PSU unexpected turning off

Hi Repetier,
I am new in reprap eletronics and I just finished my Mendel Max printer with GEN 7 V 1.3.1 eletronics few days ago.
I used tomtry Teacup with Pronterface but got some connction problems so I moved to Repetier firmeware and host.
So, first, congratulations for the hard and good workmdone! There is some amazing features in your solution which makes Our life easier!
i have no communication problem but, for some reason, during the printer job the PSU suddenly turn off and the printer stop.
The communication keep still flowing and the host keep sending the g-codes but the printer is turned off!
To turn it again is just a matter of hit the disconnect buttom and hit the connect it again, them it cames to life again!
I am using an ATX 500 w power supply.
Running on dry run method, the problem dissapear!
i have tried differente option for speed and stepper driver current ( on the board potentiometer) but the problem still persister, even with the stteper board very cold ( seems there is no overcurret on the stteper!)
I am not sure if I have some configuration prpblem or if it is and hardware problem.
i will appreciate any help on that.
Thanks

Hi Enobrega,

Check the resistance across the hot end resistor wires, and make sure you have 5 or 6 Ohms there. If it is lower than 5, then I would suspect a short.

PC Power Supplies introduce a bit of uncertainty into the mix. There are various claims about unstable voltages on the 5 volt rail, etc., but no real solid results. I've been lucky in the past, and my PC PSUs have all worked just fine by grounding the green wire.

If you want to eliminate the uncertainty, get the PSU that Lulzbot sells, or one like it. It is at least a brand(?) that can be said works fine. I don't know of a list of PC PSUs, with model numbers etc., but maybe there is something in the wiki that might help.

Hi Jcabrer,
Thanks for your tips!
I will double check the hot end resistor to be sure there is no short there. Also I will check the ground!
Maybe the PSU is not stable enough on th 5V rail.
Any suggestion in how can I test it without spending the money in a new one?
Just to be sure the PSU is the problem!
Thanks for your help!

Some psu turn off if there is no load on the 5v rail at some time when the
load is too high. I'm not sure if the 5v rail is used by gen7 or if it uses only the 12v rail like most boards. You can add a small load on 5v to prevent these problems.mA 5v fan or small lamp should suffice.

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Checked ground and add a small lamp at 5V rail but the problem still persist.
For some reason, after some minutes of normal print, the PSU shut off!
The host keep sending the gcodes, but the machine is turned off !
With the heated bed turned off the problem does not appears, at leats two printers jobs goes to the end, without PSU problem, but with the bed turned off.
Any additional tips in what would be the problem?
Thanks
Enobrega

Sounds like the load is too high with heated bed, so the PSU shuts it down to protect it. If it is a computer PSU there may be two circuits V1 and V2 with 12V with different amp ratings. Not sure how they are wired on gen7, but on RAMPS board you can use one for heated bed and one for the other electronics.

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Repetier-Software - the home of Repetier-Host (Windows, Linux and Mac OS X) and Repetier-Firmware.
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Ah yes, you may be current limited on the yellow and black wires you chose for the heated bed. In many PC power supplies, you will have multiple sets of yellow wires. These got to disk drive connectors, fans, motherboards, graphics adapters, etc.

The one that supplies the motherboard with power has a four pin molex connector with two black, and two yellow. You should use these to power your electronics. Combine the wire pairs (yelow to yellow) and you should have enough current there to power everything.

Another possibility is to use one of the six pin molex yellow/black sets. These are intended for high performance graphics adapters, and usually carry more current.

Seems the problem is solved! In Gen 7 V1.3.1 the ground for the heaters and ATmega are connect, so I suspect there was some "noise" in the ground that was affecting the ATmega and, some times, reseting it , due the mosfet actions!
I rebuilted the ground wire in order to have two ground circuits: one for the heaters and another one for the ATmega.
After this change, I was able to print several jobs with just one unexpected reset which, probably, is due to some another interference which I need to go deeper to find the cause.
I will keep you informed!
Anyway, thanks for all your support on that.