Printrboard protection

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Printrboard protection

Postby plexus » 2012-May-Tue-12-May

Wondering if there is a way to protect the printrboard from PSU issues? I was thinking at the very least a fuse on the DC input to the board would be good. is there already a fuse on the board? if not, what would an appropriate rating be for the fuse?
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Re: Printrboard protection

Postby jr57k » 2012-May-Tue-13-May

Really good question. I'd start with a 20A or 25A. I believe there are two +12V positive and 2 GND lines on that 4 pin power connector and I have no idea how they are bridged or routed on the board as I don't have mine yet.
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Re: Printrboard protection

Postby plexus » 2012-May-Tue-14-May

I don't have my PB+ yet but I plan to get a decent 12V supply for it. not a computer supply but rather an industrial OEM switcher. I will run 12 AWG or so wire to the PB+ and put a fuse in-line. also likely wrap the wire around a torroid for some EMI suppression. I think this would be a better way to go than to use a cheap computer PSU. it might cost $50-80 for this kind of supply but I'd rather rest assured my supply is of good quality rather than cheap out and take a risk of losing a Printrboard.
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Re: Printrboard protection

Postby jr57k » 2012-May-Tue-15-May

I had a post up with some options in the $40US range. As for the computer PSU, I bought a better one than is shipped with my LC+ *when it does ship*. I've got no issue with using a computer PSU, they are very good switching power supplies and pump a lot of current out IF you know what to get. Given that the LC+ has the extra power connector my ONLY concern is that the traces on the controller board need to be sufficient to support the amount of current going through those connectors. I do a lot of R/C car stuff and pumping 25A @ 7.2V through a cheap-o Tamaya connector (simiar to the PSU 4 pin) is a sure fire way to melt some plastic. Something like a deans ultra plug (~50A) is totally the way to go but would require a board redesign. I put them on my quad copter and haven't looked back.
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Re: Printrboard protection

Postby plexus » 2012-May-Tue-15-May

jr57k wrote:I had a post up with some options in the $40US range. As for the computer PSU, I bought a better one than is shipped with my LC+ *when it does ship*. I've got no issue with using a computer PSU, they are very good switching power supplies and pump a lot of current out IF you know what to get. Given that the LC+ has the extra power connector my ONLY concern is that the traces on the controller board need to be sufficient to support the amount of current going through those connectors. I do a lot of R/C car stuff and pumping 25A @ 7.2V through a cheap-o Tamaya connector (simiar to the PSU 4 pin) is a sure fire way to melt some plastic. Something like a deans ultra plug (~50A) is totally the way to go but would require a board redesign. I put them on my quad copter and haven't looked back.


I do RC stuff too: helicopters. so i know about current issues. i was also thinking about the traces on the board but figured there is not much I can do about that and I would assume the board would be able to manage the current load its designed to drive. I am going to switch all my Deans connectors with XT60's on my helis. I guess I'll see what's needed once I get the PB+. I have no issues with doing what I can to ensure safe current transfer from the PSU to the PB. often people don't realize what the current capability of wire is and go over-board with wire gauge. on the other hand too, often in RC, as you know, the wire gauge and connectors are under-spec for the current demands.
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Re: Printrboard protection

Postby jr57k » 2012-May-Tue-16-May

Yeah, I ended up using something else on the my quadcopter, but heat shrink wrapped Deans seems to handle vibration just fine. Given that the printrbot isn't vibrating THAT much..... I figure something like that should be fine. It would add just a touch to the cost of the board, but it would eliminate any concern I have with burning out the connectors running that larger 8"x8" heatbed.
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Re: Printrboard protection

Postby plexus » 2012-May-Tue-17-May

jr57k wrote:Yeah, I ended up using something else on the my quadcopter, but heat shrink wrapped Deans seems to handle vibration just fine. Given that the printrbot isn't vibrating THAT much..... I figure something like that should be fine. It would add just a touch to the cost of the board, but it would eliminate any concern I have with burning out the connectors running that larger 8"x8" heatbed.


Once we get the PB we can examine the traces on the board. im hoping/assuming that they (the manufacturers) of it made the traces appropriate for the current demands but as you know from RC, there are many corners cut. its easy enough to evaluate and to correct. to evaluate i'd just touch the trace(s) and see if they get too warm. the fix is to solder a parallel piece of wire along the trace. also touch up the solder holding the DC input connectors as those are often done on wave soldering machines and are typically inadequate for high current. but... just have to wait for the PB to find all this out. we both know, from RC, how important accommodating current demand is for reliability and performance.
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Re: Printrboard protection

Postby CL1 » 2012-May-Tue-20-May

plexus wrote:Once we get the PB we can examine the traces on the board. im hoping/assuming that they (the manufacturers) of it made the traces appropriate for the current demands but as you know from RC, there are many corners cut. its easy enough to evaluate and to correct. to evaluate i'd just touch the trace(s) and see if they get too warm. the fix is to solder a parallel piece of wire along the trace. also touch up the solder holding the DC input connectors as those are often done on wave soldering machines and are typically inadequate for high current. but... just have to wait for the PB to find all this out. we both know, from RC, how important accommodating current demand is for reliability and performance.

You don't have to wait tofind out! Here's the Schematic: http://reprap.org/mediawiki/images/d/d5 ... tic150.png
And here's the Layout: http://reprap.org/wiki/File:Printrboard ... ard300.png
The actual EAGLE BRD and SCH files are also available. See Laine's GITHUB for the latest versions.

You can see that the traces are wide and the connections involved are very close to each other. Is there a real concern about the main connector? Yes, especially with the larger heatbed. But I think everyone may be making this much harder than it needs to be.

Have a look at the schematic and then confirm on the board traces that pins 3 and 4 of JP7 are tied directly to the main 12V input trace. And then realise that these two pins are what is supplying the heatbed! So providing a separate supply to THE WIRES INTENDED TO PLUG INTO these two pins will eliminate the huge current going through the main PrintrBoard connector!

It's so simple.We already have a two wire connector for the thermistor, which will remain plugged in directly to the printrboard JP7, pins one and two. The other 2 pin connector wired directly to the heatbed will now simply plug into a separate heatbed supply voltage instead of the printrBoard.

Scantronb correctly pointed out that I have made an error shown above in red. Replace the above with the corrected version just below:

Here's the corrected version: Cut the wires on the two pins of JP7 that are closest to the Power input connector (marked 3 and 4 of JP7 on the schematic), and re-connect them to a separate Heatbed power supply for a plus, or a separate molex floppy connector for the LC and original. Plug this new floppy connector into the available floppy of the original power supply. Be sure to cut the wires right at the JP7 connector, or plan some other way to insulate the now-unused short ends remaining attached to JP7. The thermistors remain plugged into JP15 and JP16 as before.

Note:You can also do this for the hotend using JP6.

end EDIT/correction/update.

Now back to the original message. Thank you scantronb!
Change the connector or cut off the old one to suit whatever the new heatbed power source requires. *See LC and Original note below[/u] High current problem solved! Tie the grounds of the two supplies together with heavy gauge wire and you're done.[/b]

This allows you to use a higher voltage lower current supply for the PB motors, which is a great side benefit that's really worth doing even for the smaller heatbed.
Another possibility available with this new wiring is to use a much higher voltage power supply for the heatbed to lower the current demand.
Quite a few good options once you UN-couple the widely disparate power needs!

Of course the Hot end is similarly wired through pins 3 and 4 of JP6, so you can power it separately too if you want! Or keep it as part of the main supply, since its current demands are not creating any problem. I'd choose the latter.

*For an LC or original: Just replace the small .100, 2 pin connector on the wires coming from the heatbed with a floppy drive style connector. Now you can plug in the main connector as before, and your heated bed simply uses the new connector and a different set of wires from the existing PSU! This will probably work for a Plus model too, instead of or in addition to the *official* PB Y adapter.

I've been waiting for someone to notice how easy this is and report it, but no one has. So there you go. ;)

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Re: Printrboard protection

Postby hqmhqm » 2012-May-Tue-21-May

Great suggestion on separating out the heater power supply from the electronics!
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Re: Printrboard protection

Postby jr57k » 2012-May-Tue-22-May

CL1, thanks for the info. Your post outlined exactly the first thing I planned on checking and modifying on my LC+ once it arrives. I was holding off to put actual instructions with pictures up but you've outlined the exact procedure I was planning on implementing. On a related note, do you know, or have an idea of how much current is required to run supply the heatbed on the LC+? If I had that I could confirm the trace size. I did intend on running it at least for little while in its stock configuration as I'm sure Brooke has tested it.
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Re: Printrboard protection

Postby CL1 » 2012-May-Wed-05-May

jr57k wrote:On a related note, do you know, or have an idea of how much current is required to run supply the heatbed on the LC+? If I had that I could confirm the trace size.
I think the total for the Plus was something like 12-13A total, with 8-9A of that for the 8x8 heatbed. Measurements were taken using the Diablotek supply at 12V with Carl's clip-on ammeter while Brook, Laine and I kibitzed about how best to solve the problem. :lol: I remember Laine saying he'd designed the board for 19V, not 12. I don't know if the PrintrBoards are 1 or 2oz copper. Laine would know.

I did intend on running it at least for little while in its stock configuration as I'm sure Brooke has tested it.
I can confirm that it does work in the stock configuration. But Rigorous testing is not the same as it's working testing. While much of the PB design has gotten the former, this area seems to have received the latter.

There is a definite heat gradient left to right across these Prusa PCB style beds in the HQ Botfarm. The hotter side depends on how your DC is connected. The gradient can be useful, but for large parts it can be less so.

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Re: Printrboard protection

Postby scantrontb » 2012-May-Wed-21-May

CL1 wrote:Have a look at the schematic and then confirm on the board traces that pins 3 and 4 of JP7 are tied directly to the main 12V input trace. And then realise that these two pins are what is supplying the heatbed! So providing a separate supply to THE WIRES INTENDED TO PLUG INTO these two pins will eliminate the huge current going through the main PrintrBoard connector!

It's so simple. We already have a two wire connector for the thermistor, which will remain plugged in directly to the printrboard JP7, pins one and two. The other 2 pin connector wired directly to the heatbed will now simply plug into a separate heatbed supply voltage instead of the printrBoard. Change the connector or cut off the old one to suit whatever the new heatbed power source requires. *See LC and Original note below High current problem solved! Tie the grounds of the two supplies together with heavy gauge wire and you're done.

Of course the Hot end is similarly wired through pins 3 and 4 of JP6, so you can power it separately too if you want! Or keep it as part of the main supply, since its current demands are not creating any problem. I'd choose the latter.
I've been waiting for someone to notice how easy this is and report it, but no one has. So there you go. ;)

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much snippage... CL1, i hate to burst your bubble but you're wrong...

1)the Thermistors are NOT connected to JP6 and JP7... However, they ARE connected to JP-15 and JP-16... two entirely separate connectors on the other end of the PBrd from JP-6, JP-7.

2) while it would be nice to bypass the PrinterBoard (PBrd) entirely for the Extruder Hotend and the Heated Build Platform (HBP), you can't do that in the way you describe...
Using the Hotend as an example: +12vdc power comes in to the PBrd from the ATX PS, via PWR connector J-3 Pins 1 and 2... then it goes to JP-6 pins 3 and 4 OUT to the Hotend heating unit... BACK FROM THE HEATER to the SAME CONNECTOR JP-6 only this time it's on pins 1 and 2... then it goes thru the Q1, R6/R36 TEMP CONTROL section (which is the Ground connection)... then it goes back to the PBrd PWR connector J-3 pins 3 and 4, and back out to the ATX PS. thus you have a complete path for current to flow... NOW... if you swap out the JP-6 pins 3 and 4 with a different set of +12vdc power leads (assuming from the same ATX PS...) you may or may not get a complete path of current anymore, due to the second set of power wires possibly being electrically isolated from the first set INSIDE the ATX PS itself, As well as you could possibly even DAMAGE the PS ITSELF, if you DO cross them (think Ghost-busters here :-( )... assuming you DO get the +12vdc to actually power up without shorting out the PS, then you will STILL HAVE the FULL LOAD AMPS of the HBP and the Hotend ON the PBrd...

No way around it without MASSIVE Mods to the various circuitry*, sorry... but unless you want to bypass the Q1/R36/R6 section ENTIRELY, and have absolutely ZERO temperature control, and to have MAXED OUT Temperatures for both HBP AND Hot-end's 100% OF THE TIME, Then you NEED to have full load amps ON the PBrd... because the PBrd IS where your temp control is coming from, it's basically done by a signal from the CPU going thru R36 to the Q1, and basically telling it to "short circuit" the power AWAY from the pair of resistors R36/R6 (and back to ground) and instead to go thru the transistor itself directly back to ground, but, because the resistance on that path is effectively zero ohms you get A LOT of current to flow, thus causing the heater to heat up... then the CPU shuts off the signal, causing the resistors to stop being bypassed, then less current flows thru the heating element and thus the heater starts to cool off, it does this for a varying amount of time per second to keep the temps (mostly) constant... the more time current is flowing, the hotter the temps... That's where the Thermistors come into play, they provide a reference (resistance or voltage difference per degree of temp change) for the CPU to compare things to. and if it reads the temp as too low, then it keeps the signal going for a longer amount of time per second to heat up more, and conversely, if the temps are showing as too high, then it stops the signal sooner and lets the heating element cool off more than it heats up per second...

*one way to do this would be to use the existing jumpers JP-6 and JP-7 as the 12vdc control circuits for TWO EXTERNAL Power Relays (one for each HBP and Hotend) that takes 120vac mains and hooks it up to the Hotend and the HBP, which is controlled by the low volts/low currents of the PBrd. However... that would entail more cost (and possible failure points) for another set of electrical components (the relays and the mounting holders for them, and any associated wiring.) THEN the Heated Bed would have to be almost entirely rebuilt in order to provide a safe work platform for you to touch while it's operating (120vac and YOU don't mix... nor does flammable acetone and electricity, for those of us that use the ABS Glue method of print adhesion.)
and if you were going to use +12vdc to power the heating elements instead of 120vac, then why bother separating it off of the PBrd in the first place?!

EDIT: And Me being an electrician... blargh!... As CL1 so rightly pointed out, if you are going to be using 120vac directly, you need to provide an isolation transformer, and or a ckt breaker/set of fuses in order to safely use the voltage. this is currently being done internally to the ATX PS and didn't need to be modified. it's only when we ADD stuff that's NOT in the PS already that we need to worry. so again, it's even more cost but i think that in the long run it'll be better for it.
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Re: Printrboard protection

Postby CL1 » 2012-May-Thu-02-May

scantrontb wrote: much snippage... CL1, i hate to burst your bubble but you're wrong...
1)the Thermistors are NOT connected to JP6 and JP7... However, they ARE connected to JP-15 and JP-16... two entirely separate connectors on the other end of the PBrd from JP-6, JP-7.

No worries! Thank you for pointing out this error. I'm glad you caught it quickly so I could correct it! You are absolutely right about the connectors! Fortunately my bubble is still intact. It is still being made much harder than it really is! I can change only one aspect and eveything else I've written still works! (I'll edit the original post, leaving my error, but correcting it. Anyone know how to do strikethrough text on this forum?)

Here's the one needed change: Cut the wires on the two pins of JP7 that are closest to the Power input connector (marked 3 and 4 of JP7 on the schematic), and re-connect them to a separate Heatbed power supply for a plus, or a separate molex floppy connector for the LC and original. Plug this new floppy connector into the available floppy of the original power supply. Be sure to cut the wires right at the JP7 connector, or plan some other way to insulate the now-unused short ends remaining attached to JP7. The thermistors remain plugged into JP15 and JP16 as before.

Note:You can also do this for the hotend using JP6.

end of correction/update.

2) while it would be nice to bypass the PrinterBoard (PBrd) entirely for the Extruder Hotend and the Heated Build Platform (HBP), you can't do that in the way you describe...
Corrected above.
scantrontb wrote:[snip well written and correct hotend example] NOW... if you swap out the JP-6 pins 3 and 4 with a different set of +12vdc power leads (assuming from the same ATX PS...) you may or may not get a complete path of current anymore, due to the second set of power wires possibly being electrically isolated from the first set INSIDE the ATX PS itself, As well as you could possibly even DAMAGE the PS ITSELF, if you DO cross them (think Ghost-busters here :-( )...

This is not a problem. The wires inside every ATX PSU I've ever seen including the DiabloTek supplied in the kits have all grounds sharing the same pad and also the 12V wires going to a single shared pad on the PCB inside. You can open it up and look(violating any mfrs warranty and exposing you to shock hazard if you don't know what you're doing!). You can also while it is open simply cut off the bulk of the wires that we are not using to get rid of that big tangle! Be sure to carefully determine which wires are needed and which are okay to remove, and cut them close to the PCB. Do wait awhile to do this after removing the power so the capacitors involved have time to discharge fully. Finally, if you don't understand how to do this; DON'T! Just get a Power Tower which is designed to hide the tangle of wires anyway. Or live with them. :) Brook and I discussed making this mod for backers or at least telling them how to do it a few times, but I always told him that while *PrintrBot could* do it, doing so would expose PB to liability concerns, as would having a document or an employee suggest the same. So you can do it but the loss of warranty and liability is yours alone. FWIW, I've personally made this mod to literally dozens of PC power supplies used in various ways over the years. It's easy and works fine. Just cut the right wires! ;)

assuming you DO get the +12vdc to actually power up without shorting out the PS, then you will STILL HAVE the FULL LOAD AMPS of the HBP and the Hotend ON the PBrd...
You will have success using the updated instruction above with the rest of my prior post. And yes, if you are using the Added Floppy connector idea then you WILL still have the full amp load on the single supply. But that's okay. It works just fine at at PBHQ for all models.

NOTE: I personally think you WILL get better results on all models by at least using the extra floppy connector to wire direct from PSU to the Heatbed (with or without the PB supplied Y-adapter supplied with Plus models). You will definitely see an improvement on Plus Models by using a separate power source for the heat bed. Here's why: Switching supplies do not handle transients very well. The full on/full off of the heat bed and hot end control are the worst kind of transient! Next, stepper drives (especially microstepping!) are affected negatively by transients in their power supply! :ugeek:

No way around it without MASSIVE Mods to the various circuitry*, sorry...

Nope. Not necessary. Just use the new instructions above.

but unless you want to bypass the Q1/R36/R6 section ENTIRELY, and have absolutely ZERO temperature control, and to have MAXED OUT Temperatures for both HBP AND Hot-end's 100% OF THE TIME, Then you NEED to have full load amps ON the PBrd... because the PBrd IS where your temp control is coming from, [snip of how temp is controlled]
As you've written, we (as a heated bed) are only interested in one thing; whether GND is available to us through the FET (Transistor Q1 and Q2 are a type called Field Effect, thus FET. Acting as simple high current switches here.). The rest you wrote (though true) is not important from the heatbed's wiring perspective! As long as you're using a single ATX supply; or there is a substantial wire connecting the GNDS of the two power supplies (Black wires on ATX, and most other supplies too. But check!); then you will not have any problems.

Have to add that while this is certainly a USEFUL mod; it is most definitely NOT a REQUIRED mod. YMMV. Be careful. If you don't know what you're doing, ask someone to help who does!

I'll comment on your last paragraph in a separate post.

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Re: Printrboard protection

Postby CL1 » 2012-May-Thu-05-May

scantrontb wrote:*one way to do this would be to use the existing jumpers JP-6 and JP-7 as the 12vdc control circuits for TWO EXTERNAL Power Relays (one for each HBP and Hotend) that takes 120vac mains and hooks it up to the Hotend and the HBP, which is controlled by the low volts/low currents of the PBrd. However... that would entail more cost (and possible failure points) for another set of electrical components (the relays and the mounting holders for them, and any associated wiring.) THEN the Heated Bed would have to be almost entirely rebuilt in order to provide a safe work platform for you to touch while it's operating (120vac and YOU don't mix... nor does flammable acetone and electricity, for those of us that use the ABS Glue method of print adhesion.)

and if you were going to use +12vdc to power the heating elements instead of 120vac, then why bother separating it off of the PBrd in the first place?!
I outlined some reasons in the post just above. One additional reason is to use something between 12VDC and 120VAC. That's a pretty wide spread with some nice sweet spots contained. De-coupling the driver supply from all the rest is a good reason in itself. The motor Drivers are good to 35V, but I wouldn't go past 24VDC based on my experience with Allegro chips for many years now.

But this is a good writeup! There are other uses for a 4 axis computer controlled movement platform and therefore other things you may wish to control besides a heatbed. And other voltages besides 120VAC. One thing that is pretty much a MUST ADD to your writeup if mains is at all considered would be an isolation transformer. Make it other than 1:1 and you have some interesting possibilities for powering hotend and heatbed. Bringing the AC voltage down takes away some of the rebuild necessary to use the existing heatbed with AC safely. Or those other things. ;) The GADA prize expects three material extrusion. We have one Extruder. Hmmm ;)

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Re: Printrboard protection

Postby Michael@Oz » 2012-May-Fri-03-May

Unless I'm missing something the current returning to ground from the external heat bed 12+v is going through (back to the ATX) via the two black ground wires on the 2x2 ATX plug.

So you are saving the ~8A 12+ from yellow ATX wires across the board traces, but still getting the same A's through what look like smaller traces carrying ground (unless it is bigger on another layer, but the via looks small). It makes no difference if all the grounds terminate on a common rail inside the ATX unless you user some of the other black wires spliced into the 2x2 ATX plug to share the load.

IF you do drive the bed at a higher voltage then you are reducing the A's though. edit Oops Ohm's Law Violation! :oops: Thanks Mooselake - always handy to have EEs oversight :ugeek: :) /edit

I seem to recall some arduino'ish style breakout boards for MOSFETs and SSRs or old fashion relays, if there is one which is driven by 12v then it would be pretty easy to drive the Bed & Extruder via another 12v (or more) supply. I was going to look into this at some time because I was thinking (long term) of multiple extruders, so will need add-on MOSFET, thermistor (just one spare analogue pin), and say a pololu stepper driver breakout. Fab a plastic holder to house the two new boards against the Printrboard and Bobs your uncle. You could just keep tacking them on the end if you want more, ie RGB extruders... until you run out of Amtel pins.

I have bought a 450W ATX PSU with cable management (so no extras dangling around), has two independent 12V rails, I'll have to open it up to see how they are wired...
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Re: Printrboard protection

Postby CL1 » 2012-May-Fri-23-May

Michael@Oz wrote:Unless I'm missing something the current returning to ground from the external heat bed 12+v is going through (back to the ATX) via the two black ground wires on the 2x2 ATX plug.
Yes, that is correct. You've not missed anything!

So you are saving the ~8A 12+ from yellow ATX wires across the board traces,
Yes. And also saving that ~8A 12+ through the 2x2 and 1x4 connectors and local traces, where it otherwise contributes heat in this physical area of the PrintrBoard.
but still getting the same A's through what look like smaller traces carrying ground (unless it is bigger on another layer, but the via looks small).
It's a 4 layer board. The power and GND are planes. Definitely not smaller. Supposed to be a 2oz board too. So there should be plenty of ampacity.

It makes no difference if all the grounds terminate on a common rail inside the ATX unless you use some of the other black wires spliced into the 2x2 ATX plug to share the load.
Looking at it from only the amps aspect this is entirely true. But while we have not reduced the amps/heat in the two black wires, we have reduced it locally to the connector(s) and traces and wiring nearby. This by itself is a worthwhile benefit. Simply removing close to half the heat from the 2x2 and half of the 1x4 connector along with the PCB traces and planes involved does make a significant difference!

But to me the primary benefit is de-coupling the Heatbed from the motor supply. And allowing for higher voltage drive of either or both.

IF you do drive the bed at a higher voltage then you are reducing the A's though.
Yes. Agreed. But again, the real benefit is potentially using a physically smaller, yet higher voltage laptop supply for the motors! They WILL run much better at a higher voltage. Also, For PLA you no longer need the bulky ATX at all! But you can still easily add it when needed for ABS printing.

In a forum like this we have everyone from well-seasoned EE's to those who know absolutely nothing about electricity except how to plug something in and use it. And that is Okay! But it does make it hard to decide what and when and where to post potential upgrades. How much detail to supply. Personally, I'd have the FET AND the 1x4 Connector for the heatbed OFF the PrintrBoard as soon as my iron was hot. My Heatbed would return through the FET Directly to the GND of a 2nd supply. I only need a light-gauge 2 wire *HBD control* cable coming from the FET gate hole and GND of the PrintrBoard. This cable is all the interface I need for a super simple Vero-bd layout which I'd mount to the rear of the printbed. It's even possible to just design the FET and connectors into the HBD itself! But for the current parts ;) , and with less experiece I'd simply do the mod already described and let good enough be good enough.

I seem to recall some arduino'ish style breakout boards for MOSFETs and SSRs or old fashion relays, if there is one which is driven by 12v then it would be pretty easy to drive the Bed & Extruder via another 12v (or more) supply. I was going to look into this at some time because I was thinking (long term) of multiple extruders, so will need add-on MOSFET, thermistor (just one spare analogue pin), and say a pololu stepper driver breakout. Fab a plastic holder to house the two new boards against the Printrboard and Bobs your uncle. You could just keep tacking them on the end if you want more, ie RGB extruders... until you run out of Amtel pins.
Yes.

I have bought a 450W ATX PSU with cable management (so no extras dangling around), has two independent 12V rails, I'll have to open it up to see how they are wired...
I'd be interested to know the results of that! I've not kept up with recent higher current ATX power supplies. I'll look forward to seeing/hearing what you discover!

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Re: Printrboard protection

Postby scantrontb » 2012-May-Sat-14-May

CL1 wrote:
I have bought a 450W ATX PSU with cable management (so no extras dangling around), has two independent 12V rails, I'll have to open it up to see how they are wired...
I'd be interested to know the results of that! I've not kept up with recent higher current ATX power supplies. I'll look forward to seeing/hearing what you discover!

CL1


those were the kind of PS's i was talking about earlier, sorry i wasn't clear enough... :roll:

if you take the +12 from rail A and hook it to the -12/ground from rail B... not good, at the minimum, may fry the PS at the worst...
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Re: Printrboard protection

Postby Michael@Oz » 2012-May-Sat-18-May

scantrontb wrote:if you take the +12 from rail A and hook it to the -12/ground from rail B... not good, at the minimum, may fry the PS at the worst...

NOT what I was thinking. :o
Just that rail A can supply the Printrboard and rail B (35A) can supply up to 2 hotbeds (ie double Y or X). Or hotbed and extruder if you use CL1's method.
edit not 35A, 17A & 14A but still good enough, shame about the wasted 3.3v & 5v (24A & 15A resp.) :( /edit
Michael@Oz wrote:I seem to recall some arduino'ish style breakout boards for MOSFETs and SSRs or old fashion relays, if there is one which is driven by 12v then it would be pretty easy to drive the Bed & Extruder via another 12v (or more) supply.

Found it :mrgreen: , this MOSFET board ($7) can be driven by up to 20V and handle 20A@60V :shock: (may need a heatsink for that) so the 12v from the Printrboard hotbed/hotend (or) can be used to drive them from another source. (but this is future plans for me ATM)
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Re: Printrboard protection

Postby scantrontb » 2012-May-Sat-18-May

Michael@Oz wrote:
scantrontb wrote:if you take the +12 from rail A and hook it to the -12/ground from rail B... not good, at the minimum, may fry the PS at the worst...

NOT what I was thinking. :o
Just that rail A can supply the Printrboard and rail B (35A) can supply up to 2 hotbeds (ie double Y or X). Or hotbed and extruder if you use CL1's method.


nah, that's ok, i was worried about crossing over the two separate rails. i was thinking about the kind of isolated rail power supplies you posted about, when i was mentally picturing what CL1 was talking about in this post snippet (bold and underlining mine):

...This is not a problem. The wires inside every ATX PSU I've ever seen including the DiabloTek supplied in the kits have all grounds sharing the same pad and also the 12V wires going to a single shared pad on the PCB inside. You can open it up and look(violating any mfrs warranty and exposing you to shock hazard if you don't know what you're doing!). You can also while it is open simply cut off the bulk of the wires that we are not using to get rid of that big tangle! Be sure to carefully determine which wires are needed and which are okay to remove,...


but with the TWO isolated power supply rails, there would be two separate pads each for each one of the +12 and -12/gnd rails, and if you did the mods he was talking about and accidentally crossed the two... well... that's what i am worried about, but if you're careful with your cutting and rearranging, and get the +12vdc wire routed back to the same rail that it came from originally you should be OK. it's only when they cross to the other rail that it'd become a problem.
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Re: Printrboard protection

Postby Michael@Oz » 2012-May-Sun-01-May

A thousand words...

Cable Master 450 Closeup Annotated.jpg
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Re: Printrboard protection

Postby Michael@Oz » 2012-May-Sun-01-May

scantrontb wrote:but with the TWO isolated power supply rails, there would be two separate pads each for each one of the +12 and -12/gnd rails, and if you did the mods he was talking about and accidentally crossed the two... well... that's what i am worried about, but if you're careful with your cutting and rearranging, and get the +12vdc wire routed back to the same rail that it came from originally you should be OK. it's only when they cross to the other rail that it'd become a problem.

Oops got this post out of sequence...

I wasn't planning on cutting. As I said it has "cable management" ie detachable cables (apart from the main ATX24 & two 2+2s) see photo above.
Just re-examined it, the two 2+2s are from each rail (on has black/yellow other black/yellow-black-strip).
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Re: Printrboard protection

Postby Mooselake » 2012-May-Sun-12-May

IF you do drive the bed at a higher voltage then you are reducing the A's though.


I got my BSEE around 40 years ago, but they probably haven't repealed Ohm's Law yet. For the non EEs current is voltage over resistance, so higher voltage and same bed resistance would be higher current. The bed might heat up faster and have a lower average on time and lower average current (power is voltage times current), but the peak amps would be higher.

Hope I misread the comment about 120 VAC powering the bed, since while the bed would heat up a whole lot faster (probably let some magic smoke out while it did so; it'll take a bit of time for the heat to reach the thermistor) it has quite a potential (bad pun) to let the smoke out of the user at the same time.

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Re: Printrboard protection

Postby scantrontb » 2012-May-Sun-14-May

Mooselake wrote:Hope I misread the comment about 120 VAC powering the bed, since while the bed would heat up a whole lot faster (probably let some magic smoke out while it did so; it'll take a bit of time for the heat to reach the thermistor) it has quite a potential (bad pun) to let the smoke out of the user at the same time.

Kirk


nope you didn't misread, however, that WAS some of my concerns in my OP in this topic.
if you use the current HBP heater as designed, the resistance of the circuit is designed around a 12VDC voltage and i think it was mentioned at about 12 amps? (somebody correct me here, i can't find that anywhere again.), and if you change that to 120VAC (ignoring impedance issues for this discussion), you're going to have pretty much 10 times the amount of current flowing thru the circuit (I=E/R). and if the volts(E) goes up but the resistance(R) stays the same then the current(I) goes up proportionally (~120AMPS!! your house ckt bkr would trip before your bed even got lukewarm!). while the materials of the ckt board itself would probably be OK since that's what the power supply ckt boards are made of, however, the heating element traces on the board may be the wrong dimensions to handle that amount of current and consequently melt, and/or the very thin layer of electrical insulation over the tops of the ckt traces may fail and give somebody an electric shock if they touch it.

That's why i said there would have to be a massively redesigned ckt board before we can SAFELY use 120vac on it. you brought a good point up as well, about the thermistor not registering the temp right away, and the board frying because the thermistor thought it was a much lower temp than it actually was and didn't tell the CPU to cut back in time. however, i think with a properly designed board (using 120vac) that would be taken care of as the board would heat up at about the same rate and the temps would propagate thru the base material and hit the thermistor at about the correct times/temps to prevent damage.
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Re: Printrboard protection

Postby Michael@Oz » 2012-May-Sun-18-May

Yeh, I don't think anyone without qualification should be messing with mains voltages (240v here) or very high DC currents.
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Re: Printrboard protection

Postby Michael@Oz » 2012-May-Sun-21-May

Wikipedia
Multiple +12 V rails

As power supply capacity increased, the ATX power supply standard was amended (beginning with version 2.0[3]) to include:

3.2.4. Power Limit / Hazardous Energy Levels

Under normal or overload conditions, no output shall continuously provide more than 240
VA under any conditions of load including output short circuit, per the requirement of UL 1950/​CSA 950/​EN 60950/​IEC 950.
—ATX12V Power Supply Design Guide, version 2.2[4]

This is a safety limit on the amount of power that may pass, in case of a fault, through any one wire. That much power can significantly overheat a wire, and would be more likely to melt the insulation and possibly start a fire. Each wire must be current-limited to no more than 20 A; typical supplies guarantee 18 A without triggering the current limit. Power supplies capable of delivering more than 18 A at 12 V connect wires in groups to two or more current sensors which will shut down the supply if excess current flows. Unlike a fuse or circuit breaker, these limits reset as soon as the overload is removed.

Ideally, there would be one current limit per wire, but that would be prohibitively expensive. Since the limit is far larger than the reasonable current draw through a single wire, manufacturers typically group several wires together and apply the current limit to the entire group. Obviously, if the group is limited to 240 VA, so is each wire in it. Typically, a power supply will guarantee at least 17 A at 12 V by having a current limit of 18.5 A, plus or minus 8%. Thus, it is guaranteed to supply at least 17 A, and guaranteed to cut off before 20 A.

These groups are the so-called "multiple power supply rails". They are not fully independent; they are all connected to a single high-current 12 V source inside the power supply, but have separate current limit circuitry. The current limit groups are documented so the user can avoid placing too many high-current loads in the same group. Originally, a power supply featuring "multiple +12 V rails" implied one able to deliver more than 20 A of +12 V power, and was seen as a good thing. However, people found the need to balance loads across many +12 V rails inconvenient. When the assignment of connectors to rails is done at manufacturing time it is not always possible to move a given load to a different rail.

Rather than add more current limit circuits, many manufacturers have chosen to ignore the requirement and increase the current limits above 20 A per rail, or provide "single-rail" power supplies that omit the current limit circuitry. (In some cases, in violation of their own advertising claims to include it. For one example of many, see [5]) The requirement was deleted from version 2.3 (March 2007) of the ATX12V power supply specifications.[6]

Because of the above standards, almost all high-power supplies claim to implement separate rails, however this claim is often false; many omit the necessary current-limit circuitry,[7] both for cost reasons and because it is an irritation to customers.[8] (The lack is sometimes advertised as a feature under names like "rail fusion" or "current sharing".)
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Re: Printrboard protection

Postby didado » 2012-Jul-Fri-05-Jul

Michael@Oz wrote:Found it :mrgreen: , this MOSFET board ($7) can be driven by up to 20V and handle 20A@60V :shock: (may need a heatsink for that) so the 12v from the Printrboard hotbed/hotend (or) can be used to drive them from another source. (but this is future plans for me ATM)


Hi Michael. This is just what I need for an experiment to drive a hotbed from a different 36 volt source. However, I'm a mechanical guy and not so much an electronics guy. How would I hook it up? I watched this youtube movie

If I understand it correctly I should translate Source , Drain and Gate in:

Gate as Printrboard Hotend +12V,
Drain as +36 volts external source
Source as Minus/Ground connecting Printrboard Hotend minus with External Source minus

And yes, I take full responsibility for frying my components due to lack of electronics knowledge but any advise would be greatly appreciated.

Thanks
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Re: Printrboard protection

Postby Michael@Oz » 2012-Jul-Fri-22-Jul

didado wrote:
Michael@Oz wrote:Found it :mrgreen: , this MOSFET board ($7) can be driven by up to 20V and handle 20A@60V :shock: (may need a heatsink for that) so the 12v from the Printrboard hotbed/hotend (or) can be used to drive them from another source. (but this is future plans for me ATM)


Hi Michael. This is just what I need for an experiment to drive a hotbed from a different 36 volt source. However, I'm a mechanical guy and not so much an electronics guy. How would I hook it up? I watched this youtube movie

If I understand it correctly I should translate Source , Drain and Gate in:

Gate as Printrboard Hotend +12V,
Drain as +36 volts external source
Source as Minus/Ground connecting Printrboard Hotend minus with External Source minus

And yes, I take full responsibility for frying my components due to lack of electronics knowledge but any advise would be greatly appreciated.

Thanks

I only dabble in this stuff, but I believe your understanding is correct for a N-MOSFET.

You could be pushing some wattage so check the temp of the MOSFET, you may need to add a heatsink to the chip.

Also your wires should be of the appropriate gauge.

ps Let us know how you get on.
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Re: Printrboard protection

Postby didado » 2012-Jul-Sat-00-Jul

Thanks, I will keep you informed. Just ordered the mosfet board and it will take a few weeks for it to arrive.
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