Drop 5v down to 4.5v

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dan8400
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Drop 5v down to 4.5v

Postby dan8400 » Mon Dec 11, 2017 11:30 am

Hi

I have a dual rail power supply like this:

https://goo.gl/images/bNQJ9e

I am driving some servos. Using batteries at the moment. I read somewhere that servos are a bit particular on voltage (4.5v).

Question is: can I use the 5v output as it is? Or should I drop the voltage to each servo?

I don't mind which, but it would be easier not to have to drop voltages.

Thanks
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End2end
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Re: Drop 5v down to 4.5v

Postby End2end » Mon Dec 11, 2017 11:56 am

I honestly don't know but something occured to me. Why drop the voltage to EACH servo?
Wouldn't making up say, a rig of resisitors from the output drop it down to 4.5v? Or perhaps some LED's inline. You wouldn't need to see the light. You could always just paint over them.

Not the same but I've used a flashing LED connected to a normal LED to flash the normal LED.
I painted the flashing LED all over in black completely covering it as it was orange (out of one of those flickering plastic tea light candles) and the LED I wanted to flash was red. Just using this as an example of painting over a working LED but covering the unwanted light.
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Re: Drop 5v down to 4.5v

Postby TimberSurf » Mon Dec 11, 2017 12:03 pm

Servo specs are for nominal values for both 4.8V and 6V for the same device, if fed with the higher voltage, they simply develop more torque!
Running them at 5V will be perfectly fine :D
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dan8400
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Re: Drop 5v down to 4.5v

Postby dan8400 » Mon Dec 11, 2017 6:11 pm

Excellent thank you
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naugytrax
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Re: Drop 5v down to 4.5v

Postby naugytrax » Tue Dec 12, 2017 12:30 am

But if you do need to drop from 5V down to 4.5V, just put a common or garden silicon diode in series with the supply. (e.g., 1N4001). This will drop 0.7 volts, which is close enough. No need for LED's and paint!
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Re: Drop 5v down to 4.5v

Postby Gordon H » Tue Dec 12, 2017 12:23 pm

End2end wrote:Wouldn't making up say, a rig of resisitors from the output drop it down to 4.5v? Or perhaps some LED's inline.

Unfortunately, neither of these methods would work very well.

The voltage a set of resistors drop will vary considerably with the current drawn. You would have to decide at what current you want 4.5V to result, which would be virtually impossible when driving a mechanical load with a servo.

The forward voltage of LEDs is too high for this application, so you would end up with less than 4V to start with, and again, the current requires consideration, as the kind of current a servo will draw under load is far more than an ordinary LED would normally use.

As has already been mentioned, this is all rather academic really as 5V is OK anyway.


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