I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.
Most cheap multimeters would not be particularly accurate at the level
you are measuring, hence you will only get an approximate reading,
unless you have a 'better' multimeter.
--
To reply by e-mail, change the ' + ' to 'plus'.

In article ,
A.Lee wrote:
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.
Most cheap multimeters would not be particularly accurate at the level
you are measuring, hence you will only get an approximate reading,
unless you have a 'better' multimeter.

that will only measure the cold resistance. The lamp wattage is based on
the hot resistance.

--
From KT24

Using a RISC OS computer running v5.18

On 29/12/2012 17:39, A.Lee wrote:
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.
Most cheap multimeters would not be particularly accurate at the level
you are measuring, hence you will only get an approximate reading,
unless you have a 'better' multimeter.

If they are the same as normal incandescent bulbs the resistance will
show as almost nil unless the bulb is running.

The only way I can think of is to have an ammeter in series when they
are running. Wattage will be volts multiplied by amps so 20 watts at 12
volts will be about 1.67 amps.
Be careful. The start up current when the bulb is first turned on will
be a great deal higher.

On 29/12/12 17:59, Hugh - in either England or Spain wrote:
On 29/12/2012 17:39, A.Lee wrote:
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.
Most cheap multimeters would not be particularly accurate at the level
you are measuring, hence you will only get an approximate reading,
unless you have a 'better' multimeter.

If they are the same as normal incandescent bulbs the resistance will
show as almost nil unless the bulb is running.


It'll be even more marked with halogens as they run hotter.

The only way I can think of is to have an ammeter in series when they
are running. Wattage will be volts multiplied by amps so 20 watts at 12
volts will be about 1.67 amps.
Be careful. The start up current when the bulb is first turned on will
be a great deal higher.

+1

On Dec 29, 5:39*pm, (A.Lee) wrote:
ss wrote:
I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. *I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.


Afraid that won't work. The resistance varies with temperature and is
much higher when the lamp is working.

You need to measure current and voltage and multiply the two for watts.

ss wrote:
I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

If the old ones are still working, you need a multimeter with a very low
resistance range (anything more than 10 ohms full range is too high), to
compare the resistances of an old one and a new one. If they're about
the same, then they're the same power, if the new ones are roughly half
the resistance of the old, then the new ones are higher power. 12V G4
bulbs normally only come as either 10 or 20 watts, except for some "Eco"
bulbs which are 14W or so.

If you're still unsure, then dig out the manual....

--
Tciao for Now!

John.

On 29/12/2012 18:13, John Williamson wrote:
ss wrote:
I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones
as I would replace them if a higher wattage. I have a multi meter.

If the old ones are still working, you need a multimeter with a very low
resistance range (anything more than 10 ohms full range is too high), to
compare the resistances of an old one and a new one. If they're about
the same, then they're the same power, if the new ones are roughly half
the resistance of the old, then the new ones are higher power. 12V G4
bulbs normally only come as either 10 or 20 watts, except for some "Eco"
bulbs which are 14W or so.

If you're still unsure, then dig out the manual....

cooker hood was already in house so never had a manual, however have
managed to locate on line and the max wattage is 20W so thats prob whats
in already.

On 29.12.2012 18:59, Hugh - in either England or Spain wrote:
On 29/12/2012 17:39, A.Lee wrote:
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for
the downlighters in the cooker hood. I purchased 20 watt but the
old ones have no markings on them and look just as bright. Is
there a way to measure the wattage of the old ones as I would
replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a
rough idea of the wattage. Most cheap multimeters would not be
particularly accurate at the level you are measuring, hence you
will only get an approximate reading, unless you have a 'better'
multimeter.

If they are the same as normal incandescent bulbs the resistance will
show as almost nil unless the bulb is running.

The only way I can think of is to have an ammeter in series when they
are running. Wattage will be volts multiplied by amps so 20 watts at
12 volts will be about 1.67 amps. Be careful. The start up current
when the bulb is first turned on will be a great deal higher.

It is true that the start up current is higher. I do not think that is
a problem. If it was, you could just measure over a longer period.

I have this energy-meter:
http://everflourish-europe.eu/app/do.../EMT707CTL.pdf

Here it is recommended by an expert:
https://ntmm.org/~nt/elecpow/appliance_power/
Power consumption of some domestic applicances

Following on from the more detailed measurements of input current to
some computing equipment and low-energy lamps, I felt like having a
better idea of how much is wasted by several always-on appliances, as
well as some `which should I use' loads such as microwave and
conventional ovens.

Measurement by an oscilloscope, with current and voltage probes, is
time-consuming compared to a simple plug-in power meter, although the
simple meter gives no detail of the harmonic spectrum. Such a meter
was used for the following measurements: its details are
`Everflourish EMT707CTL ref:36.2897', and it has been tested against
an oscilloscope measurement, from which it was found to calculate P
and Q correctly, which is not always so for such meters (see the
meters test in the it_power page).

Much of the remainder is in plain text form, as I keep such notes in
this way and don't see much advantage to spending time making an html
table.

Here you see energy measuring by an expert:
http://www.youtube.com/watch?v=UR8wRSp2IXs
--
jo
"Anti-intellectualism has been a constant thread winding its
way through our political and cultural life, nurtured by the
false notion that democracy means that 'my ignorance is just
as good as your knowledge.'" -- Isaac Asimov

On 29/12/2012 20:03, Jo Stein wrote:


The only way I can think of is to have an ammeter in series when they
are running. Wattage will be volts multiplied by amps so 20 watts at
12 volts will be about 1.67 amps. Be careful. The start up current
when the bulb is first turned on will be a great deal higher.

It is true that the start up current is higher. I do not think that is
a problem. If it was, you could just measure over a longer period.



The problem is that the start up current might well blow the protection
fuse in the meter

On 29/12/2012 20:13, newshound wrote:
On 29/12/2012 20:03, Jo Stein wrote:


The only way I can think of is to have an ammeter in series when they
are running. Wattage will be volts multiplied by amps so 20 watts at
12 volts will be about 1.67 amps. Be careful. The start up current
when the bulb is first turned on will be a great deal higher.

It is true that the start up current is higher. I do not think that is
a problem. If it was, you could just measure over a longer period.



The problem is that the start up current might well blow the protection
fuse in the meter

..... or blow up the meter - which is why I mentioned it.

charles wrote:

In article ,
A.Lee wrote:
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.
Most cheap multimeters would not be particularly accurate at the level
you are measuring, hence you will only get an approximate reading,
unless you have a 'better' multimeter.

that will only measure the cold resistance. The lamp wattage is based on
the hot resistance.

Yes, good point, but measurement still stands as an easy way to find
out, measure the 2 different lamps, and it can clearly be seen if they
are the same wattage.
--
To reply by e-mail, change the ' + ' to 'plus'.

On 29/12/2012 20:22, Hugh - in either England or Spain wrote:
On 29/12/2012 20:13, newshound wrote:
On 29/12/2012 20:03, Jo Stein wrote:


The only way I can think of is to have an ammeter in series when they
are running. Wattage will be volts multiplied by amps so 20 watts at
12 volts will be about 1.67 amps. Be careful. The start up current
when the bulb is first turned on will be a great deal higher.

It is true that the start up current is higher. I do not think that is
a problem. If it was, you could just measure over a longer period.



The problem is that the start up current might well blow the protection
fuse in the meter

.... or blow up the meter - which is why I mentioned it.

Would it not be possible to make a cable with a parallel bypass switch
which is then opened once the bulb is operating, thus avoiding the
higher switch-on current through the ammeter?

Part Timer was thinking very hard :
Would it not be possible to make a cable with a parallel bypass switch which
is then opened once the bulb is operating, thus avoiding the higher switch-on
current through the ammeter?

Possible, but it would need to be a make before break - because the
lamp would cool down during the switch over.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

In message , A.Lee
writes
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.
Most cheap multimeters would not be particularly accurate at the level
you are measuring, hence you will only get an approximate reading,
unless you have a 'better' multimeter.

Pretty useless doing it on a cold filament


--
geoff

In message om,
newshound writes
On 29/12/2012 20:03, Jo Stein wrote:


The only way I can think of is to have an ammeter in series when they
are running. Wattage will be volts multiplied by amps so 20 watts at
12 volts will be about 1.67 amps. Be careful. The start up current
when the bulb is first turned on will be a great deal higher.

It is true that the start up current is higher. I do not think that is
a problem. If it was, you could just measure over a longer period.



The problem is that the start up current might well blow the protection
fuse in the meter

Simples - you short the meter out on startup

--
geoff

On 29/12/2012 21:26, Harry Bloomfield wrote:
Part Timer was thinking very hard :
Would it not be possible to make a cable with a parallel bypass switch
which is then opened once the bulb is operating, thus avoiding the
higher switch-on current through the ammeter?

Possible, but it would need to be a make before break - because the lamp
would cool down during the switch over.

2 parallel live or neutral cables to one terminal of bulb, other
polarity to other side of bulb.

switches in both cables, one with meter in series.

open switch on cable with meter and close other switch before connecting
power.

Connect power and when bulb lights first close switch in series with
meter and then open other one.

Take meter reading in amps and turn it all off.

Multiply amps by 12volts.

Seems a lot of trouble!

In message , A.Lee
writes
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.
Most cheap multimeters would not be particularly accurate at the level
you are measuring, hence you will only get an approximate reading,
unless you have a 'better' multimeter.

On the contrary, my cheap multimeters are (surprisingly) every bit as
accurate as my relative expensive Flukes. However, as others have
pointed out, measuring the cold resistance of a filament gives little
indication of its hot resistance. You are much better off measuring the
working AC current, and use 'watts = voltage x current'.
--
Ian

But surely the cold resistance is not going to be the same as when they are
on?
Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"A.Lee" wrote in message
...
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.
Most cheap multimeters would not be particularly accurate at the level
you are measuring, hence you will only get an approximate reading,
unless you have a 'better' multimeter.
--
To reply by e-mail, change the ' + ' to 'plus'.

On Sat, 29 Dec 2012 22:40:39 +0000, geoff wrote:

In message om,
newshound writes
On 29/12/2012 20:03, Jo Stein wrote:


The only way I can think of is to have an ammeter in series when they
are running. Wattage will be volts multiplied by amps so 20 watts at
12 volts will be about 1.67 amps. Be careful. The start up current
when the bulb is first turned on will be a great deal higher.

It is true that the start up current is higher. I do not think that is
a problem. If it was, you could just measure over a longer period.



The problem is that the start up current might well blow the protection
fuse in the meter

Simples - you short the meter out on startup

Exactly. A switch across the meter. Make sure the switch is "on"
before you power up your test rig, and when the lamp glows you turn
the switch "off" so that the lamp current flows through the meter.
Hopefully your meter has something like a 10A AC range.

--
Frank Erskine

Are these bulbs working on AC or DC?
Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Hugh - in either England or Spain" wrote in message
...
On 29/12/2012 17:39, A.Lee wrote:
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Measure the resistance of the filament, then use Ohms law to get a rough
idea of the wattage.
Most cheap multimeters would not be particularly accurate at the level
you are measuring, hence you will only get an approximate reading,
unless you have a 'better' multimeter.

If they are the same as normal incandescent bulbs the resistance will show
as almost nil unless the bulb is running.

The only way I can think of is to have an ammeter in series when they are
running. Wattage will be volts multiplied by amps so 20 watts at 12 volts
will be about 1.67 amps.
Be careful. The start up current when the bulb is first turned on will be
a great deal higher.

Besides, if the bulbs will be getting hotter if they are higher wattage then
so will the transformer, and the fittings so it might not be safe to exceed
what is there to start with. Of course you could redesign the innards to use
leds or something.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Hugh - in either England or Spain" wrote in message
...
On 29/12/2012 21:26, Harry Bloomfield wrote:
Part Timer was thinking very hard :
Would it not be possible to make a cable with a parallel bypass switch
which is then opened once the bulb is operating, thus avoiding the
higher switch-on current through the ammeter?

Possible, but it would need to be a make before break - because the lamp
would cool down during the switch over.

2 parallel live or neutral cables to one terminal of bulb, other polarity
to other side of bulb.

switches in both cables, one with meter in series.

open switch on cable with meter and close other switch before connecting
power.

Connect power and when bulb lights first close switch in series with meter
and then open other one.

Take meter reading in amps and turn it all off.

Multiply amps by 12volts.

Seems a lot of trouble!

In article ,
Ian Jackson wrote:
On the contrary, my cheap multimeters are (surprisingly) every bit as
accurate as my relative expensive Flukes.

At very low resistance - 0.something of an ohm?

--
*How come you never hear about gruntled employees? *

Dave Plowman London SW
To e-mail, change noise into sound.

On Sat, 29 Dec 2012 21:26:00 GMT, Harry Bloomfield wrote:

Would it not be possible to make a cable with a parallel bypass switch
which is then opened once the bulb is operating, thus avoiding the
higher switch-on current through the ammeter?

Possible, but it would need to be a make before break - because the
lamp would cool down during the switch over.

What switch over? The switch is a dead short across the meter. As near as
damn it all the on surge current will pass through the switch. You then
open this switch making all the steady state current flow through the
meter. Think of the switch as a socking great big shunt.

--
Cheers
Dave.

On Saturday, December 29, 2012 7:53:17 PM UTC, ss wrote:
On 29/12/2012 18:13, John Williamson wrote:
ss wrote:

I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones

managed to locate on line and the max wattage is 20W so thats prob whats
in already.

The easiest way is to resistance test new and old lamps and compare. If you want more info, cold resistance is somewhere in the region of a tenth hot resistance.


NT

On Sat, 29 Dec 2012 17:36:24 +0000, ss wrote:

I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones
as I would replace them if a higher wattage. I have a multi meter.

You don't need to measure the actual wattage, just the relative wattage.
The cold resistance will do for this, if the new and old are more or less
the same (within a few ohms) then they are the same wattage.

Just measured a selection of 60 W GLS bulbs they are about 60 Ohms cold,
various forms of 40 W ordinary tugnsten filament bulbs have a cold
resistance of around 110 Ohms. Don't have any halogen bulbs to measure
but I seen no reason why the basic principle of the above should change.

--
Cheers
Dave.

ss wrote:
I recenently purchased G4 halogen bulbs (2 pin,12 volt,small) for the
downlighters in the cooker hood.
I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones as
I would replace them if a higher wattage. I have a multi meter.

Look at the transformer wattage or current and use the same or similar
total for the lamps.
don't use lesser rated lamps than the transformer rating if it has a
copper transformer as the voltage goes up and lamp life reduces.

On Sunday, December 30, 2012 12:46:35 AM UTC, Dave Liquorice wrote:
On Sat, 29 Dec 2012 17:36:24 +0000, ss wrote:

I purchased 20 watt but the old ones have no markings on them and look
just as bright. Is there a way to measure the wattage of the old ones
as I would replace them if a higher wattage. I have a multi meter.

You don't need to measure the actual wattage, just the relative wattage.
The cold resistance will do for this, if the new and old are more or less
the same (within a few ohms) then they are the same wattage.
Just measured a selection of 60 W GLS bulbs they are about 60 Ohms cold,
various forms of 40 W ordinary tugnsten filament bulbs have a cold
resistance of around 110 Ohms. Don't have any halogen bulbs to measure
but I seen no reason why the basic principle of the above should change.

A huge 16:1 resistance ratio.


NT

In article o.uk,
Dave Liquorice wrote:
You don't need to measure the actual wattage, just the relative wattage.
The cold resistance will do for this, if the new and old are more or
less the same (within a few ohms) then they are the same wattage.

A 20 watt 12 volt halogen is something like 0.5 ohm cold. ;-)

--
*Some people are alive only because it's illegal to kill them *

Dave Plowman London SW
To e-mail, change noise into sound.

In message , "Dave Plowman (News)"
writes
In article ,
Ian Jackson wrote:
On the contrary, my cheap multimeters are (surprisingly) every bit as
accurate as my relative expensive Flukes.

At very low resistance - 0.something of an ohm?

I'll check next time I come across my cheap meter.
--
Ian

On Sun, 30 Dec 2012 10:03:46 +0000 (GMT), Dave Plowman (News) wrote:

The cold resistance will do for this, if the new and old are more or
less the same (within a few ohms) then they are the same wattage.

A 20 watt 12 volt halogen is something like 0.5 ohm cold. ;-)

And a 50 W one is? 0.2 ohm. My cheapo "sold as faulty" meter can measure
well enough for that. One does have to make sure you have good
connections between probes and object though.

--
Cheers
Dave.

On 30/12/2012 11:49, Dave Liquorice wrote:
On Sun, 30 Dec 2012 10:03:46 +0000 (GMT), Dave Plowman (News) wrote:

The cold resistance will do for this, if the new and old are more or
less the same (within a few ohms) then they are the same wattage.

A 20 watt 12 volt halogen is something like 0.5 ohm cold. ;-)

And a 50 W one is? 0.2 ohm. My cheapo "sold as faulty" meter can measure
well enough for that. One does have to make sure you have good
connections between probes and object though.

Thanks I will check them out tomorrow.