Increasing bed temperature October 26, 2015 02:35PM |
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Re: Increasing bed temperature October 26, 2015 05:49PM |
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Re: Increasing bed temperature October 27, 2015 04:16AM |
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Re: Increasing bed temperature October 27, 2015 06:14AM |
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Re: Increasing bed temperature October 27, 2015 08:02AM |
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Re: Increasing bed temperature October 27, 2015 08:54AM |
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bartdietrich
Ok thanks, that sounds like a good idea. I seem to remember seeing a potentiometer on the back of the PSU when assembling the Ormerod 2 and wondering whether that's what it was for.
So neither the Duet nor your hot end board will mind the increased voltage?
Just in case that isn't enough and we go with the external power supply, have you got a figure for the absolute maximum voltage the bed can take?
Cheers,
Bart
Re: Increasing bed temperature October 27, 2015 03:17PM |
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Re: Increasing bed temperature November 01, 2015 03:23PM |
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Re: Increasing bed temperature November 01, 2015 08:25PM |
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Re: Increasing bed temperature November 02, 2015 03:30AM |
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Re: Increasing bed temperature November 02, 2015 03:47AM |
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Re: Increasing bed temperature November 26, 2015 05:54PM |
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Re: Increasing bed temperature November 27, 2015 03:01AM |
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Re: Increasing bed temperature November 27, 2015 03:39AM |
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Re: Increasing bed temperature November 27, 2015 07:49AM |
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Re: Increasing bed temperature November 29, 2015 01:57PM |
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dmould
Well ... the word "overkill" did come to mind a couple of times while reading your post :-)
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dmould
Regarding changing only the bed voltage: The bed is switched by a MOSFET on the ground side of the bed, so ISTM that you could simply remove the + side of the bed (which is usually connected directly to the 12V supply), and connect it to your higher voltage supply instead - it will not require an additional relay. The only fly in the ointment is that the switched side of the bed is also connected to the cathode of an on-board LED, which goes to 12V via a resistor. So when supplying the bed with a higher voltage, the LED will be reverse-biased with a voltage equal to the difference between the higher bed voltage and the Duet 12V supply when the bed is switched off. If the difference is within the max. reverse voltage of the LED you will be OK. If not you could simply remove the LED and/or its resistor (D6 and R65).
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dmould
I do not however see any advantage in powering the bed from a separate supply - as said, the other components on the 12V rail won't mind the additional voltage apart from the fan, which you can drop with a series diode or two if it is an issue (or use a 5V fan powered from the 5V supply).
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dmould
I've attached the Duet schematic for convenience in case you don't already have it (had to split it due to the file size limitation of this forum), but it is available in the RRP repository.
Re: Increasing bed temperature November 29, 2015 02:34PM |
Registered: 9 years ago Posts: 106 |
Re: Increasing bed temperature November 30, 2015 07:22AM |
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bartdietrich
PS: the two antiparallel LEDs on the bed don't appear on the schematics you posted but my bed has them. They light up in alternate when you reverse the bed polarity. Dual function presumably: to allow connecting the bed either way round and still have one light up, and to protect each other from reverse breakdown.
Bart
Re: Increasing bed temperature November 30, 2015 08:06AM |
Registered: 9 years ago Posts: 106 |
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dmould
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bartdietrich
PS: the two antiparallel LEDs on the bed don't appear on the schematics you posted but my bed has them. They light up in alternate when you reverse the bed polarity. Dual function presumably: to allow connecting the bed either way round and still have one light up, and to protect each other from reverse breakdown.
Bart
The bed is not part of the Duet PCB so does not appear on the schematic (the bed driver & connector is on page 6 of the PDF). The LED I was talking about is the LED mounted on the Duet board itself, not the LEDs actually on the bed. That one is connected to the Duet 12V rail so will be reverse-biased if you feed the bed with a higher voltage. You probably will not have noticed them if your Duet is in a case, but it has SMD LEDs that come on with the bed and hotend heaters.
Dave