Author Topic: Mercury ballast size differences  (Read 1193 times)
BlueHalide
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Mercury ballast size differences « on: November 19, 2014, 11:45:51 PM » Author: BlueHalide
For the last of the while now ive been occasionally contracted to replace or retrofit mercury vapor outdoor security/area fixtures with either MH or in some cases (even though I really dont want to) with CFLs. Of course I usually save the mercury lamp (and the reason I say usually now is because if I saved every single modern chinese mercury lamp I would have enough to fill my half my garage). I do occasionally score older Westinghouse and Sylvania lamps from the 80's though, worth saving those. One peculiar thing ive noticed (as I always keep the ballasts)  is that the ballasts (175w) in the bucket/area lights that are of the cheap residential-grade variety use a very small core/coil, so small in fact that some of my good quality Advance 100w MV ballasts are actually larger in size. And the 175w MV area lights that are of better commercial grade/quality (eg. GE, NEMA) use ballasts more than twice the size of the cheap (chinese) spade-terminal ballasts. But when both ballasts are tested the wattage is within a 5% difference...how is that possible with such a huge size difference? Has anybody else noticed this?
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sol
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Re: Mercury ballast size differences « Reply #1 on: November 20, 2014, 05:34:49 AM » Author: sol
The smaller ballasts probably run hotter as they have less metal. What is important is the number of turns in the coil more than the physical size of the plates or the gauge of the wire. Smaller = less metal = cheaper to manufacture = more money for the manufacturer. Sad but true in a lot of situations nowadays...
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Medved
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Re: Mercury ballast size differences « Reply #2 on: November 23, 2014, 01:22:32 AM » Author: Medved
There are multiple aspects, their influence on the final manufacturing cost is the motivator. But it always has been so. What have changed are the relative costs of the individual materials versus their processing and even the alternatives.
So let's keep the acceptable quality level aspect aside for this moment (it is clear, lower quality requirements allow for lower cost).

What have changed was the cost of raw materials vs their processing. Decades ago mainly the raw copper was rather cheap, but the advanced thermally resistant insulation materials and processing of the advanced magnetic steels (high saturation flux, techniques to get thinner and more reliable insulation layers to prevent eddy currents,...) were rather expensive.
So it was cheaper to design the core for lower flux levels, so tolerate cheap core material, oversize the winding so it runs cooler, so no expensive high heat resistant insulation materials would be necessary and so on.

But in the meantime the cost of the copper had skyrocketed, while the advanced technologies for the high temperature tolerant insulation materials and way better performance core assembly had fallen, so the situation had changed a lot:
Now it becomes way cheaper to use high flux core steel, so you suffice with less turns. That means the wire becomes shorter. And for the same resistance the wire could be then thinner. Less turns and thinner wire means quite a lot of copper savings, the need for smaller winding window means smaller ballast size.
As the ballast get smaller, it's thermal resistance to ambient gets higher, so with the same losses it will operate at hotter. To prevent that, the losses would have to be lowered compare to the old design, so the savings won't be as high. But high temperature insulation materials and design the ballast to operate hotter, but as it becomes smaller, the reduced copper cost pays off well all the expensive insulation materials and steel processing.
With the magnetic the difference is not only the material properties alone, but as well the balancing between the core vs winding mass (smaller core means more turns, so more copper, less magnetic steel and vice versa)

But the thermal margin (that ends up as a lifetime) of that design is still the same as it was with the old one: The old operated at colder temperatures, but it's materials did not tolerate much more, so the temperature gap was not that high.
Today the operating temperature is higher, but because the materials could tolerate way more then before, the difference, so the temperature gap remains the same as with the older design, even when the resulting product is smaller and lighter.

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don93s
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Re: Mercury ballast size differences « Reply #3 on: December 26, 2014, 02:31:46 AM » Author: don93s
I have noticed that the smaller newer designed (usually made in China) 175w ballasts run lamps at around 150w whereas the older larger ones ran them at 175+ watts. Another thing of note, responding to Medved, almost all MV ballasts I come across, old and newer, all use aluminum windings. At least from the 70's onward. I would have to recheck my 60's ballasts but I think most are aluminum too.
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Medved
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Re: Mercury ballast size differences « Reply #4 on: December 26, 2014, 01:15:16 PM » Author: Medved
Aluminum does need more space for the same losses, but it is lighter material. Bottom line the overall ballast would become larger than a fully copper winding equivalent, but still lighter. But the main reason is the cost: Aluminum is way cheaper material...
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BlueHalide
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Re: Mercury ballast size differences « Reply #5 on: December 26, 2014, 11:38:25 PM » Author: BlueHalide
Ah, I see, I have also noticed the modern small mercury ballasts only drive the lamps to 150w or so too. I do have one Advance 100w mercury ballast with copper windings, but yes most are Al
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