Author Topic: Homemade MH fitting  (Read 1524 times)
sol
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Homemade MH fitting « on: July 25, 2013, 06:40:55 PM » Author: sol
I just ordered a Philips CDM 35 watt with a G8.5 base from eBay. It is colour 942. I still have to find a ballast and a socket. I indend to build my own (small) fixture for this. I have, however, several questions pertaining to safety before starting.

Since this lamp is unprotected, it needs to be fully enclosed in a fixture. Are there any types of glass that should be avoided, that would not withstand the heat of a ruptured arc tube ? I was thinking maybe getting a standard outdoor fixture for a 100 watt incandescent and changing the socket and mounting the ballast nearby. Would an ordinary clear Pyrex dish work as well ? Or maybe a glass jar for preserving food (Mason jar) ?

If any of you have design suggestions, please let me know ; I haven't even decided if it will be an uplighter or a downlighter, nor have I decided where to install it, but it will definitely be indoors.

Thanks a lot.
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Medved
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Re: Homemade MH fitting « Reply #1 on: July 28, 2013, 05:28:11 AM » Author: Medved
The explosion already loose it's energy when smashing the bulb outer, so there is really nothing much left in it. Moreover the CMH arctube is quite small and relatively mechanically weak, so it can not build up too high predssure, so the energy is really limited.
The main danger is the "shower" of o hot quartz. So the temperature robustness of the all inner materials is more important.
And be careful about ventilation and other holes, as these could be a ways for the hot quartz to escape the fixture.
I would guess fully tightly enclosed (for wet locations,...) ~100W rated incandescent fixture would do a good job.
The jar would be mechanically very good, but it's optical properties and appearance would be questionable.
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sol
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Re: Homemade MH fitting « Reply #2 on: July 28, 2013, 08:14:23 AM » Author: sol
Thanks for the info. The enclosed fitting I am considering at the moment is a vapour-proof one like this 150 watt one and would be installed base down, with a metal shade wrapped around it (much like a standard cloth lamp shade, only in metal) to prevent glare in the room. It will probably be a floor lamp with an electronic ballast. My only concern would be the heat emitted from the lamp hitting the glass but with 35 watt lamps, I guess it is not much of an issue.
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Ash
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Re: Homemade MH fitting « Reply #3 on: July 28, 2013, 02:04:31 PM » Author: Ash
If this thing is really made of glass it on't hae any problem with >100w lamps. It will however get hot inside so only use ceramic terminal blocks, glass fiber isolated wires etc
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sol
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Re: Homemade MH fitting « Reply #4 on: July 28, 2013, 07:37:10 PM » Author: sol
This is the socket I ordered from eBay. By looking at the detailed pictures, the wires seem to be silicone rubber insulation rated at 180 C. The description says it is ceramic and can be used with metal halide among other types of lamps, but there is no mention of pulse rating although it is rated for 2A at 750 volts. I am not sure how I will go about remote mounting the ballast as far as wiring goes, if I need to find pulse rated wire or not. The remote mounting distance should be no greater than 1.5 metres.

The proposed fixture is indeed glass, so I wouldn't anticipate any problems with that. It should be able to handle the heat even if mounted base down. The 35 watt MH will throw less heat than a 100 watt would, or than a 150 watt incandescent would, for that matter.
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Re: Homemade MH fitting « Reply #5 on: August 14, 2013, 03:34:44 AM » Author: Medved
The heat could be quite similar to the 100W incandescent, do not expect it to be less. The reason is, the incandescent emit majority of the "heat" not as real heat, but quite short wave infrared radiation (so very close to the visible spectrum), whatthe lantern bowl pass through, so this energy does not heat up the lanterns internal.
The 35W MH operate at way lower temperatures, so the majority of the heat energy is in the longer wave IR (farther away from the visible), where the glass bowl tend to keep that inside, so way larger portion of it stay inside the bowl and heat up the inisde of the lantern.
So bottom line the amount of heat trapped inside the fixture could be the similar ~25W for both 100..150W incandescent, as well as 39W MH.
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sol
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Re: Homemade MH fitting « Reply #6 on: March 18, 2017, 07:37:19 PM » Author: sol
OK, reviving an old thread here. I have finally made a lamp sort of like this description. It uses a vapour proof glass fixture that is mounted base down and fitted with a 35W CDM-T lamp. When running for a while, the top part of the glass gets to about 65C (~150F). I have been running it as a test for a few days at home, and no problems so far. I was wondering if it is too hot for a glass globe like that. The fixture is rated for 150W incandescent, and the instructions recommend base up (but does not really forbid base down). It is just the top part of the glass that gets that hot, the bottom (threaded part) gets only slightly warm.

Your thoughts on the temperature measurement are most welcome and greatly appreciated.
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Re: Homemade MH fitting « Reply #7 on: March 18, 2017, 09:53:08 PM » Author: Solanaceae
I wouldn't sweat it, really. Of the four vapor proof fixtures i have (one is HPS, three are designed for merc), both the 75 watt mv ones read similar temps to you and the 250w one registered higher temps (around 180 at the reflector, but it's a screw in NEMA type lens whose mounting is with the metal, not the glass itself) and the 35w HPS is about the same or cooler. You should be in the clear.
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Re: Homemade MH fitting « Reply #8 on: March 18, 2017, 11:11:26 PM » Author: Lodge
Sol, have you found a ballast yet for that light ? if not PM me I have an Advance 71A5005 ballast complete with igniter and cap that will run a 35/39 watt MH (ANSI code M-130)Order suffix 500D, no bracket, dry film Cap and igniter) if you pick up the postage (I keep it simple, what ever Canada post dings me,I will ding you, guessing about $20 CDN assuming your in Canada or if your close to Edmonton you can pick it up in person) you can have the ballast for my cost free, But I'll attach only one condition to this offer, you post your project up on the site so we can all see it when complete, but I think that's a given...  

This is the spec sheet of the ballast:> https://a89b8e4143ca50438f09-7c1706ba3fabeeda794725d88e4f5e57.ssl.cf2.rackcdn.com/spec_sheets/files/000/000/753/original/advance-71a5005500dp-specs.pdf?1440167502
« Last Edit: March 18, 2017, 11:14:53 PM by Lodge » Logged
sol
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Re: Homemade MH fitting « Reply #9 on: March 19, 2017, 12:36:52 PM » Author: sol
Thanks for the offer, Lodge. I have found some ballasts although a magnetic one sounds attractive... The design I made doesn't allow for one (size issue). When time permits, I'll post a picture.

So since my last post, I thought about this for a while. I then wired up a temporary incandescent lamp holder and put the glass globe over a 100 watt lamp (the maximum allowed on the label is 150W). I measured the temperature and got a reading of about 75C (~167F) whereas with the MH, the temperature stabilizes at about 65C (~150F). I'll stop worrying about it.

I'm not done designing and making small MH fixtures. I can't wait to start another project, which will involve a CDM-Tm of 20 watts. I'm waiting for a PGJ5 lamp holder from eBay and then I'll find a ballast and all that jazz.
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