Today I recieved my British Gas electricity monitor and I have noticed that when I turn on the kitchen lights that are two 58 watt T8 tubes running on two conventional ballast gear trays the wattage on the monitor shows a draw of 160 watts which means that if the tube draws 58w then the ballast is drawing 22watts, would this be correct?.
Trevor Smith
Just be aware that any device that only measures current cannot be an accurate watt-meter.
A
Yes, it can't take the power factor into account. Your fitting must have a power factor correction capacitor, or for a a 58W tube, it would register about 2.2 times the actual power used. A capacitor can't fully compensate though, because part of the low power factor is not simply due to phase shift, and the capacitor can only compensate for the phase shift component.
Ballast efficiency is marked with an EEI (Energy Efficiency Index) rating on the ballast.
With the information you've given, I can't tell how much of the 22W is a misreading due to power factor, and how much is ballast losses. It can't possibly all be ballast losses, because the ballast would overheat. For a 58W tube and ballast, max ballast losses are: EEI=D >12W EEI=C 12W EEI=B2 9W EEI=B1 6W
If you are interested, you could pop the cover off, and read what the ballast EEI rating is. It's no longer legal to sell EEI=C or D ballasts in the EU.
If you want a more efficient light, rewire the luminaire with an electronic ballast. You can get one which will do twin tubes (although both will go out when one dies), or separate ballasts for each tube. Electronic ballasts are required to be more efficient than even the EEI=B1 rating.
Nor the supply voltage. A
Had one of those and gave it away! Damned thing was telling me that a 15W CFL was 30W; also that my PC was about 100W - it'd catch fire! The CFL was near enough PF, but the PC has ~99% PF...
I just wanted to know what's watt.
mind if that's pasted into the wiki?
Just had a look and the ballasts are EEI=B2 and whilst I was doing that I check again the load on the monitor and it now shows that the two lights are drawing 120 watts which means with the EEI=B2 ballast losses taken into account they are more efficient than they should be. Conclusion, these monitors are a very rough guide and I will properly do what PeterC did and give it away.
Trevor Smith
For electronic ballasts, there's A3, A2, and A1, but it's more complicated how they're used, and I haven't looked up the precise details. I think A3 only allows a total of about 1W more than the tube power rating, and A2 and A1 have total power consumptions less than the tube rating. This works by underruning the tubes, and relying on the HF operation being more efficient to get the same light output as at 50Hz operation. Would need to look into that some more before it's accurate enough for the wiki though.
It won't account for power factor, so the difference will be reactive "power" which is sucked from the mains then returned.
I've just been checking various appliances on my plug in power meter. I've been assuming the figures in the handbook of my 2 year old Philips TV are correct. It claims less than 1W on standby so I've been leaving it on standby.
I now find it's taking nearer 25W and about 4W when switched off. Trading standards?? And do I demand a refund?
cheers. If you do get that extra data I'll put it in.
NT
Interesting - I've a 3yo Philips TV that shows 0.9 - 1W on the plug-in meter and I used to leave that on standby sometimes; now do so only for 30 min. gaps or less. I never checked it with BG's thing - wish had. But which is correct?
How long did you wait after switching it into standby? Our Panasonic TVs only enter their very low power standby mode after a few minutes, when there is an audible click from (presumably) a relay in the set. Until then the power consumption is much higher.
I suggest you repeat your measurement after the TV has been in standby for, say, at least ten minutes.
Richard.
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