Power Bricks - choosing the right one

[pmrid (Peter)]

For the many clever electrically-minded out there - if a device requires, say 12 VDC at 4 Amps startup and 3 amps running, do I run a risk of damaging it by connecting it to a power supply rated at say 10 Amps or even a battery?

And the reverse side of that question - what about using a supply rated at only say 2 Amps?

Peter

[big-blue]

Hi Peter
re your questions
Since power = volts x amps, you would appear to need around 48Watts to start and 36watts to run in terms of power requirements.
Firstly a 2Amp rated supply will not attain the required power level. You may also find a significant voltage drop if the supply attempts to exceed its rated current level. You may even over-heat and fry the under-rated supply.
The alternative 10Amp supply should be capable of meeting the required power and running with stable volts and amps. Basically, the load resistance will limit the supply current to 3A when running. In a short circuit situation, however, which is abnormal, the power supply might attempt to deliver its full 10 amps or more and fry itself and/or the short-circuited load. In which case, accidental short circuit represents a risk, and should be protected via (say) a 5A fuse. Short circuits can sometimes arise from (eg) cables that fray over time, or a component which becomes faulty over time. A fuse is the simplest way to protect a (more expensive) load (or supply) from over-current situations however they might arise.
I trust this helps

[pmrid (Peter)]

Originally Posted by big-blue

Hi Peter
re your questions
Since power = volts x amps, you would appear to need around 48Watts to start and 36watts to run in terms of power requirements.
Firstly a 2Amp rated supply will not attain the required power level. You may also find a significant voltage drop if the supply attempts to exceed its rated current level. You may even over-heat and fry the under-rated supply.
The alternative 10Amp supply should be capable of meeting the required power and running with stable volts and amps. Basically, the load resistance will limit the supply current to 3A when running. In a short circuit situation, however, which is abnormal, the power supply might attempt to deliver its full 10 amps or more and fry itself and/or the short-circuited load. In which case, accidental short circuit represents a risk, and should be protected via (say) a 5A fuse. Short circuits can sometimes arise from (eg) cables that fray over time, or a component which becomes faulty over time. A fuse is the simplest way to protect a (more expensive) load (or supply) from over-current situations however they might arise.
I trust this helps

That is exactly what I needed. Many thanks.
Peter

[pmrid (Peter)]

Just to round off the thread: I whacked together this simple fused distribution box this morning some bits and pieces I had in the shed. So I can run fused lines as required. It sits up the front f the scope for a bit of counterbalance for my cooled DSLR project at the other end.

Thanks again.
Peter

[RickS (Rick)]

Nice work, Peter. Very practical.

[pmrid (Peter)]

Originally Posted by RickS

Nice work, Peter. Very practical.

Thanks Rick. I was about to order another RigRunner but they're not cheap and take a month to get here. And the Australian distrubutor's price is about double the landed cost from the states. So I decided to improvise. Which I really enjoy.
Peter