12V vs 24V Power supply

I have the option of using a 12V 650Watt ATX supply to power my 3DP or to use a 24V industrial power supply.

I am powering several stepper motors, 9 in fact. a 40watt hotend, and a 360 watt Heated bed, 400mm diameter.

If I use the 12V supply, it can supply up to 52A on the 12V line, but it also has 5V and 3.3V lines which is nice. I must tie several of the 12V lines together so that it can handle the 30A load which then plug into a XT60 connector to a 40A Fuse to a SSR for the Heated bed. Makes it easy to power my controller board (CRAMPS)

Option 2:

Use a 24V probably 30A PSU, connect that to a screw terminal block first which will connect to a 24-12V converter and a 12V-5V converter. The 24V input will feed to a lower Amp SSR, (20A or so), since the bed will only be 15A instead of 30A.


I hear 24V will heat the heated bed much faster, but the higher voltage means more current is pushed which can be very dangerous if I'm handling it. On the other hand, the 12V supply will heat the bed up slower, but is safer? I don't know if soldering several high gauge wires together to hold that much amperage is all that much safer, but I don't need any down converters either.

Any help, advice or suggestion would be very much appreciated. Thanks.

24V means you can run your steppers faster with less risk of dropped steps, which IMHO is the biggest advantage.

Assuming you're using switching converters to produce 12V and 5V rails, don't double-convert the 5V rail. Take the 5V converter's input directly from the 24V supply. If you're using a 24V supply, definitely do not downconvert that to 12V to run your heater, that's just a pointless inefficiency; use a heater that's rated for an appropriate power level at your supply (24V) voltage.

The rate at which the bed heats is a function of how much power you feed it (and it's thermal properties). Whether you run it at 12V 30A or 24V 15A, that's still 360W and the same heat-up time either way. A 24V bed will heat faster only if you give it more power. For example, a 1R heater at 24V (576W) will heat faster than a 0.5R heater at 12V (288W) but a 2R heater at 24V is back to 288W again.

If your heated bed is rated as "12V 360W" then it has 0.4R resistance. If you plug it into 24V, it will draw 1440W and may not survive that.

Note that the term "SSR" usually refers to an opto-isolated triac which is suitable only for switching AC (once on, it stays on until the current drops to zero). If you want to control a large lowish-voltage DC load electronically, you typically use a big MOSFET.

24V and half the current is probably safer than 12V and twice the current, if only because the fire risk due to thermal load on cables and connectors is reduced. At least do appropriate calculations so that your wires and connectors are properly-sized!

Edited 1 time(s). Last edit at 11/05/2014 11:30PM by polyglot.

Thanks for the reply! Actually the 24V bed will be 400W, 1.44 ohms, And I found out the board I will be using (CRAMPS will have 20A connectors so no need for a big mosfet there).

Good points on not double down converting. I wasn't going to, but its good to make that clear.

It probably makes the most sense to go with the 24V Power Supply.

I would not rely on the manufacturer stating you can drive 20A on their board. Those connectors if rated for 20A will get very hot if driven at 20A for long periods of time. You may have a fire risk.

---

My Personal Blog. Build blog.
[engineerd3d.ddns.net]

Modicum V1 sold on e-bay user jaguarking11

It will be driven at 17A, still a fire risk in your opinion?

Honestly it depends on the connection being made, and the connector quality. If the board is manufactured with quality parts, it will be fine. If not I would look at upgrading the connector and beefing up the traces.

---

My Personal Blog. Build blog.
[engineerd3d.ddns.net]

Modicum V1 sold on e-bay user jaguarking11

I'll probably still use a DC-DC SSR, I have a very big fear of a fire starting and melting my expensive electronics.