I am working on a project where an Arduino UNO reads the time from a DS3231 and controls a relay FL-3FF-S-Z. The relay would be powered for a maximum of 5 mins per day. Would a 9V 1A adapter (9v 1A DC Power Adapter - RoboElements) work for 2 weeks via DC jack without burning or seriously damaging the Arduino UNO ?
A schematic would go a long way to get a better answser
Assuming you power the UNO from the Jack, hook up the relay to GND and 5V from the UNO's pin and of course have another power supply for the load.
Your relay's coil will draw ~100mA when activated and the UNO will draw a bit of current as well to run (50mA) This stays well within acceptable limits and the Arduino Uno will work fine under 9V for a long time.
You'll be participating to global warming a bit more than if you had a lower voltage as you are dissipating (wasting) ~4V x amps drawn through the regulator that will heat up.
Is there a stable way to provide a lower voltage which can also run unsupervised for a couple of weeks?
use a phone charger 5V USB power supply for example and feed that through USB. If your phone power adaptor is efficient then it's probably a better equation to do 230VAC ➦ 5VDC directly than 230VAC ➦ 9VDC ➦ 5VDC
but again, @9V with this type of current draw you should be fine for years
Due to the limitations of the on-board regulator, powering from other than 5 V is a generally bad idea.. One relay (on a module of course, with its control transistor) drawing a nominal 90 mA when actuated you may get away with at 9 V, but the risk is that at some stage you will add something else drawing current and wonder why it becomes unreliable.
Be careful with phone chargers. They are for charging. Some cheap chargers with an 5V output has actually 6-6.5V at low current consumption. If you apply such a voltage to Arduino, it will be bad for him.
yeah it has to be 5V
Most phone chargers shut down when the load current falls below a certain level. You may need to sink additional current to get it to stay on.
So how would I suuply the 5V if a 9V adapter is too much and a 5V adapter might provide higher voltage at low current levels? Is it impossible to use an arduino powered from anything apart from a USB port on a computer or a laptop?
Then how shall I power the Arduino?
I meant cheap chenese charger. Most modern chargers give 5V. Take 5V charger and check with DMM that it gives 5V±5%. Enjoy your health.
You could try using a USB power pack available form many sources, eg Big River Company.
Often used to extend the time a mobile phone will run etc.
Just use a real 5 V adapter - "phone charger".
You need 5 V. "Boffin" has spooked you to start with but corrected himself. Just check the voltage with your multimeter in case it is some piece of rubbish. A branded device such as Apple or Samsung should be the real deal or one you buy in a local shop. Ridiculously cheap ones direct from China may not only be poorly regulated, but unsafe.
I think responders are mixing metaphors.
If you supply +5V through the 5V pin, then the 5V has to be well-regulated, clean and capable of at least 1 Amp. Most phone chargers don't provide a well-regulated 5V or 1 Amp.
If you provide 7V to 12V to the barrel jack, you are OK. Anything less won't work because the 5V regulator on the PCB won't regulate to 5V. 7 to 9V is best. If you power ONLY the Arduino with 12V through the barrel jack, you will not likely ever have an issue. I have powered Uno projects using a 12V wall-wart for weeks at a time and never an issue. (Yes, the on-board regulator gets warm. Not hot). If you power downstream peripherals such as LED strings, relays or motors through the 5V pin, then you are probably out of spec and risk smoking the on-board regulator.
And, what makes you think that the Amazon or Apple branded adapters aren't the same Chinese parts with the Apple or Amazon brands on them?
Good brands are way more careful about their branded devices even if the parts are subcontracted (usually the case). They have quality control and more rigorous adherence to specifications.
I'd buy from Apple or Samsung directly if you want the real thing because there are clones that would go as far as counterfeiting the logo...
(my old iPod power supply (which is made by Samsung) is delivering 5.20V and not 5V and is pretty stable wether I draw nothing or 500mA)
Power supply or charger? I never expect a charger to be well-regulated.
it's a charger (used to charge the iPod back in the days)
Today I connected it to my iPhone's 5W charger for 12 hours and things looked fine. Not sure if it would be as fine for a couple weeks though.
I checked my iPhone charger, it outputs 5.06V even without load. So you can be calm.