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?

Years ago, when I had the money to spend on things like this, I had two
400-watt halides over a large sal****er aquarium (the corals LOVED it). I
don't recall the brand, but I bought a timer that was designed for
high-draw inductive loads. A couple of years later, I sold off the
aquarium, and the timer was still working just fine.

steve

(Mike) writes:
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

Tungsten lamps are mostly resistive.

A MH light is an inductive load because of the transformer, which is a
hassle. The transformer will give you power surges, which will in turn
provide nice sparks in a mechanical relay or wear and tear on the
oxide layers in a solid-state relay. In time, things will die,
hopefully not in a spectacular way.

The more expensive the timer is, the better the insides will be
protected from these kinds of surges. A higher power rating means more
robust parts, which will take more abuse before the part dies.

I use a mechanical 2500W digital timer. It is mounted on a tile wall
so it can go bang as loud as it wants without burning the house
down. It has lasted 18 months or so now, and it cost me about $20. I
am on 240V, so the parts only need to cope with half the current that
a 2500W part would need to handle in your part of the world. It
controls about 500W of miscellaneous lights.

YMMV.

Geir

(Mike) writes:
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

Tungsten lamps are mostly resistive.

A MH light is an inductive load because of the transformer, which is a
hassle. The transformer will give you power surges, which will in turn
provide nice sparks in a mechanical relay or wear and tear on the
oxide layers in a solid-state relay. In time, things will die,
hopefully not in a spectacular way.

The more expensive the timer is, the better the insides will be
protected from these kinds of surges. A higher power rating means more
robust parts, which will take more abuse before the part dies.

I use a mechanical 2500W digital timer. It is mounted on a tile wall
so it can go bang as loud as it wants without burning the house
down. It has lasted 18 months or so now, and it cost me about $20. I
am on 240V, so the parts only need to cope with half the current that
a 2500W part would need to handle in your part of the world. It
controls about 500W of miscellaneous lights.

YMMV.

Geir

I've used just a simple 2-prong lamp timer. I'm not recommending it,
just telling you what I did. Worked great. Your mileage may vary.


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

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 believe the label will say 1200 watts, not 1200 amps. In that case
you should be fine.

Power (wattage) = Amps * Volts

Your 400 watt lamp will draw about 3.3 amps at 120 volts, or 1.6 amps
at 240 volts.

Make sure you have enough ventilation. A small fan will help.

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 believe the label will say 1200 watts, not 1200 amps. In that case
you should be fine.

Power (wattage) = Amps * Volts

Your 400 watt lamp will draw about 3.3 amps at 120 volts, or 1.6 amps
at 240 volts.

Make sure you have enough ventilation. A small fan will help.

(Mike) writes in article dated 14 Mar 2004 11:43:40 -0800:
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?

(I think you mean 1200 Watts, not amps.)

The "right" answer to your question should be stamped on the fixture
somewhere, or on the ballast if the components were manufactured separately.

Metal halides are not a purely resistive load because of the inductors in
the ballast, but even if you double the 3.3A current required to sustain
400W it's less than 10A.

-- spud_demon -at- thundermaker.net
The above may not (yet) represent the opinions of my employer.

(Mike) wrote in
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

A 10 amp timer will work for a while but it isn't designed for an
inductive load like a ballast which is basicly a transformer. Every time
the timer switches off the ballast acts something like the spark coil in
you car causing an arc across the contacts which eventually distroys them.
A 20 amp plug in timer will last longer but 95% of plug in timers aren't
designed for incuctive loads.
I couldn't find a web sight that had a good picture of what you shuld use
but I found one on ebay. note this is a dual voltage unit and you'll only
need a single 115/120 volt unit.

I've run my fluoresent lights (36-40 watt tubes or 1440 watts) for over ten
years with no problems.


http://cgi.ebay.com/ws/eBayISAPI.dll...ategory=42 89
7

Hope this helps
dusty

How about a plug-in heavy duty timer designed for air conditioners?

Thanks to everyone for all of the feedback.
In short, my take is- Cheap will be O?K for a while- Could be a short
while and could be a bad outcome when it goes. Spend more get the
better timer.

Thanks again.