# Electronics question: dropping voltage



## paintjockey (Jan 3, 2008)

Easy question for some of you out there. I have a 14.8 volt (16v fully charged) battery. I need to drop the voltage to below 5v to run an automation motor. Whats the easiest (and cheapest) way to acomplish this? 

Thanks,
Terry


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## dbodnar (Jan 2, 2008)

Posted By paintjockey on 04 Aug 2011 02:37 PM 
Easy question for some of you out there. I have a 14.8 volt (16v fully charged) battery. I need to drop the voltage to below 5v to run an automation motor. Whats the easiest (and cheapest) way to acomplish this? 

Thanks,
Terry

Terry - the answer depends to some degree on how much power you will be delivering at the 5 volt end of the circuit. If it is not too much (say 1/2 amp or so) a 7805 voltage regulator with a decent sized heat sink will work. If you need more current that that heat will become a bigger issue.

There is a detailed article on supplying 5 volts for model railroad applications on my web page - see:

Voltage Regulator Article 

Please let me know if you have any questions.

dave


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## Greg Elmassian (Jan 3, 2008)

easiest, most efficient (since you have battery), not cheapest is to find a DC to DC converter with 5v output... 

More money, very simple to use, and your battery will last probably 3 times as long... 

Greg


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## Mike Reilley (Jan 2, 2008)

Well...if the battery has no other load on it...meaning it's JUST gonna run the automation motor...you're gonna be WAY ahead to just buy a 4.7v lithium battery.


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## Michael Glavin (Jan 2, 2009)

Terry, What kind of battery? 

Mike, Lithium is 3.6-3.7V nominal 4.2V off charge. 

Michael


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## paintjockey (Jan 3, 2008)

14.8 LiIon battery approx 4000Mah or there abouts. The battery runs the loco but i want to add one of phil's Narrow Guage motors for automation. From what I read the motor runs from 1.5 to 5 v dc. I using airwire some original some G2 boards. 

Terry


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## dbodnar (Jan 2, 2008)

Posted By paintjockey on 05 Aug 2011 10:40 AM 
14.8 LiIon battery approx 4000Mah or there abouts. The battery runs the loco but i want to add one of phil's Narrow Guage motors for automation. From what I read the motor runs from 1.5 to 5 v dc. I using airwire some original some G2 boards. 

Terry Terry - I found the web page for the motor you are using. Unless you are putting it under a great deal of stress (load) the current draw should not be very high. Any of the suggested solutions will work for you. The simplest is a separate battery. You could use 3 or 4 AA or AAA cells (rechargeable or Alkaline) or a single lithium ion battery. It all depends on how much you want to fool around with charging or replacing a 2nd battery.

The voltage regulator solution will work as will the DC to DC converter - there are a number of them on eBay - just search for DC DC CONVERTER - here is one that should work

eBay Link 


dave


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## kormsen (Oct 27, 2009)

or you just put 12 diodes in series before the motor. 
that is easy to do and does not need much space.


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## Michael Glavin (Jan 2, 2009)

I'd look at driving the animation with the G2! 

Or tap a single cell of the battery pack. 

Michael


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## Madman (Jan 5, 2008)

I found the converter on Ebay. It is sold by Asia Engineering. Look up, LM317 In DC or AC 4V-30V Out DC 2.5V-27V 1A Converter, on Ebay. I hope this helps.


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## paintjockey (Jan 3, 2008)

I will control it with the G2 but I still need something to take the voltage down from 14.8 to under 5vdc. I think the converter is the way to go. thanks for the help. 

Terry


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## Rods UP 9000 (Jan 7, 2008)

Terry 
I have the same motor from Phil that I'm going to use for the bell. The plan is to use the FnA on the G2 and 
program it to function #2. The bell is also programed for function #2 on the Phoenix board. I'm going to use 
a 1 amp 5 volt regulator to power the motor. If it is still too fast I will use a 1 watt resistor between motor and 
regulator. I will play with the value to get the speed to match with the sound board. 
Rodney


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## Dan Pierce (Jan 2, 2008)

A diode is better for dropping the voltage to a motor as they do not change voltage with current draw. 
So, 3 diodes with a .7 drop would give 2.9 volts from a 7805, but you could use a 7806 and get 3.9 or 3.2 volts ( 4 .7 diodes). 

However the DC to DC converter is best for the large drop you need and then fine tune with diodes. Check the diodes as there are .3 pr .7 volt drops for different types.


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## Greg Elmassian (Jan 3, 2008)

Easier way to determine the diode drop is whether it is an ordinary silicon diode, or a schottky diode... if it is a .3v schottky, it will be advertised as such (because they cost more).. 

Of course my suggestion way back on post #3 is the DC to DC converter, since any other method wastes a fair amount of power, the DC to DC should be 90% or more efficient. All power "dropped" by resistors, regulators, etc, is lost as heat, i.e. using battery capacity and throwing it away... (contributing to global warming to ha ha!). 

Greg


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