# Voltage And Regulators

Discussion in 'The Projects Forum' started by ElectronicLife, Jul 19, 2014.

1. ### ElectronicLife Thread Starter New Member

Jul 19, 2014
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0
Hi guys ...

I have a question on voltage division :

I have an 24 volts | 5 AMPS adapter and I want to divide it into 2 similar 12 volts | 2.5 AMPS channel. I know that I should use regulators or resistors to reduce the voltage or amps , but as far as I know this is DC power. It means when I put some resistors or regulators (like LM317T which gives alternative output voltage and more than 1.2 AMPS) , the power drains (these electrical parts consume the rest of power) and I can not make two similar power channel (12 volts and 2.5 amps).

By the way , I can not use series connection due to some features of my projects!

2. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,592
391
hi,
For efficiency I would consider using a switch mode PSU to convert the 24Vdc to 2 * 12Vdc, you will not get 100% conversion, so the 5Amp will be down by approx 5% to 10%.

Using linear regs, for 24Vdc to 12V, will be VERY inefficient
E

Last edited: Jul 19, 2014
3. ### ElectronicLife Thread Starter New Member

Jul 19, 2014
8
0
I have found STEP-DOWN DC-DC which seems to be a great convertor for me! Can I use this to do so ?!

And again the same question : Do I have to use 2 of STEP-DOWN DC-DC?! Can I use one of them for one of my channels and then the rest of the adapter power for the next one ?!

More details of STEP-DOWN DC-DC Module :

Input Voltage : 3-30
Output Voltage : 1.28-18
Output Amps : 2-3

4. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,592
391
hi,
I assume the step down is a SMPS unit.?
You can drive two SMPS units from a common 24Vdc source, just pay attention to the common 0V rails.
Some SMPS are isolated from Input to Output, some are not.
Do you have a d/s you could post for the Step Down unit.?

E

5. ### ElectronicLife Thread Starter New Member

Jul 19, 2014
8
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Here is a picture of STEP-DOWN DC-DC :

It is adjustable for output parameters.

I want to ask my question in another way :

How can I power up 2 DC 12 volts fans separately with one 24 volts adapter?! I have 2 choices between Series and Parallel connection :

I can't use series because : If one of the fans is off ,then the next one is off too!
I can't use parallel because :
If both the fans are on , then everything is OK . But when one of the fans is off , then the whole 24 volts come to one of the fans and it burns out!

6. ### Alec_t AAC Fanatic!

Sep 17, 2013
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How much current does each fan actually draw? (The label should indicate its power or current rating).

7. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,592
391
With two separate 12Vdc 2.5A SMPS driving two separate 12Vdc 2.5A fans, connected to the same 24Vdc source, how will that cause a burn out.???

8. ### ElectronicLife Thread Starter New Member

Jul 19, 2014
8
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Each of the fans needs 12 volts , around 2.5 amps.

I know that when i use SMPS , there is no problem doing it and there is no burning out! (I was just talking about different types of connections). But is there any way to do such a thing without modules or SMPS ?! Because it is not economical to buy 2 of SMPS for this simple project !!!

I have heard something about using low voltage regulators like 7805 and some diodes to power it up...

Do you know anything about that ?!

Thanks

9. ### Alec_t AAC Fanatic!

Sep 17, 2013
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I doubt it will be any more economical to do it with a 7812 or similar linear regulator. With a 2.5A load the regulator, or other voltage dropper, will have to dissipate (24-12) x 2.5 = 30 Watts !! That will require the use of an expensive heatsink.
The cheapest option might be to buy one 12V, >=5A power supply which could power both fans.

ElectronicLife likes this.
10. ### ElectronicLife Thread Starter New Member

Jul 19, 2014
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0
Do you mean to wire them up in Parallel connection ?! Because in parallel , the voltage of both the fans are the same and the amperage is sum of both of the fans (so it means 2.5 for each of them). Right ?!

But I think in the real world , the voltage of adapter drains when you have already attached one of the fans to it !

But anyway , Thanks for your guidance ...

Last edited: Jul 19, 2014
11. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,971
1,135
Correct.
There should be very little voltage drop with a good quality adapter used within its specified operating limits.

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