Author Topic: 5.5w keeps burning my MOSFETs  (Read 1463 times)

Alvis

  • Newbie
  • *
  • Posts: 46
    • View Profile
5.5w keeps burning my MOSFETs
« on: September 03, 2017, 07:34:46 AM »
Hello everyone! Hope you all good!

Normally I donít do forums but this time itís must, struggle is real!

Got myself 5.5wDIY laser (for two days and not brand named) it worked fine while on Benbox, and as I ďoutgrowĒ Benbox really quickly due to its limited options I jumped onto T2Laser software which had way more possibilities and options. Had little struggle get my axis and settings right at first but got there eventually.

 And then fun began  in first couple test runs i burned MOSFET out (went smokey and really hot) which lead to laser stuck in ON ďpositionĒ (only way to turn it off was disconnecting power supply or turning ON/OFF button to OFF) Messaged seller the problem and got refund for control board.

Once refund received I bought EleksMana SE control board because most of people using them and have no problems with them, but not me, burned MOSFET out again in couple of minutes while doing test runs(same symptoms, went hot and smoked and laser beam ON at all times). WHATS WRONG, WHAT AM I DOING WRONG I asked myself.

Got in touch with Zax from T2Laser (very responsive, instructive and helpful person, Thank You Zax!) and after messaging forwards and backwards with him i think we came to conclusion that seller have provided me laser board with insufficient current for my laser (or something on those lines, Iím very new in this), most 5.5w lasers use separate TTL/PWM (not a clue whatís this) input and then MOSFETs are ok, but without that Iím always going to damage the MOSFET.

To be fair, electrical side on it does look pretty bad (bad design and components) comparing to structural, which is sturdy.   

Now have messaged seller with case to return laser for refund, will see what he reply on Monday. (Ordered on bay from china)

I will upload pictures of:
*Arduino (first one I burned out)
*EleksMana se (second I burned out)
*board in silver casing I assume is laser module board (which is to blame to all these issues???)

The questions are:
1. What exactly causes my laser to fail?
2. What exactly I would need to get it up and running? (Maybe some links where to get from?)
3. Is there any soldering to be involved, if so, where to and what I have to solder?(jumper?)

Iím in real hope this forum will help me out on this one, as donít know what else to do, for me 430US dollars/ 330uk pounds is quite big money and donít want to waste it (obviously) on malfunctioning/useless item. 

Thank you in advance!

« Last Edit: September 03, 2017, 07:41:23 AM by Alvis »
One day,or Day one,You decide!

5.5w diy 400x380
T2 Mana se

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2392
    • View Profile
Re: 5.5w keeps burning my MOSFETs
« Reply #1 on: September 03, 2017, 09:20:42 AM »
I also burned out a number of MOSFETs during the JULY/AUGUST 2017 timeframe. I think the problem was the Nano was not fully turning the transistor fully ON/OFF. This caused the transistor to heatup which made things worse. Observed that the Nano was only delivering 4.4V for a high. Others Nanos supply 4.8V for a high.

My solution was to build a replacement board with a dedicated MOSFET driver chip. Schematic and artwork available elsewhere on this site. I have a couple blank boards that you a welcome to.

During the past year I also purchased, but have not populated, some TTL specific power MOSFETs.

You should measure the voltage and current consumed at various power (PWM) levels to verify that the problem is not with the Laser Diode circuit.

 
SARCASM - Just one more service we offer here.

Zax

  • T2Laser
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 6233
    • View Profile
    • T2Laser
Re: 5.5w keeps burning my MOSFETs
« Reply #2 on: September 03, 2017, 09:34:12 AM »
I believe the standard MOSFET is rated at 6W (some maybe 5W) so I would say the problem is that the laser driver (in the silver box) is probably exceeding that rating.

The Nano should be capable of fully turning on the gate which requires 4.5V, but yes that would significantly increase it's resistance and therefore heat.

I don't believe these boards should be used to switch a 5.5W laser, the power should be direct and the laser driver should have a TTL input for the switching.

andrewl

  • Newbie
  • *
  • Posts: 1
    • View Profile
Re: 5.5w keeps burning my MOSFETs
« Reply #3 on: January 10, 2018, 02:25:15 AM »
Hi Guys

does anyone have a solution for this?
i am going through exactly the same as alvis did, with the same setup however my laser is a 3W.

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2392
    • View Profile
Re: 5.5w keeps burning my MOSFETs
« Reply #4 on: January 10, 2018, 07:35:39 AM »
Can you measure the current being consumed?
What is the MOFET you are using?
SARCASM - Just one more service we offer here.

Zax

  • T2Laser
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 6233
    • View Profile
    • T2Laser
Re: 5.5w keeps burning my MOSFETs
« Reply #5 on: January 14, 2018, 06:32:24 AM »
I just got one of the newer Eleks boards that uses a clone of the Atmel processor, so now their "Nano" has absolutely no standard chips (a CH340 UART instead of the FTDI FT232 and a Chinese reverse engineered processor instead of the Atmel).

The outputs are low (3.6-3.8V on my o-scope), more like CMOS levels 3.3VDC instead of the required TTL 5VDC. I don't know if that's standard or I got a bad one.

I don't use these in any of my lasers, I have Nano's with both genuine chips and never get communications errors, buffer memory problems or overheating. If you are using a newer Eleks Mana, I suggest using their laser module with it and not the MOSFET.

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2392
    • View Profile
Re: 5.5w keeps burning my MOSFETs
« Reply #6 on: January 14, 2018, 06:43:19 AM »
3.8V would turn the MOSFET into a heater pretty quickly.
SARCASM - Just one more service we offer here.

Zax

  • T2Laser
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 6233
    • View Profile
    • T2Laser
Re: 5.5w keeps burning my MOSFETs
« Reply #7 on: January 14, 2018, 09:33:04 AM »
That was my point, now to be fair I haven't looked at what MOSFET they are using on the newer board so perhaps they went with a 3.3V gate. I will check later, having just got back from a very exhaustive trip I'm going to rest a while.

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2392
    • View Profile
Re: 5.5w keeps burning my MOSFETs
« Reply #8 on: January 14, 2018, 10:30:28 AM »
I think they used LR7843 with 100 ohm series resistor on the original L7 and switched to a TTL level switch on newer controllers. I fried a few 7843 chips along with the trace on one controller before finding the the Nano was not driving high properly. I purchased, but never populated some TTL MOSFETs. For my home brew controllers I used a dedicated mosfet driver chip. MOSFET cost about $1.50, driver about $4.50.
SARCASM - Just one more service we offer here.