Heatbed relay makes rapid clicking sound (SOLVED)

Hi fellow RepRapers!

I'm pretty new to 3D printing, just built my first 3D printer, the Prusa i3
I've been printing and tweaking for the last week, suddenly this issue arose and I cannot print
Whenever I turn on the heatbed, I hear the relay click sound, but not a normal 1-click ON and 1-click OFF, but a rapid series of clicks that sound very intimidating...
The clicks are very rapid, I would say it's probably ~32 clicks per second, I am afraid to turn it on for more than a second because i'm pretty sure I saw a bit of smoke once it was on for more than that

I triple checked all the wiring and tried some firmware changes (and reverted those due to lack of success), it doesn't seem like a software problem to me, as I changed nothing that could be related

My heatbed is MK3 and the relay is an SLA-24VDC-SL-A

Please see the following video for example: [youtu.be]


Can anyone please assist with this? It's driving me crazy...

Thanks in advance,
Michael

Edited 4 time(s). Last edit at 08/15/2015 05:14PM by Mavni.

Did you turn PID temperature control on?

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I figured it was supposed to be off when using an analog relay, is it the opposite?
If that's the problem, why did it start happening all of a sudden?

Here are my PID settings:

// PID settings:
// Comment the following line to disable PID and enable bang-bang.
#define PIDTEMP
#define BANG_MAX 255 // limits current to nozzle while in bang-bang mode; 255=full current
#define PID_MAX BANG_MAX // limits current to nozzle while PID is active (see PID_FUNCTIONAL_RANGE below); 255=full current
#ifdef PIDTEMP
//#define PID_DEBUG // Sends debug data to the serial port.
//#define PID_OPENLOOP 1 // Puts PID in open loop. M104/M140 sets the output power from 0 to PID_MAX
//#define SLOW_PWM_HEATERS // PWM with very low frequency (roughly 0.125Hz=8s) and minimum state time of approximately 1s useful for heaters driven by a relay
#define PID_FUNCTIONAL_RANGE 10 // If the temperature difference between the target temperature and the actual temperature
// is more then PID_FUNCTIONAL_RANGE then the PID will be shut off and the heater will be set to min/max.
#define PID_INTEGRAL_DRIVE_MAX PID_MAX //limit for the integral term
#define K1 0.95 //smoothing factor within the PID
#define PID_dT ((OVERSAMPLENR * 10.0)/(F_CPU / 64.0 / 256.0)) //sampling period of the temperature routine

// If you are using a pre-configured hotend then you can use one of the value sets by uncommenting it
// Ultimaker
#define DEFAULT_Kp 22.2
#define DEFAULT_Ki 1.08
#define DEFAULT_Kd 114

// MakerGear
// #define DEFAULT_Kp 7.0
// #define DEFAULT_Ki 0.1
// #define DEFAULT_Kd 12

// Mendel Parts V9 on 12V
// #define DEFAULT_Kp 63.0
// #define DEFAULT_Ki 2.25
// #define DEFAULT_Kd 440
#endif // PIDTEMP

// Bed Temperature Control
// Select PID or bang-bang with PIDTEMPBED. If bang-bang, BED_LIMIT_SWITCHING will enable hysteresis
//
// Uncomment this to enable PID on the bed. It uses the same frequency PWM as the extruder.
// If your PID_dT above is the default, and correct for your hardware/configuration, that means 7.689Hz,
// which is fine for driving a square wave into a resistive load and does not significantly impact you FET heating.
// This also works fine on a Fotek SSR-10DA Solid State Relay into a 250W heater.
// If your configuration is significantly different than this and you don't understand the issues involved, you probably
// shouldn't use bed PID until someone else verifies your hardware works.
// If this is enabled, find your own PID constants below.
//#define PIDTEMPBED
//
//#define BED_LIMIT_SWITCHING

// This sets the max power delivered to the bed, and replaces the HEATER_BED_DUTY_CYCLE_DIVIDER option.
// all forms of bed control obey this (PID, bang-bang, bang-bang with hysteresis)
// setting this to anything other than 255 enables a form of PWM to the bed just like HEATER_BED_DUTY_CYCLE_DIVIDER did,
// so you shouldn't use it unless you are OK with PWM on your bed. (see the comment on enabling PIDTEMPBED)
#define MAX_BED_POWER 255 // limits duty cycle to bed; 255=full current

#ifdef PIDTEMPBED
//120v 250W silicone heater into 4mm borosilicate (MendelMax 1.5+)
//from FOPDT model - kp=.39 Tp=405 Tdead=66, Tc set to 79.2, aggressive factor of .15 (vs .1, 1, 10)
#define DEFAULT_bedKp 10.00
#define DEFAULT_bedKi .023
#define DEFAULT_bedKd 305.4

//120v 250W silicone heater into 4mm borosilicate (MendelMax 1.5+)
//from pidautotune
// #define DEFAULT_bedKp 97.1
// #define DEFAULT_bedKi 1.41
// #define DEFAULT_bedKd 1675.16

// FIND YOUR OWN: "M303 E-1 C8 S90" to run autotune on the bed at 90 degreesC for 8 cycles.
#endif // PIDTEMPBED

If you are using a mechanical relay, don't use PID control. PID control is a PWM system that switches the thing at about 7 Hz in Marlin. That's why the relay chatters. It won't last long like that and it will drive you nutz until it fails.

If you want to use PID (and you should) you should use the on-board MOSFET switch, or if it can't handle your bed heater's current, use an external solid state relay (SSR).

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I managed to find the problem, my heatbed wires were soldered for 12V instead of 24V...
I have no idea why it happened all of a sudden, but it is working perfectly now

I will order a SSR anyway, should be better than an analog relay, for sure

Thank you all!