12 and 24 PSU
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Guys, I need help.
I set up a prusa i3 model printer with Duet2 wifi and a 12v PSU. Everything works perfectly. Now I want to change the Hot end to a REVO that works with 24v (a friend gifted me). Can I use a 24v PSU only for this Hot end ? Fans and Heat bed continue with 12v. And how to connect with Duet to have both PSU? I appreciate any help -
@aego, yes you can. Connect the 24V power supply to the same ground as the 12V supply and feed the 24V+ lead to the hot end (REVO). The ground/negative lead of the hot end will still go to the Duet (ie unchanged).
The Duet switches the low side (ground/negative) to activate the heater and will be able to control the hot end. -
@jens55 Excellent, that's all I needed. Thank you so much for the huge help.
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@aegoHi Jeans55, Just one more thing. Does the hot end positive connect in duet (heater) ?
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@aego I'd be a little bit nervous of doing that.
What I think @jens55 is advocating is to connect the -ve (or 0V) of both power supplies together (or conenct them both to teh same 0V input on the duet), then connect the +ve wire from the 24V power supply to the Revo, and connect teh other wire of the revo heater to the -ve side of teh duet extruder output (leaving teh +ve siude of eth duet extruder connection unconnected).
Do not connect the +24V directly to the Duet board anywhere.
The thing I'm nervous of is that while this works as far as the transistor doing the switching on the board is concerned, it puts a reverse 12V (or 24V, if the 24V supply comes on before the 12V does) on the extruder heat LED on the board. Typically you don't want to put that much reverse voltage on a LED. I think you'll fail it, and deliberately failing any components on a board is something I try and avoid.
However, if it fails as a short, then you'll be putting the 12V across R67 (4k7) (at least on the revision of the schematic I'm looking at), so I think there will only be a few milliamps flowing and you probably get away with it. Howeevr, I'm not sure what that will do to voltages elsewhere on the board (I haven't followed it any further on the schematic).
On teh other hand, if you use the bed connections, that has a diode in to protect against this case (though that depends upon whether you're using that connection for the bed).
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@achrn said in 12 and 24 PSU:
What I think @jens55 is advocating is to connect the -ve (or 0V) of both power supplies together (or conenct them both to teh same 0V input on the duet), then connect the +ve wire from the 24V power supply to the Revo, and connect teh other wire of the revo heater to the -ve side of teh duet extruder output (leaving teh +ve siude of eth duet extruder connection unconnected).
Correct
Do not connect the +24V directly to the Duet board anywhere.
Also correct
The thing I'm nervous of is that while this works as far as the transistor doing the switching on the board is concerned, it puts a reverse 12V (or 24V, if the 24V supply comes on before the 12V does) on the extruder heat LED on the board. Typically you don't want to put that much reverse voltage on a LED. I think you'll fail it, and deliberately failing any components on a board is something I try and avoid.
I must admit that I did not look at the schematics and I think it is best if the Duet team answers to the possibility of 'reverse' voltage or any other possible issues.
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@aego said in 12 and 24 PSU:
@aegoHi Jeans55, Just one more thing. Does the hot end positive connect in duet (heater) ?
I do not understand the question - I am suggesting the +24V lead from the PSU goes to one wire of the REVO and the other wire from the REVO goes to the Duet pin that is on the negative side.
As @achrn points out, the +24V does not touch the Duet at all (and this is important!)
It is also important that the wire from the REVO going to the Duet ONLY EVER connects to the negative terminal of the extruder heater on the Duet. I do not know how the board is marked but this is vital so be sure you got it right! One way of finding the right terminal (if the pcb marking isn't clear) would be to measure voltage between terminal pin and ground - if the heater is off then you will see 12V on either pin in the current configuration but if the heater is on, you should see a very low voltage on one of the pins - that would be the ground pin that you need to connect to.I DO NOT GUARANTEE TE CORRECTNESS OF WHAT I AM SAYING HERE. IF YOU ARE NOT ABSOLUTELY POSITIVE OF THE CORRECTNESS OF WHAT YOU ARE ABOUT TO DO, DON'T DO IT !!!!
Consider my ramblings as something to point you into the (hopefully) right direction, you are totally responsible for verifying that what I am saying is actually correct! -
@jens55 Ok, i will be careful. Thank you for all