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Electronics => Beginners => Topic started by: AlexTheGreatish on August 10, 2018, 04:55:07 am

Title: Alright to use Relay?
Post by: AlexTheGreatish on August 10, 2018, 04:55:07 am
So I've made a circuit where I want to use generated power to turn on a lightbulb or whatever.  I want to have the output turn off immediately when the input stops, but I need a battery in between the input and output to help run the controller and act as a capacitor, but it's causing the light to stay on long after the input has been turned off.

I am thinking of using a relay (probably an automotive one) so that if the input switches on the output (the funky colours in the diagram), but I'm not 100% sure how relays work so I'm afraid most of the current will go into the relay if I just hook it up to the input voltage and blow it up, or lead to large losses. Any examples I've seen for relays have been a small amount of voltage (from an Arduino or something) that switches on a higher voltage so I'm not totally sure about using one in this application.  If there are some more electronically inclined people here could you let me know if this is a terrible idea?
Title: Re: Alright to use Relay?
Post by: james_s on August 10, 2018, 05:00:29 am
As far as I can tell from your drawing it will work. Relays are very simple, you power an electromagnet inside the relay and it closes (or opens) one or more sets of switch contacts. Larger relays can draw a significant amount of power to run the coil but it is normally still far less than the draw of the load. Look at the datasheet for the relay you are considering to get the coil current.
Title: Re: Alright to use Relay?
Post by: Brumby on August 10, 2018, 05:31:04 am
I take it the input voltage is DC of around 24V.

In this case, just find yourself a relay with a coil specified for 24V operation that has contacts rated for the voltage and current your inverter will be delivering.

The basic concept of a relay is the same for all electro-mechanical types - but the range of applications is extremely wide - and there are literally hundreds of designs that range in size from smaller than a sugar cube to ones you will have trouble picking up.  An automotive one may not be appropriate to use on 120VAC.  Always check the specifications and make sure all of them are appropriate for the job.

This is a pretty simple setup and, from what you have described, a suitable relay will be a very simple and effective solution.