I got the following issue with the printer. Prior printing, the bed reached the desired temperature (60 degrees). After the printing is initiated, in a few minutes, the temperature of the bed became unstable and started oscillating (60 to 68 degrees) showing higher temperature readings on the repetier screen. I touched the heatbed but it felt cooler than initially was and later printing slipped off the bed. At first thought was that the wiring of the thermistor was broken so I replaced it. But the problem was still there. Then I measured the thermistor’s resistance. It was about 104 kohm at 20 deg and reading from another posts found out that it is a normal value. I use the recommended version of repetier 0.84, which is a bit old but before this problem appeared everything was ok. Thanks in advance for you help.
The repetier version surely isn’t the problem.
I use the current 1.5.3 without problems.
What can be the cause for instable bed temperatures is faulty ribbon cable or an overloaded power supply.
The stock supply is quite on it’s limits when powering both heater and heatbed.
What can also help is to rewire the Heatbed with thicker copper wires. (0.5mm or 0.75 mmspeaker cable for example)
That will reduce the voltage drop caused by the thin strands of the ribbon cable, giving a little more power to the heatbed.
What i would recommend, if you’re going to print mostly with heatbed on or higher bed temps (ABS?),
is to get a second 24v supply for the heatbed.
Thanks for your reply. I think it is not the power supply. I have already printed a few bits and there was no problem at all. There is not any significant voltage drop during printing and when bed temperature instablity occured. However, I will give it a go today with a more powerful power supply. The original one is 15V, why would you use 24V one? Would not that damage the bed ? I use PLA and 60 degrees bed temperature and it seems a good setting to me. All bits stayed well sticked on the glass. Thanks
[color=#BF0000]NEVER connect a 24V Supply to the CONTROLLER BOARDS INPUT![/color]
If you want to power the heatbed from 24v you need a relay or power expander that switches the 24v for the heatbed
controlled by the heatbed output of the board.
I did not try 24v PSU anyway. So the problem was solved by using more powerful 15v supply. It seems the original one struggles to cover the demand from the printer. The peak current I have measured was 5.2 A which is quite significant. So, once I plugged the other supply the temperature fluctuations disappeared.
Thanks for all suggestions !
I did not try 24v PSU anyway. So the problem was solved by using more powerful 15v supply. It seems the original one struggles to cover the demand from the printer. The peak current I have measured was 5.2 A which is quite significant. So, once I plugged the other supply the temperature fluctuations disappeared.
Thanks for all suggestions !
Emil[/quote]
Yes, that’s quite true.
The stock supply is pushed to it’s limits when using the heatbed.
Where is your project located on the bed.
If you are printing over the thermistor it will be fooled by the temp of the plastic.
The software will see the temp of the thermistor go up and shut down the heater for the bed.
If you watch the graph you will see spikes ever time the plastic goes over the thermistor.
I always print in the middle of the bed and I work on and print pretty much the same design all the time (with slight modifications). It just happened one day and that was it. It may be the power supply itself, overloaded, overheated or an internal fault. I have not investigated it so cannot confirm. That printer is at work so it just needs to be kept running. However, your suggestion makes sense.