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Stuck Starter I decided to see what effect a stuck starter has on a magnetic ballast's operating temperature. Pictured is a Tridonic EC18 A502K being fed exactly 240v from a variac (My mains is normally 248-253v!). The top image is with it operating normally with an 18w Philips T8. The bottom image is with an intentionally shorted starter. It's interesting to see just how much the temperature increases! Bear in mind, this is the result with a missing cover plate to expose the ballast and the end caps have also been removed to get the lamp out of the way. With those in place it would be a lot hotter, especially with my "normal" mains voltage! It's no wonder ballasts can fail when they are cooking inside a sealed fitting with a stuck starter! I might have to see what happens when you overvolt a ballast, ie running a 220 or 230v rated unit on 240 or even 250!

Stuck Starter

I decided to see what effect a stuck starter has on a magnetic ballast's operating temperature.

Pictured is a Tridonic EC18 A502K being fed exactly 240v from a variac (My mains is normally 248-253v!).

The top image is with it operating normally with an 18w Philips T8.
The bottom image is with an intentionally shorted starter.

It's interesting to see just how much the temperature increases!
Bear in mind, this is the result with a missing cover plate to expose the ballast and the end caps have also been removed to get the lamp out of the way.
With those in place it would be a lot hotter, especially with my "normal" mains voltage!

It's no wonder ballasts can fail when they are cooking inside a sealed fitting with a stuck starter!

I might have to see what happens when you overvolt a ballast, ie running a 220 or 230v rated unit on 240 or even 250!

387A4166.JPG 1777654290759.jpg stuckstarter.jpg 387A6513.JPG 125wmbtvc.JPG
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Filename:stuckstarter.jpg
Album name:FrontSideBus / Miscellaneous
Filesize:1852 KiB
Date added:30 Apr, 2026
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URL:http://80.229.24.59:9232/gallery/displayimage.php?pid=24812
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Comment 1 to 7 of 7
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AngryHorse   [30 Apr, 2026 at 08:21 PM]
That is a noticeable difference Shocked, they do go spectacularly cooked when inside a fitting.
Flurofan96   [30 Apr, 2026 at 10:54 PM]
Yeah it is crazy how hot it is when on stuck starter and even for the normal operating temperature it is still roasting hot! I'd be interested to see this done on a classic/larger old style magnetic ballast of the same wattage but don't worry if you cannot find an 18W larger old style ballast
dor123   [01 May, 2026 at 02:00 AM]
The core can reach 180*C with a stuck starter.
FrontSideBus   [01 May, 2026 at 07:03 AM]
Max winding temp is 130.
Beta 5   [01 May, 2026 at 09:22 AM]
Where are you getting 180°C from? I imagine it would burn out pretty quick if it got that hot.
Alex   [01 May, 2026 at 10:50 AM]
the maximum temperature specified on a ballast is alsways the winding temperature for the part of the winding outside of tge core, as that is the hottest part…
dor123   [01 May, 2026 at 11:12 AM]
Eltam mentioned in their site, that the core of their ballasts can reach 170*C with a stuck starter.

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