connecting a 120 fan?


 
B

BReinicke

New member
I purchased a weber offset smoker off of craigslist. The owner of it already hooked up a 5" fan to some welded ductwork and the fan operates off of a straight 120 wiring with a speed knob wired in.
I'm interested in building a HeterMeter controller and am wondering if anyone has advise on how to connect this fan instead of the smaller PC fans that seem most common. I'm not a welder and it would just be better from a construction standpoint to stick with the existing fan.
I'm willing to do some reading, but I am very much a novice when it comes to electronics. I'm slowly working my way from computer building & web design into these sorts of projects and I'm on a steep learning curve.
 
PC fans are not very common at least with what I have seen, Blower fans work much better then PC fans by far. Also it is possible to use your 120 fan but I wouldn't think it be worth your time. You have to create a totally separate controller for the fan that takes the DC fan voltage and uses it as a control signal to regulate the AC volatage.


It be easier and less time consuming to use a new dc blower fan i would think, Take a look at this thread http://tvwbb.com/showthread.php?49770-Attaching-a-Fan to get some ideas. I built a smoker out of an old water heater and I use a pipe nipple screwed into the were the element should be with a threaded 3d printed attachment.
 
There are some guys that have worked on using the HM to control electric smokers, or sous vide systems, and I think they made some sort of module that translates the variable DC output to variable AC output, but I'm not really sure on the details of that. Perhaps that would be something to look into, or perhaps it would be easier to just source a 12VDC fan that can replace the AC fan you have now....
 
Steve_M said:
I thought the HM used the SSR to module the output. I didn't think it was a binary on/off state thing.
Click to expand...

SSRs are fundamentally on/off only, but they are usually fast enough that they can do this at an AC per-cycle (or even faster, i.e. phase angle control) level. There seem to be mixed reports about the success of using SSRs and "fast" unsynchronized PWM to control AC devices. Heaters are much more tolerant of "funny" waveforms and missing cycles than motors, and in general I would argue that a proper design with an SSR should have synchronization of the PWM signal with the AC cycle phase (note this is more than just a zero crossing circuit in the SSR) to provide decent control and linearity without beats and other strange effects.

The "slow PWM" built into the HM software should work fine with an SSR as it does a slow on/off PWM with a 10s duty cycle. See http://tvwbb.com/showthread.php?52470-Looking-for-advice-on-using-HM-with-solid-state-relay&p=575681&viewfull=1#post575681 for a bit more info on slow PWM mode as it has some limitations (i.e. resolution). Depending on the size of the fan, 10s might be a bit short, but it seems reasonably straightforward to make the base interval longer by changing the firmware. Note that some commercial BBQ controllers (e.g. the BBQ Guru CyberQ) seem to only work with such a "slow" PWM mode - and they work fine!

There also is some relevant info in the "Sous vide" thread: http://tvwbb.com/showthread.php?35042-sous-vide-thread&highlight=solid+state+relay.

Steffen
 
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Thanks for passing on that info Steffen, I knew SOMEONE knew about the SSR stuff! (not me... LOL)I think that would have to be the way he would need to go IF it wants to work at all on his 120VAC fan... Though it kinda sounds like the idea of having a servo turn the speed knob he has right now might work out easier! LOL

BReinicke, why don't you post a pic of this fan in question and maybe we could come up with some suggestions... I would first suggest source a DC fan to replace the 120VAC fan, but your comment about being welded in duct work leaves me to wonder what you've got there? One of those inline duct fans? If that's the case, "I" would whip out the hacksaw or tin snips and cut off that AC fan and make a sheet metal adaptor to fit some sort of DC fan... I have no idea what type of flow you need, would have to judge that by feel or specs on the fan you have.....
 
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