Needed: transformer overheat power cutoff.

[Bob in Phx]

To All,
I have a few great old Boatanchor tube type radios. The number one issue
that I hear from others with these types of radios is transformer failure.
The majority of transformer failures are from bad capacitors that slowly
allow the amperage being pulled from the transformers to go up. This causes
the transformer to overheat and the internal windings to short. The best
protection for this issue appears to be replacing all the old capacitors
with new ones. I have done that, but still worry and am constantly check the
heating of my transformers. I do this by hand and if it feels " to hot" I
turn the radio off. So how hot is two hot, I am not sure, but I am guessing
someplace in the 110 degree to 150 degree area. I will be posing the how hot
is too hot question over on the antique radio newgroup... But for now I was
wondering if an externally powered circuit could be built to shut off the
radios main power, if the outside temperature of the transformer goes above
a certain level????? I would suspect that a termisitor, a power supply and a
relay would lashed up together. I am not sure of how to do this... I would
also like to add that I may be barking up the wrong tree and maybe all I
need is a very accurate fuse that is matched to the "highest" amperage
encountered during normal operation of the radio. Over amperage, thermal
runaway and damage of the transformer is what I am trying stop. Any
ideas?????

bob in phx.

 

[Bob in Phx]

John,
I would love a schematic and am willing to wait as long as it takes... Your
last schematic for me (a TTL sensing relay setup for an old video poker
machine, worked great and is still working!!)

thanks in advance.

bob in phx.

 

[PeterD]

To All,
I have a few great old Boatanchor tube type radios. The number one issue
that I hear from others with these types of radios is transformer failure.
The majority of transformer failures are from bad capacitors that slowly
allow the amperage being pulled from the transformers to go up. This causes
the transformer to overheat and the internal windings to short. The best
protection for this issue appears to be replacing all the old capacitors
with new ones. I have done that, but still worry and am constantly check the
heating of my transformers. I do this by hand and if it feels " to hot" I
turn the radio off. So how hot is two hot, I am not sure, but I am guessing
someplace in the 110 degree to 150 degree area. I will be posing the how hot
is too hot question over on the antique radio newgroup... But for now I was
wondering if an externally powered circuit could be built to shut off the
radios main power, if the outside temperature of the transformer goes above
a certain level????? I would suspect that a termisitor, a power supply and a
relay would lashed up together. I am not sure of how to do this... I would
also like to add that I may be barking up the wrong tree and maybe all I
need is a very accurate fuse that is matched to the "highest" amperage
encountered during normal operation of the radio. Over amperage, thermal
runaway and damage of the transformer is what I am trying stop. Any
ideas?????

bob in phx.

At the risk of being shot at dawn...

Many nicd battery packs (not single cells) have a normall closed,
opens at about 120 thermostat in them. Usually a small rectangle with
two leads in series with the cells. By carefully disassembling a pack
you can salvage the thermostat (then *recycle* the nicads) and use it
in your application.

 

[Bob in Phx]

klixon!!!!!!!! why didn't I think of that!!!!!!!!!!!!!!

Off to the store in the morning.

 

[jasen]

But for now I was wondering if an externally powered circuit could be built

It's called a "thermal cutout" (or self-resetting thermal fuse) it's a little
thing with a flat surface that you mount in contact with the equipment to be
monitored and two terminals that you wire in series with the mains.

eg: jaycar.com.au catalogue number 3823


Bye.
Jasen