Limitless Best way to power 2 fans

[Niz55]

I already have a high speed fan 8.4 for the esc. But I wanted to know if I can power 2 more fans for the motor running 8.4 from the receiver or should I just go power both of them from the balance connector on the battery using a step down voltage.
I am running 8s 2x 4 cells


Thanks

 

[SrC]

Add the amp specs of all your fans combined and compare to the BEC amp supply rating. The amps are usually printed on each fan. If you are not over the BEC amps, using the Rx as the power source for all combined it is ok. That's what I do with my Lim's motor fans. If you exceed the BEC amps, you can overload the BEC circuit. Rx Brown Outs can result. A bad thing when Speed running specifically, or any rig. Using the balance leads is one other option as well, or using even an external/aux BEC supply. Pick your poison carefully.

 

[Mastaa]

I use a separate 2s lipo to power my two motor fans and my esc fan, has done me well so far.

 

[SrC]

I use a separate 2s lipo to power my two motor fans and my esc fan, has done me well so far.

Most do that also. Using a small lipo. (Mini Quad sized lipo) Great suggestion!!!
It's always good to avoid loading your BEC, if you can avoid it.
Rx signal is always your priority. Let your Rx get all the BEC overhead it wants. A clean, isolated, and noiseless signal will result. At least in theory.

 

[jondilly1974]

I use a 3S 1100mah lipo for my 12VDC fans on my speed runners. If you’re using 5v fans, then 2S would be the max.

 

[suchtragedy]

@everyone

Any reason to not power all 3 off the receiver? My understanding was that fans don't draw that much current so powering multiple fans off the receiver didn't hurt anything as long as they weren't needing higher voltage/amps than what the onboard BEC was putting out.

I know that speedrunners prefer to power fans separately to remove as much additional load off the esc as possible since you're stretching output power to the limit but for like bashing applications it should be fine?

 

[SrC]

A fan(s) will only get the voltage the BEC will provide. 6v,7v, or 8v as provided by the ESC. Its the amp draw of each fan or any accessory (lights,etc.) that combined can exceed the BEC total amp supply.
Most fans are within a BEC amp rating. ESC supplies the volts and amps to the Rx's BEC output. If a BEC is spec'ed at 3.0 amps max and you add fan(s) that are over 3.0amps (combined), you've exceeded the BEC amp load. That's the real issue. Hope that makes sense.

 

[Niz55]

The 2 motor fans are rated at 0.45A .

I have the firma 160 amp esc (K8)

I was running all 3 fans including the esc fan off the esc port and the motor fan was acting weird.

 

[SrC]

.45A +.45A =.9amps. What is the BEC spec for the Firma 160 ESC?
What is the amp spec of the Firma Fan??? Add that number to .9amps
That will give you what the actual amp overhead that is required for all 3 fans.. must include the servo as well. If your fans appear to fluctuate as you operate your servo. You have exceeded your BEC amps.
What BEC voltage was selected within the ESC settings? As you go higher in BEC volts, you take a hit in available amp overhead? That's why I tend to keep my ESC's at 6v. I get higher amp overhead. And in all honesty, my servos are just fine running at a 6v. BEC setting.

 

[Niz55]

Bec is set to 8.4 and is rated at 5amps.

 

[SrC]

Some servos have a high current, whether at idle, no load or stalled. And this varies from servo to servo. Stalled current requires the most amps. and can exceed any BEC rating if not matched well enough to a given BEC's spec. The servos are priority here and the main objective of a BEC's output.
Servo stall current under load can be well over 5.0 amps at times depending on the servo. That's why, some servos are considered power hogs over others.
Getting back to fans, they are low demand peripherals in general and should not pose a problem. But understand the risk potential is always there.
Overloading the BEC usually bricks the ESC's power regulator, before anything else. The BEC belongs to the ESC, not the Rx. where that power is just ported to.

 

[Niz55]

So a 2000mah lipo should be enough or should I go higher in mAh?

 

[SrC]

2000 is rather high. higher capacity = larger footprint. Like above stated...1100mah is fine.
How much weight do you want to add? How much room do you have to mount?
Even 1100mah is way more than enough capacity to power tiny fans.

 

[jondilly1974]

I usually just use a 1100mah pack at storage. I rarely ever balance charge them. Not sure if that will ever be an issue, but it saves me from having to discharge them back down to storage every time.

 

[Niz55]

Honestly not much room at all. Only going to power 2 fans at 7.4v.

 

[SrC]

https://www.amazon.com/RCRunning-Ba...hvlocphy=&hvtargid=pla-4584345024270237&psc=1

 

[LibertyMKiii]

I run a separate battery for the fans also. A LiFe would be fine given the low amperage draw and then you don't have to worry about returning to balance charge after.

 

[SrC]

Even 2x Lion cells... whichever types fits best, is smallest. Lions store well also.