Smoke came out from the psu cable

I using this cable which is supplied from the ATX psu. Yoday i found out that
During print if the heat bed and hotend are activated simultaneously,
the wires getting very hot and smoke came out of the insulator smell like pvc burning.
I stop the print immediately. Question is which gage of wires i need to replace to prevent
it from burning. I guess 4 wires with 22awg as supplied is not enough to
handle current requires to power both hotend and heatbed.

Edited 1 time(s). Last edit at 05/06/2014 12:35PM by Chaisaeng.

Even if you are just using +12V supply form the ATX unit then you need the larger multi-way plugged in as well. This has two +12V connections in it as well and multiple grounds. It will spread the load current over more wires and connectors.

You could up the gauge of the wiring to something more like the wire used to go into the Duet but if you aren't going to use the multi-way then I'd go direct from the PSU to the Duet and miss out the distribution board altogether.

Quote
bobtidey
Even if you are just using +12V supply form the ATX unit then you need the larger multi-way plugged in as well. This has two +12V connections in it as well and multiple grounds. It will spread the load current over more wires and connectors.

You could up the gauge of the wiring to something more like the wire used to go into the Duet but if you aren't going to use the multi-way then I'd go direct from the PSU to the Duet and miss out the distribution board altogether.

I see, as i change my psu to 12 350w i have the same wire and connectors from my broken atx psu
That i plug into the 4 pin connector on the power board. My question. If i just double the number
of wires on to each pin on the connector and plug on to the power board, would it resolve the wire heating problem?

Having more cable area means less resistance and heat, and that heat is "spread out" over more cable, so that will fix that. You need to be careful with the connectors/screw terminals though, since that's a likely spot for some contact resistance and overheating.

As you have swapped the PSU I would say you want to abandon the 4 pin connector altogether and wire with at least twice as much conductor area directly into the Duet. If you just increase the wire and retain the 4 pin connector you will still be stressing that type of connector with more current per pin than is comfortable. The pwer distribution pcb is not doing anything of value if you are not using the ATX connectors.

Chaisaeng, what kind of PSU are you using? I guess not an ATX PSU? Is it something like this: [www.ebay.co.uk]

If it is, you don't even need to use the ATX Power PCB. Just wire the white 2-core cable directly from the PSU to the Duet.

Ian
RepRapPro tech support

Quote
droftarts
Chaisaeng, what kind of PSU are you using? I guess not an ATX PSU? Is it something like this: [www.ebay.co.uk]

If it is, you don't even need to use the ATX Power PCB. Just wire the white 2-core cable directly from the PSU to the Duet.

Ian
RepRapPro tech support

I Printed this thing [www.thingiverse.com] and fit it on my PSU.
I like the idea not to chnage anything of powering the ormerod from this thing by retaining the same connector on both end.
Not knowing that it'd have heating the wires. First attemp i do an 3 hours print but did not notice ant thing but I'm most of the time monitore the print.
Untill i see the smoke come out in the later print

I just visit molec site regarding maximum rating of this connector. It seem the standard
ATX wires the i used will not handle current requires by ormerod.

With the standard Ormerod + ATX there are 4 circuits for the 12V supply (2 in the 4 pin connector and 2 in the multi-way) so the capacity is fine even allowing for less than perfect sharing of the current.

When you use just 1 4 way connector then the load on the wire gauge as supplied is definitely excesive and the load on the connector does not leave much safety margin.

Apart from overheating you should also consider the voltage drop in the cable under load. There can be a significant drop in the 12V as supplied to the heaters when they turn on just due to the wiring from the supply to the Duet. That slows down the heat up time and limits the maximum temperature that can be achieved. This cable drop was significant even with the original wiring and will be worse using just 1 4 pin connector with original wires.

You should definitely double the size of the wires if retaining the 4 pin connector. Ideally I would increase it more or use more wires and either change the connector type or use 2 of them in parallel.

Quote
Chaisaeng
I just visit molec site regarding maximum rating of this connector. It seem the standard
ATX wires the i used will not handle current requires by ormerod.

While it is more time and effort, I would suggest changing to a more suitable connector that is rated for at least 25A, and using much thicker cable.

I used this one [uk.farnell.com]
With its mating plug [uk.farnell.com]

It is 20A per contact, but is 4-way so by paralleling 2 pairs of contacts it will handle up to 40A. It is also easy to connect & disconnect and is mechanically strong.

If your cable does not need to be too flexible you could use 30A house wiring cable. Auto parts stores usually carry more flexible high-current cables.

Dave
(#106)

I happened to have 16AWG silicone wires lying around in my RC Box which I did not look in to it for ages
These wires are using to connect the motor that derive the RC car's wheels to the speed controller.
I guess with 13A per circuits on the molex connector if i using these 16 awg wires then 2 circuit should handle up to
26 A thought there may be no or very little margin for the over current that may occurs in the power area. I think
I will give it a try.

Edited 1 time(s). Last edit at 05/07/2014 10:47AM by Chaisaeng.

Any one known the white wires size (Awg) connect the power board to the duet board?

It's twin-core 20A speaker cable.

Ian
RepRapPro tech support

The speaker cable supplied by RRP gets noticeably warm and has a significant voltage drop. I would not recommend it for the whole cable run to the PSU. I used the second thickest speaker cable that Maplin sells. It is too thick to fit the Duet terminal block so I used a piece of chocolate block connector to switch to a short piece of 30A ring main cable just outside the Duet enclosure.

---

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].

Use this to find the resistance of whatever length of wire you are going to use
[www.cirris.com]

Don't forget that the length to enter into the calculator is twice the length of wire connected (because total path is the length of -ve wire plus length of +ve wire)

That will show, for example that for a PSU connected via 15 feet of wire, the resistance of 30 feet of 16AWG is 0.12ohm. So at a current of 20 amps it will drop (20 X .12) 2.4 volts - a 12 volt power supply will be supplying less than 10 volts to the heaters and the wire will be dissipating nearly 50 watts of energy. Doubling the wires will halve the resistance, but that's still over a volt and 25 watts lost.

Dave
(#106)

I did the calculation. The plan is to use 16 awg on 2 circuits with the length as short as 8 inches one way
Calculation include the white wires connect duet to the power distribution board by assume that the white wires is 2.5mm in diameter
which roughly = awg 10 the length of the white wire is around 8 inches one way totally i assume to be awg 10 32 inch long.
The voltage drop on 12 v with load 30 A is .092 V so voltage at load will be 11.908 which is around 0.8% drop on the load side.
My Psu Currently dial up to 12.5V so it should may be compensate to 12 V at the load site should be suffice, I guess.

My duet got really burned today the white speaker cable got to hot and melted some parts of the board, do not have time to investigate it right now.
I will order a new duet right away but I really have to find out what can be done different to avoid this in the future.
This happened when i tried to go up to 120 with the bed for a big abs print i normally stay at 100.
I'm using the original power supply.

Quote
Joar107
My duet got really burned today the white speaker cable got to hot and melted some parts of the board, do not have time to investigate it right now.
I will order a new duet right away but I really have to find out what can be done different to avoid this in the future.
This happened when i tried to go up to 120 with the bed for a big abs print i normally stay at 100.
I'm using the original power supply.

I'm not printing ABS yet but will do it soon. I have a using a 12 V LED psu and test heating the bed to 120 C and the hot end to 220 C for an hour
What i notice is the white wire getting really worm but stll not to the point that can melt the duet connector or the power distribution board.
I have the supplied crimps on the wire using a connector crimping plier so i guess this must be the cause of problem if you put the wire directly
in to the connector. I plan to increase the size of the wire connect to the duet to a bigger gage to avoid the problem overheating of the wire

Quote
Joar107
My duet got really burned today the white speaker cable got to hot and melted some parts of the board, do not have time to investigate it right now.
I will order a new duet right away but I really have to find out what can be done different to avoid this in the future.
This happened when i tried to go up to 120 with the bed for a big abs print i normally stay at 100.
I'm using the original power supply.

The most likely cause was a loose terminal block screw. These should be re-tightened every week or so if you are not using crimped ferrules on the wires. With luck the board is repairable - or remove the terminal block and solder the wires direct. Terminal blocks that have the screw in direct contact with the wire are unsuitable for use with raw stranded cable - the ones with a spring leaf under the screw are better for that application, or the type that clamp the wire under a washer.

Dave
(#106)

I have these wires in my RC box which causing me confusing abot the wire gauge.
Any one know abot this. The wire i bought ages ago was Astro Flight 16 GA is it a 16 AWG?

Quote
Chaisaeng
I have these wires in my RC box which causing me confusing abot the wire gauge.
Any one know abot this. The wire i bought ages ago was Astro Flight 16 GA is it a 16 AWG?
[attachment 32401 image.jpg]

Strip off a small bit of insulation and measure the total diameter with callipers. As far as I am aware there are only two wire gauge standards - AWG and SWG (American Wire Gauge and Standard Wire Gauge).

16SWG is about 1.6mm diameter and 16AWG is about 1.3mm diameter - so if your wire is 16SWG it will be better in any case. 16AWG is only suitable for short runs at the current drawn by the Ormerod.

Dave
(#106)

Quote
dmould

Quote
Joar107
My duet got really burned today the white speaker cable got to hot and melted some parts of the board, do not have time to investigate it right now.
I will order a new duet right away but I really have to find out what can be done different to avoid this in the future.
This happened when i tried to go up to 120 with the bed for a big abs print i normally stay at 100.
I'm using the original power supply.

The most likely cause was a loose terminal block screw. These should be re-tightened every week or so if you are not using crimped ferrules on the wires. With luck the board is repairable - or remove the terminal block and solder the wires direct. Terminal blocks that have the screw in direct contact with the wire are unsuitable for use with raw stranded cable - the ones with a spring leaf under the screw are better for that application, or the type that clamp the wire under a washer.

Dave
(#106)

Yes its still works I have attached the cables direct know after removed the melted block and so far it looks good I havent tried printing yet but it heats up as it should.
I did order an extra duet so the next time i mess up I have a backup ordered the expansion board as well
/Joar