The terminal connection is on the side of the fan near one of the corners. You can get an idea if you go here http://www.sunon.com.tw/products/pdf/ac ... ac-fan.pdf
and go to the 120mmx38 fans and look at the mechanical drawing. you can see where the cable comes off. The connectors seem to be an industry standard so all the fan cables allied lists work. I would try it without stacking the fans first and see if that works before you got to all the extra work. If you do stack them you might also try putting the fans on either side of the radiator, that way the radiator will straighten out the airflow for the downstream fan so it works efficiently and you won't need the plenum in there. I would get the straight connectors btw, they give you the most low profile connection and so the most options for mounting.
Allied sell a 1000 ohm 3Watt potentiometer for $5 (EUP1400 1K, Stock number 522-0049) that you can put in series with the 2123XST fan to allow you to control the fan speed down to almost the subaudible range. You will need 1 pot per fan, Don't stick two fans on one pot or you will exceed the dissipation limits of the pot.
If the 2123XST doesn't provide enough airflow at 120V for your application you can put a 4.7uF Capacitor in series with it. This will boost the voltage across the fan to about 160Vac and speed it up considerably. This is no longer in the silent range though. You can still use the pot in series with it to control the speed if you want, but the minimum fan speed will now be greater. Allied electronics has an appropriate capacitor (stock number 613-0500) for $2.11 . You will need one capacitor for each fan.
The Sunon fans are stock number 997-2123
Fan cords are stock number 609-5642 for a 3' cord straight connector
Regular fan speed controllers (like the 3 speed variety for ceiling fans) will NOT work. They will actually increase the fan speed considerably.
You can use the Lutron continously variable speed controller from Lowe's but you need to put a 4.7uf Cap in series (see cap mentioned above) with it to keep it stable throughout it's range. Most triac dimmer/speed controllers go bonkers when you put such an incredibly inductive load on them like this fan. The Lutron controller does impart a little bit of 120Hz switching noise out of the fan but it's pretty low level. Other controllers I've tried are down right raucous if they work at all.
I'm working on a design to allow me to control the AC fans with my T-Balancer, but until then my favored solution is the above mentioned Potentiometer from allied to just set the fan speed and forget it. It's also the quietest solution.
I'm using a Black Ice Pro II 120x2 radiator btw, it's relatively thin (1") and the least restrictive I could find. At the low airflow rates the exhaust temperature of the air is almost as hot as the coolant, so a thicker radiator would not help at all.
The 2123XST has a terminal connection which you can either solder to or use a connector. Allied sells a number of different fan connector cords
I'm having trouble finding an image of that fan. Where do the connectors attach? In, next to the hub (where I'd sort-of expect). I'm thinking I'd probably need to stack a pair of these (with small plenum between) to get sufficient pressure for a 2" heater core at low noise levels - so this means I'd need the straight
connectors, right? I'm also guessing from your post that the fan connector cords are interchangeable. Is that true or is there some particular kind I need to stick to. The Allied catalog assumes
I have a background in whatever device I'm buying from them and already have this knowledge.
Re speed control. Any reason why a rheostat wouldn't work? These fans are rated for 22W at 220V - so 1 amp. Any reason why they'd draw more than that at 120V or 90? Or are they non-ohmic devices like processors?
Also, I have a couple of speed controllers for 115VAC fans
from Edmund. I figure these are at least worth trying. Any reason they'd be a bad idea?
Finally - I'm pretty sure that the real
answer to the noise/cooling trade off for 2" heater cores is to not
use 2" heater cores. Nick over at Radiator Express has offered to make up a small radiator / heater core to my specs. I'm planning to ask for one that's 6x6x.5 (finned area). Should work nearly
as well as the "old standby" - a chevette heater core as it's mostly frontal area that matters. Sorry for being off topic - except that sometimes the answer to a question is to change the question