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transformer thermal fuse

 
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waggy
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PostPosted: Fri Sep 14, 2007 1:49 pm    Post subject: transformer thermal fuse Reply with quote

i have a small battery charger to keep my classic car battery topped up,
after about 2 years of continued use it gave up, after stripping it i found the thermal fuse in the input of the transformer blown,, i replaced the fuse with the same rating but then it blew again 2 days later,, the fuse is rated 130deg at 1amp ,, is there something else that could be causing the fuse to blow, the output of the transformer is 16.5v which was correct after changing the fuse, why would the transformer suddenly overheat ,,

any help appreciated

alex
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Fri Sep 14, 2007 4:02 pm    Post subject: Reply with quote

In general, replacing the fuse SHOULD take care of the problem, but it is possible that one or some of the windings on the transformer itself has been damaged,causing it to overheat --OR some sort of electronic problem putting too much load on the txformer?
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waggy
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PostPosted: Fri Sep 14, 2007 4:20 pm    Post subject: Reply with quote

the primary 240vac side is only a lead and a plug ( which tests ok ),, connected via the thermal fuse,, secondary side is 16.5v 1amp ,, the resistance of the primary side is 214ohms,, does this look like a shorted primary,, would a fault in the secondary side cause the thermal fuse to blow? .
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Fri Sep 14, 2007 9:42 pm    Post subject: Reply with quote

Could not say for sure if the primary reading is correct or not without knowing or comparing it with another one---Your reading does not sound off though?----may also be an intermittent problem where the coil's isolation may be braking down under load?

In a txformer, any problem in the primary OR secondary can blow the safety fuse. Can you isolate the txformer from the unit & run it byitself to see if still blows the fuse or better yet monitor the current draw with something like an ISOVAC (if you are so equipped 'fcourse)
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waggy
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PostPosted: Wed Sep 19, 2007 6:22 am    Post subject: Reply with quote

good idea to try seperately , i'll need a load on the secondary ,, would a resister with high amp rating do,, what is an ISOVAC, is that some sort of digital meter,, i googled it and got "isolation products for the military" ????,
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Wed Sep 19, 2007 2:19 pm    Post subject: Reply with quote

..should have been more clear on the "isovac" ; It was meant as abrevi. for
isolated-voltage-Ac or better known as any variable transformer with a built-in amp gauge which can be very handy to monitor the AC current draw.

In theory you could use a hefty resistor(hi watts rating --not amp) but it is impractical due to the current involved as it will cause it to burn up.

It's easiest to use something such as one or several Lamps as a load.
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