Re: power supply issue

Why are you seeing 27 V instead of 24 V at the output of the transformer?
Is your line voltage 27/24 * 120 = 135 V?



"Anders Nesheim Vinje" <a-vinje@xxxxxxxxxx> wrote in message
news:u9Nde.8638$ai7.210274@xxxxxxxxxxxxxxxxx
> I took a new measurement and found out the the ac value was acutally 27V
not
> 24. So when i muliply with the square of two i roughly get 37,5V peak to
> peak.
> But why do i see the peak to peak voltage after it has been rectified???
> Even with load 40ohms load.
>
> Anders
>
>
> "Anders Nesheim Vinje" <a-vinje@xxxxxxxxxx> wrote in message
> news:7RMde.8637$ai7.208762@xxxxxxxxxxxxxxxxx
> > Hi.
> > I have built this dual power supply.
> > Transformer rating: 2 x 24 V 60VA
> > Pretty standard with a bridge rectifier and ground connected to the
center
> > tap. So i got + 24 and -24.
> > The i have two 4700uF 50v caps, one connected at each powerline to
provide
> > filtering. Then there is a 7815 and and a 7915 as regulators.
> > Ok here is the issue. When i measure the voltage over the filtercaps i
see
> > +37,5V and - 37,5V! How is this remotly possible?. Even the peak to peak
> > voltage isent that high. The 7815 and 7915 is only rated up to 35V so i
am
> > scared they might blow or something.
> >
> > Another problem is that since there is a voltage drop 37.5 -15 = 22 V
over
> > the regulators. It cant provide much current before they shut down
> > because of the heat. I know from the data*** they can handle up to
10W
> > with a decent heatsink and a max current of 1,5A. I dont need that much
> > current anyway since the transformer can only deliver 30VA / 24 = 1,25A
> > per secondery anyway.
> > I have another question too. How much current goes through the primary
> > side of the transformer with max load? I was thinking of having a fuse
> > there instead of buying a fuse to each of the secondery outputs.
> >
> > Thanks in advance
> >
> > Anders Vinje
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>


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