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Do PSUs use electricity?

sanj

sanj

Member
Joined
10 Apr 2008
Messages
1,531
Location
Coventry, UK
I have a Maxspect razor 120w over one of my tanks. It is only only on 55w max and overnight it is only on 1% output. I was testing the watt output using one of those monitors that you can get from Energy suppliers, it was reading 20w consumption when I measured it at night when the lights had gone down to moonlight 1% output. I would have expected 1-2w, but not that high.

So i was wondering if this was the PSU?
 
Good Morning Sanj,
This does seem an odd one? :wideyed: It would appear that if this reading is correct (and I have no reason to doubt it is.) It would imply that there is still voltage and current being used. Is it possible that this is the supply required to maintain the minimum programmed lighting features? If it is, it does seem to be on the high side. Or it may be implying that the 20w used are the minimum driver unit light settings.:bookworm: No matter what your lighting requirements are, which would make more sense to me? Not very efficient as can be seen but required to keep the lighting unit and driver working. Just my thoughts.
 
Troglodyte said:
New Good Morning Sanj, This does seem an odd one? :wideyed: It would appear that if this reading is correct (and I have no reason to doubt it is.) It would imply that there is still voltage and current being used. Is it possible that this is the supply required to maintain the minimum programmed lighting features? If it is, it does seem to be on the high side. Or it may be implying that the 20w used are the minimum driver unit light settings.:bookworm: No matter what your lighting requirements are, which would make more sense to me? Not very efficient as can be seen but required to keep the lighting unit and driver working. Just my thoughts.
Click to expand...

Hi there,

I just tried it now, but with lights going off completely and the wattage still remains similar to around 20w. I then went and tried a TMC PSU (duel cables) with no lights attached, it was drawing about 7w.

I remember some years ago talking to the UK supplier of Eco-lamps, he did say then that TMC PSUs also draw electricity and so their stated 12w output from an aquaray bar was not the whole picture.

Unless my meter is wrong it seems that PSU do draw some power regardless of whether lights are on or not. I dont think the meter is wrong as I then tried it on the filter and it came back with an accurate enough reading for the filter output and air pump.

While still less output than non led sources, it does leave me feeling that led manufacturers or their marketing departments are not telling the whole story.
 
You know how people say you should trust hobby grade water test kits, well the same can be said for cheap power meters, for certain types of load they read hopelessly wrong. Probably fine for electrical heater or normal tungsten filament light bulb or a kettle but may be hopelessly wrong for anything with a large motor in (try vacuum cleaner) or anything will electronics in, especially cheaper items.

Its all to do with power factor, your power meter does not take into account power factor. Power factor - Wikipedia, the free encyclopedia

I have a more expensive power meter (£20, Maplin ?) and it also reads power factor, enabling me to correct the power reading. Maplin N47KB reads real power and apparent power.

I have a set of PC speakers, which reads 20Watts when in standby (this is apparent power), however the power factor is a very poor 0.2, which gives real power (ability to work, energy/second) of 20 x 0.2 = 4Watts, which matches the manufacturers quoted value in standby.

You also get some other weird readings like my 10year old PC measures 140W when "doing nothing" and stays at about 140W when maxed out at 100% CPU, despite obvious heat being generated. However when idle power factor is 0.35 (50Watts in idle) going to 0.95 at 100% CPU.

So the real power taken by your lights when low, is liable to be significantly less than the 20W your power meter is reading (I may be wrong of course).

Oh your domestic electricity meter charges you real power (the lower value), so your 20W value is again meaningless. Industry gets charged apparent power, so they go to significant lengths to ensure power factor is as near to 1.0 as possible.
 
This is where one of the great fallacies about turning off phone chargers when not in use comes from.

Some PR bod plugs his phone charger into one of these meters, my god its consuming 23 Watts (if I remember right). Multiply that by 25million households all having 5 phone chargers -> 23W x 5 x 25,000,000 -> 2.8GW a couple of large power stations output. So turn off unused phone chargers and save CO2, power stations etc. Produce loads of posters to tell everyone to turn off their phone chargers etc etc.

Actually 23W is really quite large, just think how hot 25W normal bulb gets and my phone chargers when not in use certainly don't get that warm!!!

Except the power factor when not charging phone in was very low and meter he used hopelessly incorrect and in fact the true power when idle was less than 0.05W.

The energy saved in switching off your charger for one day is used up in one second of car-driving, so if you really want to save energy, stop driving is one of the best ways to save energy.
 
ian_m said:
This is where one of the great fallacies about turning off phone chargers when not in use comes from.

Some PR bod plugs his phone charger into one of these meters, my god its consuming 23 Watts (if I remember right). Multiply that by 25million households all having 5 phone chargers -> 23W x 5 x 25,000,000 -> 2.8GW a couple of large power stations output. So turn off unused phone chargers and save CO2, power stations etc. Produce loads of posters to tell everyone to turn off their phone chargers etc etc.

Actually 23W is really quite large, just think how hot 25W normal bulb gets and my phone chargers when not in use certainly don't get that warm!!!

Except the power factor when not charging phone in was very low and meter he used hopelessly incorrect and in fact the true power when idle was less than 0.05W.

The energy saved in switching off your charger for one day is used up in one second of car-driving, so if you really want to save energy, stop driving is one of the best ways to save energy.
Click to expand...


Slightly on the same lines. What about a TV on standby? What you think that costs per year Ian? I can't see 1 tiny red LED costing the amount people are making out it costs?
 
Depends on TV make. My mate had a Philips FreeView TV at that consumed 16W in standby !!! So that's per year (assuming £0.15 per 1000W hours) 16/1000 * 0.15 * 24 * 365 = £21 a year just to keep in standby !!! I assume it was leaving the tuner on to look for software/EPG updates 24/7.

My Panasonic Plasma TV (2008 model) quotes less than 0.7W in standby, measured by me using my works accurate power meter 0.4W so that's 0.4/1000 * 0.15 * 24 * 365 = £0.50 per year. Well worth it to save taking my bottom off the sofa to press the on switch.

I think EU regulations now quote less than 1W for audio visual devices that are in full standby.

A really good read on energy and how to save is here David MacKay FRS: Sustainable Energy - without the hot air: Contents . Free PDF as well as print copy. I have print copy as very useful to point out things to people who rave on about how we all should use wind and wave power for all our energy needs. Nuclear is the way to go, very CO2 friendly.

Basically we could cut our energy consumption by 2/3 very easily. No cars (1/3) and no air flights (1/3)....most other energy saving things are really minor. Job done.
 
All,

I had this response from Maxspect International. Thanks Gary for the contact.

"Basically all components inside the power supply will consume some power, especially the LED driver, the lower the intensity of the LED chips, the less efficient it'll become in terms of converting the higher voltage from your power outlet into lower voltage for your LED chips and the controller.

So even when all LED chips were turned off, it'll still consume about 7w of power, but at very low current. If you're concerned about this, you could use a timer to cut off power to the fixture altogether."
 
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