Can i use a 12V 1A AC to DC adapter for a cctv that uses 12V and 0.5A? - Page 1
Forum section: electronics / beginners

author: jimmyc_
author_rank: Contributor
timestamp: April 07, 2025, 11:26:43 am
content: Hello chaps!Newbie here. Can i use a 12V 1A AC to DC adapter to power a CCTV that uses 12V and 0.5A? Will the CCTV only pull 0.5A from the AC to DC adapter?

author: BadeBhaiya
author_rank: Regular Contributor
timestamp: April 07, 2025, 11:32:06 am
content: That's right. Your understanding is correct.

author: eleguy
author_rank: Regular Contributor
timestamp: April 07, 2025, 11:32:42 am
content: Based on the information you have given, yes you can. The CCTV system takes what it needs and as it is rated 0.5A it should be the max current it takes in any condition.

author: jimmyc_
author_rank: Contributor
timestamp: April 07, 2025, 11:44:06 am
content: Quote from: BadeBhaiya on April 07, 2025, 11:32:06 amThank you sir BadeBhaiya!

author: jimmyc_
author_rank: Contributor
timestamp: April 07, 2025, 11:46:49 am
content: Quote from: eleguy on April 07, 2025, 11:32:42 amThank you sir eleguy!

author: PGPG
author_rank: Frequent Contributor
timestamp: April 07, 2025, 11:54:30 am
content: Quote from: jimmyc_ on April 07, 2025, 11:26:43 amImagine car 12V accu being able to supply over 100A to the starter.If you supply 5W bulb from it the bulb will take only the current it needs and not 100A.

author: tunk
author_rank: Super Contributor
timestamp: April 07, 2025, 12:03:49 pm
content: If it's an old type with transformer and unregulated output,then the voltage can be quite a bit higher than 12V.Also check that polarity is correct.

author: jimmyc_
author_rank: Contributor
timestamp: April 07, 2025, 01:12:21 pm
content: Quote from: PGPG on April 07, 2025, 11:54:30 amThank you sir! I would like to ask this question - Will an microcontroller GPIO pins get damaged from over current?

author: jimmyc_
author_rank: Contributor
timestamp: April 07, 2025, 01:14:05 pm
content: Quote from: tunk on April 07, 2025, 12:03:49 pmThank you sir tunk for your kind sharing! I've learnt something new today! I'm using a wall wart from AC to 12V DC. It's quite light so i assume there's no transformer inside. But I'll break it open to check!

author: tunk
author_rank: Super Contributor
timestamp: April 07, 2025, 01:17:12 pm
content: If it's quite light, then most likely it's not the old type.No need to open it, post some photos, or maybe weigh it.Edit: If you have a multimeter, measure the voltage.

author: PGPG
author_rank: Frequent Contributor
timestamp: April 07, 2025, 01:47:21 pm
content: Quote from: jimmyc_ on April 07, 2025, 01:12:21 pmYou didn't described about what situation you ask for GPIO to be damaged or not.If device destined to be supplied by 12V and needing only 0.5A will be connected to 12V accu (being able to supply 100A) than nothing wrong will happen to this device GPIO pins.But if GPIO pin (having no externel protection) will be connected directly to +12V it will be damaged.

author: jimmyc_
author_rank: Contributor
timestamp: April 08, 2025, 03:36:12 am
content: Quote from: PGPG on April 07, 2025, 01:47:21 pmOk here's an example. ESP32 takes in 3.3V on the GPIO pins, for a high and 0V for a low. If I have 3.3V and 10A input to this GPIO pin, will the GPIO pin on this ESP32 be damaged?

author: PGPG
author_rank: Frequent Contributor
timestamp: April 08, 2025, 09:41:18 am
content: Quote from: jimmyc_ on April 08, 2025, 03:36:12 amI don't know ESP32 so I speak about typical GPIO and not exactly these you have.If you have 3V3 DC source with 10A current efficiency and connect it to GPIO pin of 3V3 powered device than:- if PIN is set as input or HiZ than current near 0mA will be flowing from your source and nothing wrong will happen,- if PIN is set as output and state '1' (3V3) is output than also nothing will happen,- if PIN is set as output and state '0' is output than current will be limited by output pin efficiency. In many cases internal current limiting is such that nothing wrong (except emitting some heat) will happen but what is the max output current in such case and if it is danger to GPIO pin itself you should be able to read in datasheet.The other subject is that any high current supply source should be assumed to have some overvoltages to happen and if for example your device will be powered by 3V and the 3V3 source will have a pulse being for a moment 3.7V than your whole 3V supply will get current from this 3V3 source through GPIO pin protecting diode and except diode characteristic there will be nothing else limiting that current pulse as at your device supply you probably have a capacitor with very small ESR (Equivalent Serial Resistance).Conclusion - you should avoid connecting 3V3/10A source directly to GPIO pin.

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2025, 09:54:21 am
content: A 0.5A vs 1A PSU is no problem, but it's not always that simple.It's true, the current draw is always determined by ohms law and the highest resistance will limit the current. The power supply might be rated to 100A, yet if the load only draws 100mA, then only 100mA will flow.The above assumes everything is good and there isn't a fault. The problem is, if a device rated to 100mA, is connected to a power supply, capable of delivering 100A and there's a fault i.e. a short circuit. Over 100A will flow, causing the conductors to get very hot and burn.The solution to the above is to add a circuit breaker or fuse to break the circuit, if there's a fault. The current rating of the breaker should always be a bit higher than the normal load current, to avoid nuisance tripping. If the load draws a significant surge then a slow blow/time delay, fuse/breaker should be used.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 08, 2025, 10:18:43 am
content: I often use a 24V 10 to 40A power supply to supply power to many things including 24V input that draws about 3 to 4mA. There is no protection and I never have the problem.

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2025, 11:03:41 am
content: Quote from: BeBuLamar on April 08, 2025, 10:18:43 amThat's like saying "I've never worn a seat belt, yet I've never had an accident."You're bloody lucky. Consider what would happen if a fault occurred.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 08, 2025, 12:44:59 pm
content: Quote from: Zero999 on April 08, 2025, 11:03:41 amIf a fault occurs the input would be damaged regardless what kind of protection you put in place? Put a 5mA fuse? The input is not going to draw more than that if it does there is something wrong and that input is bad regardless. And yes I did these things for about 30 years and got paid for doing so.

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2025, 02:08:27 pm
content: Quote from: BeBuLamar on April 08, 2025, 12:44:59 pmWhat about the cable and connections? They would burn with 40A going through them.I would get into big trouble, if I did anything like that, where I work.There should be a fuse, as close to the PSU, as possible.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 08, 2025, 02:11:11 pm
content: Quote from: Zero999 on April 08, 2025, 02:08:27 pmWhat kind of a fuse? What current rating?

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2025, 02:12:38 pm
content: Quote from: BeBuLamar on April 08, 2025, 02:11:11 pmWhat do you think? Hint: a fuse is there to protect against fire, due to overheating of the connections and cabling.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 08, 2025, 03:14:23 pm
content: Quote from: Zero999 on April 08, 2025, 02:12:38 pmWhat kind of a fuse?A 40A fuse at the power supply output doesn't do anything. The 40A power supply has its own over current shut down and it won't deliver more than 40A. So for something like 100 inputs at 5mA each you would put a 5mA fuse on each? For each of the 100 0.5A outputs you put a 0.5A fuse? Now I do put the fuses on the output as the load can be shorted but never at the input. Because if the input is shorted it's bad regardless. Neither the output or the input would damage the wiring when they are overloaded because they would burn up before a 20 AWG wire.

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2025, 03:25:16 pm
content: Quote from: BeBuLamar on April 08, 2025, 03:14:23 pmI couldn't make much sense of that post. What do you mean by input and output? There's just a power supply and load.A 40A PSU will burn up 20AWG wire in no time, especially if it goes into constant current mode.I'd go for a 3A fuse, as close to the PSU as possible. If that's not enough, then it can be increased, but I definitely wouldn't go any higher than 6A for 20AWG.