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Power Supply Voltage B+
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Author:  tvs [ 16 Jan 2018, 16:44 ]
Post subject:  Power Supply Voltage B+


I just finished building the power supply and did some checks with my multimeter. I'm reading about 310 Vdc on B+ left and B+ right. This surprised me as I was expecting around 150 Vdc. Am I getting these readings because I don't have the power supply attached to a load? I have verified the resistor path and read 2K from the top of C1 to each of the B+ outputs.



Author:  Suncalc [ 16 Jan 2018, 23:07 ]
Post subject:  Re: Power Supply Voltage B+

Don't know what project your building but if you don't have a load then the voltage will likely read about 1.4 times the rated secondary voltage of the transformer. A schematic and some context here would help greatly.

Author:  Danielk [ 28 Jan 2018, 02:45 ]
Post subject:  Re: Power Supply Voltage B+

You need a load so you can get some voltage drop over your resistors. The resistors can only drop your voltage if there is a current going. Ohm's law.

Author:  M. Gregg [ 28 Jan 2018, 09:35 ]
Post subject:  Re: Power Supply Voltage B+

I have seen,

very strange voltages on power supplies without a load, the difference is normally charge to peak, but if there are transients riding on the supply peak is not what you get. But its never good to run a PSU without a load unless the caps can withstand the off load voltage. (I always over rate cap voltage).
Obviously size can be limiting factor.
That's when MOV suppression is useful.

M. Gregg

Author:  gofar99 [ 28 Jan 2018, 17:04 ]
Post subject:  Re: Power Supply Voltage B+

Hi, You are certainly not the first to do this...but I highly recommend not doing it. First you will not get the results you expect and will think something is wrong. Second it is possible to damage some components if they are not rated for the unloaded votlage.

Good listening

Author:  KochiyaYamato [ 05 Feb 2018, 04:10 ]
Post subject:  Re: Power Supply Voltage B+

If you can tell us your transfomrer ac voltage output then maybe we can dig in further.

Generally with load a 310V supply may drop to 250V with a very large load, generally should get arround 280V with resonable load.

You may have been using the wrong rectifying scheme, maybe you have a ceneter tap transfomrer, wired full wave rectifer (4 diodes) on two sets of 150V ac instead of doing a full wave center tapp (2 diodes) using two sets of 150v ac and using the center of the transfomer as ground.

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