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Does say one 100watt trans running at 50 watts use much more then a 50 watt trans running at 50watts.
I want to use a monster transformer I have. Will it cost much more to run than a smaller trans using the same load? what losses are involved with doubling a trans? Would the trans increase in efficiency? And burn less heat? Or will magnetic losses increase? Thank you. It didn't google well.
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Nope- no extra cost. The extra magnetizing current does not show up on residential watt meters. The house power factor will be ever so slightly less, but a residence does not have a power factor penalty meter unlike industrial users.
The larger transformer (all other things being the same) will have greater core losses and smaller copper losses.
The overspec'd transformer will of course us a lot more energy in manufacture and shipping ...
Since peak flux density is reduced, I'd have thought the core losses would actually reduce slightly.
Mark Kelly
Nobody said the flux was lower; one of the "all other things ..." to which I referred was in fact flux density.
I assumed from the OPs post that he was running the same current and similar winding numbers with a larger core so the operating flux density would be lower, but you're right, it doesn't say that he's doing that.
Mark Kelly
In fact, less internal winding resistance with larger power transformers will result in less heat loss contributing to higher efficiency too.
While your transformer might not be "enough larger" to matter.... larger transformers are more efficent. Really big ones (think electric company) are up around 99%. Little bitty (few volt-amps) might be as bad as 80%.
The only downside is room, weight, cost....which you don't care about in this case....and the need to make sure you have adequate "interuppting capacity" in your over current devices.
It works like this: We connect the secondary wires together to form a short circuit. Next we apply voltage to primary (with variac and starting at zero) until we reach the voltage where the primary draws its rated current.
Example, lets say we have a 120 volt primary rated for ten amps. Assume with the secondary shorted the primary draws ten amps with 12 volts applied to it. It is then reasoned that since it can deliver rated amps at 1/10th of its rated voltage.....at its rated voltage it can deliver 10 times its rated current into a short circuit. So your "interuppting device" must be able to "clear a fault current" of 100 amps......as in circuit breaker contscts can't weld together, fail to function, etc.
I see circuit breakers tested at work. On larger breakers the instanteous current setting is typically set at ten times the breakers rating. Nothing like seeing 20,000 amps being pushed through a 2,000 amp breaker. Don't think for one split second that a household 20 amp breaker trips instanteously at 20 amps (more like 200 amps). Even a 20 amp fast blow fuse won't.....in fact many are required to carry 20 amps for a minimum of four hours!!
I was thinking that large trans efficiency might balance or loss from transformer losses. I have the trans already so I am not increasing my carbon footprint in that respect. Running my amps around the clock is starting to cost more then I can afford.
In theory no, a larger transformer does not use more energy than a smaller unit running at the same VA. There may be some slight difference due to resistance loses in the larger unit?As for heat, that depends on the internal loses and those can vary due to design criteria. A larger transformer may in fact run cooler at the same VA because it has more mass to dissipate the heat.
There's nothing wrong with overspeccing a transformer or any component for reliability or based on what a DIY has in the scrap box. But there have been some suggestions by a member on this forum to grossly overrate a power transformer, like multiple 10 amp secondaries on a CD player. This is just silly and can also be a safety hazard. If a rectifier, cap, or other component on the board shorts, all that extra current can be highly destructive. And let's not even get into the AC fuse bypass crap that is often suggested in the same scenario.
Edits: 08/07/14
I usually spec everything with about the same headroom you mention . You don't want to run power transformers flat-out . Hotter windings increases DCR , heat increases cause copper loss . The only caveat I think of using a monster transformer apart from size and weight is if it's old . Old iron sometimes degrades and typically 'throbs' at power on
Al
+1
If you are using PSUDII to calculate your values you should be sure to accurately measure the resistance of the primary and secondary, and calculate your load accurately too. Plug these numbers into PSUDII and you will get fairly accurate results. Otherwise your B+ may be way off what you are shooting for.
Over spec'd transformers can contribute a lot to good PS regulation, which (IMHO) is very desirable. I think they are a little harder on the rectifier and caps, and I think it is a littler more difficult to get the ripple under control (compared with a higher resistance transformer), but I think you end up with a better sounding amp.
Note that if the B+ is over spec'd then the filaments (if it has them) will probably run high also, so you may have to employ some resistance or bucking to get them right.
Yes and Yes I like PSud11 I always use it and learn gradually how to understand it I little more. I usually try what trans I have and select for amps that fit. Often with my scrounging it's more build an amp to suit the parts then the other way around. Always pays to have many amps on the go at once.
The trans I have in mind is 500volts single winding old army transmitter with bolts for taps. That will give you an idea of how big it really is. I understand that the low dcr will cause headaches but didn't consider the start up pulses and vibration's only time and some new soft start modules I bought will tell if it is useable. I used it's matching choke in a supply that worked well. Just polished those threaded taps shiny and bolted solder tabs on.
I find that in all well-designed supply iron, power transformers and chokes, "20 Ohms or less" is sounding best to me. That would be from either end of the HV winding, to the center tap, or, across a choke winding. If its a non center tapped power transformer, it would be 20 Ohms end to end. For the last eight years however, I use ten Ohms or less in all my iron, and I like that a lot. You want minimal series resistances in the supply / filter to the finals.Do you know to measure the primary's DCR and apply that to the secondary in PSUD2 ?? ( I ususally like to listen to a primary that is under one ohm. ) Here we go :
When you work with Duncan amps PSU Designer II, please use the formula for Rtransformer:
Rtr. = Rsec. + (n x n x Rprim.)
Rsec. = DC Resistance secondary [Ohm], measured between (0V - high volt) of one 'leg'.
n = step-up ratio (= voltage secundary / voltage primary)
Rprim. = DC Resistance primary [Ohm]
This is the transformer resistance as it's 'seen' by the rectifier
tube.
Jeff Medwin
Edits: 08/08/14 08/08/14 08/08/14
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