# Specific 3D Printers, Scanners, & Hardware > RepRap Format Printer Forum >  Just got MK3 heatbed, have questions.

## DBFIU

Hi,

  I have the aluminum heatbed off ebay, mK3 design. I bought a 24v 350 watt power supply and SSR for control. I want to this bed to heat up ASAP and stay EVEN heat as well as bed stay  FLAT. These have been my issues with borosilicate and PCB heated MK2a. 

Anyway, the bed came with an NTC 10k thermistor* B57621C103K62*, I am about to solder it to my bed and run the thermistor leads to my ramps. 

My question is, what thermistor table do I use in my configuration.h? 


Here is the comments





//==================================================  =========================
//============================= Thermal Settings ============================
//==================================================  =========================
//
//--NORMAL IS 4.7kohm PULLUP!-- 1kohm pullup can be used on hotend sensor, using correct resistor and table
//
//// Temperature sensor settings:
// -2 is thermocouple with MAX6675 (only for sensor 0)
// -1 is thermocouple with AD595
// 0 is not used
// 1 is 100k thermistor - best choice for EPCOS 100k (4.7k pullup)
// 2 is 200k thermistor - ATC Semitec 204GT-2 (4.7k pullup)
// 3 is Mendel-parts thermistor (4.7k pullup)
// 4 is 10k thermistor !! do not use it for a hotend. It gives bad resolution at high temp. !!
// 5 is 100K thermistor - ATC Semitec 104GT-2 (Used in ParCan & J-Head) (4.7k pullup)
// 6 is 100k EPCOS - Not as accurate as table 1 (created using a fluke thermocouple) (4.7k pullup)
// 7 is 100k Honeywell thermistor 135-104LAG-J01 (4.7k pullup)
// 71 is 100k Honeywell thermistor 135-104LAF-J01 (4.7k pullup)
// 8 is 100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup)
// 9 is 100k GE Sensing AL03006-58.2K-97-G1 (4.7k pullup)
// 10 is 100k RS thermistor 198-961 (4.7k pullup)
// 11 is 100k beta 3950 1% thermistor (4.7k pullup)
// 12 is 100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup) (calibrated for Makibox hot bed)
// 13 is 100k Hisens 3950  1% up to 300°C for hotend "Simple ONE " & "Hotend "All In ONE"
// 20 is the PT100 circuit found in the Ultimainboard V2.x
// 60 is 100k Maker's Tool Works Kapton Bed Thermistor beta=3950
//
//    1k ohm pullup tables - This is not normal, you would have to have changed out your 4.7k for 1k
//                          (but gives greater accuracy and more stable PID)
// 51 is 100k thermistor - EPCOS (1k pullup)
// 52 is 200k thermistor - ATC Semitec 204GT-2 (1k pullup)
// 55 is 100k thermistor - ATC Semitec 104GT-2 (Used in ParCan & J-Head) (1k pullup)
//
// 1047 is Pt1000 with 4k7 pullup
// 1010 is Pt1000 with 1k pullup (non standard)
// 147 is Pt100 with 4k7 pullup
// 110 is Pt100 with 1k pullup (non standard)
// 998 and 999 are Dummy Tables. They will ALWAYS read 25°C or the temperature defined below.
//     Use it for Testing or Development purposes. NEVER for production machine.
//     #define DUMMY_THERMISTOR_998_VALUE 25
//     #define DUMMY_THERMISTOR_999_VALUE 100
// :{ '0': "Not used", '4': "10k !! do not use for a hotend. Bad resolution at high temp. !!", '1': "100k / 4.7k - EPCOS", '51': "100k / 1k - EPCOS", '6': "100k / 4.7k EPCOS - Not as accurate as Table 1", '5': "100K / 4.7k - ATC Semitec 104GT-2 (Used in ParCan & J-Head)", '7': "100k / 4.7k Honeywell 135-104LAG-J01", '71': "100k / 4.7k Honeywell 135-104LAF-J01", '8': "100k / 4.7k 0603 SMD Vishay NTCS0603E3104FXT", '9': "100k / 4.7k GE Sensing AL03006-58.2K-97-G1", '10': "100k / 4.7k RS 198-961", '11': "100k / 4.7k beta 3950 1%", '12': "100k / 4.7k 0603 SMD Vishay NTCS0603E3104FXT (calibrated for Makibox hot bed)", '13': "100k Hisens 3950  1% up to 300°C for hotend 'Simple ONE ' & hotend 'All In ONE'", '60': "100k Maker's Tool Works Kapton Bed Thermistor beta=3950", '55': "100k / 1k - ATC Semitec 104GT-2 (Used in ParCan & J-Head)", '2': "200k / 4.7k - ATC Semitec 204GT-2", '52': "200k / 1k - ATC Semitec 204GT-2", '-2': "Thermocouple + MAX6675 (only for sensor 0)", '-1': "Thermocouple + AD595", '3': "Mendel-parts / 4.7k", '1047': "Pt1000 / 4.7k", '1010': "Pt1000 / 1k (non standard)", '20': "PT100 (Ultimainboard V2.x)", '147': "Pt100 / 4.7k", '110': "Pt100 / 1k (non-standard)", '998': "Dummy 1", '999': "Dummy 2" }
#define TEMP_SENSOR_0 1
#define TEMP_SENSOR_1 0
#define TEMP_SENSOR_2 0
#define TEMP_SENSOR_3 0
#define TEMP_SENSOR_BED 1


// This makes temp sensor 1 a redundant sensor for sensor 0. If the temperatures difference between these sensors is to high the print will be aborted.
//#define TEMP_SENSOR_1_AS_REDUNDANT




Right now I am using a standard bulb style thermistor. It works ok but I want to use the NTC 100k. Which number is it out of that list above? How do I get the new thermistor to read properly?






Second question. My bed resistance is showing 9.2 ohms for the 24v circuit and 6 ohms for the 12v circuit. Isnt this a little high? The bed was bought brand new off ebay from a private seller. No soldering has even taken place on the flats yet. Suggestions appreciated





Thanks!!

----------


## printbus

Looks like '4' is the only 10K option built into Marlin.  According to Mouser.com, the part number suggests this is a surface mount part. Is it? If you have a meter, I'd measure the resistance at room temperature and confirm it's really around 10,000 ohms at room temperature. If the part number is correct, note that the thermistor accuracy spec is 10% (most thermistors are 1% or 3%), and the part is only rated for up to 125 degrees C.

----------


## DBFIU

Thanks for the reply. I just measured it and it shows 11k ohms so it seems to be a 10k.

Would option 4 then be ok for me to use? Are there any other properties I need to know about this thermistor other then its resistance, so that I can use one of the number options and not have to do any more programming?

It is a very tiny rectangular looking thing.

It looks exactly like this but its 10k not 100k

http://www.ebay.com/itm/GENUINE-EPCO...-/181454391090

----------


## printbus

> Would option 4 then be ok for me to use? Are there any other properties I need to know about this thermistor other then its resistance, so that I can use one of the number options and not have to do any more programming?


You really don't have much choice but to use option 4 unless you want to incur more work.   The additional work would be to find a detailed datasheet for the 10K thermistor, and use that to assess how similar the type 4 measurement table is in thermistortables.h (again assuming Marlin is being used here).  Unfortunately the data isn't directly comparable.  I've built spreadsheets to do this comparison; programmer types feed thermistor parameters into a python script (which I think is included in the Marlin distribution), and it builds a table for you.  You'd then use that to update a table in thermisortables.h or create a new one with some new type number of your choosing.  What I can say is that for the few 100K thermistors I've compared, the differences have been pretty minor - within a few degrees of measurement error.  (Although I may have just been lucky in the parts I was comparing).

This isn't of total value, but I do have some insight into how the thermistortables concept works captured as part of this thread - Comparison of Type 1 and Type 6 thermistortables.h data

If no one else jumps in, I can apply the spreadsheet comparison approach for you, but it might take a day or two to get to it.

----------


## DBFIU

Not necessary, the time it takes to do this is not worth the 5 dollars for me to buy a 100k NTC EPCOS. I will just get that thermistor and stick with whats in the thermistor.h tables. Which number is the 100k EPCOS? I am assuming a "1" would work. Thank you!

----------


## DBFIU

Hi,


 I am using my MK3 heatbed at 12v right now and it cannot hit 110c. It maxes out at 103c and struggles to get there. I am using heavy gauge, high strand RC truck wire, soldered the 12V pads 2 and 3 to one cable and the other to pad to power. I am running through ramps at 12v. Bed just does not want to get hot. I checked resistance and it seemed to be within spec, somewhere around 1.6-1.8 ohm.

What am I missing?

----------


## printbus

I believe some people have had luck going through the process of calibrating the PID factors for the bed. Sounds like you've already got pretty robust wiring. Short of the PID tuning, your next option may be to use a 12V automotive relay or a solid state relay as a more efficient switch for the heater power.  The MOSFETs used on RAMPS aren't exactly the best possible switches, and you lose some power in the on-resistance of the MOSFETS.

----------


## printbus

I also remember some people shooting for 100 or 110 degrees on the bed cover the build plate with something to insulate it during the heating process. You still have to worry about whether the bed can maintain the desired temperature when the cover is removed, but it helps in getting the print bed to temperature quicker.

----------


## DBFIU

> I believe some people have had luck going through the process of calibrating the PID factors for the bed. Sounds like you've already got pretty robust wiring. Short of the PID tuning, your next option may be to use a 12V automotive relay or a solid state relay as a more efficient switch for the heater power.  The MOSFETs used on RAMPS aren't exactly the best possible switches, and you lose some power in the on-resistance of the MOSFETS.


Hi dude again, I just ordered a 350 watt mean-well power supply and a 25 amp solid state relay off ebay. I will be running this bed on 24v through the relay. I need this bed to get hot quick and stay hot/uniform. 

Do you have any other suggestions other then what I am doing? Does a SSR suck up lots of power, should I use a mechanical relay? I think my PSU is overkill, but I need it. I have 3 production machines that my business depends on and these beds just take forever to get hot, time = money. Thanks again

----------


## printbus

> Hi dude again, I just ordered a 350 watt mean-well power supply and a 25 amp solid state relay off ebay. I will be running this bed on 24v through the relay. I need this bed to get hot quick and stay hot/uniform. 
> 
> Do you have any other suggestions other then what I am doing? Does a SSR suck up lots of power, should I use a mechanical relay? I think my PSU is overkill, but I need it. I have 3 production machines that my business depends on and these beds just take forever to get hot, time = money. Thanks again


If you have specs for the SSR, you can compare to what is on RAMPS now.  The RAMPS D8 heat bed circuit has 0.1 ohms for the 11-amp polyfuse on the power input, and the MOSFET switch is spec'd at another 0.020 ohms for drain-source on resistance, for a total of 0.12 ohms not factoring for RAMPS circuit traces or connector losses.  The 25-amp SSR should have less than that for on-resistance, but a higher current one would be even less resistance.  For a given current rating, mechanical relays are typically lower resistance than MOSFETs or SSRs.  This is why you'll often hear people using something like a 200-amp MOSFET on a custom switch board. Overkill as far as current rating, but it'll have very low on-resistance.

----------

