I've got a project that uses an ultrasound sensor that turns on a 12 volt motor and 12 volt LED strip when something moves within a certain range of the sensor. I'd heard that LED strips and motors only draw as much current as they need so I figured I'd play go for a 5A power supply (better to have too much current than not enough).
I'd also like to run my arduino uno off the same 12 volt power supply using the power connector port thing (circular port next to the USB port). I know the 12 volt supply will work with the Arduino, but online it seems like no one can agree if the Arduino can handle 5A. I was under the impression that the arduino would only draw as many amps as it needs, but some people are saying that isn't the case and 5A is way too much.
I'd really like not to fry my arduino uno if possible. Thank you so much for any help!
slipstick:
Arduinos, like almost all electrical/electronic things, only draw the current they need. A 5A supply is no problem.
groundFungus:
I have read that the power dissipation of the 5V regulator on an Uno should be kept under 1W to avoid overheating the regulator. 1W / 7V = 0.143A
But the 5V regulator should only have to deal with as much current as the Arduino is drawing right? I'm only powering the base pins for 2 transistors (very little current needed) and then enough current for the ultrasound sensor. Or am I not understanding this correctly?
sterretje:
The Arduino will use what is needed, just like motors and leds.
The problem comes when you try to draw 5A from the 5 volt pin; you will blow the regulator out of the board
I can't tell you how much current you can draw from the 5 volt pin when you power the Arduino with 12 volt.
Lol, sounds like you might have done that before. I'm only drawing enough current for the base of 2 transistors (TIP 122 - should be very little current) and enough for the Ultra Sound sensor which shouldn't be too much either).
You are making the Arduino's onboard regulator work to get 12V down to 5V. And it will be of a bad linear type. 12V is at the upper limit of rating.
I would just use a separate buck convertor to get a clean 5V from your 12V source and give that to the Arduino's 5V line. That's what I do for all my Arduino+12V LED strip applications.
I'm only drawing enough current for the base of 2 transistors (TIP 122 - should be very little current) and enough for the Ultra Sound sensor which shouldn't be too much either).
You should be fine. Assuming that you are supplying less than 20mA to the bases of each of the transistors and the US sensor is an HCSR04 (working current is 15mA, 2mA quiescent) that's 55mA (conservatively). Add another 30mA for the rest of the Uno and you are still under 140mA.
heropants:
But the 5V regulator should only have to deal with as much current as the Arduino is drawing right? I'm only powering the base pins for 2 transistors (very little current needed) and then enough current for the ultrasound sensor. Or am I not understanding this correctly?
You have it right there.
Maximums and Requireds are different things, and both have uses determining what parts you need.
DC-DC converters are pretty cheap and very efficient. For about $2 you can get an adjustable module that can output up to 3A. Considering that the Arduino board maximum current is 200mA, a 3A source can deliver more than you could need w/o burning the board up.
My house light is on a 30A 120VAC main circuit. It draws 15W, about 1/8th of an Amp (required) vs 30A available (maximum).
INTP:
You are making the Arduino's onboard regulator work to get 12V down to 5V. And it will be of a bad linear type. 12V is at the upper limit of rating.
I would just use a separate buck convertor to get a clean 5V from your 12V source and give that to the Arduino's 5V line. That's what I do for all my Arduino+12V LED strip applications.
Okay, so you're saying that's a lot for the arduino's on board to handle. I'll probably use a buck converter but couldn't I also just use a separate fixed 5 volt voltage regulator?
The 5V regulator is what the board has and you are okay using it.
The converter is only if you want to take a step more.
Since you will only draw small power through the on-board regulator you will only get small waste there.
The thing to do is touch the running board to see if there is a hot spot and if there's not, don't fix what ain't broke!
GoForSmoke:
The 5V regulator is what the board has and you are okay using it.
The converter is only if you want to take a step more.
Since you will only draw small power through the on-board regulator you will only get small waste there.
The thing to do is touch the running board to see if there is a hot spot and if there's not, don't fix what ain't broke!
I'm not able to imagine how you are controlling a 12V motor and 12V LED strip with just a couple of transistors. Maybe it's a pretty small motor or a power darlington transistor or some such.
Either way, maybe consider using MOSFETs if you're interested in cutting down current usage.
INTP:
I'm not able to imagine how you are controlling a 12V motor and 12V LED strip with just a couple of transistors. Maybe it's a pretty small motor or a power darlington transistor or some such.
Either way, maybe consider using MOSFETs if you're interested in cutting down current usage.
Wait, what do you mean by this? I'm using a 12V 5A power supply. Without the transistors, the LED strip and the motor were pulling about half an amp when wired directly to the power supply in parallel. The transistors are rated for 5 amps but since I'm using 2 of them, the most their pulling (according to my multimeter) is around .3 of an amp. The motor and LEDs seem to be working but I'm actually worried they're drawing so little current. Even when I'm trying to stall the motor, it only draws about .35 of an amp (according to my multimeter).
It says 5 A max for the collector but the most that's going through the collector is around .35 Amp (according to my multimeter, that's what the motor draws under load) and I'm using separate transistors for the motor and the LED strip. The amount of amps it's drawing does seem low and I'm wondering if my breadboard rails can't take that much current. I know the problem isn't the transistors because I've removed the transistors (powered the motor directly to the power source) and I'm still reading about .35 amps.
GoForSmoke:
I think that someayinz are forgetting what the T in MOSFET stands for.
lol, I'm not really sure what you mean... I'm using a Tip 122 darlington transistor because I'm much more comfortable with them (and I've already got quite a few), not a MOSFET...
Just wanted to add an update to this. I found out my breadboard and jumper wires were somewhat limiting the current that the LED strip and motor needed so my amps were lower than what I was expecting. The LED strip actually draws 580 mA and the motor draws 300 mA under load. I think I still should be okay with the Tip 122 transistors though. That's what Dr. Peter Dalmaris uses for 12V LED strips, except he uses entire rolls of strips which would pull even more current than mine. And the LED is pulling more than the motor so I'm thinking I'm probably okay, right?
I have ULN2803 Darlington chips that max at 500mA and need a heat sink to do that.
OTOH I could use an IRLZ44N or other FET (Field Effect Transistor) that won't need more heat sink than the tab it's got to switch twice that and likely more, the datasheet has the numbers to tell.
Darlington's are what people who don't have FETs use. Cheap FETs are kind of this century,
Darlington's belong with incandescent light bulbs and punch cards.
