Max Fan power for HM4.1


 
B

Brian Hilgert

TVWBB Member
So I'm working on a custom HM based of the HM4.1 design/hardware and ran into a bit of a snag. I have an old 25CFM blower that I want to use that is rated for a max current of 1.2 amps vs the .22 amps of the designated blower. When I attach my blower and 'activate' it by setting an appropriate set point, it struggles to start, and then my HM board becomes unresponsive, but the fan stays on. The pi never appears to lose power (SSH session never broken, GUI is still accessible), but if I try to reset the AVR from the gui, I get the "No Communication" message on the config page. If i disconnect the blower then reset, everything communicates fine. If I slap a simple 80mm case fan (sorry, no current rating) on the blower connection, it hums along for hours no problem.

I was looking at the datasheet for the FQU11P06TU and it is rated for more than enough current, though I could be reading it wrong? Any HM power users (no pun intended) have any ideas?

Thanx
Brian
 
I've been using a blower that draws 1.2A for high heat cooking lately, and it does brown out my 12v 2A switching power supply, but I have another old school heavy transformer type 12v 2A power supply and it works fine. I do get the normal brown out situation though (with the lightweight switching mode PS), both the rPi and the HM reset and the HM display flashes on and off... This blower provides WAY more flow than I need for cooking even at 800+ degrees, I've set my max blower speed to 50% and the FauxMado and done some cooks at 700 degrees and it does fine. So I have been shopping for a more moderate blower that can be used for high heat cooking with about half the flow, haven't decided on one yet though....
I know Bryan has implemented a boost start for the blower, which starts the blower up at a higher speed than what the HM is calling for momentarily to get the blower rolling and then backs down to whatever the HM is calling for. I have asked if the HM is momentarily boosting the blower to 100% or to 50% when I have the max blower speed set to 50% but I haven't gotten an answer on that yet. I would think the best way to go would be to boost the blower up to whatever the MAX is set for rather than 100%...
 
Which MOSFET are you using?

I've been using a BFB1012H (14.4W) with my previous builds, but I was also using the FDP7030BL (HM4.0) which is rated for 60W. With this build, I switched to the P_Channel FQU11P06TU (HM4.1) is rated for 2.5W.
 
RalphTrimble said:
I've been using a blower that draws 1.2A for high heat cooking lately, and it does brown out my 12v 2A switching power supply, but I have another old school heavy transformer type 12v 2A power supply and it works fine. I do get the normal brown out situation though (with the lightweight switching mode PS), both the rPi and the HM reset and the HM display flashes on and off... This blower provides WAY more flow than I need for cooking even at 800+ degrees
Click to expand...

I've been using a 12v 2A wall wart to test during assembly. My main HM ( which has been using this fan for years) is powered my 12v 3a home-brew POE. I'll my new build off the POE and see if that helps. Have you been using your 1.2A blower with your 4.2.3 build?
 
The MOSFET for the HMv4.0 and the HMv4.1 and later are different because Bryan switched over to controlling the voltage side of the line rather than the ground (on HMv4.1 and newer), so you can't really interchange the v4.0 MOSFET with the newer ones. (HMv4.0 uses N Channel, and HMv4.1 and newer uses P-channel) I am using the standard MOSFETs on all of my builds...
Ohms law says P=I X E, so for a 1A blower P= 1A X 12V = 12W.... hmm, so we may indeed have a problem there if the new MOSFET is truely only rated at 2.5W... I looked up the part at Mouser and it does say 2.5 Watt, but then I loaded the datasheet and there are two power ratings (Ta=25C and Tc=25C), the Tc=25C rating is actually 38W for the P-Channel MOSFET, and the 60W rating on the N-Channel MOSFET is the Tc=25C rating as well, so we actually have a 60W MOSFET VS a 38W MOSFET, not 60W VS 2.5W...
 
Brian Hilgert said:
I've been using a 12v 2A wall wart to test during assembly. My main HM ( which has been using this fan for years) is powered my 12v 3a home-brew POE. I'll my new build off the POE and see if that helps. Have you been using your 1.2A blower with your 4.2.3 build?
Click to expand...

Yes, I have used the 1.2A blower with the 4.2.3 build as well as the standard HM blower. I have had the HM brown out running the 1.2A blower on my 12V 2A switching power supply, but it holds steady on my older 12V 2A discrete power supply. My switching mode PS has been used heavily though, and didn't cost too much, so maybe it is just wearing out....

At any rate, the MOSFET in my HMv4.2.3 does power the 1.2A blower at full speed without issue when the power supply is giving it enough power.....
 
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The only time I changed mosfet size was when it was still using a Linksys router to connect to the internet instead of a RPi

I never had any problems with drawing to much power from the blower using the RPI versions of the HM and my Bfb1012HH.
 
RalphTrimble said:
The MOSFET for the HMv4.0 and the HMv4.1 and later are different because Bryan switched over to controlling the voltage side of the line rather than the ground (on HMv4.1 and newer), so you can't really interchange the v4.0 MOSFET with the newer ones. (HMv4.0 uses N Channel, and HMv4.1 and newer uses P-channel)
Click to expand...

Exactly. I want to use common ground for the blower, that is why I switched to the P-Channel like in HM4.1+

RalphTrimble said:
Ohms law says P=I X E, so for a 1A blower P= 1A X 12V = 12W.... hmm, so we may indeed have a problem there if the new MOSFET is truely only rated at 2.5W... I looked up the part at Mouser and it does say 2.5 Watt, but then I loaded the datasheet and there are two power ratings (Ta=25C and Tc=25C), the Tc=25C rating is actually 38W for the P-Channel MOSFET, and the 60W rating on the N-Channel MOSFET is the Tc=25C rating as well, so we actually have a 60W MOSFET VS a 38W MOSFET, not 60W VS 2.5W...
Click to expand...

Ahh, I looked at Digikey's summary and Ta in the datasheet. My Bad. I guess I really wanted to know if anyone was running a larger fan with the FQU11P06TU, which you are so I'll try a better power source. Thanks Ralph.
 
RalphTrimble said:
Ohms law says P=I X E, so for a 1A blower P= 1A X 12V = 12W.... hmm, so we may indeed have a problem there if the new MOSFET is truely only rated at 2.5W... I looked up the part at Mouser and it does say 2.5 Watt
Click to expand...
The 2.5W on the datasheet is the Maximum Power Dissipation which is different from the amount of power it can switch. Max power dissipation is current^2 * Rds(on) for the given gate voltage versus the source (at a given temperature) and drain current. At our -12V gate and say a 2A drain, that's about 0.150 ohm * 2 * 2 = 0.6W. We can pull up to 4A continuous and still be under spec (assuming the MOSFET doesn't start getting really hot, which it probably would at that current and lack of thermal consideration in the PCB design).

It's hard to say why your HeaterMeter is locking up apart from saying I know it can put out at least an amp (tested 4.0/4.1/4.2). Have you tried the snapshot firmware to see if that makes any difference? I haven't specifically fixed any "lock ups" but there have been a number of internals changed with regard to software noise reduction which could be of use. Other than that you're going to need to get an oscilloscope I'm afraid to see what's happening.
 
It was indeed the power supply. Once I switched over to the POE unit I've been using for years everything worked as expected. Thank You for the help everyone.
 
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