Hello to all,

The local surplus & salvage store recently came into a huge lot of NOS GE lighting stuff. Among it are 175 watt mercury vapor lamps. I've never owned any MV stuff, so I'm currently entertaining the thought of picking one up. Of course, I don't own a ballast, so I'm wondering if 120 volts is adequate for a 175 watt MV lamp, using an incandescent lamp as a ballast? I would assume so because I've seen self ballasted MV lamps of up to 1000 watts that run on 120 volts, but I've also read that 175 watt lamps require upwards of 330 volts to strike, so I'm kind of at a loss. Or do self-ballasted lamps have an ignitor built into them?

Thanks,
Trent

If I remember correctly, 175 watt MV requires a minimum of 200-300 volts of OCV to strike, hence the autotransfomer ballast. The 175 watt MH lamps require 500-600 volts to strike, and requires a bigger ballast. You can use the MV with no problems on the MH ballast, but in reverse you will experience striking issues. I will do a bit of research and get back to you with any corrections.

To answer your question directly, no, you can't use an incandescent lamp to ballast 175watt MV in North America. It sometimes works in Europe, I think. Self ballasted mercury vapour have a special arc tube designed to strike at 120 volts.

After a bit of research, which you can read here and in the last post in this thread the OCV for mercury vapour is ~220 volts and for metal halide, ~300 volts. Incandescent ballasts will surely not work on 120 volt mains. You can, however, find some suitable ballasts for your lamps on eBay. Otherwise, I think mercury vapour bucket yard lights (from Home Hardware or Canadian Tire) are still sold in Canada and are typically 175 watts although I don't know about the quality of the ballasts they use. NOS ballasts from eBay would be best.

Bah, I figured as much. Thanks for the reply. I'll probably pass in the bulb itself for now, then, since what few 175W ballasts there are on eBay right now are WAY out of my price range.

I know what you mean. I sometimes find good ballasts for a very decent price (as low as 20 dollars sometimes) but the shipping can be upwards of 50 dollars, which makes it a minimum of 70-80 dollars. Hang on to the lamps if you can, you never know when you will come across a ballast for them, maybe at the surplus and salvage store.

New 175w yardlights are still available from RONA and occasionally Canadian Tire for roughly 50 bucks. If you're looking for a cheap ballast I would prowl Restore or any other similar places. They usually sell HID ballasts and sometimes used fixtures at around the $20-25 mark. Best of all the Restores here in Ontario got a sales tax exemption so it's a extra 13% off for me. 

How autotransformer ballasts can produces OCVs in the regions of >600V? This is very close to the starting voltage of the european T8 retrofits for T12 lamps (18W, 36W and 58W T8s).
A theoretical HF rapidstart ballast for F40T12 lamps with such a high OCV, theoretically should start 36W T8s with no problems, if the fixture is grounded as required (Indeed, I've seen several british members that succedded to start 36W T8 with their 40W T12 SRS ballasts).
What is the min required ignition voltage of 18W, 36W and 58W T8?

To answer your question directly, no, you can't use an incandescent lamp to ballast 175watt MV in North America. It sometimes works in Europe, I think. Self ballasted mercury vapour have a special arc tube designed to strike at 120 volts.

In 120V mains, The voltage drop across the filament of incandescent lamps isn't enough to start MV lamps, even with the auxiliary electrodes.
This is why american and japanese SBMV lamps haven't any auxiliary electrode/probe. Instead the mains electrodes are preheated by external filaments inside the arctube using a thermal snap starter, to bring them to their thermionic emission temperature (Much like how a preheat fluorescent system works). During this period, the ballast filament lights. When the thermal rely becomes hot, it open instantly, and stops the preheating. The filament then sends a pulse with a high enough voltage to strike the arctube in the first try.

The filament does not send any pulse - it is not a choke....

Probably the preheating serves in 120V SBMV lamps, only to allow the arctube to strike at plain 120V. Preheating the electrodes before the starting to their thermionic emission temperature, allows the voltage required to start the lamp to be considerably reduced.

Nowadays you can buy a 175w CWA metal halide ballast for less than a mercury CWA ballast. I've started putting these in my display fixtures because they don't draw so much current starting up, and they're quiet. I don't think it's worth experimenting with a homebrew ballast when these are so common. Easiest way to get a ballast cheap is by going on craigslist and finding someone who's getting rid of a yard light. Almost all of these are 175w.

I've got a 70's vintage HX (autotransformer with no capacitor) 175w mercury vapor ballast I'd send you for just the cost of shipping, but I know the shipping is pricey because the thing weighs like 15 pounds. Also it hums quite loudly, so that's why I haven't been using it - that gets on your nerves after a while unless it's outside where you can't hear it.

Yeah, assuming you're in the US, that's talking $50 shipping for 15 lbs (within the US at that; not to Canada). I appreciate the offer, though. I think I'll continue occassionally checking for self-ballasted units (although I can't even find them for less than $40 shipped), and ballasts in thrift stores.