Cheap and cheerful Bed Temperature control

I don't know what I did, but I believe I blew the electronics that runs the Bed on my Sanguinolulu electrics
So I was left with no way to control the temperature of the bed.....
Looking around at the thermistor controllers, they are either expensive or too complicated for a electronics dunce like me!
So I had a small brainwave, I went to Maplins and bought an adjustable timer kit and a 40A Automotive Relay.
Built the simple 555 Timer circuit up and connected it to the 40A Relay and power supply.
The timer circuit pulses the relay on for 0-5 seconds and the delay can be set from 1 to 60 seconds.
Tested it today and it works a treat!
I use a cheap IR Thermometer to check the temperature, and once I get the timer set, it holds the temperature at 60 degrees within one degree
When I first power up the bed, I turn the delay pot down so it warms up quickly, when it gets to approx. 50 degrees I turn it back to approx. 20 seconds delay

Andy

Edited 4 time(s). Last edit at 01/28/2012 07:18PM by Normsthename.

That is clever!

You could also use a variable PSU and give it the exact voltage it needs to keep the temperature stable.

Or you could modify the firmware and attach the thermistor to some of the spare pins on the sanguinololu.

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I had a similar thing happen on my ramps 1.3 board. There was solid core wire feeding the heated bed and clamped into the euro-style terminal block on the board. The contact was not good or something and it got super hot, melted the euro terminal and I lost heat.

Luckily it just damaged the terminal and the electronics were fine. I just pulled the board off and soldered a nice stranded awg 20 wire directly onto the back side. The rest of the terminal block was fine, but I replaced any solid core wire with stranded. I'm not sure why solid core would be on there at all??

I recently found the terminal block available at Ultimachine. They are great I'll leave it as for now, but next time the electronics come off...

Maybe you have the same scenario?

Hi Normsthename,

Nice . This is a great way to control the heated bed temperature.

I'm trying to get a heated bed up and running using Gen 3 electronics and this looks like just the kind of thing to power/control it.

I looked into using a thermal switch but the switch off/on temperatures range is quite high (70C open, 55C close). Translating the circuit diagram from Adrians Wiki page into a stripboard circuit is way out of my abitlity and even if i could, im not sure if there is any Gen 3 firmware out there which can manage the heated bed.

Would you be able to let me know if you are running this timer circuit from the same power supply as your printer and if so, are you are using anything to protect the circuit from any spikes in current?

Thanks.

Raj

Hi Raj
I run two separate supplys.
One is a 13.8V 20A that runs the Motors and the other is a 3 -15v 30A that runs the heated bed, I run that one at 13.8 Volts.
My Heated Bed draws 16 amps!
I have since replaced the faulty MOSFET on the board and now the MOSFET powers the 40A Relay, so there is no current on the MOSFET.
I can now use the bed thermister to control the temperature

Andy

Hi Andy,

Thanks for the info, 16 amps is a monstrous amount of power. I'm drawing 9.5 at the most. I rigged together the astable timer maplin and its working great with a 3sec on 3sec off cycle .

That said, i'm having trouble with yet another upgrade - this time it's slic3r giving me the runaround. If it ain't one thing it's smething else!

Thanks again for your help.

Raj