I just bought this closed frame power supply 24V 4.5A: digikey part: 285-1806-ND (http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&site=us&keywords=285-1806-ND&x=0&y=0) to power some buckpucks (1x1000mA + 2x 500mA + 700mA).
I would like to use this source to power 2 relay boards with 12V since the relays required this extra-powering. So I need a 24V DC to 2x12V DC converter, but I am not sure of the characteristics it should have since I have no details of the datasheet of these relays). How can I do that ( a through hole component would be better), how much current can I get on the 12V side?
Thanks
You need a simple 12 Volt regulator like this one:- http://www.reuk.co.uk/buy-12-VOLT-REGULATOR.htm
You have no need for one for each relay you can just use one to power both relays.
Dropping down from 24V to 12V means you burn up the difference in heat, but relays don't take that much so you should not have too much trouble.
Don't forget to connect the ground back to the arduino.
ok thanks. Except that there is 8 relays total (4x2boards). 4 of them are 110/220V relays, the other are 12V relays. I do not think it changes somenting to your answer, it is just to be precise.
It doesn't matter what the relay contacts will switch it matters what the coil will take in terms of current. You need to find this out and add up all the coil current to get your total current requirements.
So I measured 422 Ohms for the coil of the AC relay board, which makes the Coil power to 0.36W (30mA) exactly the same power than the relay they are selling here: JQC-3FF SPDT 12V 5A PCB Relay Datasheet even if the printed information do not match exactly.
If this is case, does that need I only need 4x30mA ... so let's say 150mA on the 12V power source for this relay board?
For the DC relay board I measured 13.66MOhms ... may be weird?
So given that what are the characteristics of the 12V power source I need, can I use 1 for both?
My idea is now to use a 24V 4.5A closed frame power supply, use 24V and 2.7A to power some buckpuck (1x1000mA+2x500mA+1x700mA), and in // use it to produce a 12V power source to power my relay boards.
1-Does this sound good?
2-Can I only use a LM78M12 to create this 12V power source out of this 24V close frame power source?
3-Do you have an idea of a schematic to do that?
Thanks
For the DC relay board I measured 13.66MOhms ... may be weird?
Yes this is not the coil. It sounds like you have measured the resistance of your skin as you held the meter probes. Go back and find the coil.
Does this sound good?
yes
Can I only use a LM78M12 to create this 12V power source
looks like it but mount it on a heat sink.
Do you have an idea of a schematic to do that?
??? It's a three terminal regulator !!!
Ground of regulator to ground. Input of regulator to 24V output of regulator to 12V, with a capacitor between 4u7 and 100uF across the input and another across the output. See the data sheet of the regulator.
I guess I was tired yesterday. The DC relay board is a 12V in/ 12V@3A out relay board, which uses a voltage regulator (and not a relay with coil) with big heat sink.
So does the input current really matter? (since I have no datasheet...)
Is it or is it a FET solid state relay. Either way where are you getting the 12V from? If you already have it then why are you regulating down from 24V?
ok, the thing is that I bought the 12V@3A relay board (4 i/o) to power fans, 12V pump, and other small items.
This card needs an external 12V power source, so I want to use the 24V power source I have to power this relay board. Is that stupid?
The relay it-self looks like a LM78M12 except that they can sustain 3A.
