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Heated bed powered by Ramps

Posted by hexitex 
Heated bed powered by Ramps
March 08, 2011 04:58AM
Hi, I have two of these [uk.farnell.com] and was wondering if the Ramps setup can power them without issue? I plan on adding heatsinks to the MOSFETS with active cooling to the whole system. Checking the datasheet doesn't give an awful lot of information about Amps but I am guessing about 1amp per unit (wild guess BTW) - they do support voltage from 10 to 30. As you can see they are quite convenient for attaching to the underside of the bed. Question is will they work and has anybody used them?

So close to finishing my build, just waiting for the stepper drivers to be shipped

BTW they also supply thermistors, taken me ages to find one [uk.farnell.com]

cheers
rob
VDX
Re: Heated bed powered by Ramps
March 08, 2011 05:26AM
Hi Rob,

they're specified with 30Volts and 50Watts, so they'll pull around 1.7Amps @30Volts.

With 12Volts the max. current will be lower too (around 0.7Amps), so you'll receive below 9Watts of heating power!


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]
Re: Heated bed powered by Ramps
March 08, 2011 05:45AM
Thanks Viktor, so is there nothing that can be done to jackup the volts, maybe through capacitors ? Sorry, please forgive my ineptitude I have just started to learn electronics (page 70smiling smiley. I also have a bunch of 6ohm resistors (about 20) would these be better and would they perform well enough in a series? I am trying to understand what Ramps will allow me to do without a relay - has anybody had success directly with ramps and if so with what?

cheers
rob
VDX
Re: Heated bed powered by Ramps
March 08, 2011 05:57AM
... the simplest way is to add a separate power supply with 24V or 30V and connect it through the MOSFETS only (scratch some threads on the PCcool smiley, so the other electroniocs are powered by 12Volts ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]
Re: Heated bed powered by Ramps
March 08, 2011 06:12AM
OK, just to confirm your suggestion. Break a MOSFET connection so it is effectively independent, hookup the 30v power supply to these broken connections so it runs through the MOSFET and bang I'll have 100Watts of heated bed or a dead ramps. What about on off control?

Rob
VDX
Re: Heated bed powered by Ramps
March 08, 2011 06:27AM
Hi Rob,

... you have only to break the connections from MOSFET to 12Volts - GND and control (Gate) stays connected to the electronics.

Then you wire GND from the 30V-power source to GND of the MOSFET and +30Volt to the pin which was connected to 12 Volts.

So the GND's of the power sources are common ground and the Arduino can switch the 30Volts through the heater independant of the 12Volts ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]
Re: Heated bed powered by Ramps
March 08, 2011 07:11AM
Interesting, thanks. So does the shared GND flow distribute the current back to the respective power supplies in the same voltages?
VDX
Re: Heated bed powered by Ramps
March 08, 2011 09:19AM
hexitex Wrote:
-------------------------------------------------------
> So does the shared GND flow
> distribute the current back to the respective
> power supplies in the same voltages?

... exactly, as long as the MOSFETS can handle the higher voltage and current and can be switched on with 5Volts from the Arduino.

The common GND is the reference for all the different voltages ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]
Re: Heated bed powered by Ramps
March 08, 2011 12:06PM
RAMPS can handle up to 30V input as long as you don't have the diode connected and you power the Arduino off of USB. That'll give you better torque at higher speed to your motors too, though it probably isn't needed. The stepper drivers are rated at 35V I believe.


Cameron

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