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Thread: Temperatuer feedback pwm

  1. #11
    Join Date
    Jul 2008
    Location
    Columbus Ohio
    Posts
    211

    temperature feedback pwm

    Got the circuit built. Fired it up, looks like it works, but much testing to do.

  2. #12
    sp1r0 Guest
    Man I wish I made it through Drexel. EE's rule!

  3. #13
    Join Date
    Jul 2008
    Location
    Columbus Ohio
    Posts
    211

    ?????

    Fired the temp feedback circuit up, set it to 100 deg f.. Bottle working fine start at 6.5 amps around 90 deg drawing 9 amps.

    When it hit setpoint it went goofy. The probe should read 400 mv, it shot up to 900 mv and floated between 700 - 900 mv..

    In my attempt to find the problem I shorted out the fet and blew it.

    Figured that was a sign, so I quit for tonight.

    Will replace fet and start again tomorrow.

  4. #14
    Join Date
    Jul 2008
    Location
    Columbus Ohio
    Posts
    211

    Still trying

    Replaced the fet, still getting nonsense output voltage from the temp sensor. Worked on it a little this afternoon, it's something to do with ground layout.

    Will put on my engineer hat and work on it this evening.

    I wish this one went as easy as the current feedback one. Oh well, problems exercise troubleshooting skills.

  5. #15
    Jaxom Guest
    If it was too easy it wouldn't be fun.

  6. #16
    donnylynn Guest
    Quote Originally Posted by ridelong View Post
    Got the circuit built. Fired it up, looks like it works, but much testing to do.
    one question about your idea. If you are using temp as feedback for the pwm, arent you concerned about lag time? Once an electrolyzer gets hot and hit your set point, it will take several minutes to cool enough to turn the pwm pulse back on. Unless you are using the signal to toggle between full on and some reduced mode of operation/reduced current???

    I appreciate the current limit circuit you posted. Much simpler than the others I have seen. I believe in K.I.S.S.

  7. #17
    Join Date
    Jul 2008
    Location
    Columbus Ohio
    Posts
    211

    lag

    donnylynn,

    I am concerned about the lag time, it could be a real problem. If the cycle time is less than 1 second, I think the circuit will work.

    If it gets over 5 seconds, it will be a problem. I don't know what I'll do with the circuit then.

    I could use it for controlling a heater in the winter.

  8. #18
    donnylynn Guest
    Quote Originally Posted by ridelong View Post
    donnylynn,

    I am concerned about the lag time, it could be a real problem. If the cycle time is less than 1 second, I think the circuit will work.

    If it gets over 5 seconds, it will be a problem. I don't know what I'll do with the circuit then.
    .

    Not sure where you are measuring temp, but I dont see a generator temp changing noticeably is less than a few minutes. The temp idea would be good to use to reduce the voltage across the cell until it cooled off though. the cell I am currently experimenting with (+nnnnn-) the current drops drastically when voltage drops from 14.4 down to 12.5VDC. (no PWM) Of course HHO output drops also.

  9. #19
    Join Date
    Jul 2008
    Location
    Columbus Ohio
    Posts
    211
    Darn, I just can't get this circuit to behave. Screwed with it for about 2 hours and it is still screwey. Found out 1 thing, the softer hot melt won't seal. The hot melt sealing the first probe came loose and let electrolyte get into the temp sensor leads.

    That was 1 problem, but not the only one. Built a new 10 mv per degree f probe. Seemed to be real stable. I replaced the 10 mv per degree c probe that had electrolyte in it. When I fired up the bottle the output went from 800 mv to 100 mv.

    Will work on it in the morning.

  10. #20
    Join Date
    Jul 2008
    Location
    Columbus Ohio
    Posts
    211

    Talking It Works!!!!

    Been in the basement all day. Finally got this sucker working. This thing works great.

    One worry was the lag time, NO problem. The circuit naturally runs about 1428 Hz, perfect.

    Been running an hour in the controller mode with controller setpoint at 151.9 deg F. During the test, temperature varied from 153.2 to 154.5, so the whole system error is less than 5 deg F.

    During the test I aimed a 4 inch fan at the generator. The temperature went down to 153.2, and I watched the pulse width increase on the scope as the circuit adjusted for the difference. Current increased from 3.8 amps to 6.25.

    I will add this circuit to my truck.

    Still have to finish the heater portion that turns on a heating element when the gen gets below 38 F.

    After that, I'll post the schematic and parts list.

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