I'm intending on running a lot of ultrasonic (SRF05) and IR (various Sharps) off of an Arduino Mega. Cumulatively, the current draw is going to be at least 500ma.
How much source current can the +5V supply on the Arduino provide?
If it can't handle that much, what are my options? Can I use the same ground pin for all of them?
Must I resort to a separate battery pack and voltage regulator? If so, does anyone have any recommendations?
Thanks,
eqfanatics
It depends on how you're powering them. If you use USB, odds are you can't source more than 500 mA from the port. If it's external power, I'm fairly certain (but not sure) that you could source that much current, but I don't know if it would generate too much heat on the regulator.
If you can keep the external power source in the 8-10 volt range you should be able to handle that much current no problem. On USB power you are near the limit as there is a 500ma thermofuse on the USB source.
Of course an idependent +5vdc power supply can always be used to power the external loads, just be sure to wire the ground side of the external +5vdc to the Arduino ground pin.
Lefty
Doesn't the current regulator only go up to 500ma at 5v anyway? I would think being right on that limit with your circuitry would be a bad practice
It's not the current that is the limit it is the power dissipation. So it depends on the input voltage to the on board regulator.
For a discussion of this see:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html
This link (Arduino Playground - WhatAdapter) seems to suggest that the limit is 1A.
However, based on what people are saying, it seems like the power dissipation from 1A could be problematic, depending on the supplied voltage, which would probably end up being 6xNIMH AA (8x1.2V).
So P=VI=(9.6V-5)(1A)=4.6W
4.6W is definitely higher than the power dissipation diagram mentioned above (http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html) would seem to allow for (1.5W).
Is this really a problem? Will there really be a significant heat buildup around the voltage regulator if I have a drop of 4.6W and current of 1A?
This is of concern to me because a sensor I'm looking to use, that really long-range Sharp IR sensor, has peak current draw of 400ma with average draw of 30-50ma.
So, with all the other sensors I'm going to be using, periodically the current draw could get close to 800ma-1000ma, but would drop back down.
In this case, is overheating around the voltage regulator still enough of a concern as to warrant a heatsink?
How would I even apply a heatsink to the voltage regulator? Any suggestions as to how and which one?
Thanks,
eqfanatics
In this case, is overheating around the voltage regulator still enough of a concern as to warrant a heatsink?
Most all voltage regulators have automatic self-protection features from over current or over temperature conditions, they simply shut down until the condition is cleared. So no real harm in just testing your application to see if it performs OK over time. If the regulator shuts down it will just cause a power reset condition when it returns on.
How would I even apply a heatsink to the voltage regulator? Any suggestions as to how and which one?
If the above test shows that the current draw/heat dissapation is a problem I think your better off using a external regulated DC supply (or battery supply) to power the loads rather then trying to modify your Mega board.
Thanks,
eqfanatics
seems to suggest that the limit is 1A.
Yes that is the current limit but the current limit is not the limiting factor. That is because you could have 2V dropped across the regulator or 4V and that doubles the power. 4W is a lot of heat in a small package.
As to peak power that is not as important as peak current. With peak power you can smooth it out to the average, so you can often stand brief pulses of power, many times over the continuous rating.
Applying a heatsink is simple, just clamp or glue a piece of metal on the regulator. The metal should have as much surface area as possible to have a low thermal resistance to the ambient.
Are there any heatsinks or thermal paste or something that people have used successfully? Any links would helpful.
I very much appreciate all the helpful answers that I've gotten.
-eqfanatics
Are there any heatsinks or thermal paste or something that people have used successfully?
Have you looked at the regulator device on your Mega board? It's a SMD mounted device that gets it's heat sinking via it's pin and underside. I can't see any way you can effectively increase it's heat dissipation other then by just lowering the external power voltage to just above it's regulation drop out specification. If you still require more current then that, use an external power supply for your loads.
Lefty
Are there any heatsinks or thermal paste or something that people have used successfully?
look at this sort of thing
http://uk.farnell.com/fischer-elektronik/ick-smd-a-22-sa/heat-sink-for-smd-34-c-w/dp/4302217