Hot Transformer

46C? and 50C no biggie

transformers are passive devices and made out of 'material'

easily take 65C, that's 150F

you may be running your AC mains at 125Vac instead of the 115Vac, which will make them run just that bit hotter to where you noticed.

One thing the OP failed to state is the voltage of his 20 amp power supply.

2000 volts at 20 amps is a much larger transformer then one might find in a 12 volt, 20 amp supply.

Actually it is 51.66 deg C which is not to hard to figure and afterall most of us down here have learnt over the years to cope with whatever the underdeveloped world chooses to use. :-?

I am using these power supplies for Ham Radio equipment. Voltage is supposed to be 13.8, but I think most people just say 12.

on, but you probably will not scream from the pain. Temperature is a significant factor in reliability calculations. I was concerned about the long term degradation of components.

I think I just answered my own question. The hottest power supply is 30 years old and the other is 20. Both appear to meet their electrical specifications.

Fred

It happens that Fred McKenzie formulated :

Do they really meet their Specs? Back then (30 years ago) the nominal in USA was more likely 110 volts whereas today to follow Harmonisation rules it should be 120 which is a like 9% increase. Of course there is a wide margin but you may be on the high side. Just a thought.

Standard 'rule of thumb' the MTBF is halved for every 10C increase in temperature. (10C ==> 18F)

The hotter one is a Kenwood KPS-21. However the insides are almost identical to an Astron RS-20A, except the Kenwood does not have a crowbar circuit installed. Date Codes on components are from 1980, and I purchased it about 1981. Its label says input voltage should be 120 VAC

The other is an Astron RS-20A with date codes from the mid-1990s. Its label says input voltage should be 115 VAC. It was recently purchased from an estate with a goal of replacing the hot KPS-21!

Line voltage here runs about 119 VAC, although equipment should be designed to operate over a +/- ten percent range (108 to 132 VAC) in the U.S.

Fred

Idiot. The saw kerf is 1/8" or wider, depending on the type of saw blade that are used for framing work. Wood expands and contracts with changes in humidity. This isn't precision machining, where you work to mill, or a percentage of a mil.

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.

notation.

that

of

1.58mm.

and

Please be more thoughtful about how quickly you judge. 1.6 mm is just about best surface smoothness over a 3 to 5 meter range of a wall, not all that shabby. If you think you can do better than skilled trades workers just give a try some time.

?-)

Efter mange tanker skrev josephkk:

My maternal grandfather was a machinist working lathes and making cogwheels. My paternal grandfather was a bricklayer. They had very different views on accuracy. Maternal grandfather could see "This shelf is 3mm lower on one side than the other" from across the room For paternal grandfather "accurate" was within the width of a joint between bricks. :-)

--

beslutning at undlade det.

"Fred McKenzie"

** FYI there is a much simpler, low tech way to find the internal temp of a transformer.

1. Measure the primary winding's resistance when at room temp.
2. Make the same measurement ( quick as you can) when the tranny's running temp has stabilised.
3. Calculate the increase as a decimal factor and multiply that by 254 to get the temp rise in degrees C.

Eg.

Room temp = 4 ohms

Hot temp = 5 ohms

Increase factor = 0.25

0.25 x 254 = 63.5 degrees C

Add on the actual room temp to get final result.

If the number is over 100C there is cause for concern.

.... Phil

"Fred McKenzie"

** It never will as the internal temp of a tranny is higher than the surface temp - the test gives the average temp of the copper wire - which is crucial for insulation purposes.

The same test is used in international standards for transformers etc to establish safe temp rise.

** Not if you pass a known current through the winding and measure the voltage drop.

Eg: Connect a 10ohm, 10W resistor in series with the winding and adjust a bench PSU each time to give 10V across the resistor - so you have 1amp. The voltage across the winding is then the same as its resistance in ohms.

Since you compute the ratio of two readings, absolute accuracy of the resistor and the voltmeter do not matter.

.... Phil