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  • Topic: USAT Hudson Conversion

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    • April 16, 2018 5:57 PM EDT
      • Kittery, ME
         
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      I am braking here, using a complementary pair of MOSFETs.  When there is no grounding pulse present, the N-channel FET grounds the motor's positive lead, applying the brakes.

      I'm not really convinced that the motor has enough momentum for this braking to be meaningful, though.  I'll have to play around with it some more.  The Super Chuffer does braking (and proportional chuff length), so I'll see if that gives me the result I want before I reinvent the wheel.  I think reducing the duty cycle may help as well.

       

       

    • April 16, 2018 6:28 PM EDT
      • Pittsburgh, Pennsylvania
         
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      The thing looks darn good from here.

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    • April 16, 2018 6:55 PM EDT
      • Carlsbad, CA
         
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      Eric I realize that the MOSFET will have a lower on resistance than a normal diode, but I guess I could use a schottky. But wouldn't the result be about the same? Or did I forget you are applying reverse voltage?

       

      I'll have to try it with and without, but in that video I posted, it spins the fan up pretty good, so maybe that momentum will make a difference.

       

      I forgot, but did the super chuffer apply reverse voltage?

       

      Greg

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    • April 16, 2018 8:05 PM EDT
      • Kittery, ME
         
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      I’m not applying reverse voltage here, but the fan wheel does stop between chuffs, at least at lower speeds. 

      I think the MOSFET I’m using is around 3 Ohms. I think a diode would probably work. I haven’t tried that. I guess a schottkey would probably be a good choice. I really don’t have much experience with motor control, so I’m figuring it out as I go. 

       

      I don’t have a schematic for the Super Chfifer, but I don’t think there enough transistors on the board to create a full H bridge. I think it’s most Likely doing the same thing I’m doing here. 

       

      One consideration that may or may not be important (I lack the experience to know) is whether the diode would be a problem when modulating the fan speed with PWM. The dual MOSFET approach would allow for selective control of the braking, using a second I/O line from the microcontroller. 

    • April 16, 2018 8:17 PM EDT
      • Shawn carries, A Purse 02B12,
         
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      Greg Elmassian said:

      Eric I realize that the MOSFET will have a lower on resistance than a normal diode, but I guess I could use a schottky. But wouldn't the result be about the same? Or did I forget you are applying reverse voltage?

       

      I'll have to try it with and without, but in that video I posted, it spins the fan up pretty good, so maybe that momentum will make a difference.

       

      I forgot, but did the super chuffer apply reverse voltage?

       

      Greg

      So your converting a Hudson as well and trying to tweak Eric's design ?

    • April 16, 2018 10:22 PM EDT
      • Carlsbad, CA
         
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      I've had a Hudson (that is already converted) before Eric got his..

       

      I'm interested in his experimenting. I don't have fan braking, but intrigued by the performance possibilities. My Hudson has a Zimo with an Aristo/Zimo smoke unit. The Zimo does the fan and heater control stock, where Eric had to build the circuitry himself.

       

      I may play with mine and maybe change it to a QSI, but since I have 34 QSI decoders to install, it's not a top priority.

       

      Greg

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      Be sure­ to visit ­my site, l­ots of tec­hnical tip­s and modi­fications,­ and you c­an search ­for topics­ and key w­ords.


      ­Click HERE for Greg­'s web sit­e
      PLEASE NOT­E: Please do NOT use private messaging, i­f you have­ a questio­n, feel fr­ee to emai­l me priva­tely, u­se regular­ email onl­y: greg@el­massian.co­m

    • April 17, 2018 9:18 AM EDT
      • Easton , Massachusetts
         
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      My Hudson is setup the same as Greg's ..... I'll just leave mine alone...

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