Heatbed mosfet @30A, 12V June 18, 2016 11:15PM |
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Re: Heatbed mosfet @30A, 12V June 19, 2016 03:05AM |
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Re: Heatbed mosfet @30A, 12V June 19, 2016 03:07AM |
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Re: Heatbed mosfet @30A, 12V June 19, 2016 07:21AM |
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Re: Heatbed mosfet @30A, 12V June 19, 2016 10:18AM |
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Re: Heatbed mosfet @30A, 12V June 19, 2016 12:01PM |
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Re: Heatbed mosfet @30A, 12V June 19, 2016 12:24PM |
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dc42
The Power Expander from reprap.me is another possibility but I suspect that the connector and PCB traces may not be rated for 30A.
Re: Heatbed mosfet @30A, 12V June 19, 2016 01:34PM |
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LarsK
Hey,
Thank you for replies so far.
@ BOBC and O_Lampe - If I opt to just use one IRLB8743 with active cooling, would that not be a potential fire-hazard seeing how these things does not have thermal shutdown? If the fan for some reason stops it can be really bad? I prefer intrinsic safe whenever possible.
Re: Heatbed mosfet @30A, 12V June 19, 2016 04:10PM |
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Re: Heatbed mosfet @30A, 12V June 19, 2016 04:30PM |
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amigob
just put 3 of them parallel with the drain on a large peace of the copper on the PCB and done. No active cooling needed.
Also you don't have to worry to much about the 10A per MOS fet pin.
Re: Heatbed mosfet @30A, 12V June 20, 2016 04:25AM |
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Re: Heatbed mosfet @30A, 12V June 20, 2016 11:38AM |
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amigob
There is one thing you really should take care of and that is that if the the wire gets cut or the control board has no power, the fet's need to switch off.
Another thing you selected a mos fet with a 4.5V on voltage, realist that you only have 3.3V at the output ( on resistance is very high with 3.3 volt, high power dissipation ).
You can try without opto coupler but I think you really need a voltage shifter. And a optocoupler can do that also. But in the simplest form a optocoupler is directly also a inverter.
So you need to add an extra transistor to make the switch non inverted because of the safety statement above.
For a project I couldn't find an cheap opto coupler that could be driven directly by the output of the 32 bit atmel.
With power electronics it is not always easy.
Re: Heatbed mosfet @30A, 12V June 20, 2016 12:55PM |
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Re: Heatbed mosfet @30A, 12V June 20, 2016 03:00PM |
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dc42
The comment about 3.3V does not apply to you, because you have said that you will use RAMPS or Duet, both of which provide 5V gate drive. However, it's not advisable to take too much notice of the characteristic curves published on the datasheet, because they show typical curves at the typical gate threshold voltage, but the gate threshold voltage can vary quite widely between devices. The safe values to use are the maximum Rds(on) values, which are quoted at a particular gate to source voltage, usually 4.5V for the mosfets we are talking about.
One of the problems with using fets to switch 30A is that the resistance of the wire between common ground that the mosfet source terminals will reduce the amount of gate drive provided. For example, if that resistance is 0.03 ohm, then at 30A you will have 0.9V voltage drop across it; so the mosfet source terminals will be at +0.9V and the gate to source voltage will be reduced by that 0.9V. Using an optocoupler or an SSR (which has an optocoupler or a digital isolator built in) avoids that problem.
Re: Heatbed mosfet @30A, 12V June 25, 2016 04:57PM |
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Re: Heatbed mosfet @30A, 12V June 27, 2016 03:17PM |
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Re: Heatbed mosfet @30A, 12V June 28, 2016 05:09PM |
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Re: Heatbed mosfet @30A, 12V June 28, 2016 08:01PM |
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Re: Heatbed mosfet @30A, 12V June 28, 2016 11:08PM |
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Re: Heatbed mosfet @30A, 12V June 28, 2016 11:48PM |
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Re: Heatbed mosfet @30A, 12V June 29, 2016 12:30AM |
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Re: Heatbed mosfet @30A, 12V June 29, 2016 12:49AM |
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Re: Heatbed mosfet @30A, 12V June 29, 2016 03:31AM |
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Re: Heatbed mosfet @30A, 12V June 29, 2016 08:48AM |
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A_Designs
so going by that chart, if I use 3 IRLB8743 mosfets in parallel with 10 awg multi-stranded wire, mount everything on heat sinks and cool the cabinet, it should be enough to prevent anything getting significantly warm? For attaching it to the heat bed, what about if I scrape off some of the silk screen covering the large copper traces at the bottom and solder the 10 awg cables to those?
Re: Heatbed mosfet @30A, 12V June 29, 2016 10:54AM |
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Re: Heatbed mosfet @30A, 12V June 29, 2016 11:17AM |
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Re: Heatbed mosfet @30A, 12V June 29, 2016 01:17PM |
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Re: Heatbed mosfet @30A, 12V June 29, 2016 01:42PM |
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Re: Heatbed mosfet @30A, 12V June 29, 2016 02:09PM |
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Re: Heatbed mosfet @30A, 12V July 12, 2016 08:09AM |
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