Actually he did get the answer when he got the volt amp number and it was much higher than the wattage. It is perfectly normal for some EI transformer cores to draw close to the same current unloaded as they do when loaded! It is just the phase angle between the voltage and current that change. This in the first measurement the wattage is low but the volts x amps rating is much higher.
All that is telling you is that an unloaded transformer is an inductor. In theory neither inductors nor capacitors dissipate power. However there is some resistance and what are grouped as core loses in an inductor or transformer. In normal transformer design the core and the resistance losses should about match in use. The better the transformer the lower the loses.
In large AC mains distribution transformers one important rating is temperature rise. This predicts service life. The ones that have a 100 degree rated rise cost less and are intended for only a few years service life. The ones that run the coolest can last 100 years or more. Most installations use ones in the middle.
Now for those wondering why someone would use the short lived ones, I have seen them used for cell phone towers. A primary and a backup. Saves money and quite simply they don't expect the installation to stay the same for long enough to matter.
i design and build all of my traffos in my builds...
my design goals, low magnetizing current, this means operating at low flux density, 06T to 0.9Tesla.....
this required more primary turns, but i am assured a cooler running traffo..
in a traffo i made for 800VA, my idle current is 0.1A and core loss is around 15 watts...
my design goals, low magnetizing current, this means operating at low flux density, 06T to 0.9Tesla.....
this required more primary turns, but i am assured a cooler running traffo..
in a traffo i made for 800VA, my idle current is 0.1A and core loss is around 15 watts...
A good design goal! However in many small transformers I see them rated as 110 or 220 volt primaries. Thus they begin to saturate at even normal line voltages. This is done for a reason it effectively provides regulation for the output voltage peak value. Thus when rectified the DC voltage is more uniform across different AC mains. For a low power transformer the added heat is not much of an issue.
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That is about 350VA, quite respectable.
This puts the 13.5W losses into perspective, and 46°C is perfectly tolerable
This puts the 13.5W losses into perspective, and 46°C is perfectly tolerable
10/15C above ambient temperature is very good performance.
Not surte how you will load them, but in principle construction is sound and core material adequate quality.
I don´t much like non interleaved laminations but I guess they press Es and Is together with a hydraulic press or something before soldering.
Contrary to some, I run high Tesla in my Musical Instrument amplifier transformers for the very good reason (in my case) of significantly lowering weight (both iron and copper) , always a consideration in portable equipment, and having better raw DC regulation,my supplies drop little under high load.
The price is using higher than usual mains fuse to avoid nuisance blowing at turn-on and in larger units adding a soft start NTC to lower inrush current.
No big deal.
Not surte how you will load them, but in principle construction is sound and core material adequate quality.
I don´t much like non interleaved laminations but I guess they press Es and Is together with a hydraulic press or something before soldering.
Contrary to some, I run high Tesla in my Musical Instrument amplifier transformers for the very good reason (in my case) of significantly lowering weight (both iron and copper) , always a consideration in portable equipment, and having better raw DC regulation,my supplies drop little under high load.
The price is using higher than usual mains fuse to avoid nuisance blowing at turn-on and in larger units adding a soft start NTC to lower inrush current.
No big deal.
An additional factor in residential and small commercial distribution: My house feeder is clearly able to support 100 Amps, but my peak load is 55 Amps for an hour and my 24 hour average is nearer 1 Amp.
"Rise" is 2 factors: no-load rise and full-load rise. In residential distribution the average is WAY less than the max, the no-load excitation (on the company side of the billing meter) is 24/7, the company does pay for low-low no-load loss (good steel and extra turns).
Evidently whatever Terry got these lumps out of was not concerned about no-load losses. The MicroWave Oven is the extreme example where no power is connected until the oven is cooking.
Back to my house: the company knows I won't run my 240V*100A= 24KVA transformer near rating for long (my bill would be killer). So they are less concerned about full-load losses (wire gauge). There's even some reason to not have losses "too low": short-circuit current. Feeders under 50' can pass over 10,000 Amps into a solid short. The breaker will try to break but at >2 MegaWatts of available power it may die violently without successfully breaking. (New residential breakers are rated 22KA.) So we like to see 24 milliOhms of impedance, some of this allocated to the transformer.
two ways to saturate a traffo, first is feeding it higher primary voltage it was not designed for, and second, overloading the secondary side by drawing currents it can not supply, such as in a short circuit...
transformers used for rectification heats more than if used with a simple resistor load...
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for my guitar amps, i do this too...but for my hifi amps, i do things quite differently...
just as i thought, for standard lams, 88/3 = 29.3; but he had 31mm....
so core area is 31 x 63.7 = 1975 sq mm or 3 sq inches,
as per page 237 chapter 5 of RDH4, that ought to give you 280 volt amperes,
so if running 120 volt primary, your full load current can be 280/120 or 2.33A,
that idle current you are getting is a small fraction of your full load current which is what it was supposed to be..
Thanks guys. As I said I bought these for bench testing. Most of my amps have toroidal transformers and they draw a lot less when unloaded. and run much cooler. That is what lead me to ask here so I'd know if they are behaving properly. Thanks for all the good information.
as you have done FTC testing, you will realize that, power draws on a traffo with sine waves are a lot different than with music, and the FTC watts will never happen listening to music....
so just enjoy....
so just enjoy....
Any transformer which becomes very hot during operation, especially, with the secondaries unloaded, is not properly designed. Some manufacturers abuse electrical engineering to save on materials and production to increase their profits. However, this practice does not justify what they do from an engineering point of view. This is abuse. A transformer should never be so hot as to be a fire hazard. It is well known at flux saturation a transformer no longer behaves like a transformer and changes status into a resistance. At saturation secondaries do not get any dΦ/dt implying NO voltage is induced. This is basic secondary school Physics. So, any manufacturer who dares to drive a transformer into magnetic saturation is abusing customers with an added and unnecessary fire hazard.
A well designed transformer is one in which the maximum magnetic flux density is designed to stay well below saturation to minimize magnetic hysteresis loss. It is also one whose winding conductors are thick enough to keep resistance losses the lowest possible. If a transformer is intended to provide mains isolation, the secondaries are also generously insulated from the primary. And finally, if one really wants a very good transformer that lasts several generations working continuously, put it inside a metal box filled with transformer oil with heat dissipation pipes/fins and insulated external connectors.
A well designed transformer is one in which the maximum magnetic flux density is designed to stay well below saturation to minimize magnetic hysteresis loss. It is also one whose winding conductors are thick enough to keep resistance losses the lowest possible. If a transformer is intended to provide mains isolation, the secondaries are also generously insulated from the primary. And finally, if one really wants a very good transformer that lasts several generations working continuously, put it inside a metal box filled with transformer oil with heat dissipation pipes/fins and insulated external connectors.