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### Topic: Is that a possible ...substitute for a voltage divider? (Read 2078 times)previous topic - next topic

#### Nachtwind

##### Mar 29, 2011, 12:15 am
Hi..
Just a small question about voltage dividers. Basically, from what i understand you Y-Split a power line with resistors to GND and the power you want in order to get the voltage you want. So much for the theory.. now in my case i need to power down like 28V to 10V but with a very high amperage - which makes, in my opinion, the use of resistors almost impossible. Therefore i thought about using two L7805 which output 5V each and then "combine" them again at the output to get - roughly - 10V.

The idea behin all this is the following.. for my current project i need lots of mAh and the possibility for a high amperage as well. So i can go wither with 11.1V LiPo batteries or, what i had in mind, a chain of 2 or more 7.whatnot LiPos and then bring them down to what i need them..

What solution would you here prefer?
Believe me, Mike, I calculated the odds of this succeeding against the odds I was doing something incredibly stupid[ch8230] and I went ahead

#### James C4S

#1
##### Mar 29, 2011, 12:20 am
Voltage dividers only work when they are connected to something of high impedance (low current draw.)  So you wouldn't use one in this situation.

As for taking two 5V supplies and combining them, just how were you planning to do that?  If you were going to use a LM series regulator, why not just use the LM7810, which provides 10V output?  However before you go there, how much current do you intend to draw?  The LM-series regulators are limited to 1A.  And that current rating is dependent on a proper heat sink.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

#### liudr

#2
##### Mar 29, 2011, 12:46 am
Chaining batteries don't give you larger amperage. You want them parallel.

#### cr0sh

#3
##### Mar 29, 2011, 12:50 amLast Edit: Mar 29, 2011, 12:52 am by cr0sh Reason: 1
Another thing to keep in mind is that it is possible to get a 7805 to output a regulated voltage greater than 5 volts - for example, see these:

http://www.goldwingfacts.com/forums/forum1/75779.html

You will still be limited in your current output, though - which you haven't stated what is needed...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

#### Nachtwind

#4
##### Mar 29, 2011, 01:03 am
Well... i read some more myself in the past hour into this sort of stuff and have to say that i see your objections now.. especially the limitation to 1A is not so good since i need 30 to 50... well, then i will have to go for a 11.1V battery.

Thanks anyway
Believe me, Mike, I calculated the odds of this succeeding against the odds I was doing something incredibly stupid[ch8230] and I went ahead

#### liudr

#5
##### Mar 29, 2011, 01:21 am
Why don't you just use a car battery since you're saying 30-50A? It's a lot even for a very serious project.  Don't sue Arduino if you fry yourself.

#### cr0sh

#6
##### Mar 29, 2011, 01:30 am
10 volts at 30-50 amps - and regulation? Maybe you should tell us what the project is for, and then maybe we can make better recommendations...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

#7
##### Mar 29, 2011, 05:15 am
Sounds like a good case for a heavy duty high frequency switching regulator.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### fkeel

#8
##### Mar 29, 2011, 08:36 am
please. i am curious. what are you trying to do?
http://embodimentlabs.tumblr.com/
http://paulstrohmeier.info/

#### Nachtwind

#9
##### Mar 29, 2011, 09:17 am
just some quadrocopter, nothing more ,0)
The Arduino wont have to suffer from the amperage since it is safe behind the 5V line of the speed controllers (and will get the "normal" Arduino power circuit as well).  The amperage will only come from the speed controllers/motors. A car battery sounded like a good idea but i have to take the weight for this into account..
I ordered 2 11.1V LiPos and will use one at a time i guess, thats the easiest way i hope.
Believe me, Mike, I calculated the odds of this succeeding against the odds I was doing something incredibly stupid[ch8230] and I went ahead

#### charliehorse55

#10
##### Mar 30, 2011, 11:26 pm
If you use 2 at once and wire them in parallel there is no different electronically, and your craft will fly for longer.

#### cr0sh

#11
##### Mar 31, 2011, 12:26 am

just some quadrocopter, nothing more ,0)
The Arduino wont have to suffer from the amperage since it is safe behind the 5V line of the speed controllers (and will get the "normal" Arduino power circuit as well).  The amperage will only come from the speed controllers/motors. A car battery sounded like a good idea but i have to take the weight for this into account..
I ordered 2 11.1V LiPos and will use one at a time i guess, thats the easiest way i hope.

Is it not possible to purchase COTS ESCs for the voltage/current requirements you need/want? If I were building such a project, that's where I'd look. Also - at a certain point, gas engines become a more attractive option (well, noise and other issues aside).
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

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