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we have a fax machine that is always busted whenever there's a power
surge,so I suspected that the power supply of the fax machine is not
regulated..instead of fixing it I decided to make one.
but the problem is all of my notes in electronics only gives me a
20volts DC output which is not enough to supply the fax machine.
(it uses a 24vDC output)

Does anyone here have a circuit diagram of a regulated 24v Power
Supply?

I will appreciate any help.

Thanks.

To get 24V DC, you need a transformer which will have a peak (with reference to zero) voltage of just over 24V on the secondary (output). The ammount over depends on whether you're using a two or four diode full-wave rectifier (don't go half wave, you get too much ripple). With the two diode full wave you need a center tapped transformer and the secondary voltage should be about 0.7 volts above what you need (voltage drop across a diode). With a bridge rectifier, you don't need a center tapped transformer and the secondary voltage should be about 1.4 volts above what you need.

I would recommend you get a bridge rectifier. It's essentially four diodes arranged in a ring, within one small package with four pins. You have two pins for AC input and two pins for + and - DC output.

I'm sure there's schematics for power supplies all over the internet, so you just need to adjust values to what you need and put them into the schematic you find. There's lots of different ways of setting up filtering and regulation. Basically what you need is a nice big filtering capacitor to remove the AC ripple, and a 24V regulator. You can put both of these in parallel with your DC output.

So if you're using a bridge rectifier, you want your secondary peak voltage to be about 25.4 volts, or maybe 26 volts if it's easier to find. But that's peak, not RMS. To convert it, you divide by the square root of two. That's about 17.9 volts RMS. So if you can find a 120V primary / 18V secondary transformer, you should be set. Then you need a regulator and a filter cap. There's some other components, but that's the basics. Look for real schematics online.

But I'm no expert here, just a student. I may not yet know enough about power supplies. Test what you get before hooking it up to your fax machine. And make sure you use a regulator, because if not when you test the voltage on something before you hook it up to a load, it will change when you hook it up.

-Tavys

Hi, I'm new to this group but old and experienced with electronic
devices. Have you thought about a surge suppressor for your device?
Just a thought! c ya

Hi, its always good to make one but i'm concern about your safety, on
your case if you are experiencing a huge amount of surge you dont
need to built one to replaced the other one the problem still there.I
would suggest to get one reliable UPS uninterruptible Power supply
this type of device has a voltage windows that can handle huge
amount of surge and sag.If out of your budget mind to get on surge
suppressor with circuit breaker.This i would like you to do if you
really want to built one first monitor your ac utility during day
and night time check how far the ac utility went beyond the nominal
voltage 110Vac, check your ac outlet where the fax machine
connected is it really properly grounded? if not have a elctrical
technicain look on it, reason why I want you to check the proper
grounding cause this in one reason why your psu on your fax keeps
busted. during that time.let me know if you needs more info on
voltage regulation.Electonics 101 advice Think first before you
jump...just be careful.safety first.

Thanks,
The safet Guy


- In Electronics_101@y..., reniar@c... wrote:

we have a fax machine that is always busted whenever there's a

power

surge,so I suspected that the power supply of the fax machine is

not

regulated..instead of fixing it I decided to make one.
but the problem is all of my notes in electronics only gives me a
20volts DC output which is not enough to supply the fax machine.
(it uses a 24vDC output)

Does anyone here have a circuit diagram of a regulated 24v Power
Supply?

I will appreciate any help.

Thanks.