Debug MH light hood?

I've got a metal halide lighting hood over my reef aquarium. One central
250W MH bulb, and two adjacent PC actinics. Two separate power cords: one
for the PC bulbs + fan, and one for the MH bulb. The MH power cord goes to
a ballast, which says that it is 400W/120V/4A.

One day recently my MH bulb would no longer turn on. Sometimes it takes
(the ballast?) a few minutes to "power up" after I turn the switch on.
This time, I had to turn it on and off a few times before it would light up.
Then everything was fine for a week. And then suddenly it wouldn't turn on
again at all.

I figured the MH bulb must have burned out (although I don't know how to
verify this). It was about 9 months old. So I bought a new 250W bulb.

Sadly, it still won't turn on, with either bulb. A voltmeter seems to suggest
that the MH housing in the hood is still getting power. If I'm reading it
correctly, it's registering about 270 volts where I screw in the MH bulb, when
I turn on the ballast.

Any ideas what to do next? Do lighting hoods, or ballasts, wear out?
Is there some other test or repair I could try? I'd hate to have to buy a
whole new lighting hood...

-- Don
__________________________________________________ _____________________________
Don Geddis http://reef.geddis.org/
If we ever discover a race of alien beings on another planet, I bet it would be
surprising just how many of them are missing part or all of a tentacle.
-- Deep Thoughts, by Jack Handey [1999]

The ballast system in a MH fixture is a two part device. A
transformer/ballast the raises the voltage to the operating voltage of the
bulb. And an Igniter that produces a high voltage surge to start the arc
inside the bulb. Either part failing can cause the lamp to not light.

For all you who thrive on information overload check this out:
http://ceenews.com/ar/electric_long_...hite/index.htm

Have Fun
JOhn :-)

"Don Geddis" wrote in message
...
I've got a metal halide lighting hood over my reef aquarium. One central
250W MH bulb, and two adjacent PC actinics. Two separate power cords: one
for the PC bulbs + fan, and one for the MH bulb. The MH power cord goes
to
a ballast, which says that it is 400W/120V/4A.

One day recently my MH bulb would no longer turn on. Sometimes it takes
(the ballast?) a few minutes to "power up" after I turn the switch on.
This time, I had to turn it on and off a few times before it would light
up.
Then everything was fine for a week. And then suddenly it wouldn't turn
on
again at all.

I figured the MH bulb must have burned out (although I don't know how to
verify this). It was about 9 months old. So I bought a new 250W bulb.

Sadly, it still won't turn on, with either bulb. A voltmeter seems to
suggest
that the MH housing in the hood is still getting power. If I'm reading it
correctly, it's registering about 270 volts where I screw in the MH bulb,
when
I turn on the ballast.

Any ideas what to do next? Do lighting hoods, or ballasts, wear out?
Is there some other test or repair I could try? I'd hate to have to buy a
whole new lighting hood...

-- Don

__________________________________________________ __________________________
___
Don Geddis
http://reef.geddis.org/
If we ever discover a race of alien beings on another planet, I bet it
would be
surprising just how many of them are missing part or all of a tentacle.
-- Deep Thoughts, by Jack Handey [1999]

Don, unlike other lights, MH don't come right on. They take about 15 minutes to
fully brighten, and if you turn them on and off, it causes a delay in this process
as the bulb cools down again for a restart. (YMMV, that is merely my observation.)

I'd take your bulbs to the LFS and have them test them for you. Odds are this is a
ballast issue. IF you bought it new, the vendor should offer a warranty on that
ballast. Some will even drop ship you the new one, and you send back the broken
one in that box.

You need to make a few phone calls, and get some help quickly so your corals won't
suffer.

Marc


Don Geddis wrote:

I've got a metal halide lighting hood over my reef aquarium. One central
250W MH bulb, and two adjacent PC actinics. Two separate power cords: one
for the PC bulbs + fan, and one for the MH bulb. The MH power cord goes to
a ballast, which says that it is 400W/120V/4A.

One day recently my MH bulb would no longer turn on. Sometimes it takes
(the ballast?) a few minutes to "power up" after I turn the switch on.
This time, I had to turn it on and off a few times before it would light up.
Then everything was fine for a week. And then suddenly it wouldn't turn on
again at all.

I figured the MH bulb must have burned out (although I don't know how to
verify this). It was about 9 months old. So I bought a new 250W bulb.

Sadly, it still won't turn on, with either bulb. A voltmeter seems to suggest
that the MH housing in the hood is still getting power. If I'm reading it
correctly, it's registering about 270 volts where I screw in the MH bulb, when
I turn on the ballast.

Any ideas what to do next? Do lighting hoods, or ballasts, wear out?
Is there some other test or repair I could try? I'd hate to have to buy a
whole new lighting hood...

-- Don
__________________________________________________ _____________________________
Don Geddis http://reef.geddis.org/
If we ever discover a race of alien beings on another planet, I bet it would be
surprising just how many of them are missing part or all of a tentacle.
-- Deep Thoughts, by Jack Handey [1999]

--
Personal Page: http://www.sparklingfloorservice.com/oanda/index.html
Business Page: http://www.sparklingfloorservice.com
Marine Hobbyist: http://www.melevsreef.com

Don, unlike other lights, MH don't come right on. They take about 15 minutes to
fully brighten, and if you turn them on and off, it causes a delay in this process
as the bulb cools down again for a restart. (YMMV, that is merely my observation.)

FYI

thats bulb/ballast dependant

--
Richard Reynolds

snip
The MH power cord goes to
a ballast, which says that it is 400W/120V/4A

snip

It was about 9 months old. So I bought a new 250W bulb.


Sounds to me like you are trying to fire a 250 watt lamp with a 400 watt
ballast.. Maybe you can try a 400 watt lamp.