Amps for 12v to 24v conversion

Hi, I have an Anycubic Delta Plus with a 240mm diameter hotbed. The heat up for temps above 60-C with 12v can be very slow. I was about to buy a 110v heated bed, but looking at the bottom of the current one it is a dual 12v/24v bed with the three pads. Pad 1 is +12v, pad 2 and 3 are soldered together for ground. I have a 24v 15A Power Supply (PS) here so thought I'd give that a try first and save some bucks and a 3+week wait from Asia.

Doing some searching it looks like I can un-bridge 2 and 3 and connect 24v to them -- via a relay, of course.

I can't measure the Resistance of the current bed as it is 2-hours in to 7-hour print. It looks to be drawing 11A for everything at the moment at 12v. And, after the print has completed, I cannot check the wiring diagram on the bottom as there is an insulating layer glued to the bottom of the bed.

Question :
Will the 15A at 24v PS be enough or do I need to get a 20A or better PS?

Thanks

Edited 1 time(s). Last edit at 03/05/2019 10:50AM by StlLooking.

Its a common misconception that switching to 24v helps heat up times on a 12/24v bed.

the bed is wired as two resistances in parallel for 12v mode and the two resistances in series for 24v mode.

What does this mean?

well lets just presume that each resistance is 2.2 ohms.

2.2 in parallel with 2.2 is 1.1 ohms put 12v through it this is 131 watts of heating power.
now 2.2 in series with 2.2 is 4.4 ohms. put 24 volt through that and its also 131 watts of heating power.

Ie they will heat up the same

What is different. 24v uses less current than 12v for the same wattage, so the wires can be thinner. If your wires are to thin for the high current at 12v then you will notice an improvement at 24volts.

now in this eg the bed uses 10.9 amps in 12v mode and 5.45 amps in 24v mode.

so your 15amp 24v power supply is fine.

And before you ask, you can technically plug 24v into your bed configured to 12v
This would up your wattage to 523!!, BUT would also increase your current to 22amps! (more than most on board mosfets can handle and way more than your supply can provide)

I would just use a separate power supply that is 2-3 volts higher (12 + 2 volt or 24 +2 volts) and set the bed at 12v for 14v supply or 24v for a 26v supply. Its makes a huge difference.
Dont just adjust your normal 12v supply, unless you check that everything else using 12v can take 14v (ramps can't)

Edited 4 time(s). Last edit at 03/05/2019 11:23AM by Dust.

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Dust
What does this mean?
... snip
they will heat up the same

OK, that makes sense, thanks for taking the time to explain that.

I have an MKS-Gen-L board in it that has 12v/24v input. Am I correct in thinking that when 24v is applied to the Gen-L board it drops it down to 12v/5v/3.3v (or whatever) for the control-logic and just uses the higher voltage direct to the hot-end and bed?

Can I adjust the stock Anycubic-supplied 12v/20A PS up to 14v then?

I accept full responsibility for any magic smoke escaping as a result of anything and everything I do.

Edited 1 time(s). Last edit at 03/05/2019 12:40PM by StlLooking.

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StlLooking

Quote
Dust
What does this mean?
... snip
they will heat up the same

...
Can I adjust the stock Anycubic-supplied 12v/20A PS up to 14v then?

I accept full responsibility for any magic smoke escaping as a result of anything and everything I do.

I always push to 14.5V as there is NO HARM but benefits ! Besides, the 12V regulator on the board will really "regulate" and provide a good 12V !

---

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

If the power supply is adjustable it will have a small variable resister that you can get to without opening it up.

I don't think the Gen-L does generate any 12v, (but I don't have one) I would expect that what ever you feed into it you get on the bed, hotends and fans pins directly. (just like a ramps)

But yes it generates the 5v

Edited 1 time(s). Last edit at 03/05/2019 01:05PM by Dust.

Quote
Dust
what ever you feed into it you get on the bed, hotends and fans pins directly. (just like a ramps)

Thanks again.

I was getting excited there, until I read "fans." How well will the cheap 12v fans last with 14v?

I guess I will just try and if I burn fans out they are cheap to replace.

I have not opened up the PS that came with the delta, but the 24v one has the adjustable-pot. Watch for rising smoke signals.

OK, no smoke but more noise from the fans. There was a 30% decrease in waiting time.

12v -- 23-C to 60-C it took 140-seconds.
14v -- 23-C to 60-C it took 98-seconds.

I think I will drill a screwdriver-hole in the front cover of the PS so I can tweak the volts up when I am running filament that needs bed temps higher than the 45-C I run PLA at.

Thanks for your help.

What is under your heated bed?

If you can add in a reflector (cardboard with alu tape on it) under the heated bed, it will reflect any heat trying to escape down back up again.
Make sure not to short the bed out on it though.

Edited 1 time(s). Last edit at 03/05/2019 03:34PM by Dust.

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Dust
What is under your heated bed?

It came with some ceramic insulation fiberboard taped to it with a single big piece of Kapton tape, so not a lot of heat goes downwards.

It's printing now and fans are not that bad. I have a 4" fan that blows air across everything under the build plate. I will stick a thermocouple in there tomorrow before starting and see how warm it is getting.

I guess the hot-end heater element is also getting the 14v so might eat those up faster too. Good reason to go for the screwdriver hole and only use 14v when doing PETG/ABS.

btw the fans are normally such low current devices you can add resistor in series to slow them down/drop the voltage without issues.

Then you could just leave it...

I would re tune your hotend pid for the new voltage also.. or it will tend to over shoot.

The variable resistors on power supplies are not designed to be changed all the time... It will wear out very quickly.

Quote
StlLooking

Quote
Dust
what ever you feed into it you get on the bed, hotends and fans pins directly. (just like a ramps)

Thanks again.

I was getting excited there, until I read "fans." How well will the cheap 12v fans last with 14v?

I guess I will just try and if I burn fans out they are cheap to replace.

I have not opened up the PS that came with the delta, but the 24v one has the adjustable-pot. Watch for rising smoke signals.

Don't worry for the fans, they can cool themselves

The waiting time you save, it's your life time ! More valuable than the fan life time isn't ?

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Gah. Nevermind.

Edited 2 time(s). Last edit at 03/06/2019 10:27AM by SupraGuy.