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Old June 30th, 2011, 12:37 PM   #1
ddeshi2
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120v ac to 24 v dc rectifier

Hi all, Can anyone please provide me the electronic circuit design for 120v ac to 24 v dc rectification. Or something similar to it.I'm not asking it to use with the PLC but for some other tool. Or else please tell me where to start to design such thing.


Thanks in advance,

Ding
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Old June 30th, 2011, 12:51 PM   #2
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Why do you need to design a 24 volt DC power supply? You can buy one much cheaper than you can design and build a one-of-a-kind. Depending on current requirement, you can probably find one for $10.

If you really have some need to design one, the place to start is to first draw a circuit diagram. At least, you need a fuse, a transformer, a full-wave rectifier, some wire, a circuit board, and either lots of luck, or a course in electronic circuits!

Last edited by Lancie1; June 30th, 2011 at 01:07 PM.
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Old June 30th, 2011, 01:06 PM   #3
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http://lmgtfy.com/?q=24vdc+power+supply+schematic
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Old June 30th, 2011, 01:10 PM   #4
ddeshi2
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@ Lancie1

Actually all the instruments on our tool requires 120 v ac. There is one flame detector that requires 24 v dc. The distance between power source and tool is like 1000 ft. If I use a 24 v dc power supply the voltage drop across the 10 AWG wire will be more than 5%. I cannot use a wire of different size because of less space for wiring. so what I'm thinking is I'll use the same 120 v ac and 10 Awg wire and I'll do the rectification near the tool to produce 24 v dc. I need a circuit design for it. Is there any thing that is readily available in the market?
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Old June 30th, 2011, 01:22 PM   #5
Lancie1
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Quote:
I need a circuit design for it. Is there any thing that is readily available in the market?
Ddeshi, where you been, buddy? There are plenty of off-the-shelf power supplies. I am sure there is one already built that will convert 120 volts to 24 VDC. In fact, I suggest buying one with an adjustable output potentiometer, so you can adjust the 24 VDC output voltage to compensate for the voltage drop in your 120 volt line.

Just listing the major vendors for 120/24 VDC power supplies would take several pages. What is the power requirement for your flame detector, in Amps? With that, anyone can pick out numerous power supplies to do this job. But to get a better fit, it is important to know the environment where the power supply will be located: outdoors? dirty? hot?. If any of those, then you need a tighter specification, maybe a NEMA type 4 enclosure on your power supply.

EDIT: Wait, is this for that down-hole well flame detector? If so, you certainly will have some problems with temperature and pressure tolerances.

Last edited by Lancie1; June 30th, 2011 at 01:33 PM.
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Old June 30th, 2011, 05:20 PM   #6
panic mode
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if you would rather make your own bench power supply, you just need to google for a sec to get things like:
http://www.electronicecircuits.com/e...-supply-0-24v/
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Old June 30th, 2011, 06:25 PM   #7
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I think this is a continuation of Ddeshi's Purple Peeper project. I think he means to build a power supply that will withstand the pressure and temperature of an oil well or something similar.
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Old June 30th, 2011, 06:26 PM   #8
Travis Latiolais
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Hey Ddeshi, i know you are in Baton Rouge. I know they sell these rectifiers at Grainger, and i also think Rielly electric supply.It is a simple hookup, you run 120 into converter, and the output is 24vdc. They are small and inexpensive
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Old June 30th, 2011, 09:43 PM   #9
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1) Transformer, bridge, cap, and an LM317 or LM350K.
2) SMPS for about $20.00.
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Old July 1st, 2011, 09:11 AM   #10
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@ Lancie

Yes, at first we thought of building something that could withstand that pressure and temperature. But our project manager has asked us to go for something that could withstand ambient temperatures as the circuit is not goin to be in the downhole (they have changed their designs)

@ Travis, Keith

Thanks for your help.

@ all

can anyone please explain this circuit in detail. I'm not good at circuit designing.
http://www.electronicecircuits.com/e...-supply-0-24v/
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Old July 1st, 2011, 09:21 AM   #11
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I don't see a circuit at your link. Internet Explorer reports "Nothing found for E -supply-0-24V".

Did you mean this one?

http://www.electronicecircuits.com/e...rcuit-diagram/

If all you need is: 120 VAC input, 24 vdc output, up to 10 Amps, located in ambient temperatures up to 100 degrees, then you should just buy a power supply off-the-shelf. Designing and building a power supply is a big waste of time, unless you need something that is not available already.

The circuit above is for a switching power supply. Advantage is that no transformer is required, disadvantage is that output is not usually clean straight Direct Current, but a chopped wave that simulates that.

Last edited by Lancie1; July 1st, 2011 at 09:33 AM.
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Old July 1st, 2011, 11:27 AM   #12
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@Lancie

We'll go for the power supply off-the-shelf.I'm talking about the link that "panic mode" has posted above. My question is why are they using those zener diode and transistors in the circuit diagram. Do they act as a filter or something?
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Old July 1st, 2011, 11:37 AM   #13
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Ddeshi,

Yes, the zener diode helps regulate the voltage, clamps it to a certain level depending on the volt rating of zener.

EDIT: I see panic had done a great detailed explanation, so I will take my pidley little marbles and go home!

Last edited by Lancie1; July 1st, 2011 at 11:44 AM.
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Old July 1st, 2011, 11:40 AM   #14
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the link i posted was just first circuit that i spoted. it is a classic power supply with voltage regulator and current limit:

1. transformer steps down voltage and provides isolation from mains. if your mains is 120VAC then that is what primary of the transformer need to be rated for.

2. D1 is single phase bridge rectifier. it converts AC into pulsing DC.

3. C1 is used as filter to smooth those pulses into fairly stable DC (although not regulated)

4. R1 is used to discharge C1 when power supply is turned off

5. D2 and C2 are again rectifier and filter (can be removed, it would be better to have C2 in parallel with zener)

6. R2 and D3 form simple voltage reference (D3 is zener diode). for this to be stable, only small current (mA) is allowed through zener diode (nearly constant current).

7. VR1 and VR2 form voltage divider so one can dial down the reference voltage

8. T2 and T3 are voltage follower, they allow output current to be large while D3 current can remain small. note that this is open loop voltage regulator.

9. R3, VR3 and T3 form current limiting circuit. when output current is large enough so voltage drop across R3 and VR3 reaches Vbe of T3 (about 0.7V), T3 will turn on and Vref will be pulled down (T1 and T2 will follow and output voltage drops). this is how current control acts. unfortunately, sensing voltage is Vbe of the T3 (depending on application, 0.7V may be fairly large). the point is that even if power supply is operating in normal condition (not current limited) output voltage varies with current drawn (output is lower when current is largest). this could have been completely eliminated either by adding feedback to voltage regulator or by moving current sensing circuitry elsewhere (for example in place of D2, it would require more changes).


as others have mentioned, you can use LM317T as simpler regulator and you can also use another LM317T as current limit. note that tihs will make lower limit about 1.2V and not zero (it is possible to get to zero too, but requires additional components). building power supply is good exercise for students learning electronics but since prices of off the shelf products are so attractive (use eBay if store prices are not low enough) it makes little sense to mess with DIY.

Last edited by panic mode; July 1st, 2011 at 11:57 AM.
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Old July 6th, 2011, 08:54 AM   #15
ddeshi2
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@ Panic

Thank you for the detailed explanation. I'm trying to find out how he got those resistor and capacitor values. If I have any questions I'll post here.

Thank you,

Ding
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