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transformer overheating?


artto

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Can a transformer, such as a power transforner in this particular case, be induced to run hotter (possibly overheat), caused by the "proximity effect" of the magnetic fields interacting with another transformer nearby (as in too close)?

Also, what's a "safe" maximum operating temperature for a flea powered Class A amp after its been on for a 2-3 hours? I've been measuring 118 degrees on the laminates with a "laser gun" thermometer.

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Transformers are made with different types of insulation- some can safely run at hotter temperatures than others. Do you know the manufacturer of this particular transformer? If so, you can contact them to obtain the necessary info. If you are concerned, why not use a small and quiet running muffin fan to dissipate the heat somewhat. All the components will be grateful for that.

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I read this a while ago i do not know if true or not http://www.audiokarma.org/forums/showpost.php?p=3177854&postcount=2477 but according to this guy yes they can heat if too close and out of phase.

OK, this is interesting. Not quite the same thing as my situation, as mine are on two different amplifiers on different chassis. BUT - I did have them very close together - trying to conceal them behind the Luxmans so my better half wouldn't notice (its the only way to conduct a long term truely blind test you understand).

What puzzled me at first - or I should say "disappointed", was the 60Hz hum. Ah, yes, that's one of the reasons they came up with push-pull (vs SET). Granted, the room has an exceptionally low noise floor, but still, was not what I wanted to hear. I had them side by side for a while. Later I turned them sort of at a 45 degree angle so I could move them closer to the preamp (cables not quite long enough). I noticed somewhat reduced the hum. So later I turned them 90 degrees (compared to the shelf front) and the hum got even lower. Now the transformers aren't side by side or close to each other. They don't seem to be getting as hot but its hard to tell because of the weather changes and interior air circulation. The 60Hz has certainly decreased which is understandable.

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Can a transformer, such as a power transforner in this particular case, be induced to run hotter (possibly overheat), caused by the "proximity effect" of the magnetic fields interacting with another transformer nearby (as in too close)?

Also, what's a "safe" maximum operating temperature for a flea powered Class A amp after its been on for a 2-3 hours? I've been measuring 118 degrees on the laminates with a "laser gun" thermometer.

I don't know if having the power transformers in close proximity to each other would cause overheating. 118 degrees isn't a problem at all for operating temp. Most PS transformers have max temp with regard to max current with load in Celcius. (Insulation rating)

If you smell the paint burning and get 3rd degree burns from touching it, there may be a problem. But 118 degrees I doubt is a issue at all.

The magnetic interacting fields from being near each each will cause the extra noise/hum. You noticed it went down as the amps were moved away from each other.

I don't know what sort of flea powered class A amplifiers you are using, but a single-ended triode with direct heating (AC) will have some filament hum. Do they have null pots? And if they do, have you tried adjusting them to possibly lower the hum more?

From a room with a low noise floor and 104dB sensitivity speakers, I can see where that could be rather objectionable.

A single-ended triode with DC heating can eliminate the filament hum the AC has. But it needs to be good clean DC, or it can dull the overall sound of the triode. IME...

Mike

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My impression is that 118 F is not very surprising. Of course I was raised on tube consumer gear and the insides of tube TVs and radios, also ham gear got very warm. And consider that a very hot day in Dallas or Phoenix gets to 110 F. So you're only 8 degrees higher.

The website for Hammond is not very helpful, or at least I can't find anything quickly, there. However Parts Express show a 110 C. rating on insulation. http://www.parts-express.com/catalog/pdf/2010/138pec10.pdf for what appears to be a typical tube power supply transformer. So you're no where close to that.

As far as coupling energy from another transformer, say 8 inches away . . . I can't see it.

My rough guess involves a 20 watt lightbulb as a heat source. I can see that heat energy of that level could heat up a piece of iron (such as what is the core of a transformer in question) to 118 F. So I'll make a wild guess that there is 20 watts of "loss" in the transformer, causing the heating without any outside influence.

In order for there to be much heating added by an outside source, like a transformer 8 inches away, you have to get 10-20 or so watts across 8 inches by a magnetic field with only air coupling. Further to this I believe the I-E cores are doing a fairly good job of keeping the field in the core and the windings. That should also mean that they are relatively poor at responding to outside fields.

One final thought are the inductively heating schemes in kitchen stoves where a metal pot or frying pan is heated by induction. If the pot is resting on the induction coil (maybe 0.5 inches away) you do get heating. But if the pot is 8 inches above, I doubt it works at all.

Wm McD

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If you're concerned about transformer-to-transformer coupling, you can always go with torodial transformers. My impression is that for a given power rating they tend to be a little less efficient and take up more real estate that traditional "E and I" type laminated iron types.

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The newer highly efficient electrical motors run hotter than can be safely touched. Have to ask the engineers why "hotter" = "more efficient".

JJK

In general less efficiency = more heat but there are other factors such as:

size, phaze, speed etc...

The smaller motor probably runs at higher speeds thus making more heat but built specifically to withstand higher temperatures and since there is less surface area for cooling heat dissipation is not as rapid.

Im no engineer but less rotating mass should lead to a more efficient design as well.

In general all things being the same a 3 phaze motor will run more efficiently than a single phaze design.

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Did we install lots of bypass caps in the power supply Cool

lol, I didn't install anything. They are Wright 3.5 mono, as far as I know, not modified.

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The amps were pretty close at first, side by side. There wasn't more than an inch or so between the power trans and rectifier tube of one amp, next to the output trans and output tube of the other. Dumb, I know, but there wasn't much space behind the other amps in the rack. I was initially having some interconnect issues because the cables were't quite long enough - too much tension pulling sideways - so I angled the amps. That's when the hum reduced and I thought "duh". Then I wondered if that might also be making the trans run hotter than it should. Later I was able to move the amps closer to the preamp by turning them "sideways" and rerouting the cables. This reduced the hum even further.

Last night I measured the temperature on the trans after several hours of operation and the temperature was only 100 degrees. The hum is still audible when I put my ear up to the bass horn, but nothing like it was.

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Jason STR:

What you say seems logical but it is not what is happening in the real world. The new efficient motors come with a decals saying do not touch when running or your fingers will get burned. We used them in a state of the art chemical factory and after touching them when running we wised up and ordered the non-efficient motors which ran cool. And we did use hundreds of totally enclosed motors.

JJK

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Artto,

120F sounds just fine. Also, the magnetic field of a transformer or Iron-core inductor lays very close to the transformer and is unlikely to interactwith another one close by.

You could always seperate them by 3 feet at a test.

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