External Mosfet board problem Hello, I have just installed an external mosfet board and appear to have wired it up correctly as nearly everything works. Everything except for the heated bed! The mosfet board shows a red led which I presume is power to the board. When I trigger the heater in the software, the Ramps LED lights up and I get 12V across D8. Should the mosfet board light a another LED when it is functioning? The signal wire to the mosfet board is apparently polarity sensitive but is NOT marked on the board. Swapping the polarity didn't make any difference. Has anyone had any experience with these mosfet board? Many thanks for any assistance, Regards, Doug https://reprap.org/forum/read.php?1,862460,862460#msg-862460 Fri, 09 Oct 2026 00:27:26 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?1,862460,862535#msg-862535 Re: External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862535#msg-862535 I swapped all the connectors from one board to the other and the same board failed to work.

Will have a close look at the board and will contact the supplier.

Thanks again for helping me through,

Cheers,
Doug]]> dggt6 General Fri, 15 Nov 2019 03:59:04 -0500 https://reprap.org/forum/read.php?1,862460,862532#msg-862532 Re: External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862532#msg-862532 I had the heated bed off and disconnected so I can turn the printer over but I connected it and the blue LED comes on and the bed heats!!
I swapped the control wires over and when I turned the hot end on the bed heated but when I turned the bed on, nothing. Perhaps my hot end has gone open or the wiring has disconnected????
Will investigate further......
Yes I still have power to the ramps board, the fans are working and the hotend and bed heating red LEDs light up when switched on.

Thanks for the suggestions,
Doug]]> dggt6 General Fri, 15 Nov 2019 03:41:20 -0500 https://reprap.org/forum/read.php?1,862460,862527#msg-862527 Re: External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862527#msg-862527
The signal wires are very very thin, are you 100% sure the wires are touching the metal in the D8 plugs? I put ferrules on mine to make sure...

With the module unplugged, put the signal wires on a 9v battery (either way) . The D2 led should light up.



Not sure were you are measuring, but if signal was getting to the optocoupler the d2 led would be on...

In your picture the optocoupler is on the right of the heatsink. On the left is the bridge rectifier

NB if this is a ramps you do still need 12v (bed power ie D8 power) plugged into the 12v 11amp side.]]> Dust General Fri, 15 Nov 2019 02:46:06 -0500 https://reprap.org/forum/read.php?1,862460,862525#msg-862525 Re: External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862525#msg-862525 dggt6 General Fri, 15 Nov 2019 01:30:03 -0500 https://reprap.org/forum/read.php?1,862460,862523#msg-862523 Re: External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862523#msg-862523 the R1 diode is lit.]]> dggt6 General Fri, 15 Nov 2019 01:15:22 -0500 https://reprap.org/forum/read.php?1,862460,862512#msg-862512 Re: External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862512#msg-862512
Thanks again,
Doug]]> dggt6 General Thu, 14 Nov 2019 19:17:51 -0500 https://reprap.org/forum/read.php?1,862460,862505#msg-862505 Re: External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862505#msg-862505
There is one marked D1 which DC-IN and one marked D2 which is Signal]]> Dust General Thu, 14 Nov 2019 18:11:09 -0500 https://reprap.org/forum/read.php?1,862460,862500#msg-862500 Re: External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862500#msg-862500 That diagram is almost identical to the one I followed except mine had the control lead swapped for polarity. I did try swapping the wires with no effect.

I only get the red LED on the mofset board.
I also get the red LED on the Ramps when the heater is activated. The printer then shuts down as the heater has not heated.

Perhaps I got 2 bad external boards?????

Cheers,
Doug]]> dggt6 General Thu, 14 Nov 2019 16:56:05 -0500 https://reprap.org/forum/read.php?1,862460,862466#msg-862466 Re: External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862466#msg-862466 easyeda.com]


The control wires do not have a polarity. They directly connect to a bridge rectifier
"You can put DC into a bridge rectifier. You don't have to worry about polarity, the bridge will route the voltage for you. You will loose about 1.4 volts through the bridge"

There are two leds on the mosfet board, one lights when control is active the other when it has DC-IN

Should be like this

]]> Dust General Thu, 14 Nov 2019 07:18:13 -0500 https://reprap.org/forum/read.php?1,862460,862460#msg-862460 External Mosfet board problem https://reprap.org/forum/read.php?1,862460,862460#msg-862460 I have just installed an external mosfet board and appear to have wired it up correctly as nearly everything works.
Everything except for the heated bed!
The mosfet board shows a red led which I presume is power to the board.
When I trigger the heater in the software, the Ramps LED lights up and I get 12V across D8.
Should the mosfet board light a another LED when it is functioning?
The signal wire to the mosfet board is apparently polarity sensitive but is NOT marked on the board.
Swapping the polarity didn't make any difference.

Has anyone had any experience with these mosfet board?

Many thanks for any assistance,
Regards,
Doug]]> dggt6 General Thu, 14 Nov 2019 06:40:01 -0500