RAMPS 1.4 and external mosfets

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

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.

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.

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?

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.

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

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

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.

Great.

Thank you for the advice.

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

I tried to add an external mosfet board to my Ramps 1.4 board, but it didn't work for me. I have a 12v S360-30 PS with three outputs.

This is what I did. I originally had two of the outputs from the PS go to the inputs of the Ramps 1.4 board, one to the 11a side and one to the 5a side. I took the third output from the PS and hooked it up to the external mosfet board on its PS connectors. Correct polarity on all of the outputs. I hooked the heatbed up to the external mosfet board on its heatbed connectors. I hooked up the sensor wires from the external mosfet board to the D8 connector on the Ramps 1.4 board where the heatbed wires were connected.

The external mosfet got really hot and the the heat bed didn't heat up. I surely messed up the wiring.

Should I have shared the PS output that went to the 11A on the Ramps board, with the input on the external mosfet board instead of using that third output?

Edited 1 time(s). Last edit at 03/07/2024 07:30PM by ChileMaker.

@ChileMaker

The wiring diagram and description sound correct

Perhaps your bed is just to to massive a current draw for the mosfet?

Edited 1 time(s). Last edit at 03/08/2024 01:51AM by Dust.

Hi Dust.

I forgot to mention some of those particulars. The board is a genuine Prusa MK52 that is 210x250 and is 12v. It is not a Prusa printer but a Mendel variant that I upgraded over time. I had been just using PLA and having the bed go to 60c. Before I added the mosfet board, I had no trouble getting the heatbed to 75c, but it wouldn't get past that before the alarm sounded due to its taking too long to heat. I wanted to try some ABS I had so that's why I added the mosfet board. I have no problem getting the hotend to temperature so it can extrude the ABS. My Prusa MK3x has no trouble getting the bed to temperature for ABS, but it is a 24v system.

When powered up, the mosfet board's little red led is lit. When I attempt to heat up the bed, the little blue led lights. The red led for the MK52 I hooked up and tried another mosfet board (same type) and the same thing happened.

Edited 3 time(s). Last edit at 03/08/2024 06:53AM by ChileMaker.

@ChileMaker

how about some pictures of the mosfet modules and where all the wires actually go?

the MK52 is about 1ohm so pulls about 12 amps, most external mosfets should be able to do that easily

This doesn't really make sense from the description...

The connection form D8 to the module is just the on/off signal, it has practically no current. It normally goes to a optocoupler so is just turning on two LEDs (the blue one and one you cant see)

Edited 1 time(s). Last edit at 03/08/2024 07:04AM by Dust.

Hi Dust.

Here are some pictures of the wiring.

1. The wiring at the module
2. The wire going to the headbed
3. The connector for the sensor at D8.
4. The power connector at the Ramps for the 11a.
5. Alternative wiring. I went ahead and tried a pass through on the power wiring
where I go from the PS to the external mosfet board and then to the Ramps at the 11a.
This diagram isn't a Ramps board, but it best shows the pass through I am talking about.
I do have a power connection to the 5a side of the Ramps, I never removed that.
6. Close up of one of the Mosfet modules I have.

Edited 1 time(s). Last edit at 03/08/2024 08:08AM by ChileMaker.

I wanted to add that with the external mosfet board attached, I can't get the heated bed to go over 33c even if I set the target temperature to 60c.

With the setup without the mosfet board, I have no trouble reaching 60c. It is not fast but it does not time out.

Edited 1 time(s). Last edit at 03/09/2024 12:01AM by ChileMaker.