Running arduino of a 24V battery

Projects General Guidance
1

Hi all,

I'm doing a project in which my power source is a 24v volt battery. The battery drives some heavy duty motors and I would also like to use this to power my arduino.

The internal voltage regulator can't handle 24v, but could it handle this just long enough to start the arduino? I would setup the arduino to set a PWM signal which modulates it's own supply voltage to a more sensible ( let's say 8V ) voltage.

I'm thinking something along the lines of this: ( vin should be the external connector )

If the battery supply voltage turns out to be swinging wildly, I could add a voltage divider to measure the actual input voltage and change the PWM signal based on the readings.

The question which remains, is this a sensible setup? Or should I just buy a switching dc-dc converter..

2

The question which remains, is this a sensible setup?

I would say no.
The 1uF cap is way too small by at least two orders of magnitude. I would also put an inductor and another cap before going into the arduino.

The internal voltage regulator can't handle 24v, but could it handle this just long enough to start the arduino?

The internal regulator can handle 30V but the capacitor across it can only handle 25V ( check this because some are different )
Running a 25 V cap at 24V is pushing it.

3

Something tells me this wouldn't be a good idea.

The LM7805 can handle up to 35 volts; to drop 24 volts to 5 volts, though, would probably require a hefty heatsink (the PCB of the Arduino is barely adequate for 12 volts). Whether it would work long enough at 24 volts to boot the code; I don't know - but then again, having the Arduino regulate its own voltage seems dicey to me.

Why not just set up a cascade of linear regulators on heatsinks, then tap those for what you need - battery to LM7812 to 7805 to Arduino (bypassing the Arduino's 7805, of course)? That, or the switching supply would probably be the better options.

4

Grumpy_Mike:
The 1uF cap is way too small by at least two orders of magnitude. I would also put an inductor and another cap before going into the arduino.

I haven't really looked into the actual values of the components, the diagram is there for illustration.

What function does the inductor add? Is it merely for smoothing the supply voltage?

The internal regulator can handle 30V but the capacitor across it can only handle 25V ( check this because some are different )
Running a 25 V cap at 24V is pushing it.

Well, in my mind, the caps may be getting the 24V for a very short amount of time, since the cap needs to load and the arduino will start it's PWM routine as soon as it's bootloader is done.

In fact, I could 'reverse' the PWM setup, that would prevent the higher voltage from ever reaching the arduino... I'll try to make a schematic

5

What function does the inductor add? Is it merely for smoothing the supply voltage?

Well it limits the ripple better than a capacitor.

Well, in my mind, the caps may be getting the 24V for a very short amount of time

Yes but the caps are not in your mind they are on the board. Replace them and you will have no trouble.

6

Honestly this seems like a lot of circuitry to solve a simple problem, why not use an external series regulator or a $12 switching module.

Rob

7

This guy has a nice discrete circuit for dropping some voltage in preparation for a linear regulator's comfortable input range:

http://sound.westhost.com/project102.htm

It's designed for dual-supply (+/- with respect to ground) circuits, but you could just cut it in half for single-supply.

8

Isnt that like trying to hang a picture with cement ?! Simplest solution is just the voltage regulators- They so simple, and will allow you to expand at a later stage if needed without much hassle !
Or am i missing the point here ?!?
Then again, when all u have is a hammer, everything starts to look like a nail !!

9

Graynomad:
Honestly this seems like a lot of circuitry to solve a simple problem, why not use an external series regulator or a $12 switching module.

I'm not sure what kind of switching module you are referring to, but if you mean something like a LM2576, I would still need an inductor, a cap and some resistors, pretty much the same as I have now.

cr0sh:
[...]
Why not just set up a cascade of linear regulators on heatsinks, then tap those for what you need - battery to LM7812 to 7805 to Arduino (bypassing the Arduino's 7805, of course)? That, or the switching supply would probably be the better options.

I don't like the fact that linear regulators are eating all the excess voltage, I don't want to waste power as this is a battery driven setup :slight_smile:
( Even though I think it could suffice for this project )

SirNickity:
This guy has a nice discrete circuit for dropping some voltage in preparation for a linear regulator's comfortable input range:
[...]

This is basically a linear regulator, the transistors will eat the excess voltage.

iyahdub:
Isnt that like trying to hang a picture with cement ?! Simplest solution is just the voltage regulators- They so simple, and will allow you to expand at a later stage if needed without much hassle !
Or am i missing the point here ?!?
Then again, when all u have is a hammer, everything starts to look like a nail !!

Well, the simplest solution is indeed a voltage regulator :slight_smile: but again, I want to take into account efficiency.

It may be a crazy idea to begin with, but experience tells me you can learn a lot by thinking outside the box, even if you find yourself choosing the safe/well-known solution in the end :slight_smile:

10

A switching module is a module you buy assembled and working so that you can stop worrying about this issue and start worrying on your actual project(!) It'll probably mean no need for heatsinks and much longer battery life on standby?

11

what kind of switching module you are referring to

Check out things like the Recom R-78xx series, Traco TSR and TMA Series, V-Infinity VBSD1-SIP series, XP IE series, Murata MPU1 series etc.

There's bound to be something pretty cheap that will do the job. All usually in the ~80% efficiency range.

Rob

12

In the end, I've gone with the advice of going for a ready made solution.
I still had on of these laying around: http://www.dealextreme.com/p/mini-car-cigarette-powered-1000ma-usb-adapter-charger-black-dc-12v-48925

You just can't make a lot of things for € 1,70 and this gives me a steady 5.1V output, internal caps are rated for 35V, but could have been easily replaced if it would have been needed :slight_smile:

This device uses a mc34063 btw.

13

uh this would classify as arduino suicide by barbequed board build an external regulation board and be sure to fuse the bastard on both in and output stages

14

VirtualDDS:
uh this would classify as arduino suicide by barbequed board build an external regulation board and be sure to fuse the bastard on both in and output stages

...With the proverbial burnt smell lol lol

15

Your arduino needs 500ma or so max of 5v DC there are piles and piles of DC to DC switching IC's that can supply that. Something like a Max 5035 7.5 - 76 volts in 5v 1a out with little muss or fuss.

16

For those of you who missed my reply:

MacGyverismo:
In the end, I've gone with the advice of going for a ready made solution.
I still had on of these laying around: http://www.dealextreme.com/p/mini-car-cigarette-powered-1000ma-usb-adapter-charger-black-dc-12v-48925

You just can't make a lot of things for € 1,70 and this gives me a steady 5.1V output, internal caps are rated for 35V, but could have been easily replaced if it would have been needed :slight_smile:

This device uses a mc34063 btw.

I would like to add that it is in fact possible to bootstrap an arduino from a non-native voltage.
See for example this page: http://spritesmods.com/?art=ucboost&page=1
Even though Sprite is talking about boosting the voltage, the same principle could apply to step down the voltage.

Also, I do believe that the Arduino is all about experimenting, so even though it is a fool-proof method to just go with existing technology, I really think one can learn a lot when trying to fix a problem for him/her self, even though the problem has been fixed a million times over.

17

It seems he does want to do it in a more simpler "DIY STYLE" method... and fair play to him as we do end up learning a lot and enjoying things much moreby doing the sometimes impossible, or doing it the hard way !! Thats whats DIY is all about to start with - Building for 100 pounds and 3 months of work what we can buy in the corner shop for 50 ... lol