Power being lost?

[Chris S]

I have a halogen light which takes two G4 bulbs.

The bulbs are rated at 12V 20W each.

I am in the UK so I supply power to the light unit at 240V ac. When I
put power meter in the main supply to the light, I see the consumption
is only 32W rather than 40w or more.

Why is this? Is there a reason how this could be so?

My power meter is a bit crap and it may be the culprit. Please help me
solve this.

Thank you.

 

[TKM]

I have a halogen light which takes two G4 bulbs.

The bulbs are rated at 12V 20W each.

I am in the UK so I supply power to the light unit at 240V ac. When I
put power meter in the main supply to the light, I see the consumption
is only 32W rather than 40w or more.

Why is this? Is there a reason how this could be so?

My power meter is a bit crap and it may be the culprit. Please help me
solve this.

Thank you.

As you say, your meter could be giving you a faulty reading. Start by
testing it with another lighting unit where you also know the wattage of the
bulb to see what it reads.

Your unit which uses the 12 volt, 20 watt bulbs must have a step-down
magnetic or electronic transformer. Often such transformers have a High-Low
switch so your unit can provide off/low/high light levels. Does yours?

Terry McGowan

 

[Ken]

What's your main supply voltage? If they are rated at 40W at 240V then
anything lower in volts will reflect in the consumed power. This is
especially true it it's a bog standard transformer. Uour European
friends have dictated that our supply volts will be 220V.

230V

 

[Andrew Gabriel]

What's your main supply voltage? If they are rated at 40W at 240V then
anything lower in volts will reflect in the consumed power. This is
especially true it it's a bog standard transformer. Uour European
friends have dictated that our supply volts will be 220V.

This is incorrect.

The EU-wide nominal voltage is 230V, but with a tolerance which means
neither 220V nor 240V supplies need to change. I believe some 220V
areas have decided to up themselves to 230V, but most areas have no
plans to change.

My mains voltage is currently 239.9V

 

[Chris S]

As you say, your meter could be giving you a faulty reading.
Start by testing it with another lighting unit where you also know
the wattage of the bulb to see what it reads.

Your unit which uses the 12 volt, 20 watt bulbs must have a
step-down magnetic or electronic transformer. Often such
transformers have a High-Low switch so your unit can provide
off/low/high light levels. Does yours?

Terry McGowan

No my unit does not have any switches except for on-off.

Maybe it is my meter then.

 

[Chris S]

What's your main supply voltage? If they are rated at 40W at 240V
then anything lower in volts will reflect in the consumed power.
This is especially true it it's a bog standard transformer. Uour
European friends have dictated that our supply volts will be 220V.

Try measuring the volts at the bulb terminals.

Rob.

Rather difficult taking the unit apart to measure at the bulb's
terminals. Will recheck my mains voltage.