First, this is for a arduino product but i don't want to connect the thing discuised here on my arduino.
I got a magnetic doorstop (a thing that can hold a door open with magnetic 'power' and when there is a fire it stops so the door closes) but the info on the sticker is like 95% gone.
The brand is HAHN and i saw that all there products are 24V DC.
They are 1.5W or either 3W (don't know if that info is needed).
If i buy a adapter what would a good ampere be?
Also there are 2 cables coming out, see the "schematic picture", the red circle is the test/stop button. Any idea what one will be + and what one will be -.
Or will it just switch the pushing / attracting when i connect it wrong?
clankill3r:
I measured the resistance, it's 377ohm.
So I = V/R
24v / 377 = 0.0636ampere
So 63 amp
I assume you meant 63 mA.
clankill3r:
So i can assume it's 1.5watts, since 1.5/24 = 0.0625 amps.
If i use less then the strength of the magnet will just be lower right?
Yes.
clankill3r:
Can i bring a 30V adapter with 1.5mA for example back to 24V with 0.064mA?
And if so what math do i need? Since now it should involve V as well current.
I assume you meant 1.5A not 1.5mA. Given that the load is more or less constant, you can use a series resistor to drop 30v to 24v. Use Ohms law again. You may find that your 30V 1.5A adapter delivers rather more than 30V when the load is only 64mA, and if so then you will need to increase the series resistor to suit.
I had a few hours sleep so sorry for the mess up with A and mA.
I assume you meant 1.5A not 1.5mA. Given that the load is more or less constant, you can use a series resistor to drop 30v to 24v. Use Ohms law again. You may find that your 30V 1.5A adapter delivers rather more than 30V when the load is only 64mA, and if so then you will need to increase the series resistor to suit.
Can it be that i need to use other things as well apart from resistors? (i'm kinda a noob).
If the only thing you want to provide 24v to is the door lock, a resistor is just fine. You could use a 24v regulator instead, but that would be overkill.
Also i looked for a adapter today, 80% was 5V, i found 1 of 30V and 1 of 22V.
I don't remember the mA but it was way more.
If you live in the U.S., you can order a 24V supply from Jameco, mouser, or Digi-Key.
Can i bring a 30V adapter with 1.5mA for example back to 24V with 0.064mA?
30V/0.064 = 469 Ohms. You measured 377 Ohms, so you need to add about 90 ohms in series.
(Don't forget to calculate the power dissipated by the resistor... With 6 Volts dropped across the resistor with 64mA flowing through it... It looks like you'll need at least a 1/2W resistor.)
The resistors sold by electronic stores are often rated at 0.25 Watts or thereabouts. This is the maximum power than can be dissipated in it without overheating. The series resistor you need will dissipate about 0.4W, that's why DVDdoug said to use 1/2W or greater.
I mentioned before that the 30v supply may produce a bit more more than 30v when loaded with only 64 mA, so I suggest you buy 100 ohm 1 Watt and 120 ohm 1 Watt (or greater) resistors and use whichever gets closest to 24v across the door stop. Alternatively, buy a bunch of 470 ohm 0.25W resistors and connect 3, 4 or 5 of them in parallel (whichever gets closest to 24v again).
For the adapter, i have a plug, what is supposed to be the + and -? (first attachment).
Also one i could open screwing, by the other i can not. Can i push the metal out by a screwdriver in the back or is that a bad idea? (2nd attachment).
For the adapter itself, i dont know which end is + and which one is -. I can check with a multimeter right? If the value is positive then the red probe is +, is the value negative then the black probe is -, or am i wrong?
The adapter will have a large smoothing capacitor across the output. If it's not connected to anything and it doesn't also have a discharge resistor, it could take quite a while for the charge in that capacitor to leak away.
Ok got it ready.
When i check the voltage of the adapter it gives 37.9 (although it should be 30V according to the information on it). When i put a 100ohms resistor in between then my multimeter still gives 37.9 instand of something around 24V, why's that?
Also if i do a check on the mA then at the 10A setting on my multimeter it gives nothing, it should give o,4A. If i check at the 200mA then it breaks the fuse (i tried cause the 10A gave me nothing...), so what's up with that?
clankill3r:
Ok got it ready.
When i check the voltage of the adapter it gives 37.9 (although it should be 30V according to the information on it).
That's not unusual for the open-circuit voltage, the 30v will be quoted at full load (1.5A I think you said).
clankill3r:
When i put a 100ohms resistor in between then my multimeter still gives 37.9 instand of something around 24V, why's that?
I presume you mean that you connected your door lock to the supply with a 100 ohm series resistor. You need to measure the voltage across the door lock in that condition, not the output from the supply.
clankill3r:
Also if i do a check on the mA then at the 10A setting on my multimeter it gives nothing, it should give o,4A. If i check at the 200mA then it breaks the fuse (i tried cause the 10A gave me nothing...), so what's up with that?
How exactly were you connecting the meter when you had it on the 200mA range and on the 10A range?
