1 Topic by JustSomeGuyTN (edited by JustSomeGuyTN 2012-11-02 16:08:22)

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Topic: Bed definately not heating up

I think my temperture drop is a bad bed.  The bed won't heat up at all now.  I checked the two black wire terminals on the electronics at the back.  The ones on the left as you're looking at the electronics.  They both report 12.74v DC so I think I'm getting power.  Anyone else have tests I should do or a fix?

Edit,

I just found Ian's picture of the electronics and realized I was checking the lights.  The heaters are the red terminals at the bottom of the board as you're looking at them.  The right hand terminal (which I assume is the hot end because it still works) is getting 12 volts.  The left hand terminal is getting about .3 volts.  So, do I have bad electronics that need to be replaced or is there a fix I can try.

2 Reply by elmoret

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Re: Bed definately not heating up

JustSomeGuyTN wrote:

I think my temperture drop is a bad bed.  The bed won't heat up at all now.  I checked the two black wire terminals on the electronics at the back.  The ones on the left as you're looking at the electronics.  They both report 12.74v DC so I think I'm getting power.  Anyone else have tests I should do or a fix?

Edit,

I just found Ian's picture of the electronics and realized I was checking the lights.  The heaters are the red terminals at the bottom of the board as you're looking at them.  The right hand terminal (which I assume is the hot end because it still works) is getting 12 volts.  The left hand terminal is getting about .3 volts.  So, do I have bad electronics that need to be replaced or is there a fix I can try.

Disconnect the bed from the board, and measure its resistance.

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3 Reply by JustSomeGuyTN (edited by JustSomeGuyTN 2012-11-02 19:44:28)

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Re: Bed definately not heating up

Measureing at the spots on the plug I get about 5.8 ohm.  I also stuck the probs under the white insulation pad and probed the copper looking block and got around 1.1 ohm.  This was with the Solidoodle off and unplugged.  I assume that makes no difference.

After I made those measurements I took the bed off by unscrewing the addjustment screws.  I think probed the two solder connections on the heating element.  I get a reading on my multimeter of .928 M ohm.

Just tried it again and got 0 ohms on the actual connection that the wires are soldered to.  I looked up the part number stamped on the resistor (HS50 3R F) and ordered a couple from Mouser.com.

4 Reply by elmoret

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Re: Bed definately not heating up

JustSomeGuyTN wrote:

Measureing at the spots on the plug I get about 5.8 ohm.  I also stuck the probs under the white insulation pad and probed the copper looking block and got around 1.1 ohm.  This was with the Solidoodle off and unplugged.  I assume that makes no difference.

After I made those measurements I took the bed off by unscrewing the addjustment screws.  I think probed the two solder connections on the heating element.  I get a reading on my multimeter of .928 M ohm.

Just tried it again and got 0 ohms on the actual connection that the wires are soldered to.  I looked up the part number stamped on the resistor (HS50 3R F) and ordered a couple from Mouser.com.

You've got a lot of different measurements for what should be consistent. Can you post a picture of what you're measuring?

Not sure what resistor you mean, either. The fact your bed measured at .928Mohm is bad news.

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5 Reply by JustSomeGuyTN

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Re: Bed definately not heating up

the resistor is what heats up the bed.  its an inch and a half or so long, copper colored, with a terminal on each end that the wires from the electronics are soldered to.  the last measurement i took was on those terminals.  it read 0 ohms.  that should never happpen with a resistor.

6 Reply by elmoret (edited by elmoret 2012-11-02 21:31:47)

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Re: Bed definately not heating up

Ah okay. That looks like a 3 ohm resistor, which is odd because SD support said the bed should be 10 ohms.

If its 3 ohms, then:

P=V^2/R=48 watts, and its rated at 50watts. If the supply voltage is just 12.3v, then you're over the limit already, which is why it's burned up.

Furthermore, that rating is when the resistor is attached to a heatsink @25C. I don't think many of us run the bed at 25C.

I'm becoming increasingly disappointed in SD's design practices.

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7 Reply by JustSomeGuyTN

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Re: Bed definately not heating up

yeah, i kind of wondered about that when tech support told me that the resistance should be 10 ohms.  so when i ordered the replacement resistor from mouser i also ordered a couple of 10 ohms big_smile

elmoret wrote:

Ah okay. That looks like a 3 ohm resistor, which is odd because SD support said the bed should be 10 ohms.

If its 3 ohms, then:

P=V^2/R=48 watts, and its rated at 50watts. If the supply voltage is just 12.3v, then you're over the limit already, which is why it's burned up.

Furthermore, that rating is when the resistor is attached to a heatsink @25C. I don't think many of us run the bed at 25C.

I'm becoming increasingly disappointed in SD's design practices.

8 Reply by elmoret (edited by elmoret 2012-11-05 03:35:12)

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Re: Bed definately not heating up

10 ohms would be about 14 watts, which isn't much. I guess it'd be enough to heat the bed.

Edit: Measured draw is ~47 watts. It's 3.3 ohms for sure.

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9 Reply by JustSomeGuyTN

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Re: Bed definately not heating up

Elmoret, would something like this be better?   http://www.mouser.com/ProductDetail/Arc … qY6dBoQ%3d

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Re: Bed definately not heating up

JustSomeGuyTN wrote:

Elmoret, would something like this be better?   http://www.mouser.com/ProductDetail/Arc … qY6dBoQ%3d

Yes, but if you're going down that road you might as well use the 100W series. Keep in mind you'd probably have to drill new holes.

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11 Reply by JustSomeGuyTN

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Re: Bed definately not heating up

I got the 3 ohm resistors from Mouser.  I took the old one off, put some new thermal compound on, put the new on, soldered the connections.  It seems to be working for the short test I gave it.  I'm going to try another print later after I get the bed re-leveled.