How to power your 12v 40mm fans off your main packs

[Ajag]

I’ve been building a lot of fans for people lately and there’s always questions around how to power them
Here’s what I do

I’ve been making plugs that will allow you to plug your 12v fans into any main pack configuration using the balance plug.

that’s all you need to do is to properly tap into the balance port

see pics attached
All configurations have the red wire on the end and then the black wire needs to be soldered on 3 pins later
See pics
This plug I made allows me to power my fans off a single 3s/4s or 6s
So pretty much any configuration we run these days

 

[jondilly1974]

My concern with this method was making my lipo cells unbalanced. I went with a buck instead.

 

[Ajag]

My concern with this method was making my lipo cells unbalanced. I went with a buck instead.

Yeah
I have tested it enough to really say whether or not the imbalance issue is a show stopper or not but theoretically it shouldn’t be a big deal. The charger should be able to re balance the pack
If the imbalance issue on a 4s/6s pack is a concern you just need to run a separate 3s pack for power

 

[jondilly1974]

Yeah
I have tested it enough to really say whether or not the imbalance issue is a show stopper or not but theoretically it shouldn’t be a big deal. The charger should be able to re balance the pack
If the imbalance issue on a 4s/6s pack is a concern you just need to run a separate 3s pack for power

With my two Delta fans I took the cells down a half volt compared to the other cells during about a ten minute span. That was more than I was comfortable with.

 

[JvG]

With my two Delta fans I took the cells down a half volt compared to the other cells during about a ten minute span. That was more than I was comfortable with.

Half a volt is really a huge difference or do you mean 0,05 volt?

 

[itizme]

you only need once balance connector, just remove the tab between the slots on the 6s connector and mark the end you need all balance leads to start at. You will find this on some balance charging boards.

 

[jondilly1974]

Half a volt is really a huge difference or do you mean 0,05 volt?

Nope. 0.50v (3.70 to 3.20) and that’s why I no longer run fans off the balance lead.

 

[JvG]

Nope. 0.50v (3.70 to 3.20) and that’s why I no longer run fans off the balance lead.

Wow that’s a lot, some mighty fans!

 

[jondilly1974]

Wow that’s a lot, some mighty fans!

They are the loudest fans I’ve used in RC. They are server fans.

 

[rotauq]

In the pc world, Delta always have been the brand with the highest CFM and total disregard for dB's

I removed my 0.7A (4X) delta fans and replaced them by 0.5A (3X)APC fans. My 450Ah 3S battery drained within 3 min and a Vdrop of 1+V You would say 35W continuous would last longer. You don't want that on a few cells. The 850Ah i use on the APC's lasts long enough to do some speedruns.

If you really wanna take some from the main lead, use a ubec to get the voltage you want.

 

[ChemEng]

Nope. 0.50v (3.70 to 3.20) and that’s why I no longer run fans off the balance lead.

Yep. I run big boy server fans to get a high static pressure (4 in Wc) for my motor cooling solution. They pull almost 2A each.

I use one of these. Works a treat and doesn’t care if I am using 2x3s or 1x6s lipos.

DC to DC 24V to 12V Step Down Voltage 12Volts Regulator Buck Converter Output 5A 60W Power Converter Module (5A) https://a.co/d/128ncLj

Edit: lol I resurrected a 3 year old thread by accident. That’s impressive, even for me.

 

[RedOctobyr]

Edit: lol I resurrected a 3 year old thread by accident. That’s impressive, even for me.

Well the thread is awake now anyhow, so... I guess if someone was running a pair of fans, and using 6S, they could use a pair of identical 12V fans, wired in series. And feed them the full 25V from the main leads (or the full width of the 6S balance connector, if you wanted to go that route), but they'll each get 12.5V. The fans are happy, and it's an even load on the pack, so it doesn't imbalance certain cells.

 

[ChemEng]

Well the thread is awake now anyhow, so... I guess if someone was running a pair of fans, and using 6S, they could use a pair of identical 12V fans, wired in series. And feed them the full 25V from the main leads (or the full width of the 6S balance connector, if you wanted to go that route), but they'll each get 12.5V. The fans are happy, and it's an even load on the pack, so it doesn't imbalance certain cells.

That’s actually a cool idea… but it would depend on both fans being very close in specs or the voltage to each fan would vary by the ratio of their internal resistances.

And if one fan got hot and shorted out (internal resistance goes to zero) then the other fan would get the full 24 V and burn up too.

All that said, I think I’ll try it (I need the space back on the chassis for another project…)

 

[RedOctobyr]

Sure, but if they're matching fans, I'll bet their respective voltage drops would be quite similar. And you could check each voltage drop pretty easily with a meter while they are running.

You'll only be above 12V/fan for a short time, until 4.20V/cell drops to 4.0V. And I would guess they can handle a little over 12V.