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How to lower the DC voltage of a transformer. Answered

Hi, at last i have got a 45-0-45 transformer @5amps, but now i have a problem, the VDC output i am getting is 74vdc but my 400watt rms mono amp's maximum input VDC is 56vdc, so i don't think its a good idea to feed the 74vdc, so is there a way to lower the 74vdc, BTW please don't advice me to unwind the secondary coil because i am new to electronics and the transformer didn't come cheap, so i don't want to break it.

i am using IN4007 diode and 4700uF 63V cap for the bridge rectifier.

​I just forgot to give some details on this topic. The transformer is to use with the 400watt rms mono amp. The amp has 8 MOSFETS side by side, 4 IRFP9240 and 4 IRFP240 and 6 transistors.

https://s23.postimg.org/l8onxw1wb/image.jpg

https://s17.postimg.org/czg1ynam7/image.jpg

BTW the transformer shows 45-0-45 VAC but when i test with a multimeter, the VAC is 53volts.

Thank you.

Regards.

Discussions

1
iceng
iceng

Best Answer 2 years ago

Strange you do not mention the explosion of the 63V cap on 74VDC ?

Here is a lower value output of your XFMR transformer..

Click pic to see whole image..

SpliXFM.JPG
0
Lima79
Lima79

Answer 2 years ago

I thought i wrote 74"VDC" not 74"VAC"(: anyways the output of the transformer is 53VAC but after rectifying it, i am getting 74VDC BTW the 400watt amp is a 56-0-56 VDC so the rectifier needs to be a center tapped. I did some experiment with diodes to lower the voltage but it took me 80 IN4007 diodes:D(i am bit despaired because this project is costing me a lot of money and lots of time wasted) to lower the DC voltage to 63VDC i can add some more diodes to get close to 56VDC but as you know, this is not a practical way, i am not sure if i can use resistors because on load the resistors might get too hot and smoke nu(: Thank you so very much my good brother, for your kind help and time, appreciated.

0
iceng
iceng

Answer 2 years ago

Here is the ckt and a 1N3309 10 volt Zener Diode 50 watt

https://www.digikey.com/product-detail/en/microsem...

Keep in mind lowering the voltage will also cut further back on the available power to your amps !

----------------------------------------------------------------------------------

Just thought of a way to lower the voltage a lot cheaper too !!

Get a small 24 Volt 2 Amp Radio Shack or eBay transformer.

See the last schematic drawing....

SpliXFM.JPGPOWER Diode.JPGSpltBuck.JPG
0
Lima79
Lima79

Answer 2 years ago

ok, i will try that, thanks once again, appreciated.

0
iceng
iceng

Answer 2 years ago

That 400 watt amp will use I=P/V = 400 / 56= 7.15 amps

But your transformer is rated for a maximum of 5 amps

This means you can only power P=VxI = 56 x 5 = 280 Watts maximum

And if there are two channels that is 140 watts per channel..

You can put a 50watt 11Vz Zener diode in the center ground return of my transformer schematic which lowers the voltage to a 53 VDC.

This is a stud 1/4-20 power device that needs a heat sink to throw away 55_watts to lower your output voltage and costs $35..

0
Lima79
Lima79

Answer 2 years ago

ok, this project is costing me lot nu(: anyways thank you so very much, appreciated.

0
NeilRG
NeilRG

11 days ago

The regulator being mentioned is a DC DC converter. What you need is called a "buck " converter. The word buck is not a brand and certainly not the price. The buck converter reduces or bucks the higher voltage. IDK if such high power converters are available or at what cost. It's not clear if your source voltage is 120 or 220.

0
inuichiban
inuichiban

23 days ago

cheers for this, I got a similar problem with my audio psu project. thx again, iceng!

0
steveastrouk
steveastrouk

2 years ago

Right now, its giving 74V. Can you load it and see what it gives you at 5A ?

You have run into something called the transformer's "Regulation". An expensive transformer has a lower regulation - like 5% or so. Yours has a regulation of around 30%.

It may be you'll have to get a high power regulator to get down to a safe voltage for your amp

0
Lima79
Lima79

Answer 2 years ago

ok, i think i know how to load the TR for test(: You meant something like this Yes(:

0
Lima79
Lima79

Answer 2 years ago

Yep!! thanks to you and all the cool brothers out here, on the amazing and the coolest diy/education/knowledge based website i have ever known :)INSTRUCTABLES(: Thank You.

0
Lima79
Lima79

Answer 2 years ago

Load into the 400watt amp or... BTW i was thinking about that but i don't have any electronics device to test the 74V TR, i have only two amps the other one is a 200watt rms mono amp which is also rated at 56VDC max. BTW if i feed the 74VDC to one of the amps, will it cook the amp(: Can i ask what is a Power Regulator, i mean to use with the TR, anyways thank you so very much my good brother, for your kind help and time, appreciated.