Hi All,
I need a reality check. I came up with an idea of using some spare parts to build a variable DC power supply. I will power the unit with my variac. The bridge rectifier is from Sjöström audio. The filter cap array is from here. The caps are rated for 100v, I will stay well below the 100v. My question, do I have to ground the star ground to the chassis? I will only output v+ and v- to test my boards and the broken power amps I am working on.
I need a reality check. I came up with an idea of using some spare parts to build a variable DC power supply. I will power the unit with my variac. The bridge rectifier is from Sjöström audio. The filter cap array is from here. The caps are rated for 100v, I will stay well below the 100v. My question, do I have to ground the star ground to the chassis? I will only output v+ and v- to test my boards and the broken power amps I am working on.
Thanks rayma. When you mean supply, are you referring to the filter caps? Like the ground star plane to the chassis?
Most dual supplies connect the two commons together (one for the + and one for the -) to form the system common.
Sometimes this node is left floating, and sometimes not. It is safer to connect it to the IEC safety ground.
Sometimes this node is left floating, and sometimes not. It is safer to connect it to the IEC safety ground.
My chassis is grounded to the IEC plug. I have powered the unit on to 56v DC, no problems. Now I connect the thermistor to the chassis, from the ground plane, and my AFC/GFC plug trips when I turn up the voltage on the variac.
a variac is no isolating transformer, it is just a varying tap on a primary winding
You need an isolation 1:1 transformer before the variac.
You say that you need +&- to test amplifiers.
Do you mean +&0?
You can't make dual polarity power supply without usage of dual output transformer.
Just a suggestion,use a dual secondary transformer, connect the primary coil to the variac output.
Do not touch anything around the primary! Danger 😈.
Use separate rectifiers for each coil secondary,two cap banks, connect the cap bank 0v to the main safety gnd.
You say that you need +&- to test amplifiers.
Do you mean +&0?
You can't make dual polarity power supply without usage of dual output transformer.
Just a suggestion,use a dual secondary transformer, connect the primary coil to the variac output.
Do not touch anything around the primary! Danger 😈.
Use separate rectifiers for each coil secondary,two cap banks, connect the cap bank 0v to the main safety gnd.
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Ok, thanks basreflex and thimios. I knew that the variac was not an isolation transformer, but did not realize that I had to lift the entire ground circuit ? Something does not make sense to me. In a toroidal transformer, is the centre tap isolated from the mains?
I don't understand the question ❓
Do you mean the center tap in the secondary?
If you mean this...yes in a 2XX (2x12 or 2x50 or or) toroidal,the center tap is just the common connection of two secondary coils.
This is isolated from the mains.
It is a transformer.
Variac is an autotransformer.
Do you mean the center tap in the secondary?
If you mean this...yes in a 2XX (2x12 or 2x50 or or) toroidal,the center tap is just the common connection of two secondary coils.
This is isolated from the mains.
It is a transformer.
Variac is an autotransformer.
Thank you. That makes sense now. I will look for an isolation transformer. And yes, I meant the secondary windings of the toroidal.
If you are looking for a dual polarity power supply you Don't need an isolation transformer BUT a dual secondary,toroidal or EI
I used a Triad 48vct Transformer I had kicking around. It is only a 48va transformer. Now the fuse would be 400mA? 48w / 120v main lines. *125% = .5A fuse ?
Any amplifier that it isn't capacitance cabling with speaker need a double polarity power supply.
You need three wires,+/0/-.
You can't use a single secondary transformer to generate a double polarity power supply.
You need double secondary or center tap transformer.
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Shoot.... I thought I could use my parts without a purchase of new equipment. Well, back to the drawing board. Looks like I will use the dim bulb tester with my variac, till I come across a proper transformer.
Thank you all for the education.... I appreciate the info.
Thank you all for the education.... I appreciate the info.