Electrical question

[megamoo]

I have a 12VDC fan which I have wired to a 12V AC adaptor which is then plugged into a timer switch, and it works fine.

I use it for cooling and air circulation on my grow shelf, but its not enough. I want to add another fan.

At the moment I am using a pedestal fan which is plugged into the wall socket 240V, because it's what I had on hand.

I could get another 12V fan and wire it to the same adaptor. From what I understand, when its wired in series or parrallel, either the two fans run at half speed or they both run normally and the adaptor pulls more juice? I don't know which is which or if this is true.. I'm not too good on electricity theory.

My question is : Is it cheaper on my electric bill to run one 12V fan and the pedestal fan? OR to run two 12V fans? (wired in either configuration, I'm quite happy for them to run at half speed because I could put them closer to the plants and it would be effective.)

A third option I could even dig up another adaptor and have each 12V fan on its own plug.


I can set it up any of these ways but my main concern is a cheapest power bill from a two fan setup, as I have two more groups of seeds to grow on after the current lot.

Thanks for any help.

 

[xXA_HillbillyXx]

Wire up the two fans in series and they should both work fine... that will put 6 volts to each fan (from the twelve volt PSU) and your current will stay the same. this way you dont have to worry about going over the PSU rated current limit. HOPE THIS HELPS!!

 

[rooze]

Assuming that the air output from the 240v fan is way more that you need, then it would make sense to remove that and use two smaller fans, regardless of whether they're 12 or 240v.

But if the real question is - which is more economical to run, a 12v fan or a 240v fan with the same output (or watt rating), then the answer is the 240v, since with the 12v, you have a lot of transformer losses at the wall adapter/convertor (appear as heat) and if the wires are a bit on the long side you'll also have a lot more volt drop, which in a 12v circuit is not a good thing.

So you need to look at the watt rating of both (or all three).

Assuming 10% additional losses in the 12v system, you would look at it like this -

If small fan1 watts + small fan2 watts is equal to or greater than 240v fan watts X 0.91, then it's cheaper to run the 240v system

But....... don't forget that your 12v system is using power even when the lights are off...so.....well.....you know where I'm headed....

Get a 240v fan, it's safer too

 

[willard3]

Wiring cost and efficiency are better with 240v.

12v is nonstandard for residential use and is intended for automotive use.

 

[Pablo_h]

While 12V DC is common around the house (computers), I have to ask what size DC fan are you running, (dimensions, watts, current?)
If you like the 12V fan because of it's size, plenty of fridges and cabinets use small AC fans. Though I'd add it's safer for you to stuff around with DC small fans than to go out and buy a small AC fan and wire that up yourself...
So stick with the 240v pedestal fan if it's not too much in the way. If you need a smaller package, there's no problem running 12v DC fans, you can wire them in parallel as long as you know their current/power doesn't exceed what the power supply can provide.

edit:

Wire up the two fans in series and they should both work fine... that will put 6 volts to each fan (from the twelve volt PSU) and your current will stay the same. this way you dont have to worry about going over the PSU rated current limit. HOPE THIS HELPS!!

Good idea. Depends on what fans mega has. If he's already got low RPM fans, there won't be much airflow though. Also some fans have trouble starting at low voltage, usually thats around 5V though. But if he has good quality medium/high speed fans it could be an option. My 140mm case fans in the lian li won't start at 5V, but never had a problem with my medium speed scythe or nexus 120mm fans that are in all my PCs.