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[SOLVED] Solution for reducing voltage from 5V to 3-4 volts.

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roineust

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Hello!

What would be the lightest solution, in terms of weight, to reduce a wire that outputs 5V to 3-4V for a small servo?

Thanks.
 
Last edited:

Re: Reducing voltage from 5V to 3-4 volts.

roineust said:
Hello!

What would be the lightest solution, in terms of weight, to reduce a wire that outputs 5V to 3-4V for a small servo?

Thanks.
Click to expand...

What current ?

As mentioned in previous post, you can use two standard rectifier SMD diodes in serie.


Best regards,
Peter
 
Re: Reducing voltage from 5V to 3-4 volts.

A variable resistor acting as voltage divider can do the work.
 
Re: Reducing voltage from 5V to 3-4 volts.

Hey Ogu Reginald!

Would the following variable resistor, do well for a micro-servo? What are the tech spec parameters, that i should look for? :

https://www.ebay.com/itm/3-x-50K-OH...195?pt=LH_DefaultDomain_0&hash=item3a6778e45b

Would a trimpot do the work as well? for example:

https://www.dipmicro.com/store/RM063-204

Hey tpetar!

To try to be as clear as possible, regarding the servo current draw, here is some data i found, about a servo that is just a little bigger than the one i am talking about:

Current Drain (4.8V): 5.0mA/idle and 130mA no load operating - would that current draw mentioned, double, triple or maybe, only 150% under load?


Thanks.

- - - Updated - - -

Hey Kripton2035,

I am a beginner with electronics,

What kind of diodes model are you referring to?

Thanks.
 

Re: Reducing voltage from 5V to 3-4 volts.

roineust said:
Hey tpetar!

To try to be as clear as possible, regarding the servo current draw, here is some data i found, about a servo that is just a little bigger than the one i am talking about:

Current Drain (4.8V): 5.0mA/idle and 130mA no load operating - would that current draw mentioned, double, triple or maybe, only 150% under load?
Click to expand...

Yes on load current will increase. Depends what load and how long you apply load,... but can be increased for sure, best is to perform measuring tests.



Best regards,
Peter
 

Re: Reducing voltage from 5V to 3-4 volts.

roineust said:
Hey Kripton2035,

I am a beginner with electronics,
What kind of diodes model are you referring to?

Thanks.
Click to expand...

for 130mA the 1N400x serie is ok and widely available for that purpose.
 

Re: Reducing voltage from 5V to 3-4 volts.

Through the information I am seeing on the second link, I think that the trimpot can do the work.
 

Re: Reducing voltage from 5V to 3-4 volts.

Ogu Reginald said:
Through the information I am seeing on the second link, I think that the trimpot can do the work.
Click to expand...

No that small trimmer cant do the job!!! Power dissipation is high for that trimmer.

Trimmer power is 0,1W and you need 0,196 (200mW) power resistor. After first minute of operation you will see smoke.

Plus trimmer have 200KΩ and you need to adjust 8,7Ω. this is very hard because this is not multiturn trimmer.


But you can use fix SMD resistor if you prefer to play with resistors.


Best regards,
Peter
 

Re: Reducing voltage from 5V to 3-4 volts.

tpetar said:
No that small trimmer cant do the job!!! Power dissipation is high for that trimmer.

Trimmer power is 0,1W and you need 0,196 (200mW) power resistor. After first minute of operation you will see smoke.

Plus trimmer have 200KΩ and you need to adjust 8,7Ω. this is very hard because this is not multiturn trimmer.


But you can use fix resistor if you prefer to play with resistors.


Best regards,
Peter
Click to expand...

Thank you for what you just pointed out. Infact if he had done it, the smoke you made mention of will not come after a second but rather it will be seen immediately there is current flowing through the trimpot.
He should look for high power variable resistor.
 

Re: Reducing voltage from 5V to 3-4 volts.

OK - here are the latest results:

I used 2x 1N4004 diodes, connected one after the other, only to the + wire, and got a voltage reduction, from 5V to 4.06V : is that good??... i mean in terms of having any future problems, in case i did not connect them right, although it seems that the voltage reduction was achieved?? why does this setup reduce voltage? isn't a diode supposed to 'deal' only with the current, not with the voltage, for the purpose of letting the current flow only in one direction?

Regarding the trimpots and the variable resistors - should i use a smaller KΩ ?? say, 5K instead of 200K? or maybe a bigger value instead of a smaller one?

How am i to connect the trimpot 3 legs? use only 2 of the legs, either only on the + wire or only on the ground wire (as i did with the diodes on the + wire) ?? which one of the legs? why are there 3 legs in a trimpot and not 2, actually? is that because it is like a transistor, having 3 legs, one of the legs is a sort of on/off control, for the passage of electricity between the other 2 legs?

Sorry for asking so many question, if you only tell me how to do it, it will be less interesting, but good as well...
 
Last edited:

Re: Reducing voltage from 5V to 3-4 volts.

roineust said:
OK - here are the latest results:

I used 2x 1N4004 diodes, connected one after the other, only to the + wire, and got a voltage reduction, from 5V to 4.06V : is that good??... i mean in terms of having any future problems, in case i did not connect them right, although it seems that the voltage reduction was achieved?? why does this setup reduce voltage? isn't a diode supposed to 'deal' only with the current, not with the voltage, for the purpose of letting the current flow only
Concerning the 4.06V you made mention of, so long as the voltage does not exceed the maximum voltage of your servo then there is no problem.
The reason why there is a voltage reduction by the two diode is that there ia always a voltage drop of approximately 0.5V to 0.7V across each diode and since there are two diodes in series, there is a voltage drop of about 1V to 1.4V (depending on the doping of the diode).
If you are able to find a higher power variable resistor of 10k it will be ok. Concerning the connection, one of the legs should be connected to 5V terminal and the other connected to ground with the middle (wiper) terminal serving as the output.
There is no problem with you asking questions. If you are not cleared you can still ask more.
Click to expand...
 
Re: Reducing voltage from 5V to 3-4 volts.

use a third diode if two are not enought ...
 
Re: Reducing voltage from 5V to 3-4 volts.

Maybe your servo can work on 5V as in allowed voltage range, did you check that?


Best regards,
Peter
 
Re: Reducing voltage from 5V to 3-4 volts.

Hey tpetar !

I will be checking this out soon!

Thanks.
 

Re: Reducing voltage from 5V to 3-4 volts.

Do you have some photo, ID or manufacturer name of servo? Manufacturer datasheet will help for sure.



Best regards,
Peter
 
Re: Reducing voltage from 5V to 3-4 volts.

Hey Peter,
Here is the servo:
https://hobbyking.com/hobbyking/store/__3714__HobbyKing_2_5g_17kg_12sec_Micro_Servo.html

I have another question: The numbers that pop up, when i look for a 1N4004 diode on the web, are 1A 400V - does this mean that i can never pass 400V and 1A or that, if i use much less volts, say a LiPo 3S 11.1V, then i can pass through more amps? Say a 3A (3000mAh) LiPo? or will such amp from a 3S 11.1V LiPo to the 1N4004, cause a problem? or will it cause no problem, but no more than 1000mAh (1A), will pass through?
 

Re: Reducing voltage from 5V to 3-4 volts.

I always use 1N4007 from this family, its up to 1000V and 1A. Price is the same.

1N4004 can pass maximum up to 1A and can handle up to 400V.

If you want to pass more current than 1A, you need stronger diode.

Its simple physical limitation of part.


This motor can work up to 6V according to posted link. To be precise motor requires minimum 4,8V and voltage between 4,8V and 6V, I will say 5V. :) You dont need diodes to drop voltage!.


Now I think you will have inverse problem, to StepUp voltage from Li-Po battery to 5V. :)


1000mAh and 1A are not the same!. 1000mAh is battery capacity and 1A is instantaneous current rating.
Check battery datasheet for discharge current rating and for /C rating.





Best regards,
Peter
 
Re: Reducing voltage from 5V to 3-4 volts.

two problems with using a trimer or pot: BIG one is that there is no way it can handle the current - it would fry instanteously, and second it would limit the current
 
Re: Reducing voltage from 5V to 3-4 volts.

How about a simple 3.3v LDO? Available as a 3 pin SMD, so it cant get much lighter.
 
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