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Power supply's

Posted by Enlightx 
Power supply's
March 08, 2014 08:37AM
Hi guys

Have been working on a 3dr for part month and fitted flex led strips down the alu extrusions and have noticed heavy strobing while the pus on heater is on.

So I got volt meter and ammeter out and started looking at the atx psu I had attached. Whole 3dr while printing never got over 4 amps usage but noticed the 12v was all over the place even as low as 10v while heating up from cold.

So I took it rubbish atx psu. Since tried 2 12v 5a switching regulated power bricks with same result. As well as my 12v 20amp supply from my i3

Is this expected? Or do I need a different type of supply?

Edited 1 time(s). Last edit at 03/08/2014 08:37AM by Enlightx.
Re: Power supply's
March 08, 2014 04:43PM
i think that even at 20 amp your on the small side with the heated bed, i am using a 350 watt computer psu


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Re: Power supply's
March 09, 2014 07:43AM
you may want to check your ATX PSU

have a look on the side of the PSU at the 12V Line that will give you the total amps the 12V line can take. Normally on 350W PSU its around 14A which is a bit light when using a heated bed.

with ATX PSU you have 3.3V, 5V and 12 V they all have a total amp rating thats how they get the 350W your only intested in the 12V for reprap.

20A is plenty last time i checked my i3 out with an ameter i was pulling around 15 amps while printing and heating.

were as delta printers with no heated bed i pull around 4 amps @ 12V tops. so 5Amp power brick can handle that easy.

problem i have is voltage drops to 10V when heating up printer wanted to know if this is normal for power supply's.
Re: Power supply's
March 10, 2014 03:05PM
Quote
dissidence
i think that even at 20 amp your on the small side with the heated bed, i am using a 350 watt computer psu
A dedicated 12V, 16A power supply will do just fine on a printer with a proper-spec PCB heated bed and single extruder, assuming the power supply isn't a cheap, over-rated Chinese supply. I have built several printers with heated beds using 203W XBox 360 power supplies, which are ~17A at 12V.

A 350W ATX PSU (especially a cheap one) will not output even close to 350W at 12V, which would be 29A. It will most likely output more like 15 to 18A at 12V (180 to 216W), and the rest of the power will be output to 5V and 3.3V. A cheap one would probably be over-rated, and put out even less than 15A at 12V.

Basically, what Enlightx said is correct.

Quote
Enlightx
problem i have is voltage drops to 10V when heating up printer wanted to know if this is normal for power supply's.
This is normal for cheap ATX power supplies, and even some better ATX supplies without the 5V rail loaded at least a little bit. Two 12V, 5A power supplies would not handle the load either, and would sag in voltage, if not cut power completely.

However, a 12V 20A supply should work just fine. It's possible that your heated bed is too low of resistance, and is trying to draw too much power. This is especially likely if your 20A supply works just fine on another printer with a heated bed.

Can you measure the resistance of your heated bed with reasonable accuracy? It should be around 1 - 1.2 Ohms.

Edited 1 time(s). Last edit at 03/10/2014 03:06PM by NewPerfection.


Cameron

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Re: Power supply's
March 10, 2014 05:43PM
Currently testing on both 3DR and a Kissel so heated bed. Get same voltage drops on every psu I have atx, power brick, 12v 20a box.

Even tried a branded £15 12v 5a power pack with same results
Re: Power supply's
March 10, 2014 06:01PM
Quote
Enlightx
Currently testing on both 3DR and a Kissel so heated bed. Get same voltage drops on every psu I have atx, power brick, 12v 20a box.

Even tried a branded £15 12v 5a power pack with same results
Looks like I misread what you had written before. So, no heated bed? And you verified that the total amperage draw was less than 4A even when heating from cold? If your 12V 20A supply doesn't drop voltage with your i3 at 15A, it definitely shouldn't drop voltage at only 4A current draw.


Cameron

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Re: Power supply's
March 11, 2014 02:42PM
yeah drops to 10V when heated the hotend just after homing. then when pwm kicks in (approx 10C before target temp) it goes back up to 12v.
iv noticed it for a while as you can hear fans on the machine tone down then back up again.


ill hook up it all up later and take a vid if possible.
Re: Power supply's
March 11, 2014 03:09PM
Quote
Enlightx
yeah drops to 10V when heated the hotend just after homing. then when pwm kicks in (approx 10C before target temp) it goes back up to 12v.
iv noticed it for a while as you can hear fans on the machine tone down then back up again.
And you've measured the current draw from the power supply when the voltage has sagged that much? I just don't see how it's possible for a 4A load to drop a 12V 20A power supply to 10V, unless there is a short, in which case the load would be much greater than 4A. Can you unplug the hot end heater and measure the resistance across it?


Cameron

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Re: Power supply's
March 11, 2014 05:25PM
I can second newperfections post on using 16.5amp 203w xbox power supplies. I have also built quite a few printers using that power supply with 8x8 heated beds. You will want to make sure that its an official Microsoft one as ive heard of issues with the knock offs. I have an entire post on my site showing how to mod the xbox psus to be used on a reprap. My site is linked below within my signature.


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