hross14

Hey all--trying to design a circuit so i can use a 4.8-6 volt RC servo in a car. So that means i need to drop the voltage from 12 volt down to 4.8-6 volts. On top of that i would like it to be robust enough to weather volt spikes, etc.....cant go over 6 volts or the servo will fry...

Willing to pay/trade/buy lunch/Give them a big pat on the back to show me how to do this.....

Thanks Henry

hross14

https://www.yotatech.com/forums/f96/...-volts-160628/

Here is my thread in the audio department--but i know nobody goes over there.

Just trying to design a circuit where i can use a 4.8-6 volt RC servo to power an HVAC Flapper off 12v (hard wired into a car).

For those electrically minded

here are the specs;

Running Current= :400mA :500mA

Thanks and i would really appreciate it

Henry

SoCalPaul

Buy a 12v to USB power adapter, it will provide a regulated 5v.

http://www.hardwarebook.info/Universal_Serial_Bus_(USB)

Paul

tc

I'm guessing it's DC? That's a bummer, because a little transformer would be nice ... no power loss.

For DC, your only option is to burn up the voltage with a resistor

4Crawler

iTrader: (3)

Just need to pick up a DC voltage converter, Radio Shack has them:
- http://www.radioshack.com/product/in...ductId=2102591

or build a voltage regulator circuit similar to the ones below:
http://ourworld.compuserve.com/homep...den/page12.htm

hross14

Thanks Crawler--i think the cigarette lighter idea is the best. I can buy that and then just take it apart to wire in my servo and switch right? Also are resistor circuits unidirectional? Meaning that if polarity was reversed i would still get the voltage reduction?

hross14

Thanks Paul

4Crawler

iTrader: (3)

A resistor would work in any direction. If the servo has a constant current then you could use a simple resistor to drop the voltage down.

JC_ez

The option of using a DC voltage converter would be nice, but those things are much too bulky (and expensive) for your needs.

Using a resistor to bring down the voltage or using a resistor setup like a voltage divider would be a poor choice for proper voltage regulation in my opinion.

I suggest using a basic LM317 IC and wire it up as either a constant current source or constant voltage source. With a max of 6 volts and 500 mA, you may have to use a tiny heat sink. I believe the LM317 has thermal overload protection and voltage spike protection built in as well. If you need a quick diagram, let me know so I can send one over to you.

Just let me know if you need to have a constant current, or a constant voltage for your applications and I can help you more from there. Also let me know which servo motor you are using so what I can see the specs for it. You will most likely need a diode with the motor to protect from high reverse voltage spikes due to the motor.

This is not true. You can use a DC-DC switching power supply in buck mode. Although very cool, this method usually requires tight tolerances with the circuit layout and introduces unwanted EMI and RF interference. It is also much too complicated for what hross14 is trying to do.

hross14

JC ez--the servo is a Hitec HSG 625 with metal gears.

The door/flapper, i do believe, would stay open once it is opened and closed once it is closed. this would lead me to believe that i would not need constant power. just on in one direction and then on in the other direction.

I am still trying to understand the current, versus watts, amps, volts.

My basic understanding of amps and volts is like Horsepower and torque--

All the other stuff i dont quite understand. So my apologies upfront for really being semi ignorant. I am reading up on it but i think it will just take me a little bit to get it....

THanks for the help

hross14

Also, i will be powering the circuit off the ignition switch--so it will turn off and on with the ignition.

4Crawler

iTrader: (3)

Power (watts) is volts times amps. So given the voltage, if you know either amps or watts, you can find the value of the other one.

96redtoy

A little off topic but what are you going to do with this servo

hross14

Crawler--so current is the same as power right?

So power/current=V * A

So 5(volt) * X (Amps)=.5 watt (solve for X)

Equals .10 Amps

But the watts is what ultimatley dictates what a system can handle--so we could have alot of amps and very little volts--but still have the system work (Cars)

Or alot of Volt but very little Amps (house) and that is why that system works

So to clear up the vocabulary--

--Watts and Power is the Same thing
--Volts are the amount of work that can be done (horsepower)
--Amps=(Ft lbs Torque)--provides the force neccesary to do the work....

This is a great thread by the way-----

hross14

This is that little black box with three pronges right?

What would be the benefit of this versus the USB/Cig lighter adapter?

"I suggest using a basic LM317 IC and wire it up as either a constant current source or constant voltage source. With a max of 6 volts and 500 mA, you may have to use a tiny heat sink. I believe the LM317 has thermal overload protection and voltage spike protection built in as well. If you need a quick diagram, let me know so I can send one over to you."

4Crawler

iTrader: (3)

Watts = power or horsepower in your terms, in fact 746 (electrical) watts = 1 (mechanical) horsepower.

Amps is current flow and would be equivalent to torque.

Volts would be similar to RPM (using an electric motor analogy).

And yes, you can have a 20000 RPM Dremel tool, lots of RPM but very little torque and thus very low power output. Or you can grab your torque wrench and put 100 ft.lbs. of torque on a bolt, lots of torque but no RPM, so no real power.

In your system, the volts would be fixed at your 6 volt regulated value, so all you have to work with is current and watts (power). Likely your servo will either list that is takes so many amps or it is so many watts.

Likely the RS cigarette lighter plug has some form of voltage regulator built into it, it has a 1000mA (1 amp) at 6 volt output. The benefit of using an IC regulator is you could design it to exactly meet your needs, so you can pick any voltage level and output current, but the cost to you would be more design and assembly work.

hross14

My mA values (current) for the servo are

:400mA and 500mA

So i think the 6 volt at 1000mA would be to much. But i get the point you are making and just need to look for an adpater meeting my requirements (400mA--500mA)

By the way--What does mA mean--Millamps?

4Crawler

iTrader: (3)

1000mA is just the maximum current that device can provide without overheating. It will provide 6 volts and from 0mA to 1000mA, so 400-500mA is within that range. And likely the servo will take more than 400-500mA of current when it first starts up or if it stalls out (or maybe that is the two ratings, 400mA normal and 500mA starting current).

Same thing as your 12 volt battery in your truck, it is 12 volts and can put out many 100s of amps while the engine is starting. But that does not mean it is putting out 100s of amps all the time, it only puts out what is needed by the engine and vehicle at any given time.

hross14

Sweet--Thanks Crawler

wish we had more technical discussions like this--scientific and technical.

JC_ez

The benefit would be:

1) Exact design to fit your needs (either provides a constant voltage output for your system, or a constant current for your system)
2) Thermal and over voltage protection
3) Very small
4) Probably cost you less than $5
5) Can be built in behind the dash with no need to have something plugged into the Cig lighter adapter

In loose terms, some electrical components and ideas can be thought of like a hydraulic system:

Voltage: a potential difference between two points. Picture a pressure difference in a pipe. It's the pressure difference that will make the fluid in the pipe flow. Voltage doesn't 'flow through' it is measured between 2 points.

Current: the fluid that actually flows through the pipe.

Resistance: the diameter of the pipe. Smaller diameter impedes current (fluid) flow in the pipe.

Capacitor: like a storage tank for fluid. In electrical terms, the capacitor is an energy storage element. It stores energy in it's electric field

Inductor: like a frictionless very massy turbine which the fluid turns. In electrical terms, the inductor is an energy storage element. It stores energy in it's magnetic field.

Diode: like a one way valve. It lets fluid flow in one direction only. Diodes have a 'breakdown voltage' where they eventually let current flow in the 'wrong' direction.

Zener diode: is just a basic diode, but one which is designed to be used in it's breakdown zone (having current flow in the 'wrong direction'. The breakdown zone and breakdown voltage of a zener diode is manufactured to be more predictable and accurate than a non zener diode.

Power: How much energy per second the system can put out. Another way to think of it is that energy is work, and how quickly you can do that work is your power. Energy is measured in Joules and Power is measured in Watts. Therefore a Watt = Joule/second.

Now some basic equations that relate this:

P = IV
Power = (Current)(Voltage) for DC circuits

V = ZI
Voltage = (Impedance)(Current) for DC and AC circuits

The impedance of a resistor is it's resistance in ohms
The impedance of a capacitor or inductor is it's reactance in ohms