Help with PSU rating?

[Tomo]

Hi all,

Rather a basic question here but I have very little experience with electronics at the moment...

I have a Parallel Relay Interface which is reasonably old. I want to connect it to my even older 8-bit computer to do some basic experimentation with motors and lights etc. Only problem is I don't have a PSU for it and don't want to plug in the wrong type and destroy the board.

I have a small document with the board which states the board requires 400mA when all the LEDS and Relays are working. Also that the 'lost' PSU provides 800mA and the power output on the board provides 350mA at 12V DC.

Could somebody recommend the rating of PSU I should use? Should it be a 12V DC at 800mA??

 

[HellasTechn]

Welcome to our on-line community Tomo !

If the stated ratings are true then yes, any 12V psu with amps rating of equal or greater than 800ma will be just fine

P.S.
Such a nice pice of hardware.

 

[Harald Kapp]

There is an L7812cv voltage regulator on board. Unless you can bypass this regulator by means of e.g. a jumper, the input voltage required needs to be higher than 12 V. The typical dropout voltage (Vin-Vout) for this regulator is 2 V (no min/max is given in the datasheet), therefore you'll have to supply at least 14 V for the regulator to operate correctly.

 

[AnalogKid]

Can you post a close up image of the writing on one of the relays? Also, a shot of the underside of the board, particularly the area around the power connector and 7812.

If the relay coils are rated at 12 V, then it probably is the case that 100% of the input power goes through the 7812, and as mentioned above the input needs to be 15 V or more. Note that there is no large filter capacitor near the 7812, so the input probably has to be DC. There is a diode behind the power connector. This might be a zener acting as transient protection. Sure would like to know that part number.

If the relay coils are 24 V, the the board runs on 12 Vdc and the 7812 is there to provide a lower operating voltage for the onboard circuits and the external power outlet.

ak

 

[Tomo]

Thanks for the replies!... Attached is another picture I will upload more when I get a chance.

 

[Tomo]

btw, Apparently it's a remake of an old Maplins kit

 

[HellasTechn]

There is an L7812cv voltage regulator on board. Unless you can bypass this regulator by means of e.g. a jumper, the input voltage required needs to be higher than 12 V. The typical dropout voltage (Vin-Vout) for this regulator is 2 V (no min/max is given in the datasheet), therefore you'll have to supply at least 14 V for the regulator to operate correctly.

Good point, i havent noticed that berfore.