Arduino Forum

Using Arduino => General Electronics => Topic started by: kday7 on Oct 20, 2017, 02:48 am

Title: Powering a servo through a 7805 regulator
Post by: kday7 on Oct 20, 2017, 02:48 am
Hi,

I'm looking to supply power to a 9g micro servo via a 7805 voltage regulator.
Currently, using a breadboard, I am supplying 9v to the input pin, ground to ground, and then the output (5v) pin to the servo.
I am also grounding the servo and attaching it to the number 10 pin on an arduino uno.

If anyone could help with my scenario and perhaps provide a schematic, it would be much appreciated!

Furthermore, I am looking to supply power to the arduino and the motor shield via the same 9v battery - before it is regulated.

Also, ultimately, I want to regulate the voltage and power 3 or 4 of the same servo's.

Thanks in advance :)
Title: Re: Powering a servo through a 7805 regulator
Post by: Southpark on Oct 20, 2017, 10:30 am
They reckon 1 amp max from the 7805. Could try one of these...TDB2912.
Title: Re: Powering a servo through a 7805 regulator
Post by: slipstick on Oct 20, 2017, 11:17 am
A 7805 might just do for a single SG90. It's definitely not enough for 3 or 4 of them.

But first, what type of "9V battery" are you using? A lot of the servos problems we see round here are people trying to use those little rectangular 9V PP3-type batteries. They will not deliver anywhere near enough current to drive even a single servo. And since you mention a motor shield I guess you have some motors too? No chance without a decent battery/power supply.

Since you're the only one who knows exactly what you're trying to do perhaps you should provide the schematic. And if you are going to use 7805 you're going to need some capacitors too.

Steve
Title: Re: Powering a servo through a 7805 regulator
Post by: Grumpy_Mike on Oct 20, 2017, 12:56 pm
Why not use a 7806 and get the full 6V for your servo?
Title: Re: Powering a servo through a 7805 regulator
Post by: promacjoe2 on Oct 20, 2017, 10:04 pm
Generally speaking, You should not use a linear regulator to power motors, solenoids or relays. Especially when using batteries. Linear regulators waste a lot of current. In this case approximately 40% of your current will be Lost as heat. You're better off using a buck regulator, which has a much higher efficiency.
Title: Re: Powering a servo through a 7805 regulator
Post by: billhowl on Oct 21, 2017, 04:53 am
You can use Battery Eliminator Circuit (BEC) to supply power to a 9g micro servo

(https://cdn.shopify.com/s/files/1/1052/4162/products/ztw-10a-bec-ubec-bec-motion-rc-16155047174_1024x1024.jpg?v=1498479947)
Title: Re: Powering a servo through a 7805 regulator
Post by: MarkT on Oct 21, 2017, 12:24 pm
Generally speaking, You should not use a linear regulator to power motors, solenoids or relays. Especially when using batteries. Linear regulators waste a lot of current. In this case approximately 40% of your current will be Lost as heat. You're better off using a buck regulator, which has a much higher efficiency.
No, they waste voltage, the current out is 99% or more of the current in for most regulators.

But here the solution is a buck DC-DC converter which will get you good efficiency with a voltage
drop.

BTW a small 9V battery is completely and utterly hopeless for powering high loads like a servo, they
only handle 100mA or so before collapsing in voltage, they are designed for a few tens of mA.  For
the 1A or more of a servo choose a high current power source or suffer the consequences...
Title: Re: Powering a servo through a 7805 regulator
Post by: promacjoe2 on Oct 22, 2017, 12:20 am
No, they waste voltage, the current out is 99% or more of the current in for most regulators.

But here the solution is a buck DC-DC converter which will get you good efficiency with a voltage
drop.

BTW a small 9V battery is completely and utterly hopeless for powering high loads like a servo, they
only handle 100mA or so before collapsing in voltage, they are designed for a few tens of mA.  For
the 1A or more of a servo choose a high current power source or suffer the consequences...
My mistake, to say . Wattage, not current.
Title: Re: Powering a servo through a 7805 regulator
Post by: kday7 on Oct 22, 2017, 02:34 am
A 7805 might just do for a single SG90. It's definitely not enough for 3 or 4 of them.

But first, what type of "9V battery" are you using? A lot of the servos problems we see round here are people trying to use those little rectangular 9V PP3-type batteries. They will not deliver anywhere near enough current to drive even a single servo. And since you mention a motor shield I guess you have some motors too? No chance without a decent battery/power supply.

Since you're the only one who knows exactly what you're trying to do perhaps you should provide the schematic. And if you are going to use 7805 you're going to need some capacitors too.

Steve
Thanks for the reply Steve,

I'm using a 'rectangular' duracell 9V battery which seems to drive one servo fine, but as soon as I wire it up to more than one, I start getting some problems.

Yes, it is for a little autonomous robot so there are motors as well as a couple sensors as well.

Could you suggest a more appropriate battery solution?

Regards
Kaleb