Aaand here I try again--- PCB Heatbed electronics question

Build type: Mendel
Electronics: gen6

I've been going into trying with a glass surface, mostly cause it doesn't bend and I don't have to level it all the time. Ah! the wonders of automation.
I understand it needs to be properly heated (I've read somewhere in these posts that someone used a hairdryer... tried it but still quite 'manual').
So I went into ordering a PCB heatbed, but the problem now is...

I have a gen6 electronics.
Doesn't seem to have any part about heatbeds there? I've read again in the threads and I already suspect it hasn't. So it was actually a rethorical question, I believe.
Is there a fix like adding a part of electronics (i read on the board there's a i2c thingy), or the only 'clean' way to go (meaning less swearing as possible) would to be ordering a new set of electronics?

I think you could pretty easily add an external power transistor board. Just make sure to connect to an unused pin that has PWM if you want that feature. Or even a relay board like the Makerbot heated bed add on board. I can't imagine that would be as much trouble than trying to set up a whole new board. Now would probably be a good time to dive into the config file and see what pins are set up as optional heater controls in the firmware.

I use a gen6 and PCB heated bed.

I just plug it in to the power supply directly and switch on/off manually. It works successfully.

I have a longer term plan to add an extension via the I2C socket, but currently I have too many other things on my todo list !

Geoff

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I think you could pretty easily add an external power transistor board.

Like this one?

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Well don't have skills or tools to make electronics myself. Could spend time on it but... can just do some soldering at best. Are these additional pieces sold somewhere?
About connecting the heated bed directly to generator: how you measure temperature that way and know when to stop heating?

I believe the heated PCBs have natural heat regulation built in. You just turn on the 12 volts and leave it on. As the traces heat up, the resistance increases, which causes the current to go down. It reaches a natural equilibrium, and stays at a somewhat constant temperature.

On the other hand, the aluminium beds with the power resistors can run away with temperature, so you need a thermistor and electronics to cycle power to maintain a constant temperature.

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Are these additional pieces sold somewhere?

A first one has been delivered, I'll PM you the details.

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About connecting the heated bed directly to generator: how you measure temperature that way and know when to stop heating?

With a thermistor, the same way the extruder heater works.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

macphyter Wrote:
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> I believe the heated PCBs have natural heat
> regulation built in. You just turn on the 12
> volts and leave it on. As the traces heat up, the
> resistance increases, which causes the current to
> go down. It reaches a natural equilibrium, and
> stays at a somewhat constant temperature.
>
> On the other hand, the aluminium beds with the
> power resistors can run away with temperature, so
> you need a thermistor and electronics to cycle
> power to maintain a constant temperature.

Oh... so you saying that not thermistor is even necessary?
Did you actually try this... or are just saying?
But why the 2nd version of the heated PCB supports for one then?


ps. And if that so, that a thermistor is not needed: what is the temperature which is designed to 'stop' naturally?

Edited 1 time(s). Last edit at 09/22/2011 07:33AM by raffaele.ragni.

It looks like the PCB maintains about 105 C @ 12V. You can get higher temperatures by raising the voltage, but its recommended to not exceed 120 C for extended periods in order to avoid damage to the PCB.

I have not actually tried this yet, but I've asked about it on the forum, and gotten some replies:

RepRap Forum

I have not seen a version that supports a thermistor... however there is a version that has pads for LEDs and resistors that limit the LED current. Is that what you are referring to?

Edited 1 time(s). Last edit at 09/22/2011 06:13PM by macphyter.

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what is the temperature which is designed to 'stop' naturally?

Natural convection. Depends heavily on ambient temperature, how good the bed is insulated at its bottom and how good the air above the bed can circulate. The later means, building a big part on it will raise the bed's temperature.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

OK, another question though.
Was reading the wiki page about it, and it doesn't say what type of resistor it needs?