Author Topic: Ballast Temperatures  (Read 8997 times)
Zelandeth
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Ballast Temperatures « on: October 24, 2011, 12:43:59 PM » Author: Zelandeth
Just a quick query here.

What sort of temperatures are normal for switchstart ballasts?

I converted an 18W T8 fixture back to switchstart yesterday, and my gut feeling (and the pain in the tips of my fingers!) is that it's getting a bit warmer than I'd like.  Currently waiting for a ballast to arrive to re-convert the 15W one as well as I didn't have one suitable for that rattling around anywhere.

Having an IR thermometer, I decided to take some temperature readings from it and some others in here.  These are all max temperatures from the surface of the laminations.

The ballast in question (Tridonic EC20 A50), enclosed within a typical metal cased fixture seems to be stabilising at a temperature of 67 degrees C.

Just around the corner, there's (in open air) a Crompton NG10045 running an F100W T12 tube propped up in the corner is sitting at 70.1C 0 that has Delta T 70 Deg C stamped on it, so probably isn't far off the mark.

Buried behind my speakers above the desk, theres's a 9W PL running on another Tridonic ballast (not sure what model that is - can't read it without moving a very heavy amplifier and sub woofer!) which is sitting at 68.7 Deg C.

Given these temperatures all seem to be hovering around the 70 mark, I'm starting to think that they're sensible.  Any thoughts on whether these are sensible?
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Medved
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Re: Ballast Temperatures « Reply #1 on: October 24, 2011, 01:21:18 PM » Author: Medved
With 25degC ambient temperature (my guess) the temperature rise (deltaT) is about 45degC, while rated is usually about 60..70degC, so I would guess pretty normal. You have to only make sure, then the fixture would have no problem with the usually rated 125..135degC maximum ballast operating temperature (electronic ballasts have usually the maximum at about 70degC).
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Ash
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Re: Ballast Temperatures « Reply #2 on: October 24, 2011, 01:48:29 PM » Author: Ash
I find on most magnetic ballasts markings like :

Tw130 dt65

Do they mean "max. temp 130C, ballast heats 65C above ambient" ?
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sol
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Re: Ballast Temperatures « Reply #3 on: October 24, 2011, 07:55:16 PM » Author: sol
Ash, my guess would be that you are correct.
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f36t8
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Re: Ballast Temperatures « Reply #4 on: October 25, 2011, 11:25:59 AM » Author: f36t8
Tw indicates the temperature at which the insulation of the wires will last for 10 years of continous use when the windings are operated at the given temperature. (Source)

The expected lifetime should go up or down by a large amount when below and above this temperature. When I finally get around to building some light fixture, I am going to put thermal grease under the ballast to lower its temperature.
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Zelandeth
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Re: Ballast Temperatures « Reply #5 on: October 25, 2011, 01:15:13 PM » Author: Zelandeth
Ash, sounds about right.

Below is a photo of a couple of ballasts picked at random here which show different methods of marking.  The 100W one at the top is pretty easy to decode, with the Tw and Delta T values clearly marked.  The Tridonic one's a little less clear though!

I'm guessing that's indicating working temperature max 130 C, Delta T 50 C, the 145 being absolute maximum working value?



I might gather a few more together at some point and actually put up a gallery post showing the differing conventions for marking things at some point, will see what variety I can find first though.
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Medved
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Re: Ballast Temperatures « Reply #6 on: October 25, 2011, 01:32:52 PM » Author: Medved
I would say so. 130degC long term working temperature, 145degC the short time (e.g. failure mode) absolute maximum rating, 50degC is the delta.
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Ash
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Re: Ballast Temperatures « Reply #7 on: October 26, 2011, 01:26:59 PM » Author: Ash
The notorious Eltam Mini N, rated Tw130 dt65. would overheat even in normal working mode. Those ballasts keep going for 28 years and more (first made in 1983), but the terminal block is becoming so brittle that moving the wires a bit is sometimes enough to break it to pieces

So is this what the Tw rating supposed to stand for ? If so, better keep a lot below it

Other ballasts with about the same ratings heat much less, and obviously will last much longer. How come ?
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Medved
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Re: Ballast Temperatures « Reply #8 on: October 26, 2011, 02:32:21 PM » Author: Medved
Tw is the maximum winding temperature for rated life.
The balast you pointed at look for me too small to meet the deltaT printed on it. My impression is, then the rating was acquired by extrapolation (while not taking into account the rising copper resistance at hot) and not real measurement. The core seems to be nearly half the size then normal ballasts, while the stated deltaT is the same as on way bigger ballasts. That make the difference worse in two fold: More turns needed, so thinner wire, so higher resistance leading to higher power dissipation. And the smaller size mean higher thermal resistance from the ballast body to ambient.
So the rating seems to me as highly optimistic...
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Ash
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Re: Ballast Temperatures « Reply #9 on: October 26, 2011, 03:38:41 PM » Author: Ash
Those ballasts dont have a rated life (in years) which i know of

Those small ballasts were introduced around 1983 (perhaps a bit earlier), so the oldest ones are 28 years old now. My school had a lot of them installed (the very first of them as it was opened in the early 80's). Probably >90% of them still work after those 28 years (the ones that failed were the ones left with stuck starters)

So in fact they are working after 28 years, and will probably work for many more years if starters replaced in time

But when the terminal block, plastic coil covers etc are so brittle from overheating that the smallest disturbance (moving the wires) will shatter them to pieces, does it really qualify as "still intact" ?
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Medved
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Re: Ballast Temperatures « Reply #10 on: October 26, 2011, 04:05:44 PM » Author: Medved
I think the winding itself withstand more then the rated 130degC (that's, why they are able to work so long; 180degC rated magnet wire insulation coat is already available for few decades), but the connectors, impregnation and other auxiliary plastic don't endure that...
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AngryHorse
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Re: Ballast Temperatures « Reply #11 on: December 03, 2011, 03:25:42 PM » Author: AngryHorse
I have notest that the Vossloh ballasts run the hottest.
My 250watt SON ballast on my outside light has, printed on it, tw130, with the delta t at 80!
When it has been running for a few hours, you can only touch it for a few seconds!!!! HOT STUFF, but at least its on a heavy metal heatsink plate :o
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