# Arduino Forum

## Using Arduino => General Electronics => Topic started by: DrJanItor on Apr 24, 2018, 06:42 pm

Title: Question about a very simple circuit
Post by: DrJanItor on Apr 24, 2018, 06:42 pm
Hi! I keep having trouble understanding some very basic things about electronics. I will try to explain with an example:

Let's say i have a very simple circuit where i get 230VAC from an outlet. I use a transformer/rectifier (not sure what the english term is) to get 24VDC that i use to power a lamp. If i know the lamp is supposed to be powered by 24VDC, what else do i need to know about the lamp and the transformer/rectifier to know that this circuit is safe?

Thanks!
Title: Re: Question about a very simple circuit
Post by: slipstick on Apr 24, 2018, 06:54 pm
Voltage is not everything.

You also need to know how much current the lamp requires and if the power supply can safely deliver it.

Steve

Title: Re: Question about a very simple circuit
Post by: DrJanItor on Apr 24, 2018, 07:04 pm
OK thank you. Then i have a follow up question. Let's say the power supply can deliver enough current. Will the lamp then "draw" that amount of current? Also if the supply can't deliver that amount of current what will happen? Will the lamp just not light up?

Also, if i supply the lamp with 24VDC but the current the supply can (or will? i think this is where i am cunfused) deliver,  will the lamp draw as much current as it needs or will it burn up?
Title: Re: Question about a very simple circuit
Post by: slipstick on Apr 24, 2018, 07:13 pm
At a fixed voltage the lamp will try to draw the current it needs. If the supply can't provide enough current then the lamp may not light up but also the power supply may burn up.

If the supply COULD provide much more than is needed then that's not a problem. The lamp will simply draw what it needs.

Steve

Title: Re: Question about a very simple circuit
Post by: DrJanItor on Apr 24, 2018, 07:13 pm
OK thanks alot!
Title: Re: Question about a very simple circuit
Post by: MarkT on Apr 24, 2018, 09:38 pm
Hi! I keep having trouble understanding some very basic things about electronics. I will try to explain with an example:

Let's say i have a very simple circuit where i get 230VAC from an outlet. I use a transformer/rectifier (not sure what the english term is) to get 24VDC that i use to power a lamp. If i know the lamp is supposed to be powered by 24VDC, what else do i need to know about the lamp and the transformer/rectifier to know that this circuit is safe?

Thanks!
The transformer must be rated for use with mains, complying with the local regulations, and it must be
wired according to the regulations too.   So you start by finding those regulations.  The regulations codify
a lot of knowledge about what not to do(!)
Title: Re: Question about a very simple circuit
Post by: Southpark on Apr 24, 2018, 11:54 pm
Also, if i supply the lamp with 24VDC but the current the supply can (or will? i think this is where i am cunfused) deliver,  will the lamp draw as much current as it needs or will it burn up?
In general, a electrical device does not draw as much current "as it needs". The 'current' that flows through (or into) the device is just determined by the circuitry (aka the electrical components in it), and the components connected to this device..... like external circuitry and components.

It's best to know the electrical specs of the lamp and electrical specs of the source --- such as voltage and current and power ratings --- that would ideally be supplied with an electrical item. Just don't use the device under conditions where the actual values like applied voltage or input current or power are higher than the specified 'rated' value(s). In this way, you can have at least some level of confidence that the item will work properly during its expected operating lifetime.

This also means - in general .... don't use any electrical device where the voltage or current or power exceed rated values.
Title: Re: Question about a very simple circuit
Post by: tinman13kup on Apr 25, 2018, 12:40 am
I wouldn't consider mains electric circuits as "simple". It is more an advanced area in which special precautions must be considered to prevent serious risk of injury, death, or fire.

"Simple" circuits are the ones used in the Arduino starter kits, where the only way it's going to kill you is if you try to eat it, and an electrical fire is not impossible, but improbable. You are more likely to release small clouds of noxious smoke.
Title: Re: Question about a very simple circuit
Post by: falexandru on Apr 25, 2018, 01:23 pm
From my (limited) knowledge, the question appears to be divided in 2 parts:
a) the transformer calculation - a transformer can only make AC from AC (at least the types I am aware of)
b) AC-> DC (in various ways, from one diode to a lot of complex circuits).

Here you have some info about power in alternating current:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/powerac.html

The commercial outlet power sources have their own characteristics. I would go, as a matter of personal option, for at least 10% more DC power in the source than the one required by the consumer at maximum.
Title: Re: Question about a very simple circuit
Post by: Grumpy_Mike on Apr 25, 2018, 06:37 pm
Quote
is) to get 24VDC that i use to power a lamp.
Every one is assuming that this lamp is rated for 24 volts, if it is a mains rated lamp then you are in a whole heap of trouble trying to drive it at 24V DC.

Also if the lamp is rated for 24V AC, then it won't work like you hope.