Power cord fuse for duet 2 wifi

Danal

@daxzero said in Power cord fuse for duet 2 wifi:

i used 240V in my country, so the fuse is using 10A should be fine?

5 should be fine.

DocTrucker

There's a good guide on the wiki for sizing the minimum power requirement for the power supply.

https://duet3d.dozuki.com/Wiki/Choosing_the_power_supply

I've killed two cheap 12V PSUs that were around 360W. Both of those were fan failures that probably could have been fixed by fan replacements but I had lost faith in the quality of parts inside the power supply by that point.

Gone for Mean Well now (fitted today) but they're not cheap!

Edit: The loading for comparison was 5 steppers (around 2ohm, 1.33-1.68A), 30W hotend, 100W bed, duet1 v0.6, hotend & part cooling fan. Heavy use since last August, but no overnight or multiple day builds.

dc42

@daxzero said in Power cord fuse for duet 2 wifi:

i used 240V in my country, so the fuse is using 10A should be fine?

Unless your printer has a large AC mains voltage bed heater, 3A would be more suitable for the AC power fuse.

A Former User

@Phaedrux want to used AC with solid state.

A Former User

@Danal why took 5A so low compare to 10A?

A Former User

@dc42 why 3A? so low..

oliof

3A at 240V is 720 Watts. The Duet 2 Wifi can take 24V at 15A (fuse limit), which is 360 Watts. So you are still at double the load the internal fuse would need to blow if you have a 3A fuse on your 240v side.

See http://www.ohmslawcalculator.com/ohms-law-calculator.

A Former User

@oliof sorry.. im not sure your meaning. So you mean 3A for 240V is still double the load?

oliof

If you add a 3A fuse on the 240V side, ~~it will trigger when the system behind that pulls 720 Watts.~~ it will trigger when the input to the power supply exceeds 720 Watts.

Since the duet Wifi's VIN fuse already triggers when the load is 360 Watts, (when run on 24V), this means the fuse on the 240V side will not trigger before the board fuse, but will give you protection in case there is a PSU failure (or the duet fails in a spectacular way making it's fuse ineffective).

Danal

Again, fuses are about protecting wiring, not circuits or components. We've all drifted off into calculating the Duet, motor, heater total demand, or matching to the fuses on the Duet, or similar.

It is true that the input side of the Power Supply needs to be LARGE enough to support the normal load with plenty of margin... and... perhaps equally importantly, or even more importantly, it really to be SMALL enough to protect the wire feeding the Power Supply (the cord).

Therefore:

Assuming 18AWG input cord, no larger than 10A, to properly protect the wire.
Assuming a 240V 400W supply that is 80% efficient, no smaller than 2.08 amps.

Given 'standard' fuse sizes, 3 or 5 would be fine 220V 400W.

Danal

@daxzero Your various questions about "Why so Small" are all answered by the fundamental Ohm's Law that Volts * Amps = Watts. And Watts are the thing that runs motors and heaters and so forth.

Therefore, if your printer is going to draw everything it can from a 400Watt supply, we find:

400W / 220V = about 1.6 amps.

Since power supplies are not perfectly efficient, we say the output may only be 80% of the input.

1.6 / 0.8 = about 2 amps.

That's why people are saying "3" and "5" and things like that.

Danal

@oliof said in Power cord fuse for duet 2 wifi:

If you add a 3A fuse on the 240V side, it will trigger when the ~~system behind that pulls 720 Watts~~.
If you add a 3A fuse on the 240V side, it will trigger when the input to the power supply exceeds 720 Watts.

Pedantic, I know...

A Former User

if i using power supply 500W / 240V = about 2A, then i should used 3A for this... is that correct?

oliof

@Danal thanks for improving my description! We are talking electricity where I think pedantry is absolutely appropriate.

Danal

@daxzero said in Power cord fuse for duet 2 wifi:

if i using power supply 500W / 240V = about 2A, then i should used 3A for this... is that correct?

Yes, you want a little margin, and 3 is still well within protecting the wiring (10).

DocTrucker

You've not factored in the AC heater you want to use yet? That will be on top of the PSU requirement.

Don't forget if your PSU is 500W it will be consuming more like 625W on the mains side. Your AC heater will be added on top of the 625W.

Edit: Unless by 'power supply' you mean the total power consumption of your system...