HM Fan Questions


 
B

BradPilling

New member
I am building a HM to control my DPP FAT 40 Smoker Below.

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I currently have two of the Pit Bull (25 CFM) fans from the BBQ Guru. I am using a 12V relay box with separate power supply to provide power to the fans because my BBQ Guru controller will only handle the load of a single fan.

My question is, when I complete the construction of the HM will the same setup work? The BBQ Guru is set up for on/off control of the fan while the HM is PWM. Do I need to build a separate fan control circuit to use both fans on the HM, or can the PWM output be set to 100%?
 
You can set it to min/max 100%/100% and the HeaterMeter will run 0 to 10 seconds as needed. However, it only works in full second increments so 0-9% is off all the time, 10-19% is 1 second out of 10, ... 90-99% is 9 seconds out of 10.
 
I believe some DC solid state relays are capable of PWM. I'm not sure how the fan's you have would react based on their motor design as I know Bryan has some code in there to deal with < 10% fan speeds for brushless motors but it could be an option if you want.

expensive SSR that might work
http://www.power-io.com/products/hdd.htm
 
How much current do those fans draw? I know I have used a single blower larger than 25cfm without a problem while running the Heater Meter on my 12V 2AMP power supply. Perhaps if you just beef up the PS a bit you might be able to run them directly from the HM rather than through the relay. IMHO it would be best to let them run on PWM rather than on/off at 0/100% (via your relay) But it would be best to calculate the current/power requirements of your blowers and see if this is a reasonable expectation first. I'm not exactly sure how much the MOSFET can handle but I am sure Bryan does, or at least can estimate...

BTW, that's a slick looking rig you have there!
 
Thanks Ralph. I found the specs for the fan on the forum. I'm going to pull the SS cover apart tonight to verify. Below is the fan.

2qn2ra1.jpg


Bryan, can the MOSFET handle both fans with a larger power supply? Thank you.
 
BradPilling said:
Thanks Ralph. I found the specs for the fan on the forum. I'm going to pull the SS cover apart tonight to verify. Below is the fan.

2qn2ra1.jpg


Bryan, can the MOSFET handle both fans with a larger power supply? Thank you.
Click to expand...

This is the spec sheet for the MOSFET we are using on the heatermeter. It would also depend on how large the in circuit wiring is (i.e. can it handle the current).
http://www.mouser.com/Search/ProductDetail.aspx?R=FDP7030BLvirtualkey51210000virtualkey512-FDP7030BL

Your fan's appear to have a 1.05AMP draw (http://www.amazon.com/exec/obidos/ASIN/B00EA0CNR4/tvwb-20) each plus the heatermeter so expect a 2+AMP total draw. If it can't handle it, you could make a very small circuit that takes the control pin from the current mosfet and use it to control multiple mosfets for your multiple fans.

My guess is the mosfet will handle it though, although you could need a heatsink. I would like to hear Bryan's thoughts.
 
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That datasheet is for the MOSFET in HeaterMeter 4.0, which can handle more power than the 4.1 version. They both _should_ be way over-speced for driving these blowers, but their specs are for heatsinked parts and ours are just in air. As they start to heat up, the max current decreases, but at room temperature:
v4.0 - ~6A continuous
v4.1 - ~3.5A continuous

However, the HeaterMeter traces are 24 mil on v4.0 and 20 mil on v4.1 which can carry only about 1.7A and 1.5A continuous (10C temperature rise), so that's more likely to be the upper limit. The larger problem would be the high pulsed current creating noise, which could be slightly more of an issue on the v4.1 boards. Also to consider is the amount of peak current draw, which will probably be easily 5x the rated current of the blower and the quality of the 12V power supply.
 
So I guess I either need to make an external circuit to control the fans with the PWM output from the HM, or just set the min/max to 100%/100% and use the existing relay box I already have.
 
BradPilling said:
So I guess I either need to make an external circuit to control the fans with the PWM output from the HM, or just set the min/max to 100%/100% and use the existing relay box I already have.
Click to expand...

That seems to summarize it. I can't imagine the external circuit to be too hard to implement. It could even be built into your fan assembly assuming the logic level output isn't running too far.
 
BradPilling said:
just set the min/max to 100%/100% and use the existing relay box I already have.
Click to expand...
What's the cycle duration of the BBQ Guru, by the way? i.e. how long is it between the time the blower turns on each time

And yeah, that's a really nice looking BBQ trailer there. Makes the green egg behind it look like a shrimp!
 
I'll check next time I use it. It's much more difficult to maintain temperature on the trailer than on the egg. The Guru holds my set point with the egg, but I found that I was within 15 degrees (depending on wind and fuel in the firebox) using it on my trailer smoker. It's still a vast improvement of smoking on the trailer without the Guru. I'm building the HM to make use of the wifi capabilities to better monitor my cooks on the trailer. Thanks for all of your work Bryan. Looking forward to testing it out.
 
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