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Question about heated bed

Posted by Koby_88 
Question about heated bed
November 05, 2016 12:37PM
Hi i ordered from aliexpress 300x300x3mm aluminium heated bed 24V. My current setup is 12V and i wanted to connect heated bed to separate power supply. My question is: what would be optimal 24v psu for this heated bed ?
Re: Question about heated bed
November 05, 2016 12:45PM
Any 24v DC PSU that delivers the neccesary wattage + a bit (10-20%). There is nothing special to look out for.


[www.bonkers.de]
[merlin-hotend.de]
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Re: Question about heated bed
November 05, 2016 12:59PM
Yes but i dont know what is correct wattage for that bed smiling smiley I couldnt find specification. The bed i order is at link down if that can help.
[ru.aliexpress.com]

Edited 1 time(s). Last edit at 11/05/2016 12:59PM by Koby_88.
Re: Question about heated bed
November 05, 2016 02:48PM
My guess is that it will draw somewhere between 10A and 15A. When it arrives, measure its resistance with a multimeter, subtract the resistance reading when the multimeter leads are touching, and divide the result into 24 to get the current.

Most low end 3D printer electronics boards can't safely switch more than about 11A. On RAMPS electronics, additionally the bed heater polyfuse is only rated at 16V.


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Full disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: Question about heated bed
November 05, 2016 03:59PM
Thanks a lot on answer, i will do that. You think that ramps cant support that heated bed ? I was thinking that ramps remain on 12V and to connect heatbed to separate 24v psu with SSR, do you think this can be a problem ?
Re: Question about heated bed
November 05, 2016 11:51PM
I don't use RAMPS, but in theory you can feed 24V to the bed power input and 12V to the other one, and replace he 11A polyfuse by an auto fuse. However, the mosfet, connectors and PCB traces on cheap RAMPS boards may fry if you go much above 10A. The mosfet is easy to replace with a better one.

If you go the SSR route then you need to choose the SSR carefully. See [duet3d.com] for recommendations.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Full disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: Question about heated bed
November 08, 2016 06:59AM
You can probably run the heated bed through the RAMPS, but it's a lot of current. A nice alternative is to wire up a MOSFET to switch it on and off. It's cheaper and more reliable than an SSR, and takes up less space.
Re: Question about heated bed
November 08, 2016 09:16AM
Quote
epicepee
You can probably run the heated bed through the RAMPS, but it's a lot of current. A nice alternative is to wire up a MOSFET to switch it on and off. It's cheaper and more reliable than an SSR, and takes up less space.

SSRs are very reliable unless you choose the wrong one - as a lot of people do unfortunately. An external mosfet (or even two or three in parallel) can work well, but only if you keep the ground resistance very low.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Full disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: Question about heated bed
November 09, 2016 05:06PM
I use this MOSFET for logic level switching:

2N06L07

  • NPN Power Mosfet
  • 2v ON gate voltage, 20v max
  • 0.007 ohm on resistance
  • 55v max drain-source voltage
  • 80A max current

Pretty much ideal for switching high currents from 3.3v or 5v logic levels.

Driving a mosfet and keeping it in it's efficient range works best if you don't approach the max current and exceed the minimum gate voltage by a good amount.
I recently drove 3 of these in parallel on a prototype for a 12v 700W heated bed.
Gate drive current was < 4ma across the three of them at 400hz PWM.
They still got warm, but I was pushing ~20A through each one.

Edited 1 time(s). Last edit at 11/09/2016 05:18PM by darenschwenke.
Re: Question about heated bed
December 04, 2016 10:29PM
Thanks a lot for answers, can you tell me what is optimal PSU for ramps 1.4 setup (arduino, fans, 40w heater...) without heatbed ? How many Amps ?
Re: Question about heated bed
December 05, 2016 11:14AM
I like the original xbox 360 PSU myself. Gives you 5v vsb (always on) at 1A and switchable 12v at ~14A.
They are cheap too. The slim version is cheaper, but gives 12A. Still enough without a heated bed.
Re: Question about heated bed
December 28, 2016 02:05AM
I have a 24V PSU with around 300-350W for the electronics (RAMPS, motors, hotend) and it seems to work fine. My heatbed through a relay feeds off another 24V PSU that's 400W, which is enough for a 400x400mm silicone heater.

Do make sure you test that relay while being ready to unplug it. The DC-current SSRs are rarer than AC counterparts, and I've come across a vendor in China that sent me a couple that nearly started a fire (they were rated for more than the current they were used for). Another vendor sent me good relays.
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