RE: More Stupid Transformer Questions.

Yep. And on into schottky diodes, and the rest. Zero conductivity. where are you?
One helpful point while we are blowing smoke, is that dual secondary transformers may be used in series or parallel. In series the configuration is the equivalent of a center tapped three wire version, however it is important that you get the phase correct. In fact when you use the windings in parallel, it is importat to get the phases correct. Here's how to do that:

Dual secondaries have at least 4 wires. It is aslo possible to center tap one or both of these two independent secondaries, increasing the number of wires beyond 4. In the case of dual secondaries which are not center tapped (and only 4 wires). If you wish to use the two secondaries in series, connect an AC voltage meter between one wire from one winding and one wire from the other secondary winding. Connect the other unconnected winding from secondary 1 to the other unconnected winding of secondary 2, and observe the AC voltage reading. If you observe a significant voltage near what you expect, the two wires connected together from the two independent windings are the two wires which should be connected together and can be considered as the center tap. If you do not get a significant voltage, reverse the wires from one winding (such as secondary 1) and retest.

To identify the correct phases for connecting the two windings in parallel, do exactly what you did above. If the voltage you measure is very near zero volts, you may connect the wires together which were connected to the AC volt meter. If you observe a large AC voltage, reverse the wires on one winding (such as secondary 1) and observe the voltage again.

If you connect the phases in error in parallel, the two secondary windings will fight each other and draw alot of current with possible damage to the transformer. Hope this is helpful. Thanks Bertho, for the additional information.

David R. Howland

-----Original Message-----
From: Bertho Boman [SMTP:boman@...]
Sent: Wednesday, August 25, 1999 9:42 AM
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO] More Stupid Transformer Questions.

From: Bertho Boman <boman@...>

Hi David,

Your explanation is very good but it should also be explained that the transformer losses also differ between the two configurations.

A full wave bridge system has lower transformer losses and higher rectifier losses.

A half wave bridge system has higher transformer losses and lower rectifier losses.

At low output voltages the half wave is more efficient but at higher voltages, the full wave wins.

If we all chip in together, we will eventually have a "power supply training session"

Bertho Boman
Vinland Corporation
========================================================

David Howland wrote:

> From: David Howland <dhowland@...>
>
> John,
>
> Not that any of this is new information, I'll add my 2 cents worth.
>
> They build transformers in configurations like (12V 0V 12V) for an interesting reason. If you need 12VDC (RMS), you may employ such a transformer in a full wave configuration using only two individual discrete rectifier diodes, and in this configuration the total diode voltage drop is half the total diode voltage drop compared to a four diode full wave bridge rectifier (4 leeds on the single full wave bridge device). When you cut the total voltage drop across the diodes in half, you cut the wasted power consumption across diodes in half. Saving wasted energy in diode drops is why the center tap was brought out of transformers. It doesn't have to be used as previously discussed.
>
> The 12VDC configuration of a (12V 0V 12V) transformer is that 0V is tied to ground, and each 12V transformer wire (2 each) is connected to the Anode of each of two diodes. The Cathodes of the two discrete diodes are then tied to each other and the voltage out at this junction is +12VDC (RMS). Typically in a power supply, the +12VDC is then connected to a large capacitor (+) positive and ground is tied to (negative) of that large capacitor. If you reverse the two diodes, you must reverse the capacitor polarity and you end up with positive ground. To obtain a 24VDC supply with a (12V 0V 12V) transformer, you must use a full wave (four diode) bridge rectifier and the certer tap is not used as previously discussed and you must live with two diode drops.
>
> An interesting point about all this is that a (24V 0V 24V) transformer makes a good +24VDC power source in the same manner and for the same reasons. When this configuration for a 24VDC supply, is used over a plain 24VAC transformer (with or without a center tap), you will save a diode drop of wasted energy in the conversion process. Let us say that a diode drop is 0.60 VDC. If you are drawing 10 Amps, then one diode drop is using up 6 Volt-amps to get the rectifier job done. A full wave bridge rectifier requires 2 diode drops whereas a center taped transformer allows you to get by with one diode drop. You do not have an option with transformers that do not have a center tap, or transformers that do not produce the voltage you want from the center tap to either of the other two windings.
>
> More often than not, we build power supplies around the transformers that we can easily obtain. If we need a 24VDC supply and we can find a transfomer in (24V 0V 24V), then we might choose this over a (12V 0V 12V) transformer and a full wave bridge rectifier to save a few volt amps.
>
> David R. Howland dhowland@...
>
> -----Original Message-----
> From: John Ross [SMTP:johnr@...]
> Sent: Tuesday, August 24, 1999 1:23 PM
> To: CAD_CAM_EDM_DRO@onelist.com
> Subject: [CAD_CAM_EDM_DRO] More Stupid Transformer Questions.
>
> From: John Ross <johnr@...>
>
> If I have a transformer that puts out 24 volts at 5amps and is center taped
> like " 24 0 24 ". can I use both 24v lines to get 10 amps like using 2
> separate 5 amp transformers? Or does this cause a problem with phasing?
>
> John Ross
>
>
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Welcome to CAD_CAM_EDM_DRO@...,an unmodulated list for the discussion of shop built systems in the above catagories.
To Unsubscribe, read archives, change to or from digest.
Go to: http://www.onelist.com/isregistered.cgi
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