Thermal cut-out/switch

[drewl]

Anyone ever see the thermal cut out open on any amps like Peavey has those black ones mounted to the power amp heatsink.
I never have.
Anyone know if they reset?

I was fixing the Whirlpool clothes dryer, an urgent request from the wife-
The non-resettable thermal cut-out had opened.
The dryer wasn't producing heat.
Replaced it this morning and now it's fine.

Why don't they use one that resets itself?
I can imagine alot if people throwing away a perfectly good appliance because of a ten dollar part.

[g1]

I think you answered your own question, which do you think they would rather sell to you, a part or a replacement unit?
Aside from that, it may be due to safety regulations.

The ones in amps on the heatsinks are self re-setting. The ones inside transformers are non-resettable.

[Chuck H]

And I would caution the same about the dryer as I would about an amp by saying that there may be a reason that thermal fuse blew and simply replacing it without knowing why it blew could be dangerous. If steam builds up inside the dryer you may have clogged vents. Or perhaps there are hot spots on the heating element (if it's electric). If it's gas it may be a regulator. Maybe a thermostat problem? pretty much anything that might make the dryer get too hot. I suppose you'll know soon enough if the new thermal fuse goes. I just hope you suffer no problems that the original thermal fuse was warning against.

[Jazz P Bass]

And they do have a current limit that can make them open permanently.

[drewl]

While testing it, I put my Fluke meter across it to measure the current.
It was somewhere around 23amps, so I quickly turned it off before blowing the fuse in the meter.
We'll see if it has a problem if it opens again.
The thing's at least 20yrs old, came with the house and I replaced the vent tube which had some lint build up.

Aside from that it's in pretty good shape.
I remember fixing the control switch like 12 yrs ago that was hanging up, so I really can't complain if it's time for a new one!

[J M Fahey]

23 amps !!!!!!!!
Aren't power outlets limited to 15 amps or something?

[Chuck H]

23 amps !!!!!!!!
Aren't power outlets limited to 15 amps or something?

Nope. They also get double ganged sometimes for the really big stuff! 23A does SEEM like a lot at, what 2700W if it's a 120V unit and 5400 if it's at 240V. But an average water heater uses a pair of 4500W elements that alternate. Larger, higher wattage units are available. Even a space heater is 1500W. I don't think it would dry clothes very fast either

[Dave H]

...The ones inside transformers are non-resettable.

I had some that were like axial resistors. They looked exposed and needed insulating so I used heat shrink sleeving. I thought I must have a bad batch when all four measured open circuit, then it hit me - thermal fuse + heat shrink sleeving, Doh!

[Chuck H]

Looking at another thread right now where a guy is about to put a third PT into a Fender combo because the internal fuse keeps popping. He's doing everything right too but the problem is either non obvious or intermittent. This is the second such thread I've seen on the matter with many others mentioning a one time failure. All two bottle Fender combos!?! With the internal fuses popping ahead of the mains fuse trouble shooting is difficult at best without a generous supply of power transformers.

IMHO, regulations or not, if excess current is flowing through any given winding in combination with normal heat from the other windings as to cause heat that pops that internal fuse it should pop the mains fuse first. The winding/s should be up graded if the transformer can't manage current that won't pop the mains fuse. It's poor engineering to just stuff a thermal fuse into a transformer to satisfy a code and leave the fallout from a lack of further consideration to the customer. Fender should be hit on the nose with a rolled up newspaper for that mess.

[Leo_Gnardo]

IMHO, regulations or not, if excess current is flowing through any given winding in combination with normal heat from the other windings as to cause heat that pops that internal fuse it should pop the mains fuse first. The winding/s should be up graded if the transformer can't manage current that won't pop the mains fuse. It's poor engineering to just stuff a thermal fuse into a transformer to satisfy a code and leave the fallout from a lack of further consideration to the customer. Fender should be hit on the nose with a rolled up newspaper for that mess.

Sounds good to me Chuck. Crate/Ampeg/Crampeg have been using PT's with internal thermal "fuse" for a long time, but all their amps I've seen have mains fusing, and rarely do I see a PT gone bad. If Fender is now using under spec PT's that pop before the mains fuse does, yes that's bad bad doggies... Fender seems to be flailing lately. One skinny letter away from failing.

[Jazz P Bass]

Obviously a 220 volt resistance heater is being used.

I hope.

Watch that electric meter spin.
Wheee.

[Jazz P Bass]

Yeah, there is also a technique for reattaching them.
Severe heatsinking is required.

I think the factories either crimp them or they are welded.

[drewl]

Yes, it is a 220v dryer.

I see many others here put their tech skills to good use in fixing things around the house!

[Chuck H]

Yes, it is a 220v dryer.

I see many others here put their tech skills to good use in fixing things around the house!

Indeed! My wife often volunteers my services elsewhere too!

Wife's friend 1: "I just can't get the surround sound working right."

Wife: "Oh, Chuck can fix that."

Wife's friend 2: "My water heater isn't working right."

Wife: "Oh, Chuck can fix that."

etc...

[Enzo]

The thermal switches - thermostats - used in like a zillion PV amps and elsewhere are just that - thermal switches. Get them hot they toggle, cool them down they toggle back.


That is different from thermal fuses, those get too hot, they open. period.


And a thermal breaker would have a reset button, while a thermostat would just be open or closed dependent upon temperature. So just because it lacks a button, that doesn;t mean it won;t reset once cool.

You can look up the part number of your defective thermal thingie and see what it is inside.

But yours opened and stayed. For all we know it simply is a failed part. We do not yet know that it is "non-resetable".



And what is this picking on Fender thing? Of the hundreds of thousands of amps they made, what percentage of them killed their PT thermal fuse? A damn small number.