Reducing dc voltage

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  #1  
Old 07-21-14, 04:32 PM
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Reducing dc voltage

OK here is what is going on. I have a 12 volt battery that is not movable. It is kept charged by a small solar panel. I would like to run a super small 6 volt motor off of this battery but the distance might be as much as 250 feet. Maybe as close as 50 ft.

There are voltage reducers that will drop 12 volt to 6 volt.

My question to you are as follows:
1. Would a long 12 volt wire run that reduces the voltage down to 6 volts be able to run the motor with no added reducers/converters? Amperage of the motor is unknown but it is just a very small motor that will only run for 10 seconds twice a day or something close to that.

2. Does a converter that is sold as 12 volt to 6 volt converter reduce an 8 volt supply to 6 volts or 4?

3. Suggestions. So I have the motor and an existing 12 volt system. What is the best way to supply the motor with or without using my existing 12 volt system.

P.S. The motor is in the shade so a close by solar panel isn't going to help.
 
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Old 07-21-14, 05:50 PM
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Welcome to the forums.

I would count on using the 12vdc supply and build a small 6v 1a regulator. It'll cost you several bucks. It uses a 6v1a regulator IC, two capacitors, a small heatsink and maybe a weatherproof box depending on your application.

The regulator is a 7806T, or an LM7806T, or an L7806T or an LM7806CT. Slightly different specs but all will work for you. In the link below is one with a heatsink. The part is available from just about anywhere..... possibly the shack too.

The good thing about a regulator like this is it will regulate and hold 6v from a supply voltage of 8-30vdc. Doesn't use up a lot of power and waste it in heat either.

7806T - 7806 6V 1A Positive Regulator
 
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Old 07-21-14, 06:29 PM
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thanks

That sounds like what I might need. Thanks. I have not been able to find out the amps pulled by the small motor.

Can you recommend a capacitor like you did with the regulators.

Battery - lots of wire - 7806T - a capacitor - small motor.

Does the above setup draw power when the motor is not in use?

I know capacitors are designed to provide powerful short burst of energy. If the motor is pulling one amp how many second will the capacitor be able to supply all the voltage required. split second/1 second/5 seconds???
 
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Old 07-21-14, 09:02 PM
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The motor is really the compnent that determines what type of circuit you need, how will you turn on and off the motor when you need to use it? Motors, like fan motors, are typically rated for continuous use, you can usually overdrive them for short periods of time as long as you never leave it over-driven long enough to overheat. You may not even need to reduce the drive circuit to 6v if you have a big enough mechanical load on the motor.

If you want to go with the 6v regulator you can just wire it up without any capacitors or a heat sink, especially if you can drive the motor on less than one amp and if it's only on for short periods... The caps allow you to draw more than one amp initially if they are fully charged and can be sized accordingly, and the heat sink is for sustained use, if the motor is on a switch and the switch is off the regulator will draw very little power, or better yet, switch the regulator off too if possible.
 
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Old 07-22-14, 12:54 AM
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DC to DC power supplies that will either reduce or increase voltage are readily available on Ebay for the same or less than it would cost to build your own. Some are just a printed circuit board, some have digital meters and some are encapsulated. Most have a fairly wide range of input voltages and some have adjustable output voltages. Current ranges from one to as much as 20 amperes output and most are less than $25. Biggest drawback is the shipping time, often four weeks or so from Asia.
 
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Old 07-22-14, 06:59 PM
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Thanks!!!

Danke- added because thanks didn't meet the minimum 25 character rule.
 
  #7  
Old 07-22-14, 11:54 PM
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If you want to go with the 6v regulator you can just wire it up without any capacitors or a heat sink, especially if you can drive the motor on less than one amp and if it's only on for short periods
A regulator like I described NEEDS a heatsink. The caps used are small and keep RF and motor brush noise from affecting the regulation.

Let us know which way you are heading.
 
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Old 07-23-14, 01:01 PM
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Is a heat sink really needed if the motor will only run for 10 seconds?
 
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Old 07-23-14, 01:49 PM
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No, heatsink is only needed if the component cannot dissipate the heat it creates on it's own fast enough (i.e. at full capacity in a constant state).

Most regulators have internal thermal cut outs, if they get hot they cut out until they can cool down. If you use one and it keeps cutting out, then you could use a heatsink.

The input capacitor helps to prevent voltage sags on the input side, but is not needed, and the output capacitor can trim down the ripple voltage on the output side, but is not needed.

Depending on what you want to use the DC motor for (and whether you care about what speed it runs at) you can change the voltage going to the motor to speed it up or slow it down. 6V is only it's recommended drive voltage which assumes a given load (fan, belt, servo, etc.)
 
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Old 07-23-14, 11:04 PM
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I don't understand it..... if you are going to build something.... why not do it right ???
 
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Old 07-24-14, 09:17 PM
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I don't understand it..... if you are going to build something.... why not do it right ???
Fair enough, but if the actual demand is truly 10s at a time with long durations in-between then even a liquid-cooled sealed heat sinking system is not going to have a chance to do anything of consequence.

Plus, the motor is in the shade so that should help too
 
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