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MOSFET module for PRUSA/RAMPS 1.4 board

Posted by Erkn 
MOSFET module for PRUSA/RAMPS 1.4 board
February 27, 2018 06:48PM

I would like to add a MOSFET module board to my ramps 1.4 board for a PRUSA printer. I have a 320 watt ATX power supply that I was considering using to power the heat bed (leaving the current PSU as is) but was hoping to get some feedback if I am on right path.

1) In terms of connecting wires, is the diagram I have attached correct?

2) Would using the ATX power supply for the heat bed be the preferred approach? versus using it for the RAMPS board and using the factory power supply for the heating bed? ... or just using the factory power supply and connect it to the module? I have not seen any wiring diagrams that show how to connect a MOSFET module for a dual powered RAMPS board.

3) Is there anything else that I should be doing? I have come across discussions on measuring the heat bed's resistance but I am not sure to what end.

Any pointers would be appreciated.

open | download - 2psu.jpg (30.8 KB)
Re: MOSFET module for PRUSA/RAMPS 1.4 board
March 15, 2018 06:50PM
Your RAMP board is different than mine so I won't comment on the connectors but it looks just fine. That's how you'd use a second PS for just the bed. My first 20A PS was BS (get it?). When heating the bed it would bog down (even the fan would) and only supply 10v or so to the bed. I replaced it with a single 30A PS which works awesomely. Personally I prefer a single PS that can power everything. You can meter the resistance of your bed and use that to determine the current. requirement at line voltage. If that requirement is satisfied by the RAMP capability then you shouldn't need to split it out. So, different options for you, but it's all science/math and budget.
Re: MOSFET module for PRUSA/RAMPS 1.4 board
March 16, 2018 01:54PM
Thanks for the reply.

I did jump ahead using 2 PSUs. I was worried that I had to somehow tie the 2 PSUs together to provide a common ground but it was necessary. Everything worked! ... but I burnt a my circuit breaker! I am talking about the one in my garage. I believe the problem was elsewhere but as a precaution, I dropped the second PSU. Fortunately the PSU that came with the kit had 3 12V taps. Two of which went to ramps 1.4 board. I used the 3rd to power the mosfet module and heat bed. It heats up slower but all seems good for now. The PSU is listed as 300 W so I guess I should be fine.

We well see.
Re: MOSFET module for PRUSA/RAMPS 1.4 board
March 16, 2018 02:13PM
If you intend to continue experimenting with this stuff you should consider getting an inexpensive multi-meter. With one, you can measure the voltage at the heat bed. I'm sure you'll find that it's under-voltage. If that's the case you're maxing the PS and stressing it, all while under-performing. A multi-meter would take all the guess work out of it. Good luck.
Re: MOSFET module for PRUSA/RAMPS 1.4 board
March 18, 2018 03:20AM
Hallo wie schlies ich das Mosfet zwischen Heitzbett an ?
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