raw input mini pro 12v ?amps

I have now two seperate power supplies. 5v for de mini pro and 12v for the ledstrip drived by pwm and a (2x) mosfet. (irf540 100V 28A)

Everything works like I want but now trying to design my first pcb and that reminded me of the two power supplies......would be great if I could use one instead.

Reading about the raw input for the mini pro I know it's possible to feed 12v, but my 12v for the ledstrip(s) gives alot of amps.

My question, is it wise to feed the Mini Pro with a 12v x? Amps adapter like these ?

Reading THIS while typing my question is probably also my answer. Hopefully someone can verify

PaulS:
Powering the Pro Mini with a 12V 120A power supply is safe, since current is pulled, not pushed.

Powering the Pro Mini with a 12V 1200mA power supply AND having the Pro Mini power the LED strip WILL cause problems.

So. have the + side of the power supply, whatever it is, go to the Pro Mini AND the LED strip. Have the - side of the power supply go to the Pro Mini AND the LED strip.

This way, the Pro Mini will draw whatever current it needs (not much) and the LED strip will draw what it needs (plenty) without all that current going through the Pro Mini.

Which reminds me, I also have an RTC & LCD running at 5v not 12v )-:

*EDIT:
(So feeding the ProMini at the Raw input with 12v28A and using the ProMini 5v output for the RTC and LCD. Feeding the ledstrips with the + 12v28A and using the irf540 mosfet to drain. Both 5v and 12v gnd are connected to each other.)

You should be OK because, yes the current depends on the load.

The only concern I have is that the LCD & RTC will share the Arduino's 5V voltage regulator, and the regulator has to handle the current of these parts.

I think you'll be OK, but there's no simple answer to how much current the little linear voltage regulator can supply. The amount of power (and related heat) the regulator dissipates depends on the voltage dropped across it (7V with a 12V source) and the current through it. (Power = Voltage X Current)

I'll probably just have to try it first and see how much smoke is blocking my visibility

Yes, the regulator on the Mini Pro is small so it won't take much power to overload it. Its the
7V dropped times the current the Mini Pro draws that's the issue, not the current capacity of
the 12V supply.

An external 7805 regulator would be better prepared to cope with the dissipation, and a DC-DC
converter would be ideal.

Oke, understand.

But....should I still provide the 5v (from the 7805 output) onto the raw input of the ProMini ? Cause I believe I read somewhere (cannot find it anymore) that the Pro Mini likes at least > 5v on the raw input to work correctly....

Its the 7V dropped times the current the Mini Pro draws

Does this also occurs with those DC 12 volt adapters I posted earlier?

Thanks for making me smarter

So feeding the ProMini at the Raw input with 12v28A

As long as your 5V regulator doesn't short out you should be fine. If it did, what would 28A do to a little 5V regulator that is shorted ?

Try this. Power a 555 chip with the same supply (but not on a breadboard. wire it direct. )
Then short the output pin of the 555 to the ps ground. (be sure to have a fire extinquisher ready and wear safety glasses. You probably shouldn't even try this indoors. The smoke will be aweful)

Feed the external 5V into the Promini VCC pin, not the RAW pin.

Promini needs ~6.5V at the RAW input to make 5V at the VCC pin, and only 150mA of 5V current is available.

I have at least a dozen primini's being powered from external 5V to the VCC pin at my fencing club, they've been running since early 2011, powered on & off several times a week.

An inline fuseholder would be a good idea for the output of that PSU!
As Rasch said, any short across that PSU could result in significant damage.

it sounds like you are going to build your own board. why not add a DC-DC chip like they use in the cigarette power adapter in cars ? you get 12v for all the external stuff and 500ma of 5vdc for the Arduino. then feed it as crossroads mentioned.

@raschemmel, can you still see me ?

@CrossRoads: would you go for the 7805 and feed it to the 5v ?

@dave-in-nj, my 'problem' is that I want my pcb as small as possible and complete without extra inline things etc. What are the pros/cons regarding the 7805 or a dc-dc converter? Putting a 7805 on the pcb is easy, but a dc-dc converter?? For now everything fits on a 5cm/10cm pcb board.

@raschemmel, can you still see me ?

I am sorry but the point of this question eludes me .

My previous post was addressing an issue with using a 28A PS. If you are not going to use it then my comment is no longer relevant.

My promini's have an offbord 7805 for 5V. They control NPNs that turn on 3 banks of LEDs powered from the 12V. The offboard 7805 gets warm but everything is AC powered so I am not concerned about running from battery.
If battery was a concern, then a little switching regulator would be ideal.
For example, this 7805 sized device

or this little guy

Battery will last way longer vs 7/12 of your battery capacity as heat in the regulator.

raschemmel:
I am sorry but the point of this question eludes me .

Wanted to point out that I understood what you meant, but I'm probably not very clear about what I want to achieve.

I want to use this and/or this as power supply for my ledstrips & arduino.

So input always DC but not only for my ledstrips but also for my arduino mini pro if possible. (so max 12v 30a)

As I'm just a hobby guy trying to learn as much as I can, so I do ask questions that are probably silly

@CrossRoads, does your answer still stand using a 7805 (in my case onboard pcb) when using such DC power supplies ?

Another possibility is bring the 12V down to 8V with a 7808 and pass that to Vin on the Pro Mini.
That finesses the issue of back-powering the on-board regulator (some regulators don't handle
back-powering well, note), and reduces the power dissipation on the Mini Pro (basically sharing
the thermal dissipation between the 7808 and the Mini Pro's regulator.)

Since a freshly charged 12V lead-acid battery is 13.8V, the 7808 will be handling up to 6V drop
so some heatsinking may be needed.

Incidentally available regulator output voltages include 3.3, 5, 6, 8, 9, 10, 12V, 15V and there are
variable regulators (and ways to use a fixed voltage regulator at a higher voltage)

You talk about acid batteries, but like I said in my previous post, I only use DC 12v adapters with up to 30A.

QUESTION:

1#Does the same logic apply ?

2# Does it matter how much Amps?

Nice idea to devide the thermal dissipation, thx! I'll use a DC 12v adapter (<30A) and a 7808 (like you said) on the Vin 'of the MiniPro'

Simple answer is that "it will very likely go wrong in a way that emits light, smoke and starts fire".

Arduino is a development board, and as such lives in that environment of error and miscalculation.
This is why an electronics workshop/lab should have voltage and current controlled power supplies.

Minimum is a fuse, and all current path to that point rated at >30A.

"wil likely in a way"

I'm interested in what way and why.(not because it could happen by human error)

"Minimum is a fuse, and all current path to that point rated at >30A"

Meaning my setup will work?

I like the thought from MarkT, it's a logical answer. Also CrossRoads answer using an alternative regulator. (OKI-78SR-5)

As a challenge I like the costs to be as low as possible and ordering this OKI costs 30$ shippingcosts for me.

Using a 7808 onboard and DC 12v <30A. In what way is this (not) good enough or could it go wrong and why?

What we aré trying to convey is that a power supply ratee for 30 A will turn a semiconductor into an incendiery device if a short occurs. Even a 10 A PS will cause a shorted semiconductor to glow and burst into flames. A 30A PS would do the same thing only 3 times faster and hotter. To not use a fuse is juste plain negligence.

Also, using 12 V on the RAW input of the Pro-Mini will cause the 5 V regulator to run hot dissipating tha 7 V diference.

Also, since you have two loads with different amperajes so you can not use a single fuse. You need two fuses.

So the setup is alright, but it could , by human error only, be shorted and it's just plain negligence to not use fuses...

So adding two fuses is the final addition to the setup. (holder1 or holder2 )

Thanks for all the help guys!!!!!

Try not rule out the unexpected. Things happen even if it's not your fault. Human error is not the only cause if device failure.