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RAMPS 1.4 on 12V; replace D2 with a 12V zener?

Posted by HugoW 
RAMPS 1.4 on 12V; replace D2 with a 12V zener?
April 02, 2017 04:09AM
Hi,

I am going to run my RAMPS 1.4 set-up on 24V, I read the tutorials / seen the youtube who-tos. But I have an idea. I need to remove D2 from the RAMPS board because that feeds the feeding voltage, in this case 24V, to the Arduio MEGA underneath. 24V being too much, leave out D2 and give the MEGA it's own power source. OK. But if I loose 12V over D2, there is 12V (or there about) left for the Arduino to run on, I think. I just need to get a rough idea of the currents flowing there, min and max. I'm pretty sure it will be less than 1A, so a 12V 1A zener should work, but if the minimum current is too low I am afraid the Zener wont open.

Please share your thoughts,
Cheers,

Hugo
Re: RAMPS 1.4 on 12V; replace D2 with a 12V zener?
April 02, 2017 05:51AM
Arduino Mega/RAMPS takes about 90mA. You need to add to that the LCD backlight current if you have an LCD display, which could be anything up to about 80mA but is probably nearer 50mA for a 12864 display. So you don't need to worry about the minimum current for the Zener, OTOH a single 1W Zener would overheat because the power dissipation would be around 1.1W even with no LCD. Maybe you could use two 6.8V zeners in series. Even better would be three 5.1V zeners in series, because that would reduce the Mega input voltage to around 9V, which would help prevent the voltage regulator overheating.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: RAMPS 1.4 on 12V; replace D2 with a 12V zener?
April 02, 2017 06:37AM
OK, good suggestion, in that case a 15V 5W zener (1N5352B ) would do the trick. That is only one diode, direct replacement for the D2, 300mA capable. Onto the shopping list!

Hugo

Edited 1 time(s). Last edit at 04/02/2017 06:37AM by HugoW.
Re: RAMPS 1.4 on 12V; replace D2 with a 12V zener?
April 02, 2017 09:16AM
Wouldn't it be easier to power the stepper drivers separately with 24V and keep the rest at 12V? There are often capacitors on Ramps only rated 16V and some ceramic caps without any labeling.

Also I'm not sure if you are right about D2 feeding the voltage to the Mega board. IMHO it's D1 under the X-driver port which does that job. Make sure the 5W diode fits in there without overheating.

It's Years ago when I played with zeners last time, but don't they need a series resistor to work properly?

Edited 1 time(s). Last edit at 04/02/2017 09:20AM by o_lampe.
Re: RAMPS 1.4 on 12V; replace D2 with a 12V zener?
April 02, 2017 11:25AM
There are no ceramic caps on my RAMPS, just the 9 elcos which are all rated 35V. Looking at the schematic I can also not find any other caps. Where should I look?

I think the combo if Chinees silkscreening, my bad eyesight and bad lighting in the evening might have had some bad effects... It is indeed D1 I need to replace, the one under the X-driver.

Well, they need some sort of load to loose the remaining voltage over. So I can either put a balast resistor in series with a 9.1V Zener, Zener to ground, and the Arduino parrallel to the Zener, or I can put the 15V Zener in series with the Arduino, Arduino to ground, which makes the Arduino the balast. This is why I was asking for a minimum current of the Arduino MEGA, as there needs to be a minimum current flow for the Zener to open / work.

Thanks for correcting the D1 / D2 mistake.

Cheers,

Hugo
Re: RAMPS 1.4 on 12V; replace D2 with a 12V zener?
April 03, 2017 02:50AM
You may be right about the ceramic caps. I might have confused that with the caps on the drivers. ( haven't seen my RAMPS for a while, 'cause it works flawless )
Re: RAMPS 1.4 on 12V; replace D2 with a 12V zener?
April 03, 2017 02:46PM
I've just checked the RAMPS 1.4 schematic and the only ceramic cap I see is C2. As its value is only 100nF, it's almost certainly rated at 50V or more.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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