# Power supply question

1. Jul 30, 2013

Ok this may be a stupid question but what the heck.

If I have a power supply giving max of 4amps with 35v
and what I am powering draws 6 amps at 35v,
then that means the device has 5.7 ohms of resistance.
If I put a 3.05 ohm resistor (ish) then this will drop the amps down to 4, but will it still power the device... functionally?

2. Jul 30, 2013

### willem2

The resistor and your device will form a voltage devider. You'll get 5.7/(5.7+3.05) * 35 = 22.8 V across your device so it is not likely to work.

The power dissipated in the resistor is I^2 R = 4*4 * 3.05 = 48.8 W wich will be a problem as well.
Your resistor might require a heatsink and a fan.

3. Jul 30, 2013

### davenn

if the device needs 6A to operate then its not likely to work with only 4 amps or if it does it will be unstable in operation
Adding a resistor is only going to make the situation worse

you need a beefier PSU

Dave

4. Jul 30, 2013

ok thanks, I forgot about the voltage divider so It seemed possible for a moment, this isn't a project i'm working on, I was just day dreaming.

BUT

Sense I have this thread open, and davenn is here:

I read that bridge mode in amplifiers will, for example, take a 100 watt amplifier at 8ohms and turn it to a 200 watt amplifier at 4ohms.

I was going to use 4 tda2050 amps, each running one speaker, but if I use 2 amps in bridge running 2 8ohm speakers in parallel, would this give me double power into both speakers? So as if each speaker had it's own amplifier twice as strong?

5. Jul 31, 2013

### sophiecentaur

As long as you realise that you don't get anything for nothing then you can't go too far wrong. Connected in a bridge, two amplifiers will (if they can) deliver twice the current into a load than they would, individually. They are each 'seeing' a load of half the resistance of the original load. If the amplifier can't deliver enough current then you won't get that power - it will clip.

6. Jul 31, 2013