power supply options??

I am using an older power supply out of a junk computer.

It takes fooooreever to heat up my mk1 heat bed about 30 minutes give or take ambient room temperature which is usually around the mid to upper 70's

What factors play into the speed the heating of the bed? my hot in can go from cold to 200+ in less than 3 minutes I understand general electronics but what makes the bed take so much longer?

what electronics and firmware are you running,

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thejollygrimreaper Wrote:
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> what electronics and firmware are you running,


ramps 1.4 wit pololu drivers

running a pc power supply you're likely giving it 12v power, if you are using marlin you'll find a "max pwm" or max current line in the configuration section,

the comments with tell you to set it to 255 for max current but in the background this gets divided by 2 if you set that to 511 then you'll get the maxium about of current delivered to the bed,
just got to make sure your power supply is capable of supplying 15 odd amps

i'm pretty sure it's the same in sprinter

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thejollygrimreaper, close but not quite:

it looks like half the value is used to know when to turn off and on the signal, not the total of the power level.
as described in the configuration.h file.

#define MAX_BED_POWER 256 // limits duty cycle to bed; 256=full current


256 is full current bang bang method. 1-255 is pwm and varies in power from 1 to 255 which is also full power.

I would suspect but do not know for sure that any value above 255 would be full on.
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in temperature.c

if ((extruder > EXTRUDERS)
#if (TEMP_BED_PIN <= -1)
||(extruder < 0)
#endif
){
SERIAL_ECHOLN("PID Autotune failed. Bad extruder number.");
return;
}

SERIAL_ECHOLN("PID Autotune start");

disable_heater(); // switch off all heaters.

if (extruder<0)
{
soft_pwm_bed = (MAX_BED_POWER)/2;
bias = d = (MAX_BED_POWER)/2;
}
else
{
soft_pwm[extruder] = (PID_MAX)/2;
bias = d = (PID_MAX)/2;
}




for(; ; ) {

if(temp_meas_ready == true) { // temp sample ready
updateTemperaturesFromRawValues();

input = (extruder<0)?current_temperature_bed:current_temperature[extruder];

max=max(max,input);
min=min(min,input);
if(heating == true && input > temp) {
if(millis() - t2 > 5000) {
heating=false;
if (extruder<0)
soft_pwm_bed = (bias - d) >> 1;
else
soft_pwm[extruder] = (bias - d) >> 1;
t1=millis();
t_high=t1 - t2;
max=temp;
}
}
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it looks like half the value is used to know when to turn off and on the signal, not the power level.
as described in the configuration.h file.

#define MAX_BED_POWER 256 // limits duty cycle to bed; 256=full current


256 is full current bang bang method. 1-255 is pwm and varies in power from 1 to 255 which is also full power.

Edited 3 time(s). Last edit at 07/22/2013 05:52AM by jamesdanielv.

this is the line that gives it away:

bias = d = (PID_MAX)/2;


setting max pwm to 511 is just a cheeky work around to make the resulting pwm duty cycle actually get to 255 currently the highest it will go is 1/2 the max pwm, but why on earth was it done this way?

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instead of 511, try 256. the divide by 2 code is just the method used to detect rising and fall of signal for pwm.

Well, storing 511 into an 8 bit variable (that's what the PWM timer is capable of) removes the upper bit, so actually 511 == 255.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

noting under 20amps - 30amps is even better. You need to power 5 motors + a heatbed + fans + perhaps a second extruder.

personally I'd run with 30 amps.

I'm really sketchy when it comes to altering the firmware settings it took me forever to track down the correct code and work the bugs out of my printer. I will have to see what the amp rating is on this one before I try that

I think im going to buy another power supply to start and if that doesn't help then I will look into changing the code. The power supply I have is out of one of those mini HP towers. Do u think one of the bench top power suppies or like a atx one is better ?

I can heat an MK2a to 60*C in a minute or so (maybe not even that long) with a high end ATX psu. I'm using an Antec 620 watt supply that is similar to this one. [www.newegg.com] Some use bench PSUs but I've had good luck with all that I've built using an ATX PSU. Just make sure it's good quality and can deliver enough current and you'll be fine.

As for editing firmware, it's good to know or at least know where to find it. I keep backup versions with the changes noted in comments in the code header. With a properly working heated bed, correctly sized PSU and stock heat settings in Marlin with a RAMPS 1.4 you shouldn't have to edit the firmware.

Get one of these:

[www.ebay.com]

I have one and it works fantastic. I can get my bed up to temp in about 10 min. Also, if youre not already using one, get a nice square of sound deadening or something similar to sit on top of the bed while its heating up.

Quote
Crussell
Get one of these:

[www.ebay.com]

I have one and it works fantastic. I can get my bed up to temp in about 10 min. Also, if youre not already using one, get a nice square of sound deadening or something similar to sit on top of the bed while its heating up.

Ive got a couple of those on my machine, and they are way better than any atx psu could ever hope to be. its cheap, the voltage doesnt drop when theres a load and they are adjustable in voltage and available with up to 48 volts. not to mention they are simple to wire, no soldering or messing around with the wires from the atx supply to make it turn on. this is what cnc machines use.

I have two of those 12V 30 amp supplies and they rock. My Cupcake had a 480W ATX PSU in it and when the heated bed and nozzle kicked on, the voltage would droop to under 11.5VDC. The 12V rail could only supply something like 11A which was entirely inadequate. The voltage doesn't sag at all now. I got mine on Amazon using Prime.

Anybody has any experience with a lower wattage industrial power supply? Mine is 12v 12a and the bed can't get to the temperature, usually I have to put a thin stack of paper on top of the bed just so it reaches ~110c. Will editing the configuration.h help?