Ramps 1.4 Diode

Morning all. Please forgive me if this has been asked before but I cannot find an answer

I have a CTC printer but I am making my own (I find making stuff myself somewhat rewarding)
Don't have all the items yet but have started with the brains. I will be using a Arduino mega2560 and a RAMPS 1.4 (from the bay) and a smart controller with LCD but I have concerns about the ramps, inperlicular the Diode's
D2 is in place but no D1. I have read this (http://reprap.org/wiki/RAMPS_1.4) but I’m a little confused

It says
" D1 should only be installed if the 5A rail is powered by 12V. It can be omitted and the Arduino will be powered from USB. You will want D1 installed if you add components to print without a PC. To reiterate, D1 MUST be omitted if you are powering the 5A rail by more than 12V, or the power is not absolutely clean, otherwise you may damage your ramps. "


I plane to run both boards from a converted PC power supply

My ? is do I need to install D1? If so can anyone tell me the value please (D2 is fitted with the value face down)
I have 4001 and 4007 but I think it may need a 4004

Can someone please advise me as to whether it should be fitted or not and if fitted the value?

Thanks for looking

D1 is the 12v link from the ramps to the mega. It provides power to the mega when the USB cable is not connected

It must be removed if you use more than 12v on the 5amp circuit as the standard mega cannot take more than 12v.

If you intend to print without a computer and are running 12v, you need it.

Its a 1N4004

Edited 2 time(s). Last edit at 01/14/2016 10:00PM by Dust.

Thanks for the reply.
I take it its still safe to connect my pc with the ramps powerd up

If you like, you can unsolder D2 and use it for D1 replacement. Be aware, that you won't have reverse polarity protection anymore!
Do at your own risk
-Olaf

It is safe. Its exactly as if you had usb and power in the dc jack of the mega, which is fine

Long boring discussion here if you want to read it [forum.arduino.cc]

Thanks
Just been surfing and found a 750w pc power supply and the 12v rail is 37a at a bargain price would this be suitable ?

With such a powerful PC PSU you can even skip the D1 Mod. Just use the12V and 5V rail of the PSU ( without D1 )
5V goes to +/- pins of an unused servo terminal, 12V to the green plug.
You can even use the 5V standby rail of the PSU and switch the Ramps on/off by software. ( Not exactly sure how, better search the forum )
-Olaf

Providing 5v like that and having the usb connected is a issue. as they will be fractionally different ~5v and will fight.
The mega doesn’t have any way to separate these two supplies.

Also the unused servo 5v terminals are not connected to anything without the appropriate jumper.

I really would advise not to do this if you ever intend to use a USB cable. (unless you cut the appropriate 5v line on the megas USB )