New Heated Bed Reads 738 degrees with no heat

Topics around mechanical design, controller and electronics. Mods & hacks welcome.
FreedomRules
Posts: 46
Joined: Thu Jan 25, 2018 4:34 pm

New Heated Bed Reads 738 degrees with no heat

Postby FreedomRules » Thu Sep 20, 2018 5:33 pm

So I'm on the tail end of upgrading my bed like Socke did with a flat thick aluminum plate. I also upgraded the heater to a keenovo 120V 750 watt silicon heater. It comes with a 2 wire 100k B25°C/50°C=3950±1% thermistor. I then followed what I saw on a couple arduino posts and wired it up with a 10k resistor as so:

This of course wires through a Omron Solid State Relay that has 120V AC on one side and DC on the other to turn on power to heater.

Resistor Leg 1 to Ground on the Raise3D
Resistor Leg 2 has multiple connections. First it connects to a 10k resistor and on that same side of the connection.
It also connects to the Signal lead on the Raise3D.
Then the other side of the resistor connects to the 5V lead on the Raise3D.

Image

I then changed the following settings in the Configuration.h.
#define TEMP_SENSOR_BED 11

Then in the Configuration_adv.h
#define BED_HYSTERESIS 1
#define BED_CHECK_INTERVAL 500

I'm curious if I've wired it up wrong or if I need to select a different Sensor type. That and I also thought about getting a temp sensor converter from reprap or build one just like it versus just using a 10k pull-up resistor. Do I even need the resistor and just hookup the 2 wires and select a completely different sensor. I also saw a couple other examples on the sensor that had it wired just a little different so thats a possibility its wired wrong as far as the resistor and what legs hook to what. I noticed that mine ohms out different than what the original bed does. Between all 3 legs on the default bed its around 130ohm on 2 legs and 10ohm on 1 leg. Where mine is 10ohm on 2 legs and 120ohm on 1 leg. Makes me think the oem is more like the one below is wired.
Image
Image

Any help would be greatly appreciated.

allanzo
Posts: 5
Joined: Fri Jul 08, 2016 4:18 pm

Re: New Heated Bed Reads 738 degrees with no heat

Postby allanzo » Thu Sep 20, 2018 9:11 pm

I have the same heater in my printer. I reused the 3 wire thermistor cable, I snipped the blue wire at the board end and connected a 4.7k resistor to that wire and to the red wire. You'll have to do a PID autotune to get the right values for your setup.

thermistor wire.jpg


In configuration.h:
#define TEMP_SENSOR_BED 13 //NTC 100K 3950 in Keenovo silicone heater pad

#if ENABLED(PIDTEMPBED)

//120V 750W Keenovo silicone heater into .25 inch aluminum tooling plate
#define DEFAULT_bedKp 134.84
#define DEFAULT_bedKi 25.72
#define DEFAULT_bedKd 176.74

#endif // PIDTEMPBED

FreedomRules
Posts: 46
Joined: Thu Jan 25, 2018 4:34 pm

Re: New Heated Bed Reads 738 degrees with no heat

Postby FreedomRules » Thu Sep 20, 2018 9:15 pm

Sweet I will try this tonight. Hopefully I have a 4.7 laying around.

socke
Posts: 239
Joined: Mon Mar 21, 2016 2:55 pm

Re: New Heated Bed Reads 738 degrees with no heat

Postby socke » Fri Sep 21, 2018 6:18 am

This is exactly the same I did, as I wrote here. I just didn't find a good photo of the wiring. ;)

FreedomRules
Posts: 46
Joined: Thu Jan 25, 2018 4:34 pm

Re: New Heated Bed Reads 738 degrees with no heat

Postby FreedomRules » Fri Sep 21, 2018 5:31 pm

Well I got a little farther last night. I cut out all the wiring I had done before and this time just did it all on a breadboard so I could rewire if necessary to find the right config. Currently my issue is that it shows 9 degree's vs 20 degree's like both my extruder's show as I'd think they'd show roughly the same temp being in the same conditioned space. I then give it a target temp like 80 to heat up to and it does start heating but then errors out 30 or so seconds later as the reported temp barely climbs upward. But the bed is getting hot for sure. It moved from 8 to 11 degree's but the bed was way hotter than that.

I think tonight I'm going to hookup the old bed and flash back the stock firmware just to make sure I don't have a board problem. If it does work I may look at trying to build my own thermistorables_XX.h file. I think I found some Arduino code you can run to build the table and I have a couple Arduino boards around.

Can anyone think of any other reason why temp would be off and not increase proportional to the heat on the table? Thanks for everyone's help on this so far. I'm excited to get it up and running so I can start playing again. I've been without my printer for months now as the stock bed is like it got hit by an earthquake as far as the waves in the board go.

FreedomRules
Posts: 46
Joined: Thu Jan 25, 2018 4:34 pm

Re: New Heated Bed Reads 738 degrees with no heat

Postby FreedomRules » Sun Sep 23, 2018 4:29 am

So when I get this hooked up is the temperature that is displayed suppose to be somewhat right or will the PID autotune fix that? I always thought PID autotune was more for how the bed heats and recovers not anything to do with what the temperature shows. It shows a temp of 295 with ABH Marlin 1.9. I found if I load Marlin 1.8 it will show a temperature of 220 using the bed sensor 13 on both firmwares.

I tested the thermistor and it ohms out according to what is show on the accompanying table provided by Keenovo. It said for 23 Celsius that ohm values would be Rmax 110.6613 Rnor 109.3221 Rmin 107.9884 and it read 109.2 so it was basically right on the normal for that temp. I wired it exactly as you have. With basically one thermistor wire going to ground and the other thermistor wire going to power with an offshoot hooking up to a 4.7k Ohm resistor going to the sensor leg and i get 0 degree. I also wired it like the drawing above that that way I get a temp of 295.

When I wired your way I changed the bed min temp to be zero so I could turn it on and heat it up. The temperature never changed on the display.

To clarify wiring. on the logic board we have ground, 5v and S. I wired 5v to one leg of thermistor and ground to other leg of thermistor. Then I wired a 4.7k resistor to the 5v wire and on the other end of the resistor I wired it to the S leg. My wires are different colors than your is why I didn't call them out by color. This way gets me zero on temp and I can heat the bed up and it doesn't change.

socke
Posts: 239
Joined: Mon Mar 21, 2016 2:55 pm

Re: New Heated Bed Reads 738 degrees with no heat

Postby socke » Mon Sep 24, 2018 8:37 am

FreedomRules wrote:To clarify wiring. on the logic board we have ground, 5v and S. I wired 5v to one leg of thermistor and ground to other leg of thermistor. Then I wired a 4.7k resistor to the 5v wire and on the other end of the resistor I wired it to the S leg. My wires are different colors than your is why I didn't call them out by color. This way gets me zero on temp and I can heat the bed up and it doesn't change.


It seems to be that is your problem! You should wire the thermistor between S and GND, instead of between 5V and GND.

FreedomRules
Posts: 46
Joined: Thu Jan 25, 2018 4:34 pm

Re: New Heated Bed Reads 738 degrees with no heat

Postby FreedomRules » Mon Oct 01, 2018 4:24 am

I had got this working but the reported temperature was jumping alot with fluctuations of 20 degrees at most but averaged 5 degree bouncing. Even when it wasn't heating. Well after a a lot of different configurations I finally landed on one that worked. Which was building a RC Low-Pass filter inline with the voltage divider. Now the reported temperature is solid and no longer bounces. I could have lived with the bouncing except one I'm anal, two it was sometimes kicking off the minimum temp protection circuit and three if would also mess with the thermal runaway circuits. It's crazy just how much noise can get picked up over a short distance.

If you hook a thermistor with just 3" of wire from the board it wouldn't fluctuate at all. I followed the same path as the original wire took. I twisted the thermistor wires together to hopefully cancel out any noise induced on one line by the twist introducing the noise into the other line. I put the wire inside a piece of sheath I striped off of some shield network cable. I was going to get some shielded metal braid but it was almost $80 for the little distance I needed. I'd assume the metal sheath would have done it so I wouldn't have needed the added circuitry. Maybe like a miniature faraday cage.


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