Replikeo Duet 0.6 in V- 24v input looking a little burnt.

I've been using a Replikeo Duet 0.6 a little bit now, with a regular, Ebay, adjustable LED power supply. For some reason, when moving the printer, the voltage dropped to around 16-18v, and I had to adjust it back up. I'm using the additional 5v attachment for the Duet, and the burnt (not melted) plastic is visible both on the output from the 5v attachment, and the input on the Duet. The + side of things isn't burnt. The voltage coming in to the 5v regulator reads 23.5-23.9v, and the same, -0.1 for the Duet's input.

I've got a 300mm heated bed, and a e3d Volcano, and 3 fans running off the board, and I first noticed the burn while running the heated bed & hot end at decent temperatures for PLA.

Needless to say, I'm not in a hurry to burn down my printer or apartment. Any advice on what I might be doing wrong?

I'm not certain but I believe the device on that little regulator board is just a 7805 linear voltage regulator. It's used to power the logic devices on the Duet board and isn't effected by your heaters, fans, etc so the timing of the smell was most likely coincidence.

Since the 7805 is a linear device, it regulates output voltage by converting unused energy into heat. In your case, regulating from 24-volts to 5 is a LOT to ask of a 7805. I have no idea how much current the Duet itself draws, but estimating 300ma the regulator would dissipate around 5 or 6 watts of heat.

Personally I'd recommend replacing the little regulator board with a switching type bucking converter, which is much more efficient. If you search on Ebay/Amazon or the like you can pick one up for a few dollars.

Edited 1 time(s). Last edit at 09/07/2016 11:58AM by w3drk.

Oh, there's not smell, just a plug that's very hot to the touch, and some obvious dark patches on the green, plastic output and input plug.

How to explain better. The 24-5v regulator has an input from the 24v PSU. Then it has an output, that goes straight in to the Duet's 24v input. The output, and the Duet's input are both blackened (slightly) in 2 places each, on the -v (black wire) side.

What I gather is happening, from what you're saying, is that the regulator board is struggling to drop 24v to 5v, and is overheating as a result. That heat is escaping through my (rather thick) output to input cables, causing the plugs to blacken. And if I was to simply remove the board, and find another way to get 5v (say some resistors, or a UBEC), I would eliminate the risk?

Quote
MortarArt
The 24-5v regulator has an input from the 24v PSU. Then it has an output, that goes straight in to the Duet's 24v input.

Just to clarify on that point, you mean the Duet's 5v input, correct?

If so than yes, a cheap 5v UBEC would certainly be a lot more efficient than a 7805--assuming it can accept 24v input. I'm pretty sure all the UBECs I used on my mini-quads specify 4s or 5s use, which theoretically would be only 21 volts. Something like this would certainly work: [www.ebay.com]

Nono. The regulator has a 24v input, and output. As well as a separate line for 5v output. The Duet has both a 24v and a 5v input. I have the PSU connected to the regulator, then the regulator's 24v and 5v output going into the respective parts of the Duet.

I thought my UBECs were rated to 6s, but I could be wrong. I'll have a look, before using them. Otherwise, I'm sure I can figure something out.

Thanks for your help, by the way.

Oh, so the regulator board is also used as a pass-through for the 24V power! So that's a different problem...if I were you I'd connect your heavy 24v power cables directly to the Duet and then feed the 5v regulator separately. There's really no need to pass all that current through those extra connections.

Oh, ok. That makes sense. Use the 5v regulator only as a 5v regulator?

And what if it's still overheating? What would be the signs?

Quote
w3drk
Oh, so the regulator board is also used as a pass-through for the 24V power! So that's a different problem...if I were you I'd connect your heavy 24v power cables directly to the Duet and then feed the 5v regulator separately. There's really no need to pass all that current through those extra connections.

Or use the onboard 5V regulator like most of us do there is a %V Enable jumper on the board JP9 IIRC but don't take my word for it!

Doug

Those little 7805s can run pretty hot, so if it's working OK I guess you could just see what happens. Do you have it fastened down to a metal surface to sink the heat away? I don't use one with my copy of the Duet 0.6--I just use the on-board bucking converter so I'm not familiar with how the external one mounts.

Edited 1 time(s). Last edit at 09/07/2016 12:42PM by w3drk.

Quote
w3drk
Those little 7805s can run pretty hot, so if it's working OK I guess you could just see what happens. Do you have it fastened down to a metal surface to sink the heat away? I don't use one with my copy of the Duet 0.6--I just use the on-board bucking converter so I'm not familiar with how the external one mounts.

There is a small 3 pin Connector above the Main V-IN connector and it just sits there with a set of V-in Passthru's for whatever is needed (Guess for the DUEX etc but the whole Reg Board can be junked and just enable the Onboard Buck converter as you say it works fine and in fact I dont recall that there is an external 5V in on the new boards but again I could be mistaken on that has I don't use the external reg anyway It went in the Junk Box?

Doug

Two issues I can think of::

1. If any of the terminal blocks looks burned or melted, this usually means that the screw in the terminal block is no longer tight. This happens easily you use stranded core wire in the terminal block without crimping the proper ferrules on the wire ends.

2. The 5V linear regulator is going to get very hot when given 24V input. Either add a heatsink to it, or ditch the linear regulator board and use the switching regulator on the Duet instead - but check that it it delivering 5V and not something higher, because I don't know whether Replikeo tests it.

---

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].

I think I'm going to try running off of the onboard regulator. The fact that Replikeo provide the additional unit, and that a few people have mentioned that they don't test it has made me wary, but I didn't come to the logical conclusion, that I too could test it!!

And this would make my wiring a lot simpler.

Edited 1 time(s). Last edit at 09/07/2016 11:52PM by MortarArt.

It is important to note that the only purpose to install an external 5V supply was to be compliant with european EMC regulation, as the on-board regulator was emitting too much EMC.
Most people don't care a lot about that, and it seems the on-board emission is not sufficiently high to creates troubles in your environment (no problem with TV, radio or other electronic). It is wise anyway to shield your electronic with metallic shield, also for fire safety.

So, you can use the on-board 5V regulator, if it works.

If using an external buck converter, while simple open buck converter are nice stuff (I use them for 12V fan supply), for the 5V I preferred the very rugged 5V converter automotive type. Their rating is so high that you will never see any heat and they are mechanically very well protected.
They are a bit more costly, but it is not much and the shipping is included.
As an example, this one: [www.ebay.com].
On e-bay, search "24V 25W step down converter".

Edited 2 time(s). Last edit at 09/08/2016 06:50AM by PRZ.

---

Pierre

- Safety [reprap.org]
- Embedded help system for Duet and RepRap Firmware [forums.reprap.org]
- Enclosed delta printers Lily [rouzeau.net] and Lily Big [rouzeau.net]
- OpenScad delta printer simulator [github.com]
- 3D printing on my site [www.rouzeau.net]

Well, I wired up a BEC just to be safe, and that works. It's a HobbyKing type with a heatsink, which is cold to the touch in operation.

Pretty happy though, to not use it, and to keep it as a backup, in case the EM interference ends up an issue. I do some analog video transmission and the like, so it might come up in future.

Ohhh, and thanks everyone for your help! This has been thoroughly explained and fixed.

Edited 1 time(s). Last edit at 09/09/2016 11:11AM by MortarArt.

Btw before reprappro decided on the linear regulator, they tried some off the shelf switching regulators and found that they couldn't meet the EMI regs using those either.

---

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].