I need some ideas on a budget 12v battery setup that can power some computer fans. I may have some free time coming up and I have a project plan. The cheaper the better. I know I could run 4x protected 26650 in series but I would prefer a better solution if one is available. It needs to be small enough to fit in a 50cal ammo can (approx. 7” wide and tall) so it can be portable.
Why not lead acid 12v batteries? They’re very cheap.
If you ‘know somebody’ in a building maintenance position, they can often get you pulls of SLA batteries from fire and exit signs. Sizes will vary as will condition. They are supposed to be replaced on a time schedule which is usually 50% to 75% into their life cycle but they can still have useful capacity for projects like this. Maybe too big, but wheelchair and scooter AGM’s or SLA’s can be had similarly if you know someone using those. And sometimes Lowes or H/D clearance lawn mower batteries but those are wet cells along with those issues.
There’s a big disparity on new SLA pricing and I settled on one size for my uses by looking at what my local battery super-store had to offer. I got 2 batteries for just a little more than what one of the next larger size cost :money_mouth_face: I also have found close-outs of SLA/AGM powered devices selling for less than with the battery inside cost alone. Be careful with those- look at the build date- as some may be so old the battery inside is useless.
A wide open mind with wide open eyes gets the best bargains 
Phil
Lead acid batteries are gonna be bulky and heavy. I’m making a hand held flashlight. It’s gonna be heavy enough as it is. I’d rather not add 10 pounds to it.
Was only thinking of size and budget- you didn’t specify weight as a factor 
Phil
How about a 12v Lipo from a hobby toy?
If you make a 12 Volts light, with Cree XPH-70 or 4 x XM-L in series you can put the fans parallel to the LED (s).
Interesting idea. I’ll have to look into that
Nope. 3v LED. Unfortunately I’m gonna have to use 2 power sources :cry:
Speaking of batteries, how many Mah would I need to target to run 3 computer fans (say 110mm) for a couple of hours?
[quote=n10sivern]
Computer fans consume between .5w and 2w,
[quote=Gilatabar]
So they’ll run forever. Will they current limit? The fans I am looking at have a max of 0.7A. If I hook them directly to a battery will they blow or will they resist the current down to what they can use?
If they won’t blow, I’ll just run 4x protected 18650’s in series
I’m looking at running these
Check out ones like this? But only problem is that you do not know max current draw from these cells.
http://www.gearbest.com/other-accessories/pp_226459.html?currency=AUD&gclid=CjwKEAjwsuK_BRDD9ISR1bawwUwSJACbOiix2Q5s8bhtoT6uL1xwFrcc5hLD_r2r1aN7KYhdBZM4ahoCR0_w_wcB
For the fans it depends on their specs, but I’m pretty sure with 4x18650 in serie they won’t like it so much, voltage too high.
Max 0.7A means they will draw that much at full speed when wired to 12v. Careful about runtime though, those are more powerful than normal computer fans. 0.7*12=8.4w so no they won’t run forever. 3 of those will eat 2100mA, so they’ll last about 1h30 on 3400mAh batteries (assuming they can run on the higher voltage or if you put a regulator)
Unfortunately I have another item I’ll be running off the 12v. So say 2 fans at 0.7a and another item at 0.4a. Looking at an Asus motherboard, some have 3a fan headers. That leads me to believe that the fans are self limiting to the current to an extent.
As for 4x 18650’s, that would be about 14.8v max, which I believe most fans can handle. I’ve run a fan off of it before.
Yes yes of course. Much like high discharge 18650 batteries that can be used in lights that draw 10A or in lights that draw .1A.
In your case .7A is what the fans will draw, and the 3A header is what the motherboard can supply. A Suzuki hayabusa can produce 172HP but you can also use it at 1HP
Did you run the fans on those batteries for long? Did it overheat? If not you’ll probably be fine
If you’ve got plenty of 18650 - there are DIY power bank cases with variable or 12V output. I have this one, which can be adjusted for 12V output:
https://www.fasttech.com/products/0/10004461/1457402-qidian-3a-4-18650-diy-power-bank-battery (currently not available, maybe eBay)
or a quick search on eBay found this one:
http://www.ebay.de/itm/5V-12V-8-24V-Output-Power-Bank-Phone-Charger-4-18650-DIY-Case-Kit-Car-Starter-/142065809132?hash=item2113c836ec:g:6M4AAOSwRQlXc5i7
maybe there are better ones for a cheaper price…
Or you could use cheap DC DC boost converter(s), maybe one for each fan, to boost some lower cell voltage (single or parallel 18650) or 5V power bank’s to 12V:
something like these:
http://www.ebay.de/itm/2A-DC-DC-Boost-Step-Up-Conversion-Modul-Micro-USB-2-24V-To-5V-28V-12V-9V-24V/331929744055?\_trksid=p2047675.c100005.m1851&\_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D39022%26meid%3D73ab89e4162c457dbdfe357c94b8113e%26pid%3D100005%26rk%3D4%26rkt%3D6%26sd%3D272280062034
http://www.ebay.de/itm/1M-USB-2-1x5-5mm-5V-DC-to-12V-DC-Boost-Step-up-Power-Module-Converter-Male-Cable-/272280062034?hash=item3f65280852:g:mN4AAOSwMNxXZ9In
If you use a regulator, I’d only use one that draws from all 18650s in the circuit. I wouldn’t advise drawing more from one of the batteries when they’re already in serie. Don’t even think about doing this with unprotected cells
The fans aren’t sensitive to amperage at the source, only voltage- too much of that will fry them. I’ve used comp fans in cars where initial charging voltage ran in the 15V+ range, but it wasn’t there long. Normal there was 13.8V so you’ll be good going that far for sure. A simple resistor mod to drop voltage will allow you to work with whatever DC input voltage you have.
Your project sounds interesting :+1:
Phil
if those are what i think they will be obnoxious screamers.
[quote=n10sivern]
I'd stay away from crappy batteries from unknown sources rewrapped with dubious/crappy/low amp PCBs.
Honestly, if those are high quality fans, I really doubt they'll moan much at 16ish volts, though they'll start pulling nearly 1A at peak battery pack voltage. The voltage will drop over time while discharging the battery. Peak voltage for a fully charged standard 4S li-ion pack is 16'8V; the 14'8 figure would be its nominal voltage, and around 12V or slightly less when mostly depleted.
If choosing the li-ion route, I'd recommend going for quality cells with a high capacity VS cost quotient, like NCR18650Bs and LiitoKala 26650s, in suitable amounts. An eightpack of LiitoKalas at Banggood will run you less than $40 with M4D M4X's deals code 975e07. 12 NCR18650s at GearBest (an eightpack plus a fourpack) cost $42'22, but you can save $1'95 if you purchase 'em through the CrApp, so $40'27. Then, add a suitable BMS board and you'll be nearly done, with the exception of interconnecting the batteries. For this last issue, some copper sheet and a nice pack of disk shaped neodymium magnets is a great alternative if you don't have access to a spot welder.
If really picky about the fan voltages, this boost/buck DC-DC power supply module will crown the system, allowing you to fine tune the output voltage (and much more) if desired.
Hope this helps. 
Cheers ^:)
i have (10) 1.2v Ni-MH 4/5SC batteries you can have, all in good shape.
PM me.