Can anyone provide guidance on how large a timer I need for a 400W
metal halide grow lamp? The vendor suggested a 15 amp grounded
outlet, the stated he likes 20 amps ones. However, I recently ran
across some nice, grounded 10 amp, outdoor timers ( Intermatic . On
the side they list capcaity as 1200 amps R Resistive or 1200 amps
Tungsten. I know that Metal halides are different, but do I really
need a 15 amp timer or will these 10 amp ones work?

Thanks
Mike

Mike wrote:
Can anyone provide guidance on how large a timer I need for a 400W
metal halide grow lamp? The vendor suggested a 15 amp grounded
outlet, the stated he likes 20 amps ones. However, I recently ran
across some nice, grounded 10 amp, outdoor timers ( Intermatic . On
the side they list capcaity as 1200 amps R Resistive or 1200 amps
Tungsten. I know that Metal halides are different, but do I really
need a 15 amp timer or will these 10 amp ones work?

Thanks
Mike


I use the cheap ungrounded ones; they last a year or two before the
contacts burn out -- just like the expensive heavy duty grounded ones. I
haven't tried the electronic timers, like what I have a bunch of
fluorescents plugged into, but they should work too.

Bob

Mike,

I use an Intermatic heavy duty grounded timer for two 430 watt lights and
another maybe 160watts of power. I'm guessing it cost maybe $10 or $12. I
think it's rated for 1600 watts.

Bought it years ago (maybe 5 or 6) at Menards, a home improvement chain in
our area (MN-WI).

The timer is not in my growing area so is not subject to constant humidity.

It is plugged into a GFI protected 20 amp outlet.

I'd vote for the 15 amp timer.

You probably dropped a couple hundred plus for the light, I wouldn't skimp
on the timer, though maybe I did?

Bob


"Mike" wrote in message
m...
Can anyone provide guidance on how large a timer I need for a 400W
metal halide grow lamp? The vendor suggested a 15 amp grounded
outlet, the stated he likes 20 amps ones. However, I recently ran
across some nice, grounded 10 amp, outdoor timers ( Intermatic . On
the side they list capcaity as 1200 amps R Resistive or 1200 amps
Tungsten. I know that Metal halides are different, but do I really
need a 15 amp timer or will these 10 amp ones work?

Thanks
Mike

Mike,

I use an Intermatic heavy duty grounded timer for two 430 watt lights and
another maybe 160watts of power. I'm guessing it cost maybe $10 or $12. I
think it's rated for 1600 watts.

Bought it years ago (maybe 5 or 6) at Menards, a home improvement chain in
our area (MN-WI).

The timer is not in my growing area so is not subject to constant humidity.

It is plugged into a GFI protected 20 amp outlet.

I'd vote for the 15 amp timer.

You probably dropped a couple hundred plus for the light, I wouldn't skimp
on the timer, though maybe I did?

Bob


"Mike" wrote in message
m...
Can anyone provide guidance on how large a timer I need for a 400W
metal halide grow lamp? The vendor suggested a 15 amp grounded
outlet, the stated he likes 20 amps ones. However, I recently ran
across some nice, grounded 10 amp, outdoor timers ( Intermatic . On
the side they list capcaity as 1200 amps R Resistive or 1200 amps
Tungsten. I know that Metal halides are different, but do I really
need a 15 amp timer or will these 10 amp ones work?

Thanks
Mike

Mike,

I use an Intermatic heavy duty grounded timer for two 430 watt lights and
another maybe 160watts of power. I'm guessing it cost maybe $10 or $12. I
think it's rated for 1600 watts.

Bought it years ago (maybe 5 or 6) at Menards, a home improvement chain in
our area (MN-WI).

The timer is not in my growing area so is not subject to constant humidity.

It is plugged into a GFI protected 20 amp outlet.

I'd vote for the 15 amp timer.

You probably dropped a couple hundred plus for the light, I wouldn't skimp
on the timer, though maybe I did?

Bob


"Mike" wrote in message
m...
Can anyone provide guidance on how large a timer I need for a 400W
metal halide grow lamp? The vendor suggested a 15 amp grounded
outlet, the stated he likes 20 amps ones. However, I recently ran
across some nice, grounded 10 amp, outdoor timers ( Intermatic . On
the side they list capcaity as 1200 amps R Resistive or 1200 amps
Tungsten. I know that Metal halides are different, but do I really
need a 15 amp timer or will these 10 amp ones work?

Thanks
Mike

Mike,

I use an Intermatic heavy duty grounded timer for two 430 watt lights and
another maybe 160watts of power. I'm guessing it cost maybe $10 or $12. I
think it's rated for 1600 watts.

Bought it years ago (maybe 5 or 6) at Menards, a home improvement chain in
our area (MN-WI).

The timer is not in my growing area so is not subject to constant humidity.

It is plugged into a GFI protected 20 amp outlet.

I'd vote for the 15 amp timer.

You probably dropped a couple hundred plus for the light, I wouldn't skimp
on the timer, though maybe I did?

Bob


"Mike" wrote in message
m...
Can anyone provide guidance on how large a timer I need for a 400W
metal halide grow lamp? The vendor suggested a 15 amp grounded
outlet, the stated he likes 20 amps ones. However, I recently ran
across some nice, grounded 10 amp, outdoor timers ( Intermatic . On
the side they list capcaity as 1200 amps R Resistive or 1200 amps
Tungsten. I know that Metal halides are different, but do I really
need a 15 amp timer or will these 10 amp ones work?

Thanks
Mike

(I also don't know what they mean
by '1200 amps R Resistive or 1200 amps Tungsten', but you are nut if you
think you're going to put 1200A into anything safe.}

Mike meant to type "Watts" rather than "Amps".

The "Resistive" rating refers to a constant resistive load. The
"Tungsten" rating refers to a (tungsten filament) incandescent lamp load.

Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

(I also don't know what they mean
by '1200 amps R Resistive or 1200 amps Tungsten', but you are nut if you
think you're going to put 1200A into anything safe.}

Mike meant to type "Watts" rather than "Amps".

The "Resistive" rating refers to a constant resistive load. The
"Tungsten" rating refers to a (tungsten filament) incandescent lamp load.

Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

(I also don't know what they mean
by '1200 amps R Resistive or 1200 amps Tungsten', but you are nut if you
think you're going to put 1200A into anything safe.}

Mike meant to type "Watts" rather than "Amps".

The "Resistive" rating refers to a constant resistive load. The
"Tungsten" rating refers to a (tungsten filament) incandescent lamp load.

Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

Actually that is bass ackwards
Tungsten filaments have a negative temperature coefficient.
Temperature rises conductivity decreases.
Back when semiconductors were young a lamp was often used to help
prevent thermal runaway in amplifier circuits by placing them in
series with the transistor.

In any case most lamp timers should be able to handle a 400w metal
halide set.
Just make sure it is a grounded timer ( 3 prong)
Better still would be a grounded timer on a GFCI protected circuit.

Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

Actually that is bass ackwards
Tungsten filaments have a negative temperature coefficient.
Temperature rises conductivity decreases.
Back when semiconductors were young a lamp was often used to help
prevent thermal runaway in amplifier circuits by placing them in
series with the transistor.

In any case most lamp timers should be able to handle a 400w metal
halide set.
Just make sure it is a grounded timer ( 3 prong)
Better still would be a grounded timer on a GFCI protected circuit.

Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

Actually that is bass ackwards
Tungsten filaments have a negative temperature coefficient.
Temperature rises conductivity decreases.
Back when semiconductors were young a lamp was often used to help
prevent thermal runaway in amplifier circuits by placing them in
series with the transistor.

In any case most lamp timers should be able to handle a 400w metal
halide set.
Just make sure it is a grounded timer ( 3 prong)
Better still would be a grounded timer on a GFCI protected circuit.

Beecrofter wrote:


Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

Actually that is bass ackwards
Tungsten filaments have a negative temperature coefficient.
Temperature rises conductivity decreases.


You're both right but you're talking about different things. The
resistivity temperature coefficient is positive, which makes the
conductivity temperature coefficient negative. At any rate, the inrush
current through a tungsten filament is much higher than the operating
current.

Beecrofter wrote:


Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

Actually that is bass ackwards
Tungsten filaments have a negative temperature coefficient.
Temperature rises conductivity decreases.


You're both right but you're talking about different things. The
resistivity temperature coefficient is positive, which makes the
conductivity temperature coefficient negative. At any rate, the inrush
current through a tungsten filament is much higher than the operating
current.

Beecrofter wrote:


Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

Actually that is bass ackwards
Tungsten filaments have a negative temperature coefficient.
Temperature rises conductivity decreases.


You're both right but you're talking about different things. The
resistivity temperature coefficient is positive, which makes the
conductivity temperature coefficient negative. At any rate, the inrush
current through a tungsten filament is much higher than the operating
current.