I'm editing the question because several (great) answers focus on the fact that the LTC3780 module (inside ajustable my power supply) can handle the inrush current (maybe, maybe not). I'm glad to know, but it doesn't answer my main question which is more global: how would you limit inrush current, in a cheap manner?
I apologized, my question wasn't clear.
(So the circuit I'm talking about below is just an example, let's say I use another power supply than the LTC3780 that deliver 12V-80W but can't handle the inrush current― but please keep the precious information provided in your answer about it).
The situation:
I want to power 5 fans in parallel (12V 0.80A, each) using an LTC 3780 (it's (DIY adjustable power supply)
Because my fan are brushless, I will have a high inrush current. My LTC 3780 can't handle more than 80W so I need to limit the current to about 6A (=80W/12V)
The possible solution:
I am looking for a simple/cheap solution (so no NTC thermistors*)
One cheap/simple solution would be to use a fixed resistor (R1) to limit inrush current to 6A, and a switch to bypass it. After a couple of second as the fans speed up, counter-electromotive force starts to limit the current. So the resistor R1 becomes useless and even inefficient as it consumes voltage/limits current that I need for my fans. The switch then allow to bypass R1.
The question is which switch : a relay, or even better, a MOSFET ? But how can I switch it? Could it work with a capacitor (or 555 timer ?)
Here is a working circuit with a relay (the fans are replaced by resistors with inductors).
How to choose the components ?
If this is a good solution, how can I determine the value for R1, R2, C1?
– If my understanding is right, R1 would need to be more than 2 ohms (= 12V/6A), so I guess a 4,7 Ohms would be right for R1.
– I guess I need a R2, but how to choose it's value.
– And what about C1? I guess the bigger it is the longer, it will take to switch on the relay.
And also how to choose the relay so that it doesn't switch on too early (before my fans reach their steady-state or C1 is full) : is there a way to know the minimum voltage/current needed to activate it? Would something like this MOFSET (or this relay) works ?
Better solutions ?
I also found this dirt cheap Time Delay Relay. If I use one with a fixed time like 5-10 seconds, would it work with my 12V/6A power supply and my five 12V, 0.8A fans?
Also is using a relay the best solution ? Couldn't I use a MOSFET as they consume less then a relay.
Here is my try at making a circuit with a MOSFET (but I can't find a way to use the capacitor to switch on the MOSFET):
(* Thermistors are expensive and I prefer to invest in components that I can re-use in other circuits.)
Best Answer
If the module you bought contains a real LTC3780, you do not need any downstream protection for it, as it is already short circuit protected.
If the chip on there is made of chinesium, and you do not trust it, you can try and hack the board to regulate the inrush current changing the cap connected to the SS pin. Limiting the inrush current will surely also limit the output current, saving the board.