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RAMPS 1.4 and external mosfets

Posted by darryn 
RAMPS 1.4 and external mosfets
October 05, 2018 03:15PM
Hi All,

I am planning on switching to a RAMPS board in the next week or so.
I have a question regarding powering the board when using 2 external mosfets (one for the heat bed and one for the extruder).
If using 2 mosfets how do I power the board? Do I need to connect power to both input blocks (5A and 11A), or just one? If just one, then the 5A or the 11A?

TIA
Re: RAMPS 1.4 and external mosfets
October 05, 2018 08:55PM
You need power to both the 5A and the 11A with 12v, just like normal.

The external bed mosfet expects to see 12v on D8 to turn on, which comes from the 11A side (its will just use a tiny fraction of the current)
The external hotend mosfet expects to see 12v on D10 to turn on, which comes from the 5 A side (a external mosfet here is really unneeded, unless your trying to extrude steel!!)

Edited 1 time(s). Last edit at 10/05/2018 08:56PM by Dust.
Re: RAMPS 1.4 and external mosfets
October 06, 2018 02:51PM
Thank you for this.

Seeing as I am intending to run 2 mosfets, and a PSU only has 3 connections for outputs, could I run the outputs as follows.

1 output to mosfet for heated bed
1 output to mosfet for hot ehnd
1 output to the 11A input on RAMPS and then jumper this to the 5A input. So basically the output of the PSU would go to the input of the 11A and then the input of the 5A. Hopefully that makes sense.

Or sould I rather run a second set of wires from one of the outputs of the PSU?

TIA.
Re: RAMPS 1.4 and external mosfets
October 08, 2018 06:26PM
When deciding on how to use the wires (and connectors) from the PSU, then you need to be aware of how many amps is used at each unit you are connecting to.

How many amps can your PSU deliver at 12V?
This is usually shown on the side of the PSU, if it is a PC PSU.

Will your Heat bed be a standard 20x20cm Heat bed?

Is your hot-end a standard hot-end?
With a 25W or 40W heater cartridge?


Generally speaking:
Typically each wire/pin from a PC ATX PSU, there is a max of 10Amp, but some (newer/cheaper) PSU's use thinner wires, so it is recommended to have a lower load on each wire/pin.

Some 12V connectors from a PC PSU will have several yellow (and several black) wires going to one connector. Especially for the heat-bed it is wise to ensure several yellow (and several black) wires are used. So the Amp load on each wire will be much less that 10Amp per wire yellow/black wire set.

How many yellow wires does each of your connectors have?
Re: RAMPS 1.4 and external mosfets
October 10, 2018 02:38AM
Thank you for the reply.

The Meanwell type PSU that I am using is rated at 30A.

The heat bed is 220mmX220mm.
It will be a standard hot end, an E3D bowden clone to be exact.
Not sure of the wattage of the heater cartirdge.

Just to be clear, I will be powering the heat bed and hot end off 2 separate mosfets (each connected directly to the PSU by 14AWG silicone wire).
My question is about the power connectors on the RAMPS board. Seeing that I am not going to be powering the hot end and heated bed off the RAMPS, I am not sure how I should be powering the RAMPS board.
I know that there is a 5A and 11A input on the RAMPS. Do I need to connect power to both inputs if using separate mosfets? If I only need to power 1, then which one?

Hopefully that makes sense.
Re: RAMPS 1.4 and external mosfets
October 10, 2018 04:16AM
am I invisible?

Quote
Dust, from 5 days ago
You need power to both the 5A and the 11A with 12v, just like normal.

The external bed mosfet expects to see 12v on D8 to turn on, which comes from the 11A side (its will just use a tiny fraction of the current)
The external hotend mosfet expects to see 12v on D10 to turn on, which comes from the 5 A side
Re: RAMPS 1.4 and external mosfets
October 10, 2018 04:28AM
No, not at all.
I did thank you for your post. Please see a 'copy and paste'

"Thank you for this.

Seeing as I am intending to run 2 mosfets, and a PSU only has 3 connections for outputs, could I run the outputs as follows.

1 output to mosfet for heated bed
1 output to mosfet for hot ehnd
1 output to the 11A input on RAMPS and then jumper this to the 5A input. So basically the output of the PSU would go to the input of the 11A and then the input of the 5A. Hopefully that makes sense.

Or sould I rather run a second set of wires from one of the outputs of the PSU?"

Thank you once again for your input.


Quote
Dust
am I invisible?

Quote
Dust, from 5 days ago
You need power to both the 5A and the 11A with 12v, just like normal.

The external bed mosfet expects to see 12v on D8 to turn on, which comes from the 11A side (its will just use a tiny fraction of the current)
The external hotend mosfet expects to see 12v on D10 to turn on, which comes from the 5 A side
Re: RAMPS 1.4 and external mosfets
October 10, 2018 04:53AM
Quote
darryn
1 output to mosfet for heated bed
1 output to mosfet for hot end
Yes thats fine

but for the ramps run a decent wire from the power supply to the ramps 5amp line (this still powers the steppers motors, stepper drivers,the mega and fans) so still using a few amps.Then connect a small wire from the + 5amp line to the + 11amp line. Its only needs enough current to turn the bed mosfet on.

You don't need a second wire from -5 amp to -11amp as they are already connected on the ramps board.

NB do not solder the wires going into the the ramps power plugs, Use stranded wire only, or if you really want to solder them, solder the wires directly to the plug pins under the board or remove the plugs

Edited 3 time(s). Last edit at 10/10/2018 05:12AM by Dust.
Re: RAMPS 1.4 and external mosfets
October 10, 2018 07:22AM
Great.

Thank you for the advice.

The wire running from the PSU to the RAMPS board will be 14AWG silicone wire.
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