12v dc power supply with multiple devices

[jmreynol]

Here is my dilemma: I have just built a new aquarium and the setup requires a number of 12v power supplies. When done I will be running (3 )12v 1.4W fans and four 12vCoil 120v dpdt relays. Currently I am running 2 fans from a 12v .5A power supply and 2 relays from a 12v 1A power supply. I would like to run all of the devices from one 12V power supply. I have not seen anything on the web that will provide what I need. I have been thinking about using an ATX Computer Power supply or building my own from a 120V AC-DC transformer. I know enough about electronics to put something together but I need some guidance. Does anyone have any suggestions ?

Thanks in advance,
JMR

 

[alexan_e]

Have you tried to use only one power supply , the 12v 1A unit.
I think it is more than enough
You can measure the current of one relay to help calculations but i assume less than 100mA
fans 3x 0,12A = 0.36A
relays 4x 0.1A = 0.4A
--------------------------------
Total 0.76A

Unless you have some other device connected.

Alex

 

[jmreynol]

I haven't tried using just using just one ps. I will try and see what happens.

Thanks,
JMR

 

[jmreynol]

I am reviving my question since things have changed. I did manage to run my fans from the single power supply but now my needs are changing. The number of 12v outputs for my system has risen to 6 with varying amperage. My questions is these:
1) Are most devices self limiting when it comes to amperage ? ex: 12dc 5A feeds (2x) 1.5amp devices, (4x) 200ma devices
2) If I just split the power supply to 6 outlets will I get a surge to the others as devices drop in and out ?

Thanks in advance
JMR

 

[alexan_e]

I don't know what you mean exactly with self limiting.
Each device has a current consumption for the specified voltage, so when it say 12v 1A it will draw 1A at 12v input.

The surge has to do with the power supply and load but I don't think it will be a problem for the other devices in the same psu.

Alex

 

[jmreynol]

Thanks for the quick reply.
Here is what I mean by self regulating. If I put a device that takes a load of 12v dc @1.5 amp and it is be served by a power supply that is 12v dc @5A will the device regulate the incoming voltage/amperage or will it overload ? Or do I need to look at each device to see what its tolerance is and then regulate each output accordingly.

Thanks,
JMR

 

[alexan_e]

The power supply can only provide a constant voltage level for the load (regulated),
the amount of current drawn from the power supply has to do with the load, as the load resistance gets lower the current increases,
the only way to increase the current to a specific load is to increase the voltage.

It is based on the Ohms law , when you have 10v and 10ohm load then the current is 10v/10ohm=1A, when the load is 5ohm it is 10v/5ohm=2A.
The source can't increase the current while the voltage is constant, only the load can alter the current.
current= voltage/resistance (I=V/R)

The power supply can provide up to the specified max current, as long as the load is specified to work with the voltage of the psu and you are not over the max current of the source you have no problem.

Alex

 

[kak111]

I drow a picture for you.
It show you what happens.

View attachment Power supply vs load.pdf

Hope this helps.

Regards KAK

 

[Syncopator]

If I put a (12V) device that takes ... 1.5 amp and it is be served by a power supply that is 12v dc @5A will the device regulate the incoming voltage/amperage or will it overload

The voltage is dependent on the power supply. The unit which the supply powers will draw whatever current (your "amperage") it needs - assuming it isn't more than the supply can deliver.

So, a 12V device which needs 1A, when connected to a 12V source which can deliver 100A, will draw just 1A.