a 10w will show as 70w if everything else is turned off

 

[Malcolmkeith]

Thank you to all who replied. For me the important thing is what is my house meter is recording because that's what I'm paying for. Unfortunately I have a new digital meter which only displays whole kWh units. As I remember, the old aluminium dicsc type used to show fractions of a unit so it would have been feasible to switch everything off except the fluorescent lights and see what it recorded in say an hour. Is there a reasonably priced meter available which will record power correctly?

 

[ericmark]

Its not the price that's the problem it's how you would use it. There are loads of plug in meters that will monitor power used but how would you connect it to your lights?

 

[Stoday]

Electronic kWh meters normally have a flashing red LED. There should be a caption saying how many flashes/kWh or Wh/flash so that you can check low consumption.

 

[thedonkey68]

Older style fluorescent battens with wire wound control gear (i.e. flicker flicker on) typically use 25% more energy than that of the HF electronic gear (which is only 10%) - these values are to be added on top of the actual wattage of the lamp. This will give you a clearer indication as to what the overall wattage/ energy being used will be. [/u][/b]