Bed took too long to heat - so I fixed the problem.

Topics around mechanical design, controller and electronics. Mods & hacks welcome.
charles@linquist.net
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Joined: Fri May 27, 2016 11:45 pm

Bed took too long to heat - so I fixed the problem.

Postby charles@linquist.net » Thu Aug 03, 2017 4:23 pm

I'm impatient. My heated bed took 13-20 minutes to reach 105C (which I use for ABS), depending on the temperature of the room the printer is located in. I have another 3D printer (FlashForge), and it is "ready to go' in about 5 minutes. I wanted the RAISE to keep up.

The RAISE heater normally consumes about 192W (8A @ 24V). The only convenient way to increase the heater power is to give it a higher voltage, but I didn't want to raise the voltage to the entire system. I removed the heated bed and looked at the traces and decided that it should be able to handle some extra power without a problem.

So I bought a MEANWELL NES-350-27, 350W, 27V (nom) power supply on Ebay for $50 and adjusted the voltage to 30. I built a two FET, one transistor circuit that acts as a switch to apply 30V to the bed heater whenever the controller outputs 24V. Schematic attached. I used mating connectors on my circuit such that I didn't have to modify the RAISE wiring at all - except that I wired the MEANWELL to the RAISE power switch. I also drilled a 1/2" hole so I could run the wires through the bottom plate of the printer. I mounted the circuit and the new power supply underneath. If you build the circuit, mount the two power transistors on a small aluminum sheet (I used 1" X 2") to act as a heatsink.

Now the RAISE bed heats to operating temperature in about 5 minutes. With a 30V supply, the bed draws about 11A (330W). That is a 71% increase. Of course, if you aren't brave, you can adjust the voltage down a bit.

An added bonus is that the RAISE power supply no longer has to deal with the bed .
Attachments
RAISE3DMOD.jpg
RAISE 3D Heated bed mod to increase power.

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Brandon
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Joined: Fri May 05, 2017 1:22 pm

Re: Bed took too long to heat - so I fixed the problem.

Postby Brandon » Thu Sep 07, 2017 2:27 am

That is a unique solution. Good work.

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walshlg
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Joined: Wed Mar 23, 2016 12:01 pm

Re: Bed took too long to heat - so I fixed the problem.

Postby walshlg » Mon Sep 11, 2017 3:21 am

nifty, I think I follow but it looks like you have a voltage divider across the control voltage for the 2 fets in parallel. Did I get that right?

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woofy
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Joined: Sun Jun 12, 2016 4:09 pm

Re: Bed took too long to heat - so I fixed the problem.

Postby woofy » Mon Sep 11, 2017 7:50 am

Its because the 30v supply exceeds the transistors 20v gate limit.

Its the 100n capacitor I don't understand. Its just going to hold the transistors in the danger zone for 1ms every cycle.
Raise3D N2+, Ultimaker2 & UP plus printers.

frjez
Posts: 40
Joined: Tue Jan 24, 2017 2:55 am

Re: Bed took too long to heat - so I fixed the problem.

Postby frjez » Sun Sep 24, 2017 3:46 am

Wouldn't be just easier to use a relay? Preferable a solidstate and of course some resistors :-)
But, yeah a good design idea was to use the old "power source" as a trigger.

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Julia Truchsess
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Joined: Mon Mar 21, 2016 1:30 pm
Location: Connecticut
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Re: Bed took too long to heat - so I fixed the problem.

Postby Julia Truchsess » Sun Sep 24, 2017 1:03 pm

I don't think you'd want a relay chattering away constantly as the bed control PID loop varies the pulse width of the drive. Look at the way the LED flickers - a relay would be doing the same thing. As for a "solid-state" relay, well that's basically what the OP has presented here with the MOSFETs.


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