# Split input?

Discussion in 'The Projects Forum' started by goldeneye123454321, Oct 5, 2008.

1. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
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hey, is it posible to split one input, 12vdc @ 2 amps, to 4 outputs and not have any power loss when all outputs have a load? if not, how do i fix it?

2. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
If the sum of your loads does not exceed 2A, you can simply connect them all together to the power supply.

If the sum of your loads exceeds 2A, then you need to get a more powerful supply, or do something to the loads that reduces their current demand.

Otherwise, the power supply may either "fold back" (go to 0v until the overload is removed) or supply 2A at a much lower voltage than normal.

3. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
0
ok. well, all i know is that i have 4 micro fans that run @ 12 vdc and 1.56W. i dont know how many amps that is or the current draw is, but, do you think 4 will not over load the adadpter?

4. ### beenthere Retired Moderator

Apr 20, 2004
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P = IE. So for 12 volts and 1.56 watts, the current per fan is .13 amps.

5. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
0
so, 1.3 mA?? thats good. so that means i can connect 4 to one input and all will be running at 12 volts with out any drop from input to output?

6. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
No, 130mA, or 0.13A.
I = P / E = 1.56W/ 12v = 0.13A = 130mA

0.13A x 4 = 0.52A
You have 2A available.
2A / 0.13A = 15.38
You could power up to 15 of those fans with your 2A supply.

7. ### scubasteve_911 AAC Fanatic!

Dec 27, 2007
1,202
1
Or, you can do it all in the 'power domain', 12V @ 2A = 24W, so you can power 24/1.56 fans (integer of course)..

Steve

8. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Just following on from what Steve said:

Since P(ower in Watts) = E (Voltage) x I (Current in Amperes), then 12 Volts x 2 Amps = 24 Watts.
24W/1.56W = 15.38... also.
Note that you always need to match the voltage requirements; just going by Watts or Amperes isn't enough.

Something that wasn't covered is the type of power supply that you are considering using to power the fans. If it is a regulated power supply, then the voltage output will remain constant at 12v for loads of 0A up to 2A.

However, if it is an unregulated supply such as a "wall wart" (a transformer that plugs into a wall) your mileage will vary - perhaps considerably. "Wall warts" do not generally have internal regulators, only a transformer and a rectifier or rectifier bridge. Their output rating is approximate.

Even with a wall warts' rated load, the actual output voltage may vary 10% from the specified voltage. If they are lightly loaded, the actual output voltage may be significantly higher.

9. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
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no, its a regulated adapter used to power one of those external hard drives. the plug says "+12 ~ 2A" to im guessing that its constant no mater what to load.

10. ### scubasteve_911 AAC Fanatic!

Dec 27, 2007
1,202
1
golden,

It doesn't work that way. The supply will not always supply 24W, regardless of load. It means that it is capable of supplying 2A if it needs to. This is analogous to having a car that can go 100MPH, it doesn't mean that it always goes that speed, it just can if you need it to.

Steve

11. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
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i think i know what you mean. so as long as i dont use 2amps or 24w the whole time, or under a load, it will give the same voltage?? sorry if im not geting it, its a lot to understand.

12. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Try measuring it's output under no load using a voltmeter. I'll bet that the regulator is inside the drive rather than in the adapter.

13. ### Audioguru Expert

Dec 20, 2007
11,226
1,333
A DC electic motor has a surge current when starting and when stalled maybe 10 times its running current. The power supply must be able to produce the high current. Maybe from a big capacitor across the supply.

14. ### goldeneye123454321 Thread Starter Member

Oct 1, 2008
19
0
i checked to voltage. it held a steady 12.35 vdc for 5 minutes.