What is ideal power supply for 24V 360W heatbed

Hi all,
have question. I have Ramps connected to 24V 360W heatbed through SSR. Does it take difference if I use 24V 30A vs 24V 15A or vs 24V 20A ?

A bed of those spec uses 15amps

now sadly we live in a society of thieves lairs and con artists... so it is very rare to find a power supply that is labelled as 15amps that can actually provide a sustained 15amps

So you need something > 15amp..

Exactly how much depends on just how much the supplier is lying

I would go with 30amp, as it has most chance of working and if its over spec that is not an issue, current is pulled not pushed,

OK lets look.

P = I * E ( Power equals Current multiplied by Voltage
so
Power divided by Voltage equals Current

360 / 24 = 15 amps

This means that if you have a 15 amp Power Supply you can only power the Hot Bed.
If you include a 40 watt Hot-end this come to a total of 400 watts

400 / 24 = 16.667 amps

This means that the minimum size power supply is a 480 watt this will supply 2 Hot-ends with 40 watt left for the Remaining equipment attached.

I ment if heatbed could be heated faster with higher power supply. From ramps goes 12V to SSR and it can hold easily 30A from 24V supply, so does it
affect the heating time of bed?

Depending on how your PID settings are configured and with a current upgrade alone no, but with the voltage doubling then twice a fast.

I have a 3D Printer running on a 12V 20 amp 250 watt with one Hot-end, and it has been running on this power supply for 1 year now.

And you say how can you do this!

So the PWM, or Pulse Width Modulation is a powerful way of controlling circuits Switching power supplies utilizing this technology over classic power supplies,
reaching up to 60% power saving! Using this to power your Hot-Bed are much more energy efficient.

If we take this into consideration, and stating that we only save 50% then half of 360 watt hot bed is only a 180 watts.

Power divided by Voltage equals Current

180 / 24 = 7.5 amps

And this is how we are able to power a 3D Printer with a 250 watt power supply. And yes it will take about twice a long to heat up the Hotbed.

Edited 7 time(s). Last edit at 09/09/2017 06:13AM by Roberts_Clif.

I believe you

But I need simply answer like, yes with 30A heating time will be shorter or It will be the same because heatbed cannot cunsume more power than 15A.

Only by increasing the voltage will you be able to decrease the hotbed heating time, Or by changing the settings controlling the software PWM Hot-bed.

Current has a set rate of flow into a into a resistance load, the voltage potential allows the current to flow a higher rate into a load.

simply speaking increasing the current rating does not make it flow at higher rate. only increasing the voltage can make current change to a higher rate.

Edited 1 time(s). Last edit at 09/09/2017 06:42AM by Roberts_Clif.

Ok, so it seems that 24V 20A can be good with its reserve.

Yes this is my assessment. If you ever watched Home Improvement, Tim The Tool Man Taylor said MORE POWER!, however more power can lead to disastrous results.

When you have the correct power requirements if a short occurs the breaker/fuse blows saving the equipment.
When you have overpowered the equipment the same short occurs everything melts down, fire occurs the house burns to the ground.

Safety features in the firmware help stop this from happening, though many have not installed, simply refuse to use them or modified them so they don't work.

Edited 7 time(s). Last edit at 09/09/2017 07:29AM by Roberts_Clif.

Quote
Arnold
Ok, so it seems that 24V 20A can be good with its reserve.

If you find the heating rate too slow at 24V, then a typical 24V supply can be turned up to about 28V. On a 28V supply your bed heater will take 360 * (28/24)^2 watts. A 24V 20A PSU is good for 480W if it is a good one (Meanwell PSUs are supposed to be good), less if it is a cheap one.

I don't think you have said how large the bed is, so I can't comment on whether 360W will be enough. In most cases I recommend a heater power of 0.4W per sq cm.

For large printers I also recommend using good electronics and a single PSU instead of two PSUs and an SSR to work around just one of the limitations of budget electronics; but that is another story.

Edited 2 time(s). Last edit at 09/09/2017 11:19AM by dc42.

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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].