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I am wondering how many fans can be connected to the EXT 0 output of the Rambo Board? Can EXT 1 Fan output also be used, even though only 1 extruder is used? I have 2 connected to the Ext 0 currently. Is that ok?

I'm sure that's fine. A fan isn't going to draw a lot of current compared to the heater resistors in the hot-end. They use the same kind of output. From the RepRap Wiki on the RAMbo:

Extruders and fans, 5A 12-24V (fuse can be exchanged for up to 10A capacity) 10V-26V input voltage

What I don't know is if this is for the whole buss, or if this is per output.

Jimustanguitar wrote:I'm sure that's fine. A fan isn't going to draw a lot of current compared to the heater resistors in the hot-end. They use the same kind of output. From the RepRap Wiki on the RAMbo:

Extruders and fans, 5A 12-24V (fuse can be exchanged for up to 10A capacity) 10V-26V input voltage

What I don't know is if this is for the whole buss, or if this is per output.

The fuse is for all 4 outputs.
All the outputs both fans and extruders are identical, unless you want to do something stupid like run 20 fans off one output I wouldn't worry about it.
In my firmware the second extruder output is actually set as a second fan output driven by repetier's extruder fan control, which enables the fan when the hotend is on and when it's above 50C, pretty much ideal for cooling the peek part of a hotend.

hmm.. with the new cartridge style heaters that everyone is using that's 3 amps alone just for the heater cartridge.

12v 40w = 3amps, considering this, you would have 2 amps to spare. so just keep that in mind when adding fans. (fans don't require a lot of current) unless like stated above, u can up the fuse rating.

for example.: if you have a fan that uses 1amp of current, then you could add two. but most fans are considerably less than this.

if you have a fan that uses 500ma, then you could add 4 fans...

Just look at the specs of the fan...just do the math

Thanks guys.

If you pick a fan using using ~500mA that would still be a strong little fan., I think my best fan on my computer is 0.60 A @ 12v and it's a decent size (120 x 38mm) that makes some noise and moves some air (3,000 rpm 45.90dBA 133.60CFM) and it's meant to have a high static pressure.

Don't want high jack the thread but quick question...I have a peek fan with three wires? One for rpm status- any place on the Rambo for this?

Batteau62 wrote:Don't want high jack the thread but quick question...I have a peek fan with three wires? One for rpm status- any place on the Rambo for this?

No there is no RPM feedback, just ignore it. Wire the +/- 12V lines.

My PEEK fan is a little tiny 5V unit. What would be the best to power it, somewhere on the Rambo? or direct red wire from the psu?

Batteau62 wrote:My PEEK fan is a little tiny 5V unit. What would be the best to power it, somewhere on the Rambo? or direct red wire from the psu?

I'd probably power it directly off the PSU, there are a ways to run a 5V fan off the RAMBO board, but it's not the easiest thing in the world to do.

Batteau62 wrote:My PEEK fan is a little tiny 5V unit. What would be the best to power it, somewhere on the Rambo? or direct red wire from the psu?

The cheapo way would be to adjust the fan speed slider in Repetier until you get about 5V across the terminals, then write down that setting and always use it.

The "right" way to do it would be to either solder a resistor or a voltage regulator in series. Here is how you'd do the resistor:

V/I=R, where:
V = Voltage drop (12 -> 5 = 7)
I = Current sunk by your fan, in amps
R = Resistor ohms

Suppose you look up the specs for your fan, and discover that it's 5 volts and sinks 100mA (0.1 amps.) Since you want to drop the voltage by 7 volts, you would do 7/0.1 = 700. So you would need to solder a resistor in series with the fan (either + or - terminal) of 700 ohms to get your "perfect" output. I don't know that they actually make such a resistor, but I do know they make a 680 ohm resistor and that's good enough. You should be able to get one at any Radio Shack or other electronics store.

In case I'm dumb at math (SPOILERS: I AM) you'd want to double-check the voltage with a multimeter before you hook up your fan.

Another alternative is to use a LM7805 voltage regulator. That will step down the voltage to 5V and keep it there regardless of current draw from the fan. It's usually used to power small 5V circuitry (like Arduinos.) If you happen to have one around (or can scavenge one) it should work great. Radio Shack probably carries them as well.

To make the install clean, put heat shrink tubing over any bare wire leads. Use a multimeter to make sure nothing is shorted, unless you want to buy a new fuse.

Batteau62 wrote:My PEEK fan is a little tiny 5V unit. What would be the best to power it, somewhere on the Rambo? or direct red wire from the psu?

I powered my 5volt on the first fan port.

The fan can be turned down in repetier host.