24 volt PS upgrade

Hey all, suppliers make it sound like a 24 volt power supply is interchangeable with a 12 volt. Quicker heatup times and stepper tourqe. Will my Melzi board handle this. I do have a 12v/24v heat bed. Thanks.

Been doing some reading. I think I'm going to use the 24volt ps for my heatbed only. Just want to use the 24 volt heatbed feature to speed up heating times. Thanks.

You know, that was completely stupid. I need the control board to regulate the heatbed. I guess a voltage divider for the pc board power. Anyone built a divider and if so what resistance and wattage resistors did you use. Please don't make me use Ohm's Law. It hurts the brain.

Three words...Solid State Relay. Get the bed current completely off the board, especially if you want more power. The screw terminals for the bed power are a known weak spot of the Melzi. Especially if you want more power, do the bed power right before it gives you an excuse to upgrade your electronics too.

I tried to connect a 24V 15A PS to the the 11A power in connectors on RAMPS 1.4 - but my PS switches off - if i go back to my 15V 7A everything works fine. Is there something i forgot ? The 11A connectors are used for heat bed only ??

Hey Boring, something like this?
[www.ebay.com]

Perhaps you have a non standard RAMPS board that links the 5A and 11A inputs together? You can check that with a multimeter.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

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

I don't speak Mandarin to make sense of that diagram, but it's not what I'm familiar with. The four (apparently) output posts are unusual, though the diagram appears they're to be wired in parallel, probably to get sufficient capacity in the screw terminals.

What I'm about to install on mine is a Crydom D1D40. There are (dramatically) cheaper ones available, but I've read posts from people who've said they went with the cheap ones and would be doing a Crydom next time. Apparently you get what you pay for on these, as the cheap ones are reported to have a propensity to melt or fail in such a way as to go to uncontrolled full power.

Beds heating up faster with 24v is a myth! *(if your using one of these 12/24v pcb heaters)

with 24v bed the resistance is (edit: doubled ) quadrupled so the wattage remains the same (ie the rate at wich it heats up)

If you do find it heats up quicker than on 12v. your 12v supply had insusficient current or your wires were not thick enough.

You can of course get 24v beds that are higher wattage, which do heat up faster, by design.

Now in saying that the steppers will be faster on 24v vs 12v.

Putting more voltage into a 12v bed say 13.5 volt, will heat it up much faster. Putting 24v into a 12v bed however will require 20amps! and will probbaly kill your mosfet. use a SSR and a big power supply (but I still woundnt recomend this)

Edited 4 time(s). Last edit at 05/14/2015 01:22AM by Dust.

Quote
Dust
Beds heating up faster with 24v is a myth! *(if your using one of these 12/24v pcb heaters)

with 24v bed the resistance is doubled ...

You seriously need to check your math. Resistance is multiplied by four when these PCB heatbeds are configured for 24V operation. That's what keeps the wattage constant, since we are doubling the voltage, and power is proportional to the square of voltage, and inversely proportional to resistance (W = V^2/R).

Umm...V=IR, so I=V/R. P=IV, so P=V^2/R. Twice the resistance would keep the current the same on both configurations, but a 24V bed will deliver more power than a 12V bed if it has less than four times the resistance. Your analysis of a 12V bed at 24V is correct...It will be a monster, and absolutely require an SSR.

Edited 1 time(s). Last edit at 05/14/2015 12:14AM by IMBoring25.

Very informative discussion. Thanks all.

Quote
IMBoring25
Umm...V=IR, so I=V/R. P=IV, so P=V^2/R. ...

Indeed...

I don't understand the rolleyes. It's exactly the same thing you wrote except I showed work from the standard forms of the fundamental equations involved. I was writing it at the same time you were (mine might have gone in first if the site hadn't lagged) and it wasn't worth deleting.

Here is the least expensive Crydom SSR I've found.

[www.zoro.com]

Your right the resistance quadurples... not sure where I got doubles from but the orriginal statement is still correct, the power is the same

heated beds are two resitors in series or parallel depending on 12v/24v hookup

12v is in parallel, 24v is in series

Cant remember actul values but let say its 2.2 Ω per 'resistor'

so 12v with resistors in parallel
1/(1/2.2Ω + 1/2.2Ω ) = 1.1 Ω

and 24v with resistors in series
2.2Ω+2.2Ω = 4.4 Ω

now on to wattage, as it looks like I was not clear...

for 12v

i = v/r where v = 12 and r = 1.1 Ω
= 10.9090909 amps
p = i^2*r where i = 10.9090909 and r = 1.1
= 130.90 (rounded)

for 24v

i = v/r where v = 24 and r = 4.4 Ω
= 5.45454545 amps
p = i^2*r where i = 5.45454545 and r = 4.4
= 130.90 (rounded)

Ie they are the same!

Or you if you want you can use p=v^2/r

for 12v its still 12^2 / 1.1 = 130.90 (rounded)
and 24v its still 24^2 / 4.4 = 130.90 (rounded)

Edited 11 time(s). Last edit at 05/14/2015 01:37AM by Dust.

Quote
elwood127
Here is the least expensive Crydom SSR I've found.

[www.zoro.com]

If we add up the costs for a 24V PSU, the SSR you posted above, the SSR heatsink and whatever else you'll need to change in your current setup to get your 24V mod going, we'll get something like $100, plus you are dramatically increasing the power dissipation in case of a short circuit, hence the associated risks of a fire and/or severe burns.

There are safer and much cheaper ways to decrease the heat up times for a 12V PCB heatbed, for example, adding a 2mm cork sheet ($1) to the bottom side of the PCB heatbed, making sure your PCB heatbed is correctly oriented (copper traces should be topside), increasing wire gauge of all wires in the heatbed circuit (hence decreasing losses), and eventually using a MOSFET with a lower RDSon (IRLB8743, a $1 mod).

As for increasing stepper torque, this is irrelevant for 3D printers, most NEMA 17 steppers provide more than enough torque @ 12V, it's only really relevant for CNC applications and most of the time these use larger NEMA 23 or NEMA 34 steppers or servos.