1 Topic by Diecrusher

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Topic: Upgrading power supply issues.

I've gone ahead and done Lawsy's awesome PCB heat-bed upgrade along with his recommended Sanguino mods.

I first tried powering the new setup with a modified ATX power supply rated a 12v@19amps, but when I kick on the heat bed the power supply shuts down.  I read that this is probably due to the fact that there is no load on the 5V and the protection is shutting it down.

Instead of adding a 5v load to the ATX supply I tried hooking up a 203w Xbox power supply rated at [email protected] which seems to be well used in the reprap community and doesn't required a 5v load.  Same issue.  So am I correct in concluding that the Solidoodle and Lawsy's heat-bed draws over 16.5amps even with the extruder off?  I am an electronics novice here but that seems high.  What am I missing?

Any input appreciated! smile

2 Reply by elmoret

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Re: Upgrading power supply issues.

The QU-BD bed draws 12A, and his heats even faster so it's probably around 15A. The SD draws about 2A with extruder off.

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3 Reply by Zarni

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Re: Upgrading power supply issues.

Sounds like an excess current issue shutting the PSU down. Possible short on the board somewhere?

If you measure the resistance for the bed this could show up the problem? Or at least give you an idea of what sort of current it is expecting to draw.

If you were feeling brave (and had no other means to diagnose the issue), you could put both power supplies in parallel, 12v @35A should either work or cause something to melt. Actually that is is daft idea running two unknown switch mode power supplies you 'll probably just end up with a lightning storm in the supplies (nice to watch if you know it is going to happen, not good for the supply) and both would end up dead along with a nice fire if it went pear shaped.

4 Reply by RavensCrest

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Re: Upgrading power supply issues.

can someone direct me to the Sanguino mods for power supply?
I look at some of the posts and still don't understand which part needs to be strengthened on sanguino board

Solidoodle2 with Ceramic tile heated bed http://www.soliforum.com/topic/2544/my- … eated-bed/
"1kg should last for an while" is a lie!

5 Reply by 2n2r5

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Re: Upgrading power supply issues.

RavensCrest wrote:

can someone direct me to the Sanguino mods for power supply?
I look at some of the posts and still don't understand which part needs to be strengthened on sanguino board

http://www.soliforum.com/topic/1819/hea … isonsstls/

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6 Reply by RavensCrest

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Re: Upgrading power supply issues.

2n2r5 wrote:
RavensCrest wrote:

can someone direct me to the Sanguino mods for power supply?
I look at some of the posts and still don't understand which part needs to be strengthened on sanguino board

http://www.soliforum.com/topic/1819/hea … isonsstls/

thank you,
i was expecting some wiki page but sure. this will work.

Solidoodle2 with Ceramic tile heated bed http://www.soliforum.com/topic/2544/my- … eated-bed/
"1kg should last for an while" is a lie!

7 Reply by Diecrusher

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Re: Upgrading power supply issues.

Well after some quick math with my novice electronics experience, I may have found the problem.

The resistance of my heat-bed pcb is .5ohm and that combined with 12vdc = 24amps current draw, right?  Well that obviously is way beyond the specs of my power supply.

If the pcb resistance raised to .8ohms it would only draw approx. 15amps and my current 19amp supply might be sufficient.  Could I just add another power resistor to the circuit to achieve this?

8 Reply by adrian

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Re: Upgrading power supply issues.

You can theoretically, however, given that the resistor will also have 15amps running through it, the amount of power it would need to dissipate would be huuuuuge. It'd be as hot as the bed itself.

I think the only way you can solve this is etch another board.

Post a pic of the one you made, maybe the issue is obvious.... *shrug*

9 Reply by adrian

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Re: Upgrading power supply issues.

you could etch another board and put them in series... double or single sided ? and did you etch both sides ?

10 Reply by lawsy

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Re: Upgrading power supply issues.

Just measured mine at 1.1 Ohms. So 11 amps at 12.1 volts (as measured).

Since Diecrusher is measuring pretty much half the resistance, could it be that the etched board is twice as thick as mine?

Adrian's idea about etching a second board in series to halve the resistance is a very simple and clever solution.

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11 Reply by Diecrusher

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Re: Upgrading power supply issues.

Well, I had another thought also.

The board I eched was 2oz copper, double-sided, but I only etched the one side.  I noticed that even though there are no "bridges" anywhere in the loop, the etched gap is pretty thin.  I am planning on throwing the board on a milling machine and widening the gaps thereby reducing the width of the traces until I arrive at the proper pcb resistance of 1.1ohms.

Thoughts?

Thanks again everyone. smile

12 Reply by Diecrusher

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Re: Upgrading power supply issues.

Dang, wrong again..... My meter must have been screwy because I checked the pcb heatbead at work today and got a good reading of 1.1ohms, right where it is supposed to be.  So my problem must be somewhere else...... sad

13 Reply by lawsy

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Re: Upgrading power supply issues.

The resistance will change with temperature (colder = higher), but you wouldn't think by that much.

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14 Reply by ronsii

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Re: Upgrading power supply issues.

Diecrusher wrote:

Dang, wrong again..... My meter must have been screwy because I checked the pcb heatbead at work today and got a good reading of 1.1ohms, right where it is supposed to be.  So my problem must be somewhere else...... sad

What does your meter read when you just short it's leads together? make sure and minus this reading off of the reading you are getting from the pcb to get accurate results.

15 Reply by Zarni

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Re: Upgrading power supply issues.

As you changed the power supply at the same time as the heatbed, have you tried connecting the old heatbed up to the new supply?

16 Reply by Diecrusher

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Re: Upgrading power supply issues.

Well,  I thinned the traces even more today and will test tonight with and inline current meter to get an actual value in circuit.  I did have it working but current draw still to high and you could hear the drag on the other components.