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Relay switch addition to prevent heat bed cutting out

Discussion in 'Mods and Upgrades' started by Jerry RoBo 3D, Nov 23, 2013.

  1. tesseract

    tesseract Moderator
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    The original polyfuses were 11A and the main upgrades move to a 14A replacement. I am not sure how it relates to the MOSFET change but I believe the 14A should work especially when it is in addition to a fan.

    As far as what to do next, what this fix did was to allow enough current to flow to keep the bed operating if it got too warm it would simply shut down BUT would start working again after it cooled off.

    If you are seeing a flat line in the heater at the onset then you have another issue going on I would check the wiring itself make sure nothign came loose as a completely dead heat bed is not too common.

    Remember though you should never see a reading of 0 degrees temp as that means you have a disconnected thermistor for whatever reason.
    The thermistor when correctly connected and working will always show the air temp so unless it just happens to 0 degrees out side you have another problem.

    A shorted thermistor will show a very high temp in error and one not connected at all will show zero.

    This should give you some good starting points.
     
  2. felixkalm

    felixkalm New Member

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    Hi Thanks for your response. I've opened it up and checked all the wiring and nothing seems disconnected or damaged, i've even tightened a few of the connections just to makes sure. Not exactly sure how to isolate a potential connection problem beyond visual confirmation.
     
  3. felixkalm

    felixkalm New Member

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    I check D8 with a multimeter while the heating bed was activated and it didn't read any current :/
     
  4. tesseract

    tesseract Moderator
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    The key is what is the bed temp when it is just turned on not heating but just on it should read AT LEAST room temp if not then the thermistor wiring is where you need to look...really it is the only place to look at that point if this is zero it will not heat up at all the system has a prevent circut so that it must be at a certain minimum or it just won't heatup. It is a safety thing.
     
  5. felixkalm

    felixkalm New Member

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    The temperature reads at 0 so it must be the thermometer not being connected proper but all the wiring looks in good order, i'm weary to start cutting the different connections to redo them in case i make it worse. :/
     
  6. felixkalm

    felixkalm New Member

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    Also where is the thermostat for the bed? is it the set of wires that run parallel to the heater?
     
  7. tesseract

    tesseract Moderator
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    For comfort you may want to drop by the shoutbox where you can chat real time with people and can verify what I am saying and what my ideas were. In my case I would see error messages in the log showing a mintemp error so if you are using repetier you probably see the same thing if you are using MC then there is a log window but it is not the easiest to get to if I remember correctly.
     
  8. Jerry RoBo 3D

    Jerry RoBo 3D Administrator
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    Sounds like you have a loose connection on the bed thermistor. Check the wires and the connection of the heat bed thermistor.
     
  9. Mark Anthony

    Mark Anthony Member

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    Can you show me how to check with the voltmeter if the power supply is bad?
     
  10. Mike Kelly

    Mike Kelly Volunteer

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    Is your name really mark anthony or just a reference?

    Also measure the voltage coming off the power supply before and after enabling the heater bed. It it drops below 11v it's bad
     
  11. Mark Anthony

    Mark Anthony Member

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    Yes thats really my name. My fuse blows every time i turn my machine on. I cant get it to stay on for more than a tenth of a second.
     
  12. Mark Anthony

    Mark Anthony Member

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    its not the switch because i tried the switch on my other robo 3d r1
     
  13. SteveC

    SteveC Well-Known Member

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  14. printern00b

    printern00b New Member

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    How much current can that connector supply? Currently I'm looking for a 12V source to power 2 fans, one for cooling the RAMPS and one for the fan of a soon to arrive E3D.

    Oh and this is my first post. Hi everybody :)
     
  15. Galaxius

    Galaxius Well-Known Member

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  16. Jerry RoBo 3D

    Jerry RoBo 3D Administrator
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    You can run two fans off the 12V pins (second picture above). This is also a safer thing to do since there is some protection from a short instead of powering the fan directly off the power supply (first picture above).
     
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  17. printern00b

    printern00b New Member

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    I'm probably going to use the 12V pins so I don't have to find a fuse for directly using the PSUs 12V rail. But later I might add some LEDs, can I power those from the 12V connector, too? I couldn't find any specs for the connector (max A).
     
  18. Jerry RoBo 3D

    Jerry RoBo 3D Administrator
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    I would power the LED's directly from the power supply. No need to have protection on those guys as long as your wiring is clean.
     
  19. Mike Kelly

    Mike Kelly Volunteer

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    Protection is largely unnecessary, unless an accident happens, then it protects you.

    Wait I feel like that statement is redundant....

    Generally good habit to use a fuse, but you there's absolutely no need if you're careful.

    The 12v connector on the ramp is fused by a MFR500 polyfuse for a max amp trip at 5A at ambient temperature. Thus on the 12v connector you get 5A minus the amperage needed for the stepper motors and heaters.

    I suggest adding a terminal strip for connecting LED's and having an in-line automotive fuse going to the power supply.
     

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