12v DC Fan, Current Limiting or not

Thread Starter

anishkgt

Joined Mar 21, 2017
529
Hello All,

I have a super-capacitor project which is charged at 10A the supply is powered by CPU power supply rated 12v 30A. The power supply is in its own casing and has its own fan. I am also adding a CUI branded fan into the case that houses the super-capacitor and its charger, my question is would it require a current limiting method in way ? i mean is it required/standard design to have it. I came across the MAX4789 current limiter which seems to be a bit costly considering its function.
Annotation 2020-06-17 153645.png
 

ci139

Joined Jul 11, 2016
1,696
see your super-cap datasheet ... the last time i saw one - such allowed quite high input currents . . . 10A is not that much for some minutes . . . perhaps

. . . however the super-caps don't want to get over-voltage /!\
 

dl324

Joined Mar 30, 2015
11,845
I am also adding a CUI branded fan into the case
This is a common concern by newbies that's really a non-issue.

Consider this case. If you plug a 100W lamp operating at 120VAC into an outlet on a circuit that can provide 15A, the lamp will draw 100W nominally even though the circuit can provide much more than that. If you plug a USB charger into the same circuit, it also will only consume the power it needs (on the order of almost nothing, if it isn't charging anything, to up to around 10W).

A 12V fan can be powered from 12V without needing to be fused. But, you could add one if you're worried about the fan putting a larger load on the power supply if it failed.


Regarding your super capacitor charging current. If you charge it with a 30A supply, it won't limit it's charging current to 10A without some current limiting circuitry.
 
Last edited:

Thread Starter

anishkgt

Joined Mar 21, 2017
529
The super-capacitor charge current is limited to 10A by its charge IC BQ24640.
About the fan then, its ideal to limit any device to its rated current. How likely would a brushless fan consume more than the require current ? One way I could think of is when dust gets accumlated on its leafs.
 

dl324

Joined Mar 30, 2015
11,845
About the fan then, its ideal to limit any device to its rated current.
Design usually requires a number of compromises. Every fuse you use adds cost and points of failure. You have to weigh the "risks" of not doing an overly conservative design.
How likely would a brushless fan consume more than the require current ?
If something caused the motor to stop spinning while power was on, the stall current could cause problems. The question you need to ask is what harm could it cause if it failed?
 

Thread Starter

anishkgt

Joined Mar 21, 2017
529
From what the datasheet of the fan says, it stops when halted and restarts automatically does that also mean a stall as well ?
 
Top