Ormerod1 PSU mods to print ABS

Hi forum. I've modded a new PSU to print ABS. I've taken some photos and have some advice for people which has been figured out during the course of trying to get ABS going. Thought I'd post here as it may be useful to others.

Firstly the original PSU cannot work. The regulation for the required current is out of spec (see manufacturers ratings and ATX PSU standard).

The PSU was replaced with a modded ANTEC unit (have pics, hopefully I can add them here). The Antec unit has a potentiometer under the power inlet connector (VR1). I turned this fully clockwise to get 12.5V.

Secondly, standard PSU wire cannot actually deliver 30 amps of currect without a significant voltage drop. Physics shows us that the resistance of a wire is related to the square of its diameter (because the area of a circle, discovered by Pythagoras, is pi*r*r). I removed all the original 12V wires and replaced them with some solar panel wire I had lying around.

It may be beyond peoples ability to hack the PSU. If you don't feel confident doing this then stop reading now. There are dangerous voltages in side a PSU and they are present even when you've disconnected the power cord.

Essentially what I did was unsolder the original wires, then drilled a large hole for the new wires. The 12V bypassed the original Ormerod power control box and went directly to the Duet (essentially because there was a significant voltage drop that occured by going through that unit).

Also a piece of cardboard was inserted under the PSU board to provide electrical insulation just in case my poor soldering made contact with the case.

The unit is now in operation and successfully printing ABS. However, a further mod was required to get the power from the Duet PCB to the hot bed. Again some solar panel wire was used and soldered to the Duet in the provided empty connector pads on the PCB. The wires are cable tied to the top of the Z axis and make a big loop down to the bed. I have a picture somewhere which I'll post.

I can now get 120 degrees and beyond from the hot bed.

I also discovered that hairspray, while goodish, is no match for acetone-ABS slurry on tape mentioned in these forums.

I did pretty much a lot of work on the topic and am now printing abs the easy way:

[forums.reprap.org]

With Ormerod 2, we have reverted to using a dedicated 12V 20A PSU, as also used with our Mendel printer. This makes the power supply wiring more complex, but it's a more consistent power supply, and holds up better when there is a high current demand. It also has an adjuster, which allows the voltage to be increased up to around 14V, which is the maximum I would recommend for the heated bed, or it will draw too much current.

Ian
RepRapPro tech support

There is a decent guide for modding the supplied Alpine PSU to provide a bit higher voltage and more stable +12V rail. I did and go much improved voltage stability under load, essentially no voltage drop even with all heaters running. I set it at 13.2V because somewhere around 13.4-13.5V the PSU detects the overvoltage and shuts down and I wanted a bit of margin. Have used that for a couple months now with no issues.

Is the +12V rail on the Antec supply more stable when under load? It seems most ATX PSU's will have unstable voltages on +12V when the +5V rail is essentially unloaded.

I was using a Corsair CX430M atx psu for a while, and that kept the 12V supply up a lot better than the Alpine did. But no voltage adjustment. I'm now using a 12V 25A psu with voltage adjustment.

---

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].

There are several 12V PSUs designed for LED lighting or CCTV that are reasonably priced. e.g. [www.ebay.co.uk] (but there are many more). A dedicated 12V PSU is probably better than a PC PSU which will be designed to control the 3.3 and 5V supplies more tightly than the 12V.

Dave

This is just a quick post as I have to head out to lunch at resto (very important).

The first pic show the beer cartons used to shield the printer from drafts (one panel removed). This requires drinking beer :-)

Second pic shows the x-carriage for my PCB router being printed in ABS.

Looks like many people have come to the same conclusion.

The large wires from the Duet to the bed overcome the need for a high voltage. Essentially the ribbon cable cannot work because the diameter of the wire is too small leading to a high resistance and therefore voltage drop.

The regulation on the Antec is pretty good. There are various sites on the web that review PSUs. They are no holds barred and will poo-poo any unit which can't hold regulation within spec. This Antec unit, while not top of the line, does a reasonable job. It's about 75-80% efficient. It costs less than $5AU more than the original.

The glass mirror on the bed comes from Ikea in a pack of 4 200x200 for $AU9.95.

The clips are from OfficeWorks. 50 for $AU4.99.

The fan duct is a modded version from ThingiVerse. Essentially just added some support in the exhaust so it would print correctly.

I've started reprinting some of the hot end components in ABS to withstand ABS temps.

I don't necessarily think the ribbon cable is too small in terms of cable area. Each wire is tiny, but there's lots of them. Fixing the PSU voltage stability issues and "overvolting" just a little bit enables my bed to reach 132°C, and ABS printing temperatures (I run at 100-110°C) in reasonable time. With the stock PSU, no amount of cabling could ever fix it.

WIth the stock cabling and both heaters running, there is about half a volt of drop between the PSU and the Duet (which includes the PSU cabling, the power board, and the cable to the Duet), and another half a volt out to the bed. I would guess more of that is in the various connectors than the actual cabling. It would be interesting to see what voltages you get at various parts of the system when under load, with that PSU and the humongous bed cables.

Quote
melbcycle
Looks like many people have come to the same conclusion.

Which conclusion is that, btw?

I agree about the ribbon cable being OK.

The power drop to the heated bed in original Ormerod 1 is made up of a number of components in decreasing order of significance.

Power regulation of +12V of ATX PSU under ~10A load
Drop in ATX to Duet cabling
Drop in ribbon cable
Drop in Duet switch control

With the original components you can get a loss of about 1.3V in total leading to about 11V typically at the heated bed which is marginal for high temperature (ABS) use and leads to long warm up times.

The power regulation of the ATX is a major contributor followed by the PS to Duet cabling, The Duet drop is very low due to a 5mOhm FET Switch.

The ribbon load is spread over 12 wires. Each wire has about 160 mOhm resistance. Giving a resistance of about 13 mOhm. Doubled for there and back this should give a drop of about 0.26V. I see about 0.35 volt which is consistent.

The load on the cable is also well within the wire and connector rating for < 30C rise even if the power were on all the time.

Getting the PSU regulation right (either by mods or replacement) together with lowering cable resistance to Duet can lower the drop from 1.3V to about 0.45V which is then largely down to the ribbon.

If the +12V can then be additionally adjusted up a bit then you can get 12.5 or 13V out at the bed which gives a lot more power than the default.

Of course even lower Duet to bed cabling could be used to give a bit more benefit, but one needs to tackle the major components first.

Try the method i post first...

Hi Bob,

What you say is mostly correct. However the 11 volts at the bed is incorrect.

The ATX PSU version 2.2 specification states that a correctly functioning PSU shall deliver 12 volts within 5%. That is to say a PSU which delivers 11.4 volts is functioning correctly.

Taking the 1.3 volt drop you've measured, which I also measured, that can leave people with 10.1 volts on their heater bed. I suspect there are indeed people getting that voltage too.

The voltage drop of 1.3 volts represent more than 10% of all power consumed by the Ormerod. That combined with the knowledge that a PSU is entitled to deliver 11.4 volts represents fully unacceptable design.

I haven't checked the credentials of the power FET used for switching, however, I do have experience with solar FET switches which have similar currents. 10 milliohm for p-channel switches is normal. N-channel devices are typically 10 times better. In solar applications where 20 amps is switched with 10 milliohms will burn 4 watts of power. Anything much higher in terms of on resistance will obviously burn more and require heat sinking. Also the voltage drop would be about 0.2 volt.

Here is a web page that shows the thermal imaging of the Duet power FET. [blog.think3dprint3d.com] They measured a power dissipation of 1.3 watts at 20 amps. All in all the Duet itself seems OK to me. Ah ok a re-read of your post shows 5 milliohm for the FET. That's pretty good.

The giant cable is indeed soldered directly to the bed. The connectors are indeed an issue. This is also typical in solar stuff.

The ribbon cable dissipates 20*20*0.013 = 5watts. That is to say a piece of wire consumes more power than the power FET switch, and the actual measurement is 7 watts. Far too much (a tad under 2% of all power is consumed by this piece of wire). Just as a side note, in solar and automotive crimping is used. That's because the voltage drop across a connector could well see 10 watts of power or more dissipated. That sort of power can cause connectord to heatup to a point where solder may become viscous (a claim made to me by a solar salesman). I checked this with Anderson Power products who sent me an email confirming that soldered connections need to be crimped as well to gain UL certification. i.e. pins soldered into a PCB may not be acceptable for UL purposes. I have noticed, when hacking away at the Antec PSU, that the wires are crimped and soldered to the PCB making it quite difficult to remove them.

The giant wire is low tech, easy to solder in (possibly a bit harder at the Duet end) and resolves the connects/ribbon cable issue. Not sure it looks that good though. Still if you're going to cover this machine with beer cartons, hey :-)

I have not checked the LED power supply specifications people have spoken about. From what I can tell these units are not manufactured to any recognised standard apart from electric safety.

I am not trying to defend the original unmodded version just that the mods I made but still retaining the ribbon work OK.

The 11V at the bed under load is what I measured on my machine before making any mods. I did say typically. Mine had an unloaded output of 12.3V. It is not untypical for this to be a bit on the high side unloaded, although obviously some supplies may be lower and still be within nominal spec.

The current to the bed is typically 10A not 20A so power in the ribbon is about 2.6W (10 * 10 * 2 * 0.013).

Each pin on the connector is rated to 1.5A and 12 are in parallel so the load is not excessive.

The power lead into the Duet on the screw terminals is more of a concern and does need to be secure and maybe periodically checked. Having abandoned the original ATX wiring and distribution box I used 30A flex which I managed to crimp before inserting into the screw connectors.

Quote
melbcycle
...represents fully unacceptable design.

I think you're being unfairly harsh in saying that. The stock design works, even with ABS. I could get the bed no higher than 110°C, and going to 100°C took quite a while, but it printed ABS just fine. Sure, things can be improved power-wise, but the stock setup is by no means unusable. And many Ormerod users probably just print PLA anyway, so "max temperature" doesn't really matter.

jstck, the point is that the Ormerod 1 kit was advertised to be capable of printing ABS, but this was NOT true with the stock ATX PSU. It could very well extrude ABS, but that's pointless if the extruded material doesn't stick to the build platform. I remember struggling with the heated bed to get it to 110°C, but that was nearly impossible with the ATX PSU. At first I tried to cover the heated bed with alu foil, but once I took it off again, the temperature dropped to ~93°C within a few minutes, which caused all my ABS prints to warp. Exchanging the PSU with a better one, a 12V 300W LED PSU, solved these issues for me.

But anyway, I don't want to start flaming all over again and IMHO it doesn't make sense to argue about this since RRP correctly decided to deliver Ormerod 2 kits with adjustable PSUs (Ian, good move, really!).

I was able to heat the bed to more than 115C using the supplied Alpine PSU, although it took about 20 minutes.

---

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 could get to 110 with the original Ormerod, but it took a heck of a long time (well over 30 minutes) and the heater was on continuously so I used to print ABS with the bed at 100. Having said that, the supplied PSU was DOA so I used a PSU of the same rating but different make that I had lying around. It was not ideal but ABS printing was certainly possible. I now have a beefy LED PSU that I've cranked up to 14V and can get and maintain 110 in a reasonable time.

Dave

Quote
melbcycle
Hi forum. I've modded a new PSU to print ABS. I've taken some photos and have some advice for people which has been figured out during the course of trying to get ABS going. Thought I'd post here as it may be useful to others.

Firstly the original PSU cannot work. The regulation for the required current is out of spec (see manufacturers ratings and ATX PSU standard).

The PSU was replaced with a modded ANTEC unit (have pics, hopefully I can add them here). The Antec unit has a potentiometer under the power inlet connector (VR1). I turned this fully clockwise to get 12.5V.

Secondly, standard PSU wire cannot actually deliver 30 amps of currect without a significant voltage drop. Physics shows us that the resistance of a wire is related to the square of its diameter (because the area of a circle, discovered by Pythagoras, is pi*r*r). I removed all the original 12V wires and replaced them with some solar kits wire I had lying around.

It may be beyond peoples ability to hack the PSU. If you don't feel confident doing this then stop reading now. There are dangerous voltages in side a PSU and they are present even when you've disconnected the power cord.

Essentially what I did was unsolder the original wires, then drilled a large hole for the new wires. The 12V bypassed the original Ormerod power control box and went directly to the Duet (essentially because there was a significant voltage drop that occured by going through that unit).

Also a piece of cardboard was inserted under the PSU board to provide electrical insulation just in case my poor soldering made contact with the case.

The unit is now in operation and successfully printing ABS. However, a further mod was required to get the power from the Duet PCB to the hot bed. Again some solar panel wire was used and soldered to the Duet in the provided empty connector pads on the PCB. The wires are cable tied to the top of the Z axis and make a big loop down to the bed. I have a picture somewhere which I'll post.

I can now get 120 degrees and beyond from the hot bed.

I also discovered that hairspray, while goodish, is no match for acetone-ABS slurry on tape mentioned in these forums.

You have done great job..I do need to build similar hot bed so I will follow your post information..

Edited 1 time(s). Last edit at 09/27/2014 02:30AM by BlaineFabels.