MK138 mod

Leeway · Post by **Leeway** » Mon Mar 26, 2012 8:59 pm

I know I saw the information in the Yahoo Group, but it isn't mine. Would someone like to migrate that information to the Forum here for those that have not yet completed the MK138. I think there is a resistor to change and a jumper to add.
That is if this is the right spot for such info.

kilroyo · Post by **kilroyo** » Thu Mar 29, 2012 5:22 pm

Also does anyone know if you can use the stocked thermistor that came in the kit to control a heat bed or do you have to go with the one that seemecnc has?? Was wondering if I could just change some resistors to get it to work, , thanks

Chris Muncy · Post by **Chris Muncy** » Thu Mar 29, 2012 5:43 pm

I'm using the thermister that came with the MK138 to control the temp of my bed with no issues and no mods to the board.

mhackney · Post by **mhackney** » Thu Mar 29, 2012 5:55 pm

Chris, I am not sure how or why that is working for you! The instructions even say the upper temp is something like 90°F. Are you able to go hotter? I believe the reason SeeMeCNC uses a different thermistor is because they needed a higher temp rating and a smaller form factor. For a hot bed, the existing thermister should be fine since the upper limit is around 212°F or so. I don't know the actual rating for the one included in the kit but it should be able to handle that.

When I tried my stock MK138 today with my nichrome hot bed, it only got up to about 90°F when the pot was maxed. I then replaced R5 with a 3 15K resisters in series to get a 45k Ω resistance. Thinking that this would get me in the ballpark. Unfortunately, I blew something in the MK138 because when I tested I saw the LED come on, go off and that was it. I am going to try to pick up the diode you posted in my thread at Radio Shack tonight and swap those out and try again.

cheers,
Michael

Chris Muncy · Post by **Chris Muncy** » Thu Mar 29, 2012 6:10 pm

Tell ya what I'm gonna do......
I'll fire up the printer tonight and either take pics or shoot video on how hot my bed gets.

Plus as an added bonus I'll verify my resistors on the MK138.

Chris Muncy · Post by **Chris Muncy** » Thu Mar 29, 2012 6:15 pm

Just found this on the Yahoo Groups:

If you want to use a Velleman board to control a heated bed, with the stock
SeeMeCNC thermistor(NOT the one included in the Velleman kit), then replace R6
with a wire jumper to get a good temperature range.

Leave R5 as the stock(kit) 120K.

Andy

Here's the start of the conversation: Using Velleman board for heated bed

Chris Muncy · Post by **Chris Muncy** » Thu Mar 29, 2012 6:21 pm

In my video, Printing a snake on my H-1 to show off the new heated print bed around 14:45 you can see the temp I get to.

mhackney · Post by **mhackney** » Thu Mar 29, 2012 11:08 pm

Hey Chris, I watched your video and saw the hot bed temp. Did you verify your resisters? I wasn't able to get to the shack for diodes tonight. I'll do that in the morning. I'd really like to get this hot bed project wrapped up!

Which thermistor are you using?

Cheers,
Michael

JTCUSTOMS · Post by **JTCUSTOMS** » Thu Mar 29, 2012 11:21 pm

Chris, does your temp gun have an adjustable emissivity factor?
Reflective surfaces will wreak havoc with infrared temp gun readings.
I have done several thermal "audits" for the Co. I used to work for and it is amazing the difference in readings between a contact thermocouple and infra-red on shiny surfaces. Some guns are better than others though.

Chris Muncy · Post by **Chris Muncy** » Fri Mar 30, 2012 8:26 am

JTCUSTOMS wrote:Chris, does your temp gun have an adjustable emissivity factor?
Reflective surfaces will wreak havoc with infrared temp gun readings.
I have done several thermal "audits" for the Co. I used to work for and it is amazing the difference in readings between a contact thermocouple and infra-red on shiny surfaces. Some guns are better than others though.

Yea I was thinking about that too but fight after I built the bed I had an additional thermocouple from a VOM that I used to verify and set the temp so I am pretty confident on the settings.

Michael, no resister changes in my MK138 for the bed.

Leeway · Post by **Leeway** » Fri Mar 30, 2012 9:12 am

Okay, Guys. I think I managed to solder the MK138. My Gen 6 board does not have a spot to attach the heat bed to, so this will be manual operation for now. I will verify my temp settings manually too.
Is there any issue with inrush current on this little board?

I want a switch before the 12 VDC + connection, correct?
Then the heat bed wire goes to Com and NC?

Just double checking with you guys. I do have a spare kit here just in case.

Also I found that the correct sized soldering iron and a magnifying glass take a lot of the intimidation out of soldering this kit. It took me about 30 minutes. The hardest part was aligning the legs on the IC to plug into the socket. Mine looked like someone had attempted to kill a caterpillar but stomping on it.

Chris Muncy · Post by **Chris Muncy** » Fri Mar 30, 2012 9:34 am

you want one side of the bed connected to ground and the other side connected to the normally open (NO). Connect your +12vdc supply to the relay common on the board.

mhackney · Post by **mhackney** » Fri Mar 30, 2012 10:03 am

Thanks Chris, which thermistor are you using?

Chris Muncy · Post by **Chris Muncy** » Fri Mar 30, 2012 10:54 am

I'm using the thermister that shipped with the MK138 for the heated bed.

Leeway · Post by **Leeway** » Fri Mar 30, 2012 11:07 am

Chris Muncy wrote:you want one side of the bed connected to ground and the other side connected to the normally open (NO). Connect your +12vdc supply to the relay common on the board.

Gotcha.
Forgot about the relay being a switch.
Thanks.

mhackney · Post by **mhackney** » Fri Mar 30, 2012 12:05 pm

Thanks Chris. I just don't get it then! If you are using the MK138 kit stock with thermistor, shouldn't it only be able to control temp in the range of 41° to 86°F as stated in the docs?

That is exactly what mine did (before it blew when I changed R5).

cheers,
Michael

Chris Muncy · Post by **Chris Muncy** » Fri Mar 30, 2012 12:23 pm

I'll verify what I have but I'm 99.99% sure I didn't have to change anything.

Chris Muncy · Post by **Chris Muncy** » Fri Mar 30, 2012 11:49 pm

I'll post here *just* to make sure all of the bases are covered. You will need to short out R5 in order to get the 100C temps at the print bed. My short was under the circuit board that I had mounted.

mhackney · Post by **mhackney** » Sat Mar 31, 2012 10:22 am

Thanks Chris, I essentially verified that on my board. I plugged in a 1K resister and that gets me to where I need to go (over 200°F).

cheers,
Michael

Leeway · Post by **Leeway** » Sat Mar 31, 2012 10:35 am

Okay.
I have a question. The MK138 comes with one 0 K resistor for use in the board. What is the difference between it and a jumper? I could better understand it if it was a fuse. Would placing a rated resistor there yield other mods such as the jumpers we are using?
Just curious is all.

Chris Muncy · Post by **Chris Muncy** » Sat Mar 31, 2012 10:49 am

Lee,

Nothing. You can use that jumper in place of R5.

Leeway · Post by **Leeway** » Sat Mar 31, 2012 7:07 pm

Thanks abunch, Chris. I just used some extra wire to jump R5 on the bottom side. That should just bypass the resistor.
Next question.
I have a thermistor here that is extra or spare that I ordered for my hot end. Should I use some Kapton and tape that to the center of my heat bed circuit board? Or did you tape the blue lollipop on yours? My guess is that either way will work, but when I guess about electronics I better figure on ordering more.

mhackney · Post by **mhackney** » Sat Mar 31, 2012 7:12 pm

Lee, I made my hot bed (see my build thread) and simply used the blue thermistor and the wire jumper on R5. That combo works fine and will work for you too. I used Kapton tape to attaché the thermistor in the middle of the hot bed.

cheers,
Michael

hopefully John will knock off these spammers soon! I deleted over 25 posts manual but couldn't keep up.

Leeway · Post by **Leeway** » Sat Mar 31, 2012 7:17 pm

Also the diagram on this pdf seems to conflict with what you mentioned earlier about the connections. I just found this one and it doesn't make anything clearer.

http://store.qkits.com/moreinfo.cfm/use ... _VM137.pdf

Leeway · Post by **Leeway** » Sat Mar 31, 2012 7:21 pm

Ouch. Thanks, Michael.
That is what I suspected.
I am a moderator on another Forum and the spammers can really take up valuable time and space. It is worth it to hem them up early.

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