Hi all,
I'm wondering if the attached schematic is ok. I'm trying to get two 0-50 volt dc supplies, for two mono SE amp boards. I have a xfmr that has dual 35 vac secondaries. My confusion is that I'm not sure if the dual secondaries share the center tap or if they are independent. My understanding is that if they are independent then their voltage is relative. (If not then I would be grounding the 0 of one to the -50 of the other, right?)
Measuring resistance between secondaries all seem to be about 0.1-0.4 ohms.
Thanks for the help, and or advice for how to best do this. Also if it would be better to run the secondaries in parallel and use a single bridge, please advise.
gary
I'm wondering if the attached schematic is ok. I'm trying to get two 0-50 volt dc supplies, for two mono SE amp boards. I have a xfmr that has dual 35 vac secondaries. My confusion is that I'm not sure if the dual secondaries share the center tap or if they are independent. My understanding is that if they are independent then their voltage is relative. (If not then I would be grounding the 0 of one to the -50 of the other, right?)
Measuring resistance between secondaries all seem to be about 0.1-0.4 ohms.
Thanks for the help, and or advice for how to best do this. Also if it would be better to run the secondaries in parallel and use a single bridge, please advise.
gary
Your schematic looks correct, there are two floating power supplies, each connected with its negative output
to one common ground point, creating two positive voltage supplies.
To check the isolation between the two secondary windings, use your dvm to see if there is an ohmic connection
between them, probably not. Having separate supplies is usually better than one larger one if you have the space,
especially for single-ended amplifiers.
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thanks for the reply rayma,
can you help me understand how to best connect the power supply to ground then; When these two separate secondary supplies are floated and not connected to earth via the negative rail they each show about 52 vdc unloaded. When I connect the negative rail of each to chassis and earth ground, the lightbulb tester continues to glow and the dc voltage between + and - on both sides starts to climb. I allowed the caps to charge to 90 vdc (both sides) before shutting everything down. My understanding is that the connection between PS and earth/safety ground is ideal at the negative terminal of the first cap. No?
I will search "floating" on this forum
Totally appreciate all the help
gary
can you help me understand how to best connect the power supply to ground then; When these two separate secondary supplies are floated and not connected to earth via the negative rail they each show about 52 vdc unloaded. When I connect the negative rail of each to chassis and earth ground, the lightbulb tester continues to glow and the dc voltage between + and - on both sides starts to climb. I allowed the caps to charge to 90 vdc (both sides) before shutting everything down. My understanding is that the connection between PS and earth/safety ground is ideal at the negative terminal of the first cap. No?
I will search "floating" on this forum
Totally appreciate all the help
gary
There must be some unknown connection between the two secondary circuits.
With the power off and discharged, disconnect the ground connections you made,
and connect an Ohm meter between the two secondaries. It doesn't matter which leads,
just between one lead from each winding. There should be an open circuit. I'm guessing there isn't.
Floating means no connection elsewhere.
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There's some kid of connection then. What's the brand and model number of the transformer?
Can't find any docs on that one. So, disconnect all the secondary leads.
Connect an Ohm meter to one lead. Check the resistance to the other 3 leads.
If measurements to 2 of the 3 other leads aren't an open circuit, there is an unknown connection.
If there is an open for 2 of the 3 leads, then there are indeed two separate secondaries,
but you may have some of the secondary leads miswired.
Would expect that each secondary has one yellow lead and one black lead.
But, if you didn't use the correct black lead for the particular yellow lead,
the wiring would be wrong. You have to use the meter to correctly pair the leads.
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Thanks,
there are no open circuits for any combination of secondary connections, as listed in previous post, there is minimal resistance between all connections.
This is good to know though, dual secondaries, just like schematics show, will not have any continuity between windings, even given the big magnet they are wrapped around.
How can I determine if this xfmr is good for anything?
gary
there are no open circuits for any combination of secondary connections, as listed in previous post, there is minimal resistance between all connections.
This is good to know though, dual secondaries, just like schematics show, will not have any continuity between windings, even given the big magnet they are wrapped around.
How can I determine if this xfmr is good for anything?
gary
Connect each secondary lead to a fixed isolated terminal so they can't move around or short together.
Apply power and use your DVM to measure the AC voltage between every pair of leads.
Mark them as B1, B2, Y1, Y2. Record the measurements. Then we'll try to sort out wtf is going on with that thing.
The implication is that there will be 0VAC between the leads of one of the pairs (only).
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There you have it. The center tap is both black wires. The yellow wires are the other two ends.
So you have an 80V Yellow-Yellow winding, with two black center taps.
With this transformer you can make a bipolar +/-56VDC supply using one bridge rectifier
and grounding both of the black wires.
You can't parallel the windings by connecting the two yellows together, because the 2 windings
would be in the wrong (opposite ) phase and short out.
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I had convinced myself that it was a "dual secondary" transformer because it was advertised as such. And I wanted it to be that way so I could build 2 +50 volt supplies for a pair of Zen amps. Turns out that +50 and -50 is what I have. (thanks to rayma for his pragmatism) Nothing unusual I guess. This is not the first time as a novice DIYer that I have bought something based on its description to find out that either the description is wrong or...I'll leave it at that.
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