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24V to 12 V buke converter for RAMPS

Posted by viren 
24V to 12 V buke converter for RAMPS
December 02, 2017 08:35AM
Old question but needs some expert advice....

I came understand that with Buke DC to DC converter I can reduce voltage to 12 V. Now after that I could remove that D1 on RAMPS, remove LED for heatbed indication (or increase the resister value) and change the PTC fuse to automobile one (Awesome!). Here are my doubts :
0. Will heating time of hot bed reduce significantly if I use 24 Volt?
1. Will E3D V6 hot end heater work on 24 Volt if I power up RAMPS without any modifications?
2. Will NEMA17 motor run without any problem and will I be able to upgrade to NEMA 23 if i want to? spinning smiley sticking its tongue out
3. Buke converter will reduce voltage from 24 V to 12 V. On some forum I read that reducing voltage will increase current so that power remains same. What will be implications on RAMPS and associated electronics due to this if I use buke converter.

The big idea here is to do minimum modifications for using available 24 Volt, 14.6 A SMPS for my ultimaker clone.
Re: 24V to 12 V buke converter for RAMPS
December 02, 2017 06:03PM
0) depends on bed resistance. If you use a pcb heater that is 12/24v switchable and switch it to 24v mode. no it will take same amount of time. If you power a standard 1.1ohm 12v bed with 24v yes, but it will use lots of amps (21amps!) and burn out ramps (use a external mosfet)
1) it needs a 24v heater cartage, or it will burn out
2) depend on the steppers. Current is the issue.most larger stepper need > 2 amp per coil, so wont work with pololu drivers. Steppers that work on 12v will work on 24v
3) a standard mega can not take 24v and must be powered from 6-12v (ie remove D1 and power it separately)

yes reducing voltage and keeping the same power needs higher amperage... important for heated bed and hotends to determine wire thickness. If was designed for 24v if you switch to 12v you need to check your wires are adequate to carry the additional current

fans also need to be 24v or they will burn out.
Re: 24V to 12 V buke converter for RAMPS
December 03, 2017 01:37AM
Dear Dust,

Many thanks for your guidance.

0. Clear. Action on my side : Use of external mosfet.
1. Clear. Action on my side : Use 12 V for E3D V6 heater or use Buke converter with higher wattage
2. Clear. Action on my side : Don't dream about NEMA 23 for 3D Printer. NEMA 17 would do fine with 12 V supply.
3. Clear. Action on my side : Remove D1. Power standard mega with 12 V or use Buke converter

Summary of actions : it boils down to usage of 12 V instead of 24 V if I want to be happy-go-lucky with first attempt in 3D printing arena. This is because except motor speed, I could not see any great advantage and as you have mentioned, I will use 24 V for powering up heat bead with external mosfet.

One last question thoughconfused smiley : what is the purpose/significance of of 5A and 11A written on RAMPS and what should be Watt of 24 to 12 V Step down buke converter ?

Edited 1 time(s). Last edit at 12/03/2017 02:46AM by viren.
Re: 24V to 12 V buke converter for RAMPS
December 03, 2017 03:14AM
5amp and 11amp are the design speck of the circuits at 12v (more or less)

11amp side is just connected to the heated bed. 5amp is for everything else.

they also have separate fuses.

I suspect you mean buck converter, or perhaps its not english?

Output needs to be 12v 5amp for everything excluding heated bed.
NB 11amp circuit still needs 12v power to switch the on board bed mosfet that drives the exteral mosfet, but since its only turning on the external mosfet it doesn't use much current.
24v is fed into the external mosfet board for the heated bed.
Re: 24V to 12 V buke converter for RAMPS
December 03, 2017 03:34AM
yep...buck converter (sorry spell monster at play ...lol). Which Buck converter should I use ? Can you provide some link for buying or specification as I am not sure about how much watt is enough...in fact I just know that buck converter steps down, that's it. Rest of the part is dark to me.

update : you mentioned that 5A for everything else at 12V which means 12x5 = 60 Watt buck converter or may be slightly high should work.

As I understand... Everything else = Stepper motors + Hot End + Hot End Fans (you may add here).

Please check my understanding...

Edited 1 time(s). Last edit at 12/03/2017 03:38AM by viren.
Re: 24V to 12 V buke converter for RAMPS
December 03, 2017 03:38AM
Dust already said what you'd need, but don't forget the efficiency of the buck converter. ( rule of thumb is 80% )
12V x 5A = 60W output power, but 60W /0.8 ( eff. ) = 75W input.
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